CN105675846A - Foundation pit excavation model testing device capable of cooperatively hoisting phreatic water level and pressure-bearing water head - Google Patents

Abstract

The invention discloses a foundation pit excavation model test device in which a water level and a pressurized water head cooperate to rise and fall. Including model box, water tank, symmetric surface retaining unit, foundation pit support structure, pressure-bearing overhead layer, pressure-bearing head adjustment system and measurement system; model box includes model box frame, reaction plate, etc.; water tank is set in the model box The upper right inside; the symmetrical surface retaining unit is fixed on the frame of the model box by bolts; the pressure-bearing overhead layer is set at the bottom of the model box and connected with the pressure-bearing head adjustment system; Composed of a bottle and a bracket; the invention can simulate the rise and fall of the phreatic level and the pressurized water head during the excavation of the foundation pit; measure the water and soil pressure and deformation of the foundation pit under different phreatic levels and pressurized water heads, sort out relevant test data and determine the foundation pit Issues such as the development law of force and deformation provide effective experimental data support for the study of foundation pit problems caused by the rise and fall of phreatic level and confined water head, and provide a basis for the subsequent theoretical analysis model.

Description

Foundation Pit Excavation Model Test Device for Coordinated Lifting and Lowering of Water Level and Confined Water Head

technical field

The invention relates to a foundation pit model test device, in particular to a foundation pit excavation model test device under the condition of rising and falling water levels and pressure water heads, which can be used for simulating pressure bearing layers and overlying weak points when the water level and pressure water heads rise and fall. The interaction between soil in permeable foundation pits is used to study the water and soil pressure response and deformation of foundation pits under different phreatic levels and confined water heads.

Background technique

There is abundant groundwater in the coastal and riverside areas, and the project often faces the situation that there is still a confined layer below the aquitard at the bottom of the deep foundation pit. Due to large-scale precipitation, seasonal drought, and seasonal changes in the water level of rivers or lakes, the water level will The rise and fall of the water level and the confined water head will further affect the water and soil pressure, deformation and stability of the foundation pit. The deformation and instability of the foundation pit caused by the rise and fall of the phreatic level and the confined water head are one of the major risk sources for deep foundation pit engineering in such areas .

Compared with the theoretical analysis method and the finite element numerical method using the established soil constitutive model, the calculated phreatic water level and the soil water and soil pressure and deformation of the soil caused by the rise and fall of the confined water head have a great influence on the selection of calculation parameters. Dependency; in actual engineering, it is difficult to monitor the water and soil pressure at the bottom of the foundation pit (located in the excavation area of the foundation pit) in real time, and carry out statistical analysis of a large number of similar engineering monitoring data to obtain the pit caused by the rise and fall of the phreatic level and the confined water head. The method of deformation law of the bottom aquitard is also difficult to realize; in view of the fact that the geotechnical model test under constant gravity does not affect the microstructure of the soil, the size of the soil particles and the interaction relationship between soil particles are consistent with the actual situation, and can objectively reflect the groundwater and foundation conditions. The interaction between soil particles in pit soil is widely used in microscopic studies considering the stress-strain relationship of soil.

At present, the traditional geotechnical model test research on the action of groundwater does not consider the unsaturated soil problem that may be caused by the gas in the water entering the test soil; the foundation pit model test considering the constant phreatic level has been studied (Peng Shuquan. Sand retaining wall failure Mechanism macro and micro research [D]. Tongji University, 2007.) The method of connecting the retaining wall and the model box by applying epoxy resin after the film passes through the corona, this method can obtain the excess static pore water pressure and earth pressure in the test soil and the deformation data of the foundation pit, but the film corona process is relatively complicated. When the displacement of the retaining wall is large, the film may be torn during the movement or damaged due to the friction of soil particles, and the test cannot be successfully completed or repeated tests. Considering the impact of underground water level changes on foundation pit model tests, there are studies (Sun Wei. Experimental and theoretical research on the behavior of deep foundation pits in coastal areas [D]. Zhejiang University, 2015.) using the method of fixing retaining walls, this method only The changes of the excess static pore water pressure in the soil can be obtained, but the accurate data of the earth pressure change and the deformation of the foundation pit cannot be obtained, which is still quite different from the response of the actual foundation pit project under the action of the phreatic level and the confined water head.

