Test system for simulating three-dimensional stress field and cyclic freeze-thaw environment of tunnel portal in cold region

Abstract

The test system for simulating three-dimensional stress field and cyclic freeze-thaw environment of tunnel portal in cold region comprises a tunnel model, a rigid-flexible combined boundary control system, a ground temperature control system, a refrigeration control system, a loading system and a data measurement and acquisition system, the tunnel model comprises a box body, an insulation layer, an insulation sleeve, a lining and surrounding rock, the rigid-flexible combined boundary control system comprises springs, thin steel plates and thick steel plates, and the data measurement and acquisition system comprises multiple temperature sensors, multiple strain gauges, multiple pressure cells and a data acquisition device. The three-dimensional stress field of the tunnel portal section is reproduced by the rigid-flexible combined boundary design, the three-dimensional temperature field of the tunnel in cold region is simulated through the ground temperature control system and the refrigeration control system, the three-dimensional stress field and the cyclic freeze-thaw environment of the tunnel portal in cold region are simulated, important test system design guidance is provided for the frost heaving force of the portal section and the mechanism research of the frost damage caused by the frost heaving force, and the test system has good scientific research and engineering application value.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of cold region tunnels, and particularly relates to a test system for simulating a three-dimensional stress field and a cyclic freezing-thawing environment of a cold region tunnel portal. BACKGROUND

[0002] The tunnel frost damage problem caused by the severe weather conditions in cold regions is increasingly prominent, seriously threatens the safe operation of tunnel engineering, and poses great challenges to the frost resistance design and operation and maintenance of cold region tunnels, and fully studying the development law of the temperature field and frost heaving force load of the surrounding rock of cold region tunnels is an important basis for the design of tunnel frost damage prevention. A simulation test system is an efficient, economical and true-to-life technical means that restores the characteristics of actual engineering, and is widely used in the field of cold region tunnel frost damage research. The tunnel portal section is a location where frost damage frequently occurs and is relatively severe, and the study of its frost damage mechanism has attracted widespread attention from scholars. However, the current tunnel physical simulation test mainly uses a plane strain model, and is designed with a rigid boundary, which cannot truly reflect the three-dimensional stress field state of the surrounding rock of the tunnel portal section where frost damage is relatively severe and the stress and deformation law of the structure, and affects the study of the frost damage mechanism of the cold region tunnel portal section. SUMMARY

[0003] The technical problem to be solved by the present application is to provide a test system for simulating a three-dimensional stress field and a cyclic freezing-thawing environment of a cold region tunnel portal, which solves the technical problem of the prior art. The test system innovatively uses a rigid-soft combined boundary to reproduce the three-dimensional stress field of the tunnel portal section, simulates the three-dimensional temperature field of the freezing-thawing cycle of the cold region tunnel throughout the year through a ground temperature control system and a refrigeration control system, realizes the simulation of the three-dimensional stress field and the cyclic freezing-thawing environment of the cold region tunnel portal, provides important test system design guidance for the study of the frost heaving force of the portal section and the frost damage mechanism caused thereby, and has good scientific research and engineering application value.

