LARGE-SCALE MODEL TEST DEVICE AND METHOD FOR EXCAVATION, WATER FILLING AND SPLITTING OF HIGH INTERNAL AND EXTERNAL WATER PRESSURE TUNNELS

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Chinese Patent Application No. 202411517618.5, filed on Oct. 29, 2024, the entire disclosures of which are incorporated herein by reference.

TECHNICAL FIELD

The present application belongs to the field of geotechnical engineering technology, specifically a large-scale model test device and method for excavation, water filling and splitting of high internal and external water pressure tunnels.

BACKGROUND

Geotechnical engineering serves as a vital field for infrastructure construction and resource development. It faces numerous challenges, including issues such as high in-situ stress, high temperature and high pressure, rock mass fracturing, and tunnel water gushing, while also undertaking important tasks in underground mining, tunnel construction, and geotechnical research. The smooth progress of geotechnical engineering is directly related to the safety, stability, and sustainability of projects. Natural rock masses contain a large number of structural planes and fault zones, which significantly alter the integrity of the rock mass and affect the stability of engineering rock masses. These characteristics make rock masses prone to engineering disasters such as earthquakes, collapses, and rock bursts when exposed to high temperature and high water pressure. Such disasters cause damage to construction, casualties, and economic losses to projects. Therefore, in-depth research on the complex and diverse underground geotechnical conditions and the exploration of new devices are of great significance.

On one hand, geotechnical engineering projects are often carried out deep underground. The presence of groundwater means that underground devices need to operate under high water pressure conditions. On the other hand, as underground rock mass projects continue to expand into deeper areas, the impact of temperature on rock damage has become increasingly prominent. Generally, for every 100-meter increase in depth, the rock mass temperature rises by 3° C., and at a depth of approximately 5,000 meters underground, the temperature can reach 180° C. Temperature is one of the key factors affecting the deformation and damage of deep hard rocks.

Various situations often occur underground, one of which is the rise and fall of groundwater. During the rise and fall of groundwater, the tunnels within the area alternate between water-filling and water-draining states. When the water pressure is excessively high, it may further lead to hydraulic fracturing of the rock mass.

Current conventional tunnel shield excavation simulation test device, such as open-type shield excavation simulation device, is only suitable for construction in stable soil layers and requires additional assistance when the soil layer stability is poor. For closed-type shield excavation simulation device, direct observation by personnel is not possible.

In summary, the current conventional large-scale physical model test devices and methods for tunnels still have the following shortcomings: they cannot effectively simulate the underground environment with high temperature and high water pressure; they cannot simulate the hydraulic fracturing of surrounding rock in high-temperature tunnels under three-dimensional stress and water-rich conditions, nor the water-filling and water-draining simulation of high-temperature tunnels with internal and external water pressure linings under three-dimensional stress; it is difficult to monitor and collect information such as stress, deformation, temperature, and water pressure; and they cannot simulate different excavation methods. Some device can simulate high water pressure or high temperature environments, but fails to integrate these functions and cannot achieve intelligent monitoring and information collection.

In addition, the existing device has a single excavation method, only providing one type of method, and cannot achieve full coverage of the rock cross-section excavation methods used in engineering simulations. Therefore, improving large-scale physical model test devices and technologies for tunnels to more truly simulate the failure mechanism involving shield excavation is of far-reaching significance for enhancing the safety and stability of geotechnical engineering.

Based on this, it is necessary to develop a test device that can simultaneously realize intelligent excavation simulation under the coupling of multiple conditions such as high temperature and high water pressure, and monitor and collect data on stress, deformation, and temperature, and observe the working conditions and performance of linings and surrounding rock. This device will be used to conduct excavation experiment research under the coupling of multiple conditions such as high temperature and high water pressure.

SUMMARY

In view of the problems existing in the related art, the present application provides a large-scale model test device and method for excavation, water filling and splitting of high internal and external water pressure tunnels, aiming to simulate indoor excavation under the coupling of multiple conditions such as underground high temperature and high pressure, simulate the hydraulic splitting of cofferdams caused by water pressure, and observe the damage caused by external water pressure, and record and observe the lining failure performance and its working conditions under high water head pressure.

To achieve the above purpose, the present application adopts the following technical solutions:

A large-scale model test device for excavation, water filling and splitting of high internal and external water pressure tunnels, comprising:

• • an intelligent control excavation support telescopic system, an intelligent control excavation load application system, a barrel-shaped triaxial reaction system, a triaxial stress loading system, an internal water pressure controlling and sealing system, an external water pressure control system, a temperature control system, a multi-element monitoring information collection system, and a lined tunnel physical model;
  • wherein a water pressure tunnel model comprises the barrel-shaped triaxial reaction system, the triaxial stress loading system, the internal water pressure controlling and sealing system, the external water pressure control system, the temperature control system, and the multi-element monitoring information collection system;
  • wherein a drilling rig assembly comprises the intelligent control excavation support telescopic system and the intelligent control excavation load application system;
  • wherein the barrel-shaped triaxial reaction system is a main frame of the water pressure tunnel model, and the triaxial stress loading system is provided inside the barrel-shaped triaxial reaction system;
  • wherein the temperature control system, attached to the lined tunnel physical model, is provided in a middle of the triaxial stress loading system;
  • wherein the intelligent control excavation support telescopic system is placed right in front of the barrel-shaped triaxial reaction system, and the intelligent control excavation load application system is provided above the intelligent control excavation support telescopic system;
  • wherein the multi-element monitoring information collection system is connected to and provided inside the barrel-shaped triaxial reaction system, the triaxial stress loading system, the internal water pressure controlling and sealing system, the external water pressure control system, and the temperature control system, and
  • an oil circuit loading system controls the start of the large-scale model test device;
  • wherein the triaxial stress loading system comprises front and rear bladders, pressure plates, hydraulic pillows, and wedge-shaped pressure heads; the front and rear bladders each are square metal plates with a circular hollow in a middle, fixed on a model bearing cover plate and connected to a vertical loading pump on a right side of a horizontal loading pump,
  • wherein the horizontal loading pump satisfies a balanced loading of a pressure of the front and rear bladders on both sides of the barrel, ensuring that a stress on a loaded model remains unchanged when a water injection pressure increases:

P w × S 1 = ( P 0 + Δ ⁢ P f ) × S 2 ( 1 )

• • wherein P_w is a water injection pressure, S₁ is an area of the front and rear bladders, P₀ is an initial stress, ΔP_f is an increased stress, and S₂ is a contact area between the front and rear bladders and the lined tunnel physical model;
  • wherein the pressure plates are metal plates with a same size and shape as the front and rear bladders, provided inside the front and rear bladders; the wedge-shaped pressure heads are four rectangular metal plates attached to an outside of the heating plate;
  • wherein the hydraulic pillows are four rectangular metal plates attached to an outside of the wedge-shaped pressure heads to apply pressure to the lined tunnel physical model and are connected to the front and rear loading pumps;
  • wherein the barrel-shaped triaxial reaction system comprises a base, a model bearing cylinder, a model bearing cover plate, and a reaction pad; the base is a frustum with a hollow cuboid in a middle, and left and right sides of the frustum are designed with semicircular holes with a same radian as the frame, provided at the bottom of the large-scale model test device, in continuous arc contact with a model bearing cylinder, the model bearing cylinder is a thick-walled cylinder provided on the base and closely attached to the base; a wall thickness of the model bearing cylinder is determined as follows:
  • the wall thickness of the model bearing cylinder is determined according to four working conditions of an unfavorable combination of operating conditions:
  • a first working condition: internal water pressure of a model tunnel:

σ θ p = 2 ⁢ r 1 ( 2 - 2 ) ( P s ⁢ r 1 2 r 2 2 + P p ) ⁢ r 1 2 r 2 2 - r 1 2 ⁢ ( 1 + r 2 2 r 2 ) ( 2 ) σ r p = P s ⁢ r 1 2 r 2 2 ⁢ r 1 2 r 2 2 - r 1 2 ⁢ ( 1 + r 2 2 r 2 ) ( 3 ) σ z p = ( σ 1 ⁢ a 2 - P s ⁢ r 1 2 r 2 2 ⁢ π ) ⁢ S g ⁢ r 1 2 π ⁢ r 1 ⁢ h ⁡ ( r 1 2 - r 2 2 ) ( 4 )

• • a second working condition: combined action of internal water pressure of the model tunnel and a maximum principal stress of the model:

σ θ p = 2 ⁢ r 1 ( 2 - 2 ) ( P s ⁢ r 1 2 r 2 2 + P p + σ 1 ⁢ a 2 2 ⁢ π ⁢ r 1 ⁢ h ) ⁢ r 1 2 r 2 2 - r 1 2 ⁢ ( 1 + r 2 2 r 2 ) ( 5 ) σ r p = ( P s ⁢ r 1 2 r 2 2 + σ 1 ⁢ a 2 2 ⁢ π ⁢ r 1 ⁢ h ) ⁢ r 1 2 r 2 2 - r 1 2 ⁢ ( 1 + r 2 2 r 2 ) ( 6 ) σ z p = ( σ 2 ⁢ b 2 - P s ⁢ r 1 2 r 2 2 ⁢ π ) ⁢ S g ⁢ r 1 2 π ⁢ r 1 ⁢ h ⁡ ( r 1 2 - r 2 2 ) ( 7 )