In the foundation pit model test, most studies focus on the force and deformation of the foundation pit under the completion of each level of excavation and support, without considering the force of the foundation pit during excavation or support and deformation. In the model test considering the excavation process of the foundation pit, some studies have used soil bags of equal volume and weight to unload (Azevedo RF. Centrifuge and Analytical Modeling of Excavation in Sand. PhDthesis, University of Colorado, Boulder, CO, USA, 1983.) .Géotechnique, 1987,37(3):335-353.) and other methods to simulate soil excavation and unloading, this kind of method cannot accurately simulate the change of stress field in the soil caused by foundation pit excavation, and it is different from the actual foundation pit excavation There are still some differences in the stress and deformation of the foundation pit caused. A large number of model tests simulating the excavation of foundation pits adopt the method of pre-burying and installing the supporting retaining wall, and directly excavate the soil of the foundation pit without additional support operations. This method is relatively simple, but all the internal supports preset All will be stressed during the entire excavation process, which is obviously inconsistent with the stress of the actual engineering pit, and it is impossible to accurately simulate the stress and deformation of the foundation pit without support during the excavation process. At present, some studies have used the hydraulic jack to apply force to the retaining wall support to simulate the installation of the support. This method uses a hydraulic device, which is more complicated, and this method is not applicable when the excavation width of the foundation pit is large. In addition, the excavation symmetry plane of most foundation pit excavation models is a vertically fixed baffle, and the excavation of the foundation pit is realized by grabbing or digging down the soil. This method cannot clearly define the excavated soil layer and will disturb the unexcavated soil. soil; this method is cumbersome and difficult to operate, especially when the size of the excavation model of the foundation pit is large or there are many soils to be excavated, the workload of the test operation is quite large. Therefore, how to realize accurate soil excavation and support installation is the key problem to be solved in the foundation pit excavation model test.

Contents of the invention

In order to overcome the deficiencies of the above-mentioned prior art, the present invention provides a foundation pit excavation model test device in which the phreatic level and the pressurized water head cooperate to rise and fall, which solves the simulation problem of the phreatic level and the pressurized water head coordinated rise and fall in the test, and can simulate the phreatic level The interaction between groundwater and foundation pit soil when it rises and falls in conjunction with the confined water head, measures the water and soil pressure and deformation of the foundation pit under different phreatic levels and confined water heads, sorts out relevant test data and determines the coordination between the phreatic level and the confined water head Issues such as the force and deformation development law of foundation pits during lifting provide effective experimental data support for the study of foundation pit problems caused by the rise and fall of phreatic level and confined water head, and provide a basis for the subsequent theoretical analysis model.

The technical solution adopted by the present invention to solve the technical problem is: a foundation pit excavation model test device for coordinated lifting of the water level and the pressure water head, including a model box, a water tank, several symmetrical surface retaining units, and a foundation pit support structure , pressure-bearing overhead layer, pressure-bearing head adjustment system and measurement system seven parts; the model box is composed of model box frame, tempered glass, model box bottom plate, top frame, reaction plate and model box base; the model box The bottom plate of the model box is fixed on the bottom of the box frame, and the tempered glass is fixed on the front and rear sides; the frame of the model box and the reaction plate are fixed on the base of the model box, and the top is connected by the top frame; the bottom of the right side of the model box is installed and connected The second water valve of the pressurized overhead layer is used to connect the model box and the pressurized water head adjustment system;

The water tank is composed of an aluminum plate with a water hole, a strip aluminum plate, a water tank bracket, a water tank bracket fixing screw, a scale and a first water valve, and is installed on the upper right of the model box through the water tank bracket for control and observation The water level in the soil rises and falls; the surface of the aluminum plate with water holes is pasted with anti-filtering geotextiles to prevent the loss of the test soil during the change of groundwater; the scale is pasted on the tempered glass and can be used for direct observation and recording of diving Position changes; the first water valve is set on the right side of the model box in order to communicate with the water tank;

The soil retaining unit on the symmetrical surface is a U-shaped stainless steel strip, which is fixed on the model box frame by bolts; the U-shaped stainless steel strips are connected by an H-shaped water-stop rubber strip, and the U-shaped stainless steel strip and the model box frame are connected by an S-shaped Water-stop rubber strip connection;