[0004] The application adopts the technical scheme that a test system for simulating a three-dimensional stress field and a cyclic freezing-thawing environment of a tunnel portal in a cold region comprises a tunnel model, a rigid-flexible combined boundary control system, a ground temperature control system, a refrigeration control system, a loading system and a data measurement and acquisition system, the tunnel model comprises a box, an insulation layer, an insulation sleeve, a lining and surrounding rock, the lining is arranged through the center of the surrounding rock, the box is arranged outside the surrounding rock and the insulation layer, the insulation sleeve is arranged outside the box, the insulation layer is arranged above the surrounding rock, the top plate of the box and the insulation layer have a height difference, the rigid-flexible combined boundary control system is arranged on the upper side of the tunnel portal, the rigid-flexible combined boundary control system comprises springs, a thin steel plate and a thick steel plate, the thin steel plate is arranged vertically on the upper side of the lining, the inner side of the thin steel plate is attached to the outer side of the surrounding rock, the side plate of the box near the upper side of the tunnel portal is the thick steel plate, the outer side of the thin steel plate and the inner side of the thick steel plate have a receiving cavity, a plurality of springs are arranged in the receiving cavity in an up-down interval, the thin steel plate and the thick steel plate are connected through the plurality of springs, the ground temperature control system is used for controlling the temperature of the top and bottom of the surrounding rock, the refrigeration control system is used for controlling the temperature of the tunnel portal and the tunnel hole, the loading system is used for pressing the top of the surrounding rock, the data measurement and acquisition system comprises a plurality of temperature sensors, a plurality of strain gauges, a plurality of pressure cells and a data acquisition device, the plurality of temperature sensors are arranged at different depths of the surrounding rock at intervals, the plurality of strain gauges and the plurality of pressure cells are arranged at intervals on the inner and outer surfaces of the lining and the outer side of the surrounding rock respectively, the plurality of temperature sensors, the plurality of strain gauges and the plurality of pressure cells transmit the collected data to the data acquisition device respectively, the data acquisition device is used for transmitting the received data to a computer terminal for processing, and the evolution law of the frost heaving force, the temperature field of the surrounding rock and the deformation of the lining in the cyclic freezing-thawing process of the tunnel portal in the cold region is obtained by coupling simulation of the computer terminal.

[0005] The working principle of the test system for simulating the three-dimensional stress field and the cyclic freezing-thawing environment of a tunnel portal in a cold region is as follows: firstly, a rigid-flexible combined boundary control system is used to perform flexible constraint and rigid constraint on the portal side and the body side of the tunnel model respectively, and the flexible constraint is mainly composed of a thin steel plate, a spring and a thick steel plate, and the rigid constraint is mainly composed of a thick steel plate; then, a loading system is used to apply pressure to the top of the surrounding rock to simulate different overburden pressure of the tunnel portal and to realize the initial three-dimensional stress field state of the tunnel portal section; subsequently, a ground temperature control system is used to control the temperature of the top and bottom of the surrounding rock to be constant to simulate the initial ground temperature field of the surrounding rock; then, a refrigeration control system is used to control the temperature of the tunnel portal and the tunnel hole to reach a target low temperature to simulate the three-dimensional temperature field of the cyclic freezing-thawing environment behind the tunnel portal wall and in the tunnel hole to realize the cyclic freezing and thawing process of the surrounding rock of the tunnel portal in a cold region; finally, the evolution law of the cyclic frost heaving force and the temperature field of the tunnel portal in a cold region is obtained by computer simulation of the coupling of the three-dimensional stress field and the three-dimensional temperature field.

[0006] As preferred, the ground temperature control system comprises a first control pipeline, a second control pipeline and a control tank, the control tank is arranged outside the box, the first control pipeline is horizontally laid on the top of the surrounding rock, the second control pipeline is horizontally laid on the bottom of the surrounding rock, and the first control pipeline and the second control pipeline are respectively connected with the control tank to form a ground temperature control loop. Further, the refrigeration control system comprises a refrigeration pipe grid, a refrigeration spiral pipeline, a first circulation tank and a second circulation tank, the first circulation tank and the second circulation tank are respectively arranged outside the box, the refrigeration pipe grid is arranged in the accommodating cavity, the refrigeration pipe grid is connected with the first circulation tank to form a portal refrigeration loop, the refrigeration spiral pipeline is arranged in the lining, and the refrigeration spiral pipeline is connected with the second circulation tank to form a spiral refrigeration loop in the tunnel. Through the linkage control of the above ground temperature control system and the refrigeration control system, the special freezing simulation of the normal direction behind the tunnel portal wall and the radial direction of the surrounding rock in the tunnel can be realized to ensure the authenticity of the simulation results.

[0007] As preferred, the loading system comprises a plurality of jacks, a bearing plate and a plurality of groups of reinforcing cross beams, the bearing plate is horizontally laid on the top surface of the surrounding rock, the thermal insulation layer is horizontally laid on the top surface of the bearing plate, the plurality of jacks are arranged between the top plate of the box and the bearing plate, the top ends of the plurality of jacks are respectively abutted against the top plate of the box, the bottom ends of the plurality of jacks are respectively abutted against the top surface of the bearing plate through the thermal insulation layer, and the plurality of groups of reinforcing cross beams are arranged at the top and bottom of the box. The above loading system is convenient to use, and the plurality of groups of reinforcing cross beams can limit the deformation of the box.