• • a third working condition: combined action of internal water pressure of the model tunnel and a second principal stress of the model:

σ θ p = 2 ⁢ r 1 ( 2 - 2 ) ( P s ⁢ r 1 2 r 2 2 + P p + σ 2 ⁢ b 2 2 ⁢ π ⁢ r 1 ⁢ h ) ⁢ r 1 2 r 2 2 - r 1 2 ⁢ ( 1 + r 2 2 r 2 ) ( 8 ) σ r p = ( P s ⁢ r 1 2 r 2 2 + σ 2 ⁢ b 2 2 ⁢ π ⁢ r 1 ⁢ h ) ⁢ r 1 2 r 2 2 - r 1 2 ⁢ ( 1 + r 2 2 r 2 ) ( 9 ) σ z p = ( σ 3 ⁢ c 2 - P s ⁢ r 1 2 r 2 2 ⁢ π ) ⁢ S g ⁢ r 1 2 π ⁢ r 1 ⁢ h ⁡ ( r 1 2 - r 2 2 ) ( 10 )

• • a fourth working condition: combined action of internal water pressure of the model tunnel and a third principal stress of the model:

σ θ p = 2 ⁢ r 1 ( 2 - 2 ) ( P s ⁢ r 1 2 r 2 2 + P p + σ 2 ⁢ c 2 S g ) ⁢ r 1 2 r 2 2 - r 1 2 ⁢ ( 1 + r 2 2 r 2 ) ( 11 ) σ r p = ( P s ⁢ r 1 2 r 2 2 + σ 3 ⁢ c 2 S g ) ⁢ r 1 2 r 2 2 - r 1 2 ⁢ ( 1 + r 2 2 r 2 ) ( 12 ) σ z p = σ g ⁢ S g ⁢ r 1 2 π ⁢ r 1 ⁢ h ⁡ ( r 1 2 - r 2 2 ) ⁢ wherein ⁢ σ θ p , σ r p , σ z p ( 13 )

• •  are a circumferential average stress, a radial average stress, and an axial average stress respectively; a first principal stress in the cylinder under internal pressure is a circumferential stress, r1 is an inner diameter, i.e., a vertical straight-line distance from a center of the model bearing cylinder to an inner surface, r2 is an outer diameter, i.e., the vertical straight-line distance from the center of the model bearing cylinder to an outermost surface, r is the vertical straight-line distance from the center of the cylinder to the center of the inner and outer surfaces, P_s is an initial water pressure, P_p is a reaction force of the loading component, σ_g is a tensile stress of the model bearing cover plate, S_g is an area of the model bearing cover plate, h is a length of the model bearing cylinder, σ₁ is the first principal stress, σ₂ is the second principal stress, and σ₃ is the third principal stress;
  • t is a wall thickness of the model bearing cylinder, a circumferential stress is mainly generated by a balance between a tensile stress of the cylindrical steel plate and the water pressure; a radial stress is mainly provided by a normal water pressure and an axial deformation compression during loading; the tensile stresses on both sides are mainly provided by the model bearing cover plates on both sides to prevent rock mass deformation, and the water pressure acting on the model bearing cover plates on both sides and the axial stress acting on a rock mass;
  • a strength judgment criterion for the model bearing cylinder is:

p ⁢ K ⁢ 3 2 K 2 - 1 ≤ [ σ ] ( 14 ) P = σ r p 2 + σ z p 2 + σ θ p ⁢ 2 ( 15 )

• • wherein K is a ratio of inner and outer diameters, i.e., a ratio of the vertical straight-line distance from the center of the cylinder to the outermost surface to the vertical straight-line distance from the center of the cylinder to the inner surface;

t = 3 ⁢ p ⁢ r 2 3 ⁢ p + 4 [ σ ] ( 16 )

• • wherein stress states of the four working conditions are substituted into formula (16) respectively to obtain the wall thickness of the model bearing cylinder corresponding to the four working conditions: t1 is the wall thickness of the model bearing cylinder calculated for working condition 1, t2 is the wall thickness of the model bearing cylinder calculated for working condition 2, t3 is the wall thickness of the model bearing cylinder calculated for working condition 3, and t4 is the wall thickness of the model bearing cylinder calculated for working condition 4;
  • determining that a minimum wall thickness of the model bearing cylinder is not less than a maximum value of the wall thickness of the model bearing cylinder calculated for above four working conditions: tmin≥[t1, t2, t3, t4] max;
  • wherein [σ] is a allowable stress of a material, finally, when designing the wall thickness of the model bearing cylinder, a safety factor M is multiplied considering a safety during operation, i.e., a final designed wall thickness of the model bearing cylinder is Mtmin;
  • the model bearing cover plate is a metal component with a closed internal space, fixed on a thick-walled cylinder by bolts; a thickness of the model bearing cover plate is calculated, first the external force is simplified; a direction of an external force that mainly affects the thickness of the model bearing cover plate is radial; the cover plate is regarded as a component composed of multiple small cylinders; a single cylinder separately is analyzed, which is subject to radial external force everywhere; the external force on a single cylinder is regarded as a uniform load applied by a radial average stress on a single cylinder; a most unfavorable section is where a bending moment is the maximum; the single cylinder is analyzed to draw a bending moment diagram caused by the radial force to find that a most unfavorable section is a middle of the single cylinder, set as a dangerous section B;

M yB = 1 8 ⁢ σ r p ⁢ L 2 ( 17 )

• • wherein M_yB is the bending moment at the dangerous section B, L is a length of the single cylinder; according to the most unfavorable principle, the single cylinder with the largest L is taken, i.e., one in a middle of the model bearing cover plate, for the following analysis;
  • wherein the wall thickness of the model bearing cylinder of the model bearing cover plate, i.e., a diameter of the single cylinder, satisfies:

d ≥ ( 1 8 ⁢ σ r p ⁢ L 2 ) 2 3 [ σ ] ⁢ Π 3 ( 18 )

• • wherein d is the thickness of the model bearing cover plate, [σ] is an allowable stress; the reaction pad is an arc-shaped metal block attached to the model bearing cylinder, attached to an inside of the model bearing cylinder to provide reaction support for the device;
  • wherein the lined tunnel physical model is provided in the middle of the triaxial stress loading system, which is a cuboid rock lined tunnel physical model, the tunnel physical model and engineering site conditions must maintain similarity in shape and size, with corresponding equal angles, i.e., a prototype and the model maintain a certain proportional relationship, λ represents a scale ratio of the prototype quantity and the model quantity, a cross-sectional size of the lined tunnel physical model must satisfy a length scale:

{ λ 0 =   A 1 ⁢ L 2 A 2 ⁢ L 1 λ =   L y L S ( 19 )

• • wherein L_y is a size of the prototype, L_s is a mold size of the tunnel physical model, λ₀ is a scale ratio between an on-site tunnel and a model simulated tunnel, A₁ is a cross-sectional area of the on-site tunnel, L₁ is a cross-sectional perimeter of the on-site tunnel, A₂ is a cross-sectional area of the model simulated tunnel, and L₂ is a cross-sectional perimeter of the model simulated tunnel;
  • a brittleness similarity scale between the tunnel physical model and an original rock must satisfy:

λ ε ⁢ d = ε p ε m = 1 ( 20 )

• • wherein ε_p is a prototype peak strain, ε_m is a peak strain of the tunnel physical model;
  • a dynamic elastic modulus E_d and a dynamic Poisson's ratio μ_d are important indicators of rock dynamic characteristics; a dynamic elastic modulus similarity scale λ_Ed and a dynamic Poisson's ratio similarity scale λ_μd satisfy a following formulas:

λ Ed = λ σ λ ε = λ σ = λ y ⁢ λ L ( 21 ) λ μ ⁢ d = μ p μ m = 1 ( 22 )

• • wherein λ_σ is a stress similarity scale; λ_ε is a strain similarity scale, strain is a dimensionless physical quantity, so λ_ε=1;
  • to avoid boundary effects, a cross-sectional edge length a of the lined tunnel physical model must satisfy the following formula:

{ a d M > 5 D 2 = 4 ⁢ A 1 π ⁢ L 1 ( 23 )

• • wherein d_M is a hole diameter after drilling of the lined tunnel physical model, D₂ is a diameter of the model simulated tunnel; a size of the lined tunnel physical model in a tunnel axis direction is N times the cross-sectional size, and N>0.3; a grouting material of the lined tunnel physical model is similar to mechanical properties of the original rock, such as stress, strain, peak residual strength, seepage characteristics, and hydraulic splitting strength; a peak strain and stress of the lined tunnel physical model are the same as those of the original rock at an engineering site, and the seepage coefficient, seepage law, and hydraulic splitting strength are all the same as those of the original rock at the engineering site.