The support structure of the foundation pit includes a retaining wall, a retaining wall bracket and several supporting units; the upper part of the retaining wall is fixed with bracket fixing bolts to fix the retaining wall bracket, and the middle part is provided with a threaded hole, through which the threaded hole is threaded to install the support The support and fixing bolts required by the unit are grooved on both sides to fix the water-stop rubber strip; the water-stop rubber strip ensures that the contact surface with the model box does not leak during the movement of the retaining wall; one end of the support unit has an internal thread port , the internal threaded port is threaded with the support fixing bolts to realize the installation of the support unit;

The pressure-bearing overhead layer is composed of a stainless steel plate with a water hole, a stainless steel short column and a filter geotextile; the stainless steel short column is fixed at the bottom of the stainless steel plate with a water hole, and placed on the bottom plate of the model box in the model box , and sealed with the four sides of the model box; the surface of the stainless steel plate with water holes is pasted with filter geotextile;

The pressurized water head adjustment system consists of a water pressure gauge, a Marriott bottle and a bracket; the water pressure gauge is connected to the model box and the Marriott bottle through a three-way pipe; a fixed pulley is installed on the bracket, and the wire rope goes around The fixed pulley connects the Marriott bottle and the hand shaker, and the hand shaker controls the ups and downs of the Marriott bottle to adjust the size of the pressurized water head; the Marriott bottle is composed of a plexiglass cylinder, an air inlet valve, and a third water pass Valve, air outlet valve and air bag; the bottom of the plexiglass cylinder is provided with an air inlet valve and a third water valve, and the top is provided with an air outlet valve; the air inlet valve is connected to the air bag;

The measurement system includes a miniature pore water pressure sensor, a miniature earth pressure cell, a displacement sensor, a multi-channel data acquisition instrument and a digital camera; A data acquisition instrument; the digital camera is placed directly in front of the model box.

Further, the support unit includes a solid aluminum rod, a telescopic rod and a supporting connecting bolt; the solid aluminum rod has several grooves, and one end has an internal thread; the telescopic rod is a hollow aluminum tube, and the telescopic rod is opened There are several threaded holes; said supporting connecting bolts pass through the threaded holes on the telescoping rods against the grooves of the solid aluminum rods.

Further, the support unit includes a first support rod, a second support rod and a sleeve; one end of the first support rod has an external thread; one end of the second support rod has an internal thread opening, and the other end has an external thread thread; the sleeve has an internal thread channel, one end is threaded to the first support rod, and the other end is threaded to the second support rod.

Further, the digital camera should eliminate interference during the test, and its position cannot be moved; light sources can be added according to shooting needs.

Further, the model box frame is welded by 10mm thick stainless steel bars and stainless steel plates; the tempered glass is installed inside the model box frame with construction glue; the model box bottom plate and reaction plate are 10mm thick stainless steel steel plate; the top frame is welded by 20mm thick stainless steel bars; the main body of the model box and the reaction plate are fixed on the base of the model box by spot welding around; the retaining wall is an aluminum plate, and its thickness is simulated by the test The stiffness of the retaining wall is calculated; the retaining wall support is a 20mm thick strip aluminum plate; the retaining wall is always kept perpendicular to the tempered glass during the movement; the first water valve and the second water valve , The intake valve, the third water valve, and the outlet valve are copper core valves.

Further, the diameter of the solid aluminum rod, the wall thickness of the telescopic rod, the diameter of the first support rod, the diameter of the second support rod and the wall thickness of the sleeve are all calculated from the stiffness of the inner support simulated by the test.

Further, nitrogen gas of 1 atm is housed in the air bag.

Further, the liquid in the water tank and the plexiglass cylinder is anaerobic water.

Further, the bottom test soil in the model box is gravel sand; the overlying test soil is weakly permeable soil.

Further, the weakly permeable soil is clayey silt; the gravel and weakly permeable soil are saturated with airless water.

Compared with prior art, the beneficial effect of the present invention is:

1. The present invention uses an airless water-saturated test soil before the test, and provides an airless pressurized water environment during the test, so that the pores of the test soil are filled with anaerobic water. The above operation has two advantages: one is to avoid air bubbles in the water Entering the impermeable soil layer causes the unsaturated problem of the soil (compared with the saturated soil, the mechanical properties of the unsaturated soil are quite different and uncertain); the second is to avoid the air bubbles in the water from interfering with the miniature pore water pressure sensor and affecting its measurement precision.