[0008] Compared with the prior art, the present application has the following advantages:

[0009] (1) The test system of the present application adopts a rigid-flexible combined boundary design to simulate the flexible constraint at the tunnel portal side and the rigid constraint at the tunnel body side, i.e. the flexible constraint composed of a thin steel plate, a spring and a thick steel plate at the portal side and the rigid constraint composed of a thick steel plate at the tunnel body side, and combines a loading system to simulate different overburden pressure at the portal, so that the three-dimensional stress field of the tunnel portal section can be truly restored, and the present application is suitable for cold region tunnels with different portal wall types;

[0010] (2) The test system of the present application simulates the special cyclic freezing and thawing conditions at the portal of a cold region tunnel through a ground temperature control system and a refrigeration control system, so that the coupling of the three-dimensional stress field and the three-dimensional temperature field of the surrounding rock at the portal section under cyclic freezing and thawing can be realized, the evolution law of the cyclic frost heaving force and the temperature field at the portal of a cold region tunnel can be truly simulated, the technical level of the physical simulation test of a cold region tunnel is improved, important design guidance for the test system is provided for the study of the frost heaving force at the portal section and the mechanism of the frost damage caused thereby, and the present application has good scientific research and engineering application value;

[0011] (3) The test system of the present application comprehensively considers the real three-dimensional stress field, the special freezing mode and the overburden load of the surrounding rock at the portal section of a cold region tunnel, so that the coupling simulation of different complex engineering and meteorological conditions of a cold region tunnel can be realized, and the understanding of the complex mechanism of the frost damage of a cold region tunnel is improved. BRIEF DESCRIPTION OF DRAWINGS

[0012] Figure 1 Fig. 1 is an axial sectional view of the test system in the embodiment;

[0013] Figure 2 Fig. 2 is a lateral view of the test system in the embodiment;

[0014] Figure 3 Fig. 3 is a schematic view of the refrigeration circuit at the portal in the embodiment;

[0015] Figure 4 Fig. 4 is a schematic view of the arrangement of the data measurement and acquisition system in the embodiment;

[0016] Fig. 1 is an axial sectional view of the test system in the embodiment; DETAILED DESCRIPTION

[0017] The application will be described in further detail below with reference to the drawings.

[0018] The test system for simulating the three-dimensional stress field and the cyclic freezing-thawing environment of the tunnel portal in the cold region of the embodiment, as shown in the figure, comprises a tunnel model, a rigid-flexible combined boundary control system, a ground temperature control system, a refrigeration control system, a loading system and a data measurement and acquisition system. The tunnel model comprises a box 11, an insulation layer 12, an insulation sleeve 13, a lining 14 and surrounding rock 15. The lining 14 is arranged through the center of the surrounding rock 15. The box 11 is placed outside the surrounding rock 15 and the insulation layer 12. The insulation sleeve 13 is placed outside the box 11. The insulation layer 12 is placed above the surrounding rock 15. There is a height difference between the top plate of the box 11 and the insulation layer 12. The rigid-flexible combined boundary control system is arranged on the upper side of the tunnel portal. The rigid-flexible combined boundary control system comprises springs 21, a thin steel plate 22 and a thick steel plate 23. The thin steel plate 22 is vertically arranged on the upper side of the lining 14. The inner side of the thin steel plate 22 is attached to the outer side of the surrounding rock 15. The side plate of the box 11 close to the upper side of the tunnel portal is the thick steel plate 23. There is a receiving cavity 24 between the outer side of the thin steel plate 22 and the inner side of the thick steel plate 23. A plurality of springs 21 are arranged in the receiving cavity 24 in an upper-lower interval. The thin steel plate 22 and the thick steel plate 23 are connected through the plurality of springs 21. The ground temperature control system is used to control the temperature of the top and bottom of the surrounding rock 15. The refrigeration control system is used to control the temperature of the tunnel portal (i.e. the entrance of the lining 14) and the tunnel inside (i.e. inside the lining 14). The loading system is used to press the top of the surrounding rock 15. The data measurement and acquisition system comprises a plurality of temperature sensors 31, a plurality of strain gauges 32, a plurality of pressure cells 33 and a data acquisition device 34. The plurality of temperature sensors 31 are arranged at different depths of the surrounding rock 15 at intervals. The plurality of strain gauges 32 and the plurality of pressure cells 33 are arranged on the inner and outer surfaces of the lining 14 and the outer side of the surrounding rock 15 at intervals, respectively. The plurality of temperature sensors 31, the plurality of strain gauges 32 and the plurality of pressure cells 33 transmit the collected data to the data acquisition device 34, respectively. The data acquisition device 34 is used to transmit the received data to a computer terminal 35 for processing. The evolution law of the frost heaving force, the temperature field of the surrounding rock 15 and the deformation of the lining 14 in the cyclic freezing-thawing process of the tunnel portal in the cold region is obtained by coupling simulation of the computer terminal 35.