In one embodiment, the temperature control system comprises heating plates, which are four rectangular metal plates with electric heating wires inside, attached to the lined tunnel physical model.

In one embodiment, the internal water pressure control and the sealing system of the internal water pressure control comprises an internal water pressure loading pump, an internal water diversion pipe, a water filling and draining valve, end plugs on both sides, connecting tie rods for end plugs on both sides, an inner hole sealing sleeve, and a sealing loading pump;

• • the connecting tie rods are metal rods with threads on both sides, connected to the end plugs on both sides through threads;
  • the inner hole sealing sleeve is composed of a large cylinder and a small cylinder, with the centers of the two cylinders aligned and connected, used for sealing to prevent water overflow and provided on the end plugs;
  • the end plugs are composed of three circular cakes with a circular hole in the middle, and the circular cake on a side close to the connecting tie rods is also provided with multiple circular holes around the middle circular hole, used to block the water flow in the circular hole and further fixed with the connecting tie rods of the end plugs on both sides through fixing nuts;
  • the internal water pressure loading pump is connected to the external water pressure loading pump outside the water pressure tunnel model;
  • in the internal hole, both ends of the internal water pressure loading pump are respectively connected to both ends of the water filling and draining valve; the water filling and draining valve is a control device for controlling water filling and draining of the internal water pressure system;
  • the sealing loading pump is provided on a right side of the internal and external water pressure loading pumps and connected to both sides of a water tunnel seal.

In one embodiment, the external water pressure control system comprises an external water loading pipe, external water inlet and outlet valves, connecting pipes, connecting pipe seals, inner liners and the external water pressure loading pump;

• • the external water loading pipe is a spiral pipe with one-way holes; the connecting pipes are right-angle iron pipes; the inner liners are rock components loaded inside the holes after drilling; the external water inlet and outlet valves are control devices for water filling and draining of external water pressure; the connecting pipe seals are thick cylindrical rubber sleeves sleeved at joints between the connecting pipes and the external water loading pipe;
  • the external water pressure loading pump is connected to the internal water pressure loading pump outside the water pressure tunnel model, and connected to left and right connecting pipes inside the water pressure tunnel model.

In one embodiment, the intelligent control excavation support telescopic system comprises a drilling rig base, guide rails, an X-axis moving block, a trolley motor, a servo motor, sliding blocks, a tray and a base support;

• • the drilling rig base is a rectangular steel wire frame, which is composed of a rectangular wire frame connected to a square wire frame, and then the square wire frame connected to a rectangular wire frame, serving as a bottom part of the intelligent control excavation support telescopic system;
  • the guide rails are groove-shaped long rails fixed on the base by bolts; the sliding blocks are groove-shaped metal components matching a size of the guide rails, provided on the guide rails and connected to the supporting plate by bolts;
  • the supporting plate is a rectangular steel plate placed on the sliding blocks; the X-axis moving block is an annular metal component with a parameter of a circular hole being a diameter of an extension rod of the trolley motor; the X-axis moving block is strung on the trolley motor, and the servo motor is provided at a right end of the trolley motor; the integral structure composed of the X-axis moving block, the trolley motor and the servo motor is placed in a middle of two pairs of sliding blocks under the supporting plate;
  • the base support is a rectangular steel frame composed of two small rectangular frames, and the bearing cylinder smaller than the base is fixed on the supporting plate by bolts.

In one embodiment, the intelligent control excavation load application system comprises a drill bit, a connecting shaft, supports, linear bearings, reaction rods, tapered roller bearings, a planetary reducer, an oil pressure cylinder and pull rods;

• • the drill bit has a variety of shapes and sizes, and a diameter of the drill bit satisfies a ratio of a tunnel diameter at the engineering site to a scale ratio of prototype quantity and model quantity;
  • the connecting shaft is composed of a large thick cylinder and a small thick cylinder, with centers of the two cylinders aligned and connected, serving as an intermediate device for connecting the drill bit and the planetary reducer;
  • the support is a square steel plate with a circular hole in the middle, and a reaction rod insertion hole at each of four corners of the steel plate, providing a working platform for drill bit excavation; the tapered roller bearing is a radial-thrust rolling bearing, which is a circular steel plate with a circular hole in the middle, provided on the planetary reducer;
  • the oil pressure cylinder provides power for the drill bit operation, a left end of the oil pressure cylinder is connected to the planetary reducer through the reaction rod and a right end of the oil pressure cylinder is provided on the right support; the pull rods are rod-shaped metal components used for connecting the left and right supports; the reaction rods are rod-shaped metal components.

In one embodiment, the multi-element monitoring information collection system comprises a professional engineering camera, an acoustic emission instrument and a multi-functional data monitoring recorder;

• • the professional engineering camera is placed in a drilled hole of the lined tunnel physical model to shoot and record internal changes;
  • the acoustic emission instrument is a device that uses sound waves to detect cracks, damage positions and damage conditions of the lined tunnel physical model, and placed on both sides of the instrument and connected to the lined tunnel physical model through sensing wires;
  • the multi-functional data monitoring recorder comprises water pressure needles for monitoring water pressure changes of the lined tunnel physical model during water filling and draining, and deformation optical fibers, pressure needles, crack measuring needles, flow needles, pore pressure needles and steel bar needles for monitoring working conditions of the lining and surrounding rock;
  • the multi-functional data monitoring recorder is provided inside the lining, between a hydraulic pillow and the lined tunnel physical model, between the front and rear bladders and the lined tunnel physical model, between a heating plate and the lined tunnel physical model, and between the lining and the surrounding rock;
  • the lining of the lined tunnel physical model is formed by concrete pouring and curing, and a number of circumferential steel bars are provided at intervals perpendicular to a longitudinal axis of the pressure tunnel inside the lining of the lined tunnel physical model, and a number of longitudinal steel bars are provided at intervals parallel to the longitudinal axis of the pressure tunnel;
  • a crack is preset on an inner wall of the lined tunnel physical model; two monitoring sections A-A and B-B perpendicular to an axis of the pressure tunnel are selected at intervals along an axial direction of the pressure tunnel;
  • the crack measuring needles are provided at cracks of the monitoring section containing a preset crack, and two crack measuring needles are provided across the preset crack; a top center of the cylindrical cylinder is a 0° direction, and the pore pressure needles are provided at the 0°, 45°, 90°, 135°, 170°, 225°, 270° and 315° positions of the A-A and B-B monitoring sections respectively in a clockwise direction;
  • the pore pressure needles on each monitoring section are at a same distance from a central axis of the pressure tunnel; a top center of the cylindrical cylinder is the 0° direction, and the water pressure needles are provided on an outer wall of the lining at the 0°, 100°, 150°, 225° and 280° positions of the A-A and B-B monitoring sections respectively in the clockwise direction; the top center of the cylindrical cylinder is the 0° direction, and the steel bar needles are provided on the lining steel bars at the 0°, 30°, 150°, 210° and 320° positions of the A-A and B-B monitoring sections respectively in the clockwise direction;
  • when pouring the lining, the flow needles are pre-wound into a circle and provided in a circle around an edge inside a lining mold, and four circles of the deformation optical fibers are evenly provided inside the lining mold;
  • the surrounding rock of the lined tunnel physical model is made by pouring, cutting and polishing the selected rock mass, and four cracks are preset in the surrounding rock;
  • one monitoring section 1-1 perpendicular to the axis of the pressure tunnel is set along the axial direction of the pressure tunnel;
  • with the top center as the 0° direction, four cracks are preset at 0°, 90°, 180° and 270° positions respectively in the clockwise direction;
  • a top center of the square surrounding rock is the 0° direction, and the pressure needles are provided inside the surrounding rock at the 15°, 75°, 105°, 165°, 195°, 255°, 285° and 345° positions in the clockwise direction;
  • the pressure needles are at a same distance from the central axis of the pressure tunnel; the water pressure needles are provided at the preset cracks, and three water pressure needles are provided across each preset crack; and
  • when making the surrounding rock, four circles of the deformation optical fibers are evenly provided inside the lining mold.