2. The water tank of the present invention is erected in the model box, and glass glue is used to seal the gap between the water tank and the model box. The aluminum plate with water holes makes the water level in the water tank communicate with the water level of the test soil body. The water level in the water tank can be adjusted to The rise and fall of the phreatic level of the simulated test soil; the scale on the water tank is pasted on the tempered glass, which is convenient for direct observation and recording of the phreatic level change. The improved Marriott bottle is used to balance the air pressure inside and outside the Marriott bottle through the nitrogen in the airbag, and the characteristics of nitrogen insoluble in water are used to create an airless pressurized water environment for the test soil, effectively avoiding the conventional Marriott. Unsaturated soil problems caused by air bubbles dissolved in water when the bottle is supplied with water; use the self-locking function of the hand shaker to fix the height of the Marriott bottle to ensure a stable pressurized water head pressure; the water pressure gauge connects the model box with the pressurized Head adjustment system for accurate reading of the applied confined head pressure.

3. On the one hand, the pressure-bearing overhead layer in the present invention can fully saturate the test soil in the model box from bottom to top, which is beneficial to the discharge of gas in the test soil; on the other hand, it is connected with the pressure-bearing water head adjustment system to provide pressure-bearing The different confined water heads of the gravel sand layer are similar to the burial conditions of natural confined water; the direct contact between the confined gravel sand layer and the overlying weak permeable soil layer will objectively simulate the pressure between the confined layer and the overlying weak soil layer during the rise and fall of the confined water head. The interaction between the permeable soil layers is conducive to further revealing the water and soil pressure response of the foundation pit soil caused by the rise and fall of the confined water head and the deformation law of the foundation pit soil. The anti-filter geotextile is pasted on the surface of the aluminum plate with water holes in the water tank and the stainless steel plate with water holes in the pressure-bearing overhead layer to prevent the loss of the test soil during the change of groundwater. Experimental research under constant gravity does not affect the microstructure of the foundation pit soil, making the size of soil particles and the interaction relationship between soil particles consistent with the actual situation, which is conducive to the development of microscopic research involving the interaction between soil particles.

4. The present invention uses the water tank and the pressure-bearing overhead layer to control the coordinated lifting of the phreatic level and the pressure-bearing head, and can realize the following three types of experimental operations:

(1) Close the first water valve of the water tank (diving level remains unchanged), adjust the height of the Marriott bottle to change the size of the pressurized water head, and study the influence of the rise and fall of the pressurized water head on the water and soil pressure response and deformation of the foundation pit soil. The water level line displayed by the scale line of the water tank can be used to know the influence of the rise and fall of the confined water on the change of the diving level of the foundation pit;

(2) Fix the Marriott bottle at the specified height (the pressure-bearing water head remains unchanged), open the first water valve to adjust the water level line of the water tank to control the phreatic level of the test soil, and study the impact of the phreatic level rise and fall on the soil water and soil of the foundation pit. The influence of pressure response and deformation, through the pressure of the confined water head displayed by the water pressure gauge, the influence of the rise and fall of the phreatic level of the foundation pit on the pressure change of the confined water head is known;

(3) Adjust the joint rise and fall of the phreatic level and the confined water head, and study the influence of the coordinated rise and fall of the phreatic level and the confined water level on the water and soil pressure response and deformation of the foundation pit soil.

5. The present invention adopts a detachable symmetrical surface retaining unit to temporarily support the unexcavated soil in the passive area of the foundation pit. The symmetrical surface retaining unit can be removed in advance before excavating each layer of soil. The excavation of the foundation pit is carried out by digging the symmetrical surface and unloading the soil. Compared with the traditional method of digging down and taking soil, the present invention can make it clear that each layer of excavated soil will not affect the unexcavated soil, and the operation is convenient, which greatly reduces the The workload of foundation pit excavation and soil unloading.

6. The present invention can simultaneously simulate the foundation pit excavation and support process, and obtain the change of the foundation pit stress field caused by the foundation pit excavation and support installation process, compared with the traditional foundation pit model test that only considers the foundation pit excavation To carry out research at a certain depth or in a specific state where support is completed, more comprehensively and accurately reflect the response of foundation pit stress and foundation pit deformation in the process of foundation pit excavation and support installation; the present invention does not It will disturb the unexcavated soil of the foundation pit; the internal support and the retaining wall are fixedly connected by threads, compared with the traditional foundation pit model test where the internal support is erected on the retaining wall or directly against the retaining soil The method of adding support to the wall can more objectively reflect the support situation during the excavation of the actual foundation pit; by controlling the diameter of the solid aluminum rod, the wall thickness of the telescopic rod, the diameter of the first support rod, the diameter of the second support rod and the sleeve The wall thickness of the foundation pit realizes the simulation of the support stiffness, which more objectively reflects the engineering impact of the internal support on the excavation of the foundation pit; the number of internal support elements and the internal support on the retaining wall can be adjusted according to the requirements of the geotechnical model test Fix the position and quantity of bolts to simulate the excavation of different foundation pits.