[0019] Specifically, the ground temperature control system includes a first control pipe 41, a second control pipe 42, and a control trough 43. The control trough 43 is located on the outside of the housing 11. The first control pipe 41 is laid horizontally on the top of the surrounding rock 15, and the second control pipe 42 is laid horizontally on the bottom of the surrounding rock 15. The first control pipe 41 and the second control pipe 42 are respectively connected to the control trough 43 to form a ground temperature control loop. The refrigeration control system includes a refrigeration grid 51, a refrigeration spiral pipe 52, a first circulation trough 53, and a second circulation trough 54. The first circulation trough 53 and the second circulation trough 54 are respectively located on the outside of the housing 11. The refrigeration grid 51 is located in the accommodating cavity 24. The refrigeration grid 51 is connected to the first circulation trough 53 to form a tunnel entrance refrigeration loop. The refrigeration spiral pipe 52 is arranged through the lining 14. The refrigeration spiral pipe 52 is connected to the second circulation trough 54 to form an in-tunnel spiral refrigeration loop.

[0020] Specifically, the loading system includes several jacks 61, a bearing plate 62, and six sets of reinforcing beams 63. The bearing plate 62 is laid horizontally on the top surface of the surrounding rock 15, and the insulation layer 12 is laid horizontally on the top surface of the bearing plate 62. Several jacks 61 are spaced apart between the top plate of the box 11 and the bearing plate 62. The top ends of several jacks 61 abut against the top plate of the box 11, and the bottom ends of several jacks 61 pass through the insulation layer 12 and abut against the top surface of the bearing plate 62. Three sets of reinforcing beams 63 are provided at the top and bottom of the box 11.

[0021] The systems, devices or components not specified in this invention all employ conventional techniques in the field.

[0022] The experimental process of the test system for simulating the three-dimensional stress field and cyclic freeze-thaw environment at the entrance of a tunnel in a cold region, as described in the above embodiment, is as follows:

[0023] Step 1: Open the control tank 43 and continuously input constant temperature liquid into the first control pipeline 41 and the second control pipeline 42. After the temperature of the surrounding rock 15 and the lining 14 stabilizes, take the readings of the pressure box 33 and the strain gauge 32 at this time as the initial readings, and take the temperature of the surrounding rock 15 at this time as the initial ground temperature.

[0024] Step 2: Open the first circulation tank 53 and the second circulation tank 54 to reduce the temperature of the tunnel entrance cooling circuit and the tunnel interior spiral cooling circuit to the actual low temperature value of the tunnel site area at the designed cooling rate. After the temperature of the surrounding rock 15 and the reading of the pressure box 33 stabilize, close the first circulation tank 53 and the second circulation tank 54. After the temperature of the surrounding rock 15 returns to the initial ground temperature, one freeze-thaw cycle is completed.

[0025] Step 3: Repeat step 2 and continuously monitor the temperature of surrounding rock 15 and the frost heave load of lining 14 and tunnel portal wall during the freezing process. Stop the test when the equivalent number of freeze-thaw cycles in the tunnel is reached.

[0026] Fourth step: the monitoring data of pressure, temperature and strain in the process of freeze-thaw cycle are drawn into the curves of frost heaving force-time, surrounding rock 15 temperature-time, lining 14 strain-time, respectively, to obtain the evolution law of frost heaving force, temperature field of surrounding rock 15 and deformation of lining 14 in the process of freeze-thaw cycle of tunnel portal in cold region.