Installation method and usage method of the large-scale model test device for excavation, water filling and splitting of high internal and external water pressure tunnels includes:

• • Step 1: placing the base at a set position, installing the model bearing cylinder above the base and fitting the model bearing cylinder tightly with bolts, and fixing the reaction pad on an inner side of the model bearing cylinder;
  • Step 2: fixing the hydraulic pillow horizontally in a square shape on the inner side of the reaction pad, then installing the wedge-shaped pressure head on an inner side of the hydraulic pillow and mounting the multi-functional data monitoring recorder, and finally installing the heating plates on inner sides of the wedge-shaped pressure heads and mounting the multi-functional data monitoring recorder;
  • Step 3: placing the drill bit and the base at a proper position right in front of a provided instrument and fix the drill bit and the base, installing a guide rail above the drill bit and the base and fixing the guide rail with bolts, embedding the sliding block in the guide rail, and then fixing the supporting plate with the sliding block through bolts;
  • Step 4: assembling the X-axis moving block, trolley motor and servo motor into an integral kit, installing the integral kit in the middle of the guide rail under the supporting plate, and then fixing the base support on the supporting plate with bolts;
  • Step 5: installing the tapered roller bearing on the planetary reducer, connecting and fixing the oil pressure cylinder at a right end of the planetary reducer, installing the linear bearing on the reaction rod and passing it through the oil pressure cylinder, enclosing all the above parts between the left and right supports, connecting and fixing the left and right supports through pull rods, and finally connecting the drill bit to the tapered roller bearing through the connecting shaft;
  • Step 6: connecting an interface of the computer to force sensors of each loading oil cylinder, displacement sensors and deformation sensors in all directions respectively, and recording the force values and displacement deformation data of the lined tunnel physical model in all directions during experiment through a computer; and collecting sound information during rock sample experiment in real time by means of acoustic emission and microseismic monitoring;
  • Step 7: installing the lined tunnel physical model in the triaxial stress loading system, and fitting various functional metal components tightly with each other and finally with the lined tunnel physical model firmly;
  • Step 8: after placing the lined tunnel physical model, fitting pressure plates on front and rear sides of the lined tunnel physical model, then fitting the front and rear bladders tightly with the pressure plates, installing the multi-functional data monitoring recorder after confirming no errors, covering the model bearing cover plate and fixing the model bearing cover plate with bolts;
  • Step 9: starting the loading device connected to the heating plate to heat up the lined tunnel physical model, and starting the internal and external water pressure loading devices to filling water pipes with water, and applying water-rich conditions to a rock mass near a one-way hole pipe through one-way holes on the water pipes;
  • Step 10: after heating up to a specified temperature, starting front-rear and vertical loading devices; the front and rear bladders starting to apply pressure to the pressure plates, wherein the pressure is transmitted to front and rear sides of the lined tunnel physical model through the pressure plates; the hydraulic pillow starts to apply pressure to the wedge-shaped pressure heads, and the pressure is transmitted to the heating plates through the wedge-shaped pressure heads and finally to an upper, lower, left and right directions of the lined tunnel physical model through the heating plates;
  • Step 11: transmitting the pressure applied by the front and rear bladders and hydraulic pillows to the lined tunnel physical model through metal components to complete preloading; after preloading is completed, increasing the oil pressure and performing formal loading on the lined tunnel physical model until the pressure specified in the experiment is reached;
  • Step 12: starting the intelligent control multi-mode excavation system; the drill bit starting to rotate, and the trolley motor driving the supporting plate to move along an X-axis towards the lined tunnel physical model on the guide rail through the sliding block; after contact, starting excavation and record data such as stress and deformation during excavation until the excavation is completed; after excavation, operating the trolley motor to drive the supporting plate to move along the X-axis away from the lined tunnel physical model on the guide rail through the sliding block until the drilling rig leaves an inside of the water pressure tunnel model;
  • Step 13: after drilling the lined tunnel physical model, installing a professional engineering camera in a drilled hole, then installing the water tunnel seal, starting the loading device to fill water into the internal hole sealed by the water tunnel seal and applying internal water pressure to the internal hole; a force applied by the sealing loading satisfies

P m > ( ∑ x = 0 n ( P t / S ) × S x ) ± Δ ⁢ P

• •  and is sufficient to keep a sealing loading force greater than the water pressure; turning on a flow control of the water pipe to fill the water pipe with water and applying water-rich conditions to the lined tunnel physical model through the one-way holes opened on the water pipe; recording the internal water pressure, deformation, temperature change and stress, and observing the lining damage through the professional engineering camera;
  • Step 14: performing step-by-step water filling and draining into the water tunnel seal formed by the experimental device to simulate groundwater pressure and the internal water pressure loading and unloading working conditions; connecting the pressure water pump to a joint of the water tunnel seal, and performing step-by-step water filling into the water tunnel seal; during the water filling process, continuing filling until the lining is damaged, recording the data at this time, and continuing filling until hydraulic splitting of the surrounding rock occurs which is an end point of the water filling stage; recording the hydraulic splitting data; after a step-by-step water filling stage is completed, opening the water tunnel seal for step-by-step water draining; to refine the water pressure conditions during lining damage and hydraulic splitting in a water filling process, setting a water filling pressure gradient; since the water pressure at water use points in the tunnel is generally not less than 0.3 MPa and 1.5 times that under working conditions, rounding it up and setting the water filling pressure gradient to 0.5 MPa per level, and setting each water filling pressure increment to one-tenth of the water filling pressure gradient; wherein a number of water filling steps when the water filling pressure is 0.5 MPa, a total number of water filling steps, and a total number of water filling and draining steps are as follows:

S 1 = P 1 Δ ⁢ P ( 24 ) S = P t Δ ⁢ P ( 25 ) S total = 2 × S ( 26 )

• • wherein S1 is the number of water filling steps when the water filling pressure is equal to a set value; S is the total number of water filling steps; S_total is the total number of water filling and draining steps; P1 is a water filling pressure of the set value; Pt is a designed water head of the pressure tunnel, unit in MPa; ΔP is a loading and unloading amplitude of step-by-step water filling and draining pressure, unit in MPa;
  • Step 15: during the step-by-step water filling and draining into the water tunnel seal, if no damage occurs at each level or the value does not change significantly, proceed to a next step according to the plan after meeting a following time requirement; wherein a duration of pressure loading or unloading for each level of water filling and draining is:

T k = ⁢ { 120 ⁢ s , 0 < K ≤ S 1 240 ⁢ s , S 1 < K ≤ S 120 ⁢ s , S < K ≤ S total ( 27 )

• • wherein Tk is a duration of pressure loading or unloading for a K-th level of water filling and draining; K is a number of step-by-step water filling and draining steps; during the step-by-step water filling and draining into the water tunnel seal, reading a pressure gauge reading and record the change of internal water pressure; during the step-by-step water filling and draining into the water tunnel seal, recording a change of lining crack width in real time; during the step-by-step water filling and draining into the water tunnel seal, wherein the multi-functional data monitoring recorder performs data recording and monitoring, the professional engineering camera shoots and records video files, and the acoustic emission instrument collects sound information;
  • Step 16: during the internal water pressure loading and unloading process, the front and rear bladders cooperate with the water filling pressure change formula and water draining pressure change formula to load and unload pressure on the pressure plates; a dynamic pressure adjustment of the front and rear bladders meets the following formulas:

F t = P + F 1 ( 28 ) F = ( F t - P ) / 2 ( 29 )

• • wherein Ft is the total pressure and kept unchanged; F1 is a total pressure on both sides; F is a pressure on one side;
  • P is the water pressure and satisfies

( ∑ x = 0 n ( P t / S ) × S x ) ± Δ ⁢ P ,

• •  where S_x is a x-th water filling step to ensure a coordination between the internal water pressure of the lined tunnel physical model and the external loading pressure, and balance the loading and the internal water pressure of the surrounding rock under a condition that the total pressure remains unchanged for dynamic adjustment, so that an overall stress of the surrounding rock remains unchanged during the water filling process; continuing to observe and simulate the hydraulic splitting extending from the hole inside the surrounding rock, and record pressure and deformation data; observing, monitoring and recording the stress, strain, water content of the lined tunnel physical model, an audio and video of lining damage, the audio and video of hydraulic splitting of the surrounding rock, and a change of crack width during the water filling and draining process; observing, monitoring and recording a stress change and strain change of the lined tunnel physical model during triaxial stress loading and temperature adjustment; and
  • Step 17: after all experimental items are completed, starting to unload, cool down and reduce oil pressure, saving data and audio-visual materials, and finally checking the condition of the device to complete an experiment.

Beneficial Effects of the Present Application

Compared with the related art, the present application has the following significant advantages: first, it truly simulates the underground environment with high temperature and high water pressure, and subdivides the water pressure into internal water pressure and external water pressure to make the simulation of the underground environment more realistic. It realizes THM multi-field coupling excavation under three-dimensional stress. Multiple conditions can be applied and adjusted independently, which greatly improves the multi-dimensional functions of the experiment. In addition, multiple experiments can be carried out separately, that is, one set of device can meet the device conditions for multiple experiments. On this basis, it can realize the simulation of the operation of water-filling and draining lined tunnels under high internal and external water pressure after lining application, the physical simulation of the whole process of hydraulic splitting of surrounding rock, and the monitoring of multiple information such as stress, deformation, internal and external water pressure, seepage, cracking and temperature gradient of surrounding rock and lining. Moreover, video data can be used to record the changes in the inner cavity. Second, in order to meet the needs and ensure the normal operation of the device, the overall structure of the thick-walled cylinder is improved, the overall strength is enhanced, and the operation steps are simplified. The present application provides practical and feasible hardware conditions for studying the simulation of underground real geotechnical materials and excavation under multiple factors in complex environments, and is of great significance to the field of rock mechanics research.

BRIEF DESCRIPTIONS OF THE DRAWINGS

FIG. 1 is a three-dimensional (3D) schematic diagram of a structure of a large-scale model test device for excavation, water filling and splitting of high internal and external water pressure tunnels according to the present application.

FIG. 2 is a front view of the large-scale model test device for excavation, water filling and splitting of high internal and external water pressure tunnels according to the present application.

FIG. 3 is a top view of the large-scale model test device for excavation, water filling and splitting of high internal and external water pressure tunnels according to the present application.

FIG. 4 is a 3D schematic diagram of a water pressure tunnel model of the large-scale model test device for excavation, water filling and splitting of high internal and external water pressure tunnels according to the present application.

FIG. 5 is a cross-sectional view of the water pressure tunnel model of the large-scale model test device for excavation, water filling and splitting of high internal and external water pressure tunnels according to the present application.

FIG. 6 is a front cross-sectional view of the water pressure tunnel model of the large-scale model test device for excavation, water filling and splitting of high internal and external water pressure tunnels according to the present application.

FIG. 7 is a 3D schematic diagram of a drilling rig assembly of the large-scale model test device for excavation, water filling and splitting of high internal and external water pressure tunnels according to the present application.

FIG. 8 is a cross-sectional view of the drilling rig assembly of the large-scale model test device for excavation, water filling and splitting of high internal and external water pressure tunnels according to the present application.

FIG. 9 is a side cross-sectional view of the drilling rig assembly of the large-scale model test device for excavation, water filling and splitting of high internal and external water pressure tunnels according to the present application.

FIG. 10 is a schematic diagram of an external water pressure filling device of the large-scale model test device for excavation, water filling and splitting of high internal and external water pressure tunnels according to the present application.

FIG. 11 is a schematic diagram of an internal water pressure filling device of the large-scale model test device for excavation, water filling and splitting of high internal and external water pressure tunnels according to the present application.

FIG. 12 is a schematic diagram of a monitoring section position of a lining of the large-scale model test device for excavation, water filling and splitting of high internal and external water pressure tunnels according to the present application.

FIG. 13 is a schematic diagram of a monitoring section position of a surrounding rock of the large-scale model test device for excavation, water filling and splitting of high internal and external water pressure tunnels according to the present application.

FIG. 14 is a schematic diagram of an arrangement position of monitoring device on the 1-1 section of a surrounding rock of the large-scale model test device for excavation, water filling and splitting of high internal and external water pressure tunnels according to the present application.

FIG. 15 is a schematic diagram of the arrangement position of steel bar meters on the A-A section of the lining of the large-scale model test device for excavation, water filling and splitting of high internal and external water pressure tunnels according to the present application.

FIG. 16 is a schematic diagram of the arrangement position of monitoring device on the B-B section of the lining of the large-scale model test device for excavation, water filling and splitting of high internal and external water pressure tunnels according to the present application.

FIG. 17 is an oil circuit diagram of the large-scale model test device for excavation, water filling and splitting of high internal and external water pressure tunnels according to the present application.

FIG. 18 is a schematic diagram of the step-by-step water filling and draining scheme of the water pressure tunnel model according to the present application.

DETAILED DESCRIPTIONS OF EMBODIMENTS

The present application will be further described in detail below with reference to the accompanying drawings and embodiments.

To achieve the above objective, the present application adopts the following technical solutions:

A large-scale model test device for excavation, water filling and splitting of high internal and external water pressure tunnels includes:

• • an intelligent control excavation support telescopic system, an intelligent control excavation load application system, a barrel-shaped triaxial reaction system, a triaxial stress loading system, an internal water pressure controlling and sealing system, an external water pressure control system, a temperature control system, a multi-element monitoring information collection system, and a lined tunnel physical model 13;
  • wherein a water pressure tunnel model comprises the barrel-shaped triaxial reaction system, the triaxial stress loading system, the internal water pressure controlling and sealing system, the external water pressure control system, the temperature control system, and the multi-element monitoring information collection system;
  • wherein a drilling rig assembly comprises the intelligent control excavation support telescopic system and the intelligent control excavation load application system;
  • wherein the barrel-shaped triaxial reaction system is a main frame of the water pressure tunnel model, and the triaxial stress loading system is provided inside the barrel-shaped triaxial reaction system;
  • wherein the temperature control system, attached to the lined tunnel physical model 13, is provided in a middle of the triaxial stress loading system;
  • wherein the intelligent control excavation support telescopic system is placed right in front of the barrel-shaped triaxial reaction system, and the intelligent control excavation load application system is provided above the intelligent control excavation support telescopic system;
  • wherein the multi-element monitoring information collection system is connected to and provided inside the barrel-shaped triaxial reaction system, the triaxial stress loading system, the internal water pressure controlling and sealing system, the external water pressure control system, and the temperature control system, and
  • an oil circuit loading system controls the start of the large-scale model test device;
  • wherein the triaxial stress loading system comprises front and rear bladders 7, pressure plates 8, hydraulic pillows 3, and wedge-shaped pressure heads 4; the front and rear bladders 7 each are square metal plates with a circular hollow in a middle, fixed on a model bearing cover plate 6 and connected to a vertical loading pump on a right side of a horizontal loading pump,
  • wherein the horizontal loading pump satisfies a balanced loading of a pressure of the front and rear bladders 7 on both sides of the barrel, ensuring that a stress on a loaded model remains unchanged when a water injection pressure increases:

P w × S 1 = ( P 0 + Δ ⁢ P f ) × S 2 ( 1 )

• • wherein P_w is a water injection pressure, S₁ is an area of the front and rear bladders 7, P₀ is an initial stress, ΔP_f is an increased stress, and S₂ is a contact area between the front and rear bladders 7 and the lined tunnel physical model 13;
  • wherein the pressure plates 8 are metal plates with a same size and shape as the front and rear bladders 7, provided inside the front and rear bladders 7; the wedge-shaped pressure heads 4 are four rectangular metal plates attached to an outside of the heating plate 5;
  • wherein the hydraulic pillows 3 are four rectangular metal plates attached to an outside of the wedge-shaped pressure heads 4 to apply pressure to the lined tunnel physical model 13 and are connected to the front and rear loading pumps;
  • wherein the barrel-shaped triaxial reaction system comprises a base 11, a model bearing cylinder, a model bearing cover plate 6, and a reaction pad 2; the base 11 is a frustum with a hollow cuboid in a middle, and left and right sides of the frustum are designed with semicircular holes with a same radian as the frame, provided at the bottom of the large-scale model test device, in continuous arc contact with a model bearing cylinder, the model bearing cylinder is a thick-walled cylinder 1 provided on the base 11 and closely attached to the base 11; a wall thickness of the model bearing cylinder is determined as follows:
  • the wall thickness of the model bearing cylinder is determined according to four working conditions of an unfavorable combination of operating conditions:
  • a first working condition: internal water pressure of a model tunnel:

σ θ p = 2 ⁢ r 1 ( 2 - 2 ) ( P s ⁢ r 1 2 r 2 2 + P p ) ⁢ r 1 2 r 2 2 - r 1 2 ⁢ ( 1 + r 2 2 r 2 ) ( 2 ) σ r p = P s ⁢ r 1 2 r 2 2 ⁢ r 1 2 r 2 2 - r 1 2 ⁢ ( 1 + r 2 2 r 2 ) ( 3 ) σ z p = ( σ 1 ⁢ a 2 - P s ⁢ r 1 2 r 2 2 ⁢ π ) ⁢ S g ⁢ r 1 2 π ⁢ r 1 ⁢ h ⁡ ( r 1 2 - r 2 2 ) ( 4 )

• • a second working condition: combined action of internal water pressure of the model tunnel and a maximum principal stress of the model:

σ θ p = 2 ⁢ r 1 ( 2 - 2 ) ( P s ⁢ r 1 2 r 2 2 + P p + σ 1 ⁢ a 2 2 ⁢ π ⁢ r 1 ⁢ h ) ⁢ r 1 2 r 2 2 - r 1 2 ⁢ ( 1 + r 2 2 r 2 ) ( 5 ) σ r p = ( P s ⁢ r 1 2 r 2 2 + σ 1 ⁢ a 2 2 ⁢ π ⁢ r 1 ⁢ h ) ⁢ r 1 2 r 2 2 - r 1 2 ⁢ ( 1 + r 2 2 r 2 ) ( 6 ) σ z p = ( σ 2 ⁢ b 2 - P s ⁢ r 1 2 r 2 2 ⁢ π ) ⁢ S g ⁢ r 1 2 π ⁢ r 1 ⁢ h ⁡ ( r 1 2 - r 2 2 ) ( 7 )

• • a third working condition: combined action of internal water pressure of the model tunnel and a second principal stress of the model:

σ θ p = 2 ⁢ r 1 ( 2 - 2 ) ( P s ⁢ r 1 2 r 2 2 + P p + σ 2 ⁢ b 2 2 ⁢ π ⁢ r 1 ⁢ h ) ⁢ r 1 2 r 2 2 - r 1 2 ⁢ ( 1 + r 2 2 r 2 ) ( 8 ) σ r p = ( P s ⁢ r 1 2 r 2 2 + σ 2 ⁢ b 2 2 ⁢ π ⁢ r 1 ⁢ h ) ⁢ r 1 2 r 2 2 - r 1 2 ⁢ ( 1 + r 2 2 r 2 ) ( 9 ) σ z p = ( σ 3 ⁢ c 2 - P s ⁢ r 1 2 r 2 2 ⁢ π ) ⁢ S g ⁢ r 1 2 π ⁢ r 1 ⁢ h ⁡ ( r 1 2 - r 2 2 ) ( 10 )

• • a fourth working condition: combined action of internal water pressure of the model tunnel and a third principal stress of the model:

σ θ p = 2 ⁢ r 1 ( 2 - 2 ) ( P s ⁢ r 1 2 r 2 2 + P p + σ 3 ⁢ c 2 S g ) ⁢ r 1 2 r 2 2 - r 1 2 ⁢ ( 1 + r 2 2 r 2 ) ( 11 ) σ r p = ( P s ⁢ r 1 2 r 2 2 + σ 3 ⁢ c 2 S g ) ⁢ r 1 2 r 2 2 - r 1 2 ⁢ ( 1 + r 2 2 r 2 ) ( 12 ) σ z p = σ g ⁢ S g ⁢ r 1 2 π ⁢ r 1 ⁢ h ⁡ ( r 1 2 - r 2 2 ) ( 13 ) wherein ⁢ σ θ p , σ r p , σ z p

• • are a circumferential average stress, a radial average stress, and an axial average stress respectively; a first principal stress in the cylinder under internal pressure is a circumferential stress, r1 is an inner diameter, i.e., a vertical straight-line distance from a center of the model bearing cylinder to an inner surface, r2 is an outer diameter, i.e., the vertical straight-line distance from the center of the model bearing cylinder to an outermost surface, r is the vertical straight-line distance from the center of the cylinder to the center of the inner and outer surfaces, P_s is an initial water pressure, P_p is a reaction force of the loading component, σ_g is a tensile stress of the model bearing cover plate 6, S_g is an area of the model bearing cover plate 6, h is a length of the model bearing cylinder, σ₁ is the first principal stress, σ₂ is the second principal stress, and σ₃ is the third principal stress;
  • t is a wall thickness of the model bearing cylinder, a circumferential stress is mainly generated by a balance between a tensile stress of the cylindrical steel plate and the water pressure; a radial stress is mainly provided by a normal water pressure and an axial deformation compression during loading; the tensile stresses on both sides are mainly provided by the model bearing cover plates 6 on both sides to prevent rock mass deformation, and the water pressure acting on the model bearing cover plates 6 on both sides and the axial stress acting on a rock mass;
  • a strength judgment criterion for the model bearing cylinder is:

p ⁢ K ⁢ 3 2 K 2 - 1 ≤ [ σ ] ( 14 ) P = σ r p 2 + σ z p 2 + σ θ p ⁢ 2 ( 15 )

• • wherein K is a ratio of inner and outer diameters, i.e., a ratio of the vertical straight-line distance from the center of the cylinder to the outermost surface to the vertical straight-line distance from the center of the cylinder to the inner surface;

t = 3 ⁢ pr 2 3 ⁢ p + 4 [ σ ] ( 16 )

• • wherein stress states of the four working conditions are substituted into formula (16) respectively to obtain the wall thickness of the model bearing cylinder corresponding to the four working conditions: t1 is the wall thickness of the model bearing cylinder calculated for working condition 1, t2 is the wall thickness of the model bearing cylinder calculated for working condition 2, t3 is the wall thickness of the model bearing cylinder calculated for working condition 3, and t4 is the wall thickness of the model bearing cylinder calculated for working condition 4;
  • determining that a minimum wall thickness of the model bearing cylinder is not less than a maximum value of the wall thickness of the model bearing cylinder calculated for above four working conditions: tmin≥[t1, t2, t3, t4] max
  • wherein [σ] is a allowable stress of a material, finally, when designing the wall thickness of the model bearing cylinder, a safety factor M is multiplied considering a safety during operation, i.e., a final designed wall thickness of the model bearing cylinder is Mtmin;
  • the model bearing cover plate 6 is a metal component with a closed internal space, fixed on a thick-walled cylinder 1 by bolts; a thickness of the model bearing cover plate 6 is calculated, first the external force is simplified; a direction of an external force that mainly affects the thickness of the model bearing cover plate 6 is radial; the cover plate is regarded as a component composed of multiple small cylinders; a single cylinder separately is analyzed, which is subject to radial external force everywhere; the external force on a single cylinder is regarded as a uniform load applied by a radial average stress on a single cylinder; a most unfavorable section is where a bending moment is the maximum; the single cylinder is analyzed to draw a bending moment diagram caused by the radial force to find that a most unfavorable section is a middle of the single cylinder, set as a dangerous section B;

M yB = 1 8 ⁢ σ r p ⁢ L 2 ( 17 )

• • wherein M_yB is the bending moment at the dangerous section B, L is a length of the single cylinder; according to the most unfavorable principle, the single cylinder with the largest L is taken, i.e., one in a middle of the model bearing cover plate 6, for the following analysis;
  • wherein the wall thickness of the model bearing cylinder of the model bearing cover plate 6, i.e., a diameter of the single cylinder, satisfies:

d ≥ ( 1 8 ⁢ σ r p ⁢ L 2 ) 2 3 [ σ ] ⁢ Π 3 ( 18 )

• • wherein d is the thickness of the model bearing cover plate 6, [σ] is an allowable stress; the reaction pad 2 is an arc-shaped metal block attached to the model bearing cylinder, attached to an inside of the model bearing cylinder to provide reaction support for the device;
  • wherein the lined tunnel physical model 13 is provided in the middle of the triaxial stress loading system, which is a cuboid rock lined tunnel physical model 13, the tunnel physical model and engineering site conditions must maintain similarity in shape and size, with corresponding equal angles, i.e., a prototype and the model maintain a certain proportional relationship, λ represents a scale ratio of the prototype quantity and the model quantity, a cross-sectional size of the lined tunnel physical model 13 must satisfy a length scale:

{ λ 0 = A 1 ⁢ L 2 A 2 ⁢ L 1 λ = L y L S ( 19 )

• • wherein L_y is a size of the prototype, L_s is a mold size of the tunnel physical model, λ₀ is a scale ratio between an on-site tunnel and a model simulated tunnel, A₁ is a cross-sectional area of the on-site tunnel, L₁ is a cross-sectional perimeter of the on-site tunnel, A₂ is a cross-sectional area of the model simulated tunnel, and L₂ is a cross-sectional perimeter of the model simulated tunnel;
  • a brittleness similarity scale between the tunnel physical model and an original rock must satisfy:

λ ε ⁢ d = ε p ε m = 1 ( 20 )

• • wherein ε_p is a prototype peak strain, ε_m is a peak strain of the tunnel physical model;
  • a dynamic elastic modulus E_d and a dynamic Poisson's ratio μ_d are important indicators of rock dynamic characteristics; a dynamic elastic modulus similarity scale λ_Ed and a dynamic Poisson's ratio similarity scale λ_μd satisfy a following formulas:

λ Ed = λ σ λ ε = λ σ = λ y ⁢ λ L ( 21 ) λ μ ⁢ d = μ p μ m = 1 ( 22 )

• • wherein λ_σ is a stress similarity scale; λ_ε is a strain similarity scale, strain is a dimensionless physical quantity, so λ_ε=1,
  • to avoid boundary effects, a cross-sectional edge length a of the lined tunnel physical model 13 must satisfy the following formula:

{ a d M > 5 D 2 = 4 ⁢ A 1 π ⁢ L 1 ( 23 )

• • wherein d_M is a hole diameter after drilling of the lined tunnel physical model 13, D₂ is a diameter of the model simulated tunnel; a size of the lined tunnel physical model 13 in a tunnel axis direction is N times the cross-sectional size, and N>0.3; a grouting material of the lined tunnel physical model 13 is similar to mechanical properties of the original rock, such as stress, strain, peak residual strength, seepage characteristics, and hydraulic splitting strength; a peak strain and stress of the lined tunnel physical model 13 are the same as those of the original rock at an engineering site, and the seepage coefficient, seepage law, and hydraulic splitting strength are all the same as those of the original rock at the engineering site.

The temperature control system comprises heating plates 5, which are four rectangular metal plates with electric heating wires inside, attached to the lined tunnel physical model 13.

The internal water pressure control and the sealing system of the internal water pressure control comprises an internal water pressure loading pump, an internal water diversion pipe 46, a water filling and draining valve 102, end plugs 101 on both sides, connecting tie rods 103 for end plugs 101 on both sides, an inner hole sealing sleeve 104, and a sealing loading pump;

the connecting tie rosd 103 are metal rods with threads on both sides, connected to the end plugs 101 on both sides through threads;

• • the inner hole sealing sleeve 104 is composed of a large cylinder and a small cylinder, with the centers of the two cylinders aligned and connected, used for sealing to prevent water overflow and provided on the end plugs 101;
  • the end plugs 101 are composed of three circular cakes with a circular hole in the middle, and the circular cake on a side close to the connecting tie rods 103 is also provided with multiple circular holes around the middle circular hole, used to block the water flow in the circular hole and further fixed with the connecting tie rods 103 of the end plugs 101 on both sides through fixing nuts 105;
  • the internal water pressure loading pump is connected to the external water pressure loading pump outside the water pressure tunnel model;
  • in the internal hole, both ends of the internal water pressure loading pump are respectively connected to both ends of the water filling and draining valve 102; the water filling and draining valve 102 is a control device for controlling water filling and draining of the internal water pressure system;
  • the sealing loading pump is provided on a right side of the internal and external water pressure loading pumps and connected to both sides of a water tunnel seal 10.

The external water pressure control system comprises an external water loading pipe 9, external water inlet and outlet valves 43, connecting pipes 42, connecting pipe seals 44, inner liners 12 and the external water pressure loading pump;

• • the external water loading pipe 9 is a spiral pipe with one-way holes; the connecting pipes 42 are right-angle iron pipes; the inner liners 12 are rock components loaded inside the holes after drilling; the external water inlet and outlet valves 43 are control devices for water filling and draining of external water pressure; the connecting pipe seals 44 are thick cylindrical rubber sleeves sleeved at joints between the connecting pipes 42 and the external water loading pipe 9;
  • the external water pressure loading pump is connected to the internal water pressure loading pump outside the water pressure tunnel model, and connected to left and right connecting pipes 42 inside the water pressure tunnel model.

The intelligent control excavation support telescopic system comprises a drilling rig base 20, guide rails, an X-axis moving block 25, a trolley motor 22, a servo motor 23, sliding blocks 16, a tray and a base support 19;

• • the drilling rig base 20 is a rectangular steel wire frame, which is composed of a rectangular wire frame connected to a square wire frame, and then the square wire frame connected to a rectangular wire frame, serving as a bottom part of the intelligent control excavation support telescopic system;
  • the guide rails are groove-shaped long rails fixed on the base 11 by bolts; the sliding blocks 16 are groove-shaped metal components matching a size of the guide rails, provided on the guide rails and connected to the supporting plate 27 by bolts;
  • the supporting plate 27 is a rectangular steel plate placed on the sliding blocks 16; the X-axis moving block 25 is an annular metal component with a parameter of a circular hole being a diameter of an extension rod of the trolley motor 22; the X-axis moving block 25 is strung on the trolley motor 22, and the servo motor 23 is provided at a right end of the trolley motor 22; the integral structure composed of the X-axis moving block 25, the trolley motor 22 and the servo motor 23 is placed in a middle of two pairs of sliding blocks 16 under the supporting plate 27;
  • the base support 19 is a rectangular steel frame composed of two small rectangular frames, and the bearing cylinder smaller than the base 11 is fixed on the supporting plate 27 by bolts.

The intelligent control excavation load application system comprises a drill bit 14, a connecting shaft 15, supports, linear bearings 17, reaction rods 32, tapered roller bearings 18, a planetary reducer 30, an oil pressure cylinder 26 and pull rods;

• • the drill bit 14 has a variety of shapes and sizes, and a diameter of the drill bit 14 satisfies a ratio of a tunnel diameter at the engineering site to a scale ratio of prototype quantity and model quantity;
  • the connecting shaft 15 is composed of a large thick cylinder and a small thick cylinder, with centers of the two cylinders aligned and connected, serving as an intermediate device for connecting the drill bit 14 and the planetary reducer 30;
  • the support is a square steel plate with a circular hole in the middle, and a reaction rod 32 insertion hole at each of four corners of the steel plate, providing a working platform for drill bit 14 excavation; the tapered roller bearing 18 is a radial-thrust rolling bearing, which is a circular steel plate with a circular hole in the middle, provided on the planetary reducer 30;
  • the oil pressure cylinder 26 provides power for the drill bit 14 operation, a left end of the oil pressure cylinder 26 is connected to the planetary reducer 30 through the reaction rod 32 and a right end of the oil pressure cylinder 26 is provided on the right support; the pull rods are rod-shaped metal components used for connecting the left and right supports; the reaction rods 32 are rod-shaped metal components.

The multi-element monitoring information collection system comprises a professional engineering camera 36, an acoustic emission instrument 34 and a multi-functional data monitoring recorder 35;

• • the professional engineering camera 36 is placed in a drilled hole of the lined tunnel physical model 13 to shoot and record internal changes;
  • the acoustic emission instrument 34 is a device that uses sound waves to detect cracks, damage positions and damage conditions of the lined tunnel physical model 13, and placed on both sides of the instrument and connected to the lined tunnel physical model 13 through sensing wires;
  • the multi-functional data monitoring recorder 35 includes water pressure needles 38 for monitoring water pressure changes of the lined tunnel physical model 13 during water filling and draining, and deformation optical fiber 37s, pressure needles 47, crack measuring needles 41, flow needles 48, pore pressure needles 39 and steel bar needles 40 for monitoring working conditions of the lining and surrounding rock;
  • the multi-functional data monitoring recorder 35 is provided inside the lining, between a hydraulic pillow 3 and the lined tunnel physical model 13, between the front and rear bladders 7 and the lined tunnel physical model 13, between a heating plate 5 and the lined tunnel physical model 13, and between the lining and the surrounding rock;
  • the lining of the lined tunnel physical model 13 is formed by concrete pouring and curing, and a number of circumferential steel bars are provided at intervals perpendicular to a longitudinal axis of the pressure tunnel inside the lining of the lined tunnel physical model 13, and a number of longitudinal steel bars are provided at intervals parallel to the longitudinal axis of the pressure tunnel;
  • a crack is preset on an inner wall of the lined tunnel physical model 13; two monitoring sections A-A and B-B perpendicular to an axis of the pressure tunnel are selected at intervals along an axial direction of the pressure tunnel;
  • the crack measuring needles 41 are provided at cracks of the monitoring section containing a preset crack, and two crack measuring needles 41 are provided across the preset crack; a top center of the cylindrical cylinder is a 0° direction, and the pore pressure needles 39 are provided at the 0°, 45°, 90°, 135°, 170°, 225°, 270° and 315° positions of the A-A and B-B monitoring sections respectively in a clockwise direction;
  • the pore pressure needles 39 on each monitoring section are at a same distance from a central axis of the pressure tunnel; a top center of the cylindrical cylinder is the 0° direction, and the water pressure needles 47 are provided on an outer wall of the lining at the 0°, 100°, 150°, 225° and 280° positions of the A-A and B-B monitoring sections respectively in the clockwise direction; the top center of the cylindrical cylinder is the 0° direction, and the steel bar needles 40 are provided on the lining steel bars at the 0°, 30°, 150°, 210° and 320° positions of the A-A and B-B monitoring sections respectively in the clockwise direction;
  • when pouring the lining, the flow needles 48 are pre-wound into a circle and provided in a circle around an edge inside a lining mold, and four circles of the deformation optical fibers 37 are evenly provided inside the lining mold;
  • the surrounding rock of the lined tunnel physical model 13 is made by pouring, cutting and polishing the selected rock mass, and four cracks are preset in the surrounding rock;
  • one monitoring section 1-1 perpendicular to the axis of the pressure tunnel is set along the axial direction of the pressure tunnel;
  • with the top center as the 0° direction, four cracks are preset at 0°, 90°, 180° and 270° positions respectively in the clockwise direction;
  • a top center of the square surrounding rock is the 0° direction, and the pressure needles 47 are provided inside the surrounding rock at the 15°, 75°, 105°, 165°, 195°, 255°, 285° and 345° positions in the clockwise direction;
  • the pressure needles 47 are at a same distance from the central axis of the pressure tunnel; the water pressure needles 38 are provided at the preset cracks, and three water pressure needles 38 are provided across each preset crack; and
  • when making the surrounding rock, four circles of the deformation optical fibers 37 are evenly provided inside the lining mold.

Installation method and usage method of the large-scale model test device for excavation, water filling and splitting of high internal and external water pressure tunnels includes:

• • Step 1: placing the base 11 at a set position, installing the model bearing cylinder above the base 11 and fitting the model bearing cylinder tightly with bolts, and fixing the reaction pad 2 on an inner side of the model bearing cylinder;
  • Step 2: fixing the hydraulic pillow 3 horizontally in a square shape on the inner side of the reaction pad 2, then installing the wedge-shaped pressure head 4 on an inner side of the hydraulic pillow 3 and mounting the multi-functional data monitoring recorder 35, and finally installing the heating plates 5 on inner sides of the wedge-shaped pressure heads 4 and mounting the multi-functional data monitoring recorder 35;
  • Step 3: placing the drill bit14 and the base 11 at a proper position right in front of a provided instrument and fix the drill bit14 and the base 11, installing a guide rail above the drill bit14 and the base 11 and fixing the guide rail with bolts, embedding the sliding block 16 in the guide rail, and then fixing the supporting plate 27 with the sliding block 16 through bolts;
  • Step 4: assembling the X-axis moving block 25, trolley motor 22 and servo motor 23 into an integral kit, installing the integral kit in the middle of the guide rail under the supporting plate 27, and then fixing the base support 19 on the supporting plate 27 with bolts;
  • Step 5: installing the tapered roller bearing 18 on the planetary reducer 30, connecting and fixing the oil pressure cylinder 26 at a right end of the planetary reducer 30, installing the linear bearing 17 on the reaction rod 32 and passing it through the oil pressure cylinder 26, enclosing all the above parts between the left and right supports, connecting and fixing the left and right supports through pull rods, and finally connecting the drill bit 14 to the tapered roller bearing 18 through the connecting shaft 15;
  • Step 6: connecting an interface of the computer to force sensors of each loading oil cylinder, displacement sensors and deformation sensors in all directions respectively, and recording the force values and displacement deformation data of the lined tunnel physical model 13 in all directions during experiment through a computer; and collecting sound information during rock sample experiment in real time by means of acoustic emission and microseismic monitoring;
  • Step 7: installing the lined tunnel physical model 13 in the triaxial stress loading system, and fitting various functional metal components tightly with each other and finally with the lined tunnel physical model 13 firmly;
  • Step 8: after placing the lined tunnel physical model 13, fitting pressure plates 8 on front and rear sides of the lined tunnel physical model 13, then fitting the front and rear bladders 7 tightly with the pressure plates 8, installing the multi-functional data monitoring recorder 35 after confirming no errors, covering the model bearing cover plate 6 and fixing the model bearing cover plate 6 with bolts;
  • Step 9: starting the loading device connected to the heating plate 5 to heat up the lined tunnel physical model 13, and starting the internal and external water pressure loading devices to filling water pipes with water, and applying water-rich conditions to a rock mass near a one-way hole pipe through one-way holes on the water pipes;
  • Step 10: after heating up to a specified temperature, starting front-rear and vertical loading devices; the front and rear bladders 7 starting to apply pressure to the pressure plates 8, wherein the pressure is transmitted to front and rear sides of the lined tunnel physical model 13 through the pressure plates 8; the hydraulic pillow 3 starts to apply pressure to the wedge-shaped pressure heads 4, and the pressure is transmitted to the heating plates 5 through the wedge-shaped pressure heads 4 and finally to an upper, lower, left and right directions of the lined tunnel physical model 13 through the heating plates 5;
  • Step 11: transmitting the pressure applied by the front and rear bladders 7 and hydraulic pillows 3 to the lined tunnel physical model 13 through metal components to complete preloading; after preloading is completed, increasing the oil pressure and performing formal loading on the lined tunnel physical model 13 until the pressure specified in the experiment is reached;
  • Step 12: starting the intelligent control multi-mode excavation system; the drill bit 14 starting to rotate, and the trolley motor 22 driving the supporting plate 27 to move along an X-axis towards the lined tunnel physical model 13 on the guide rail through the sliding block 16; after contact, starting excavation and record data such as stress and deformation during excavation until the excavation is completed; after excavation, operating the trolley motor 22 to drive the supporting plate 27 to move along the X-axis away from the lined tunnel physical model 13 on the guide rail through the sliding block 16 until the drilling rig leaves an inside of the water pressure tunnel model;
  • Step 13: after drilling the lined tunnel physical model 13, installing a professional engineering camera 36 in a drilled hole, then installing the water tunnel seal 10, starting the loading device to fill water into the internal hole sealed by the water tunnel seal 10 and applying internal water pressure to the internal hole; a force applied by the sealing loading satisfies

P m > ( ∑ x = 0 n ( P t / S ) × S x ) ± Δ ⁢ P

• •  and is sufficient to keep a sealing loading force greater than the water pressure; turning on a flow control of the water pipe to fill the water pipe with water and applying water-rich conditions to the lined tunnel physical model 13 through the one-way holes opened on the water pipe; recording the internal water pressure, deformation, temperature change and stress, and observing the lining damage through the professional engineering camera 36;
  • Step 14: performing step-by-step water filling and draining into the water tunnel seal 10 formed by the experimental device to simulate groundwater pressure and the internal water pressure loading and unloading working conditions; connecting the pressure water pump to a joint of the water tunnel seal 10, and performing step-by-step water filling into the water tunnel seal 10; during the water filling process, continuing filling until the lining is damaged, recording the data at this time, and continuing filling until hydraulic splitting of the surrounding rock occurs which is an end point of the water filling stage; recording the hydraulic splitting data; after a step-by-step water filling stage is completed, opening the water tunnel seal 10 for step-by-step water draining; to refine the water pressure conditions during lining damage and hydraulic splitting in a water filling process, setting a water filling pressure gradient; since the water pressure at water use points in the tunnel is generally not less than 0.3 MPa and 1.5 times that under working conditions, rounding it up and setting the water filling pressure gradient to 0.5 MPa per level, and setting each water filling pressure increment to one-tenth of the water filling pressure gradient; wherein a number of water filling steps when the water filling pressure is 0.5 MPa, a total number of water filling steps, and a total number of water filling and draining steps are as follows:

S 1 = P 1 Δ ⁢ P ( 24 ) S = P t Δ ⁢ P ( 25 ) S t ⁢ otal = 2 × S ( 26 )

• • wherein S1 is the number of water filling steps when the water filling pressure is equal to a set value; S is the total number of water filling steps; S_total is the total number of water filling and draining steps; P1 is a water filling pressure of the set value; Pt is a designed water head of the pressure tunnel, unit in MPa; ΔP is a loading and unloading amplitude of step-by-step water filling and draining pressure, unit in MPa;
  • Step 15: during the step-by-step water filling and draining into the water tunnel seal 10, if no damage occurs at each level or the value does not change significantly, proceed to a next step according to the plan after meeting a following time requirement; wherein a duration of pressure loading or unloading for each level of water filling and draining is:

T k = ⁢ { 120 ⁢ s , 0 < K ≤ S 1 240 ⁢ s , S 1 < K ≤ S 120 ⁢ s , S < K ≤ S total ( 27 )

• • wherein Tk is a duration of pressure loading or unloading for a K-th level of water filling and draining; K is a number of step-by-step water filling and draining steps; during the step-by-step water filling and draining into the water tunnel seal 10, reading a pressure gauge reading and record the change of internal water pressure; during the step-by-step water filling and draining into the water tunnel seal 10, recording a change of lining crack width in real time; during the step-by-step water filling and draining into the water tunnel seal 10, wherein the multi-functional data monitoring recorder 35 performs data recording and monitoring, the professional engineering camera 36 shoots and records video files, and the acoustic emission instrument 34 collects sound information;
  • Step 16: during the internal water pressure loading and unloading process, the front and rear bladders 7 cooperate with the water filling pressure change formula and water draining pressure change formula to load and unload pressure on the pressure plates 8; a dynamic pressure adjustment of the front and rear bladders 7 meets the following formulas:

F t = P + F 1 ( 28 ) F = ( F t - P ) / 2 ( 29 )

• • wherein Ft is the total pressure and kept unchanged; F1 is a total pressure on both sides; F is a pressure on one side;
  • P is the water pressure and satisfies

( ∑ x = 0 n ( P t / S ) × S x ) ± Δ ⁢ P ,

• •  where S_x is a x-th water filling step to ensure a coordination between the internal water pressure of the lined tunnel physical model 13 and the external loading pressure, and balance the loading and the internal water pressure of the surrounding rock under a condition that the total pressure remains unchanged for dynamic adjustment, so that an overall stress of the surrounding rock remains unchanged during the water filling process; continuing to observe and simulate the hydraulic splitting extending from the hole inside the surrounding rock, and record pressure and deformation data; observing, monitoring and recording the stress, strain, water content of the lined tunnel physical model 13, an audio and video of lining damage, the audio and video of hydraulic splitting of the surrounding rock, and a change of crack width during the water filling and draining process; observing, monitoring and recording a stress change and strain change of the lined tunnel physical model 13 during triaxial stress loading and temperature adjustment; and
  • Step 17: after all experimental items are completed, starting to unload, cool down and reduce oil pressure, saving data and audio-visual materials, and finally checking the condition of the device to complete an experiment.