7. The present invention uses telescopic support elements, which can simulate foundation pit excavation tests of different widths. Compared with traditional foundation pit excavation model tests, fixed-length supports or telescopic supports are only used to realize the experimental ideas of support installation. , the same test device can be used to carry out multiple sets of excavation tests of foundation pits with different widths, which reduces the modification of the test device, saves the test cost and model making time, the working principle is simple, the operation is convenient, and it has great practicability.

Description of drawings

Figure 1(a) is a side view of the foundation pit excavation model test device using the first type of support for the coordinated rise and fall of the phreatic level and the confined water head.

Figure 1(b) is a side view of the foundation pit excavation model test device using the second type of support for the coordinated rise and fall of the phreatic level and the confined water head.

Figure 2(a) is a top view of the model box using the first type of support.

Figure 2(b) is a top view of the model box using the second type of support.

Fig. 3 is a schematic diagram of the symmetry plane of foundation pit excavation;

Fig. 4 is a side view of the water tank;

Figure 5(a) is a plan view of the pressure-bearing overhead layer structure.

Figure 5(b) is a side view of the pressure-bearing overhead layer structure.

Figure 6 is a schematic diagram of the retaining wall.

Figure 7(a) is a schematic diagram of the foundation pit support structure of the first type of support.

Figure 7(b) is a schematic diagram of the foundation pit support structure of the second type of support.

In the figure: model box 1; model box frame 1-1; tempered glass 1-2; model box bottom plate 1-3; top frame 1-4; reaction plate 1-5; model box base 1-6; water tank 2; Aluminum plate with water hole 2-1; strip aluminum plate 2-2; water tank bracket 2-3; water tank bracket fixing screw 2-4; scale 2-5; first water valve 2-6; symmetrical surface retaining Unit 3; Bolt 4 for fixing the retaining unit on the symmetrical plane; Retaining wall 5; Water-stop rubber strip 5-1; Retaining wall bracket 6; Bracket fixing bolt 7; Support unit 8; Rod 8-2; supporting connecting bolt 8-3; first supporting rod 8-4; second supporting rod 8-5; sleeve 8-6; supporting fixing bolt 8-7; The stainless steel plate 9-1 of hole; Air valve 12-2; third water valve 12-3; air outlet valve 12-4; air bag 12-5; bracket 13; fixed pulley 13-1; wire rope 13-2; -1; clayey silt 14-2; airless water 15.

detailed description

The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

As shown in Fig. 1 and Fig. 2, the foundation pit excavation model test device of the present invention that the phreatic level and the pressurized water head cooperate to rise and fall includes a model box 1, a water tank 2, several symmetrical surface retaining units 3, foundation pit support structures, The pressure-bearing overhead layer 9, the pressure-bearing water head adjustment system and the measurement system consist of seven parts.

Described model box 1 is made up of model box frame 1-1, tempered glass 1-2, model box bottom plate 1-3, top frame 1-4, reaction plate 1-5 and model box base 1-6; The bottom of the box frame 1-1 is fixed to the bottom plate 1-3 of the model box, and the tempered glass 1-2 is fixed to the front and rear sides; the model box frame 1-1 and the reaction plate 1-5 are fixed to the I-beam by spot welding around On the welded model box base 1-6, the top is connected by spot welding around the stainless steel top frame 1-4; the model box frame 1-1 is welded by 10mm thick stainless steel bars and stainless steel plates; The toughened glass 1-2 is installed on the inside of the model box frame 1-1 by construction glue; the bottom plate 1-3 of the model box and the counter force plate 1-5 are stainless steel plates with a thickness of 10mm; the top frame 1-4 is made of 20mm thick Welded stainless steel bars;

The water tank 2 is composed of a vertically placed aluminum plate 2-1 with water holes, a horizontally placed strip-shaped aluminum plate 2-2, tempered glass 1-2 on the front and rear sides, and the inner wall of the model box frame 1-1 through glass glue. The connection is formed, and the water tank bracket 2-3 is erected on the upper right