Claims

1. A test system for simulating a three-dimensional stress field and a cyclic freeze-thaw environment of a tunnel portal in a cold region, characterized in that, The application relates to a tunnel model, a rigid-flexible combined boundary control system, a ground temperature control system, a refrigeration control system, a loading system and a data measurement and acquisition system, wherein the tunnel model comprises a box, an insulation layer, an insulation sleeve, a lining and surrounding rock, the lining is arranged through the central position of the surrounding rock, the box is arranged outside the surrounding rock and the insulation layer, the insulation sleeve is arranged outside the box, the insulation layer is arranged above the surrounding rock, the top plate of the box and the insulation layer have a height difference, the rigid-flexible combined boundary control system is arranged on the upper side of a tunnel portal, the rigid-flexible combined boundary control system comprises springs, a thin steel plate and a thick steel plate, the thin steel plate is vertically arranged on the upper side of the lining, the inner side of the thin steel plate is attached to the outer side of the surrounding rock, the side plate of the box near the upper side of the tunnel portal is the thick steel plate, the outer side of the thin steel plate and the inner side of the thick steel plate have a containing cavity, a plurality of springs are arranged in the containing cavity in a spaced manner, the thin steel plate and the thick steel plate are connected through the plurality of springs, the ground temperature control system is used for controlling the temperature of the top and bottom of the surrounding rock, the refrigeration control system is used for controlling the temperature of the tunnel portal and the tunnel hole, the loading system is used for pressing the top of the surrounding rock, the data measurement and acquisition system comprises a plurality of temperature sensors, a plurality of strain gauges, a plurality of pressure boxes and a data collector, the plurality of temperature sensors are arranged at different depths of the surrounding rock in a spaced manner, the plurality of strain gauges and the plurality of pressure boxes are arranged on the inner surface and the outer surface of the lining and the outer side of the surrounding rock in a spaced manner, the plurality of temperature sensors, the plurality of strain gauges and the plurality of pressure boxes transmit the collected data to the data collector, the data collector is used for transmitting the received data to a computer terminal for processing, and the evolution law of the frost heaving force, the temperature field of the surrounding rock and the deformation of the lining in the cyclic freezing and thawing process of the tunnel portal in a cold region is obtained through computer coupling simulation.

2. The test system for simulating the three-dimensional stress field and the cyclic freeze-thaw environment of the tunnel portal in cold regions according to claim 1, characterized in that, The ground temperature control system comprises a first control pipeline, a second control pipeline and a control groove, the control groove is arranged outside the box, the first control pipeline is horizontally arranged on the top of the surrounding rock, the second control pipeline is horizontally arranged on the bottom of the surrounding rock, and the first control pipeline and the second control pipeline are in communication with the control groove to form a ground temperature control loop.

3. The test system for simulating the three-dimensional stress field and the cyclic freeze-thaw environment of a tunnel portal in a cold region according to claim 1 or 2, characterized in that, The refrigeration control system comprises a refrigeration pipe grid, a refrigeration spiral pipeline, a first circulation groove and a second circulation groove, the first circulation groove and the second circulation groove are arranged outside the box, the refrigeration pipe grid is arranged in the containing cavity, the refrigeration pipe grid is in communication with the first circulation groove to form a portal refrigeration loop, and the refrigeration spiral pipeline is arranged through the lining, the refrigeration spiral pipeline is in communication with the second circulation groove to form a spiral refrigeration loop in the tunnel hole.

4. The test system for simulating the three-dimensional stress field and the cyclic freeze-thaw environment of the tunnel portal in cold regions according to claim 1, characterized in that, The loading system comprises several jacks, a bearing plate and several groups of reinforcing cross beams, the bearing plate is horizontally laid on the top surface of the surrounding rock, the heat preservation layer is horizontally laid on the top surface of the bearing plate, the several jacks are arranged at intervals between the top plate of the box body and the bearing plate, the top ends of the several jacks are respectively abutted against the top plate of the box body, the bottom ends of the several jacks are respectively abutted against the top surface of the bearing plate through the heat preservation layer, and the several groups of reinforcing cross beams are arranged at the top and bottom of the box body.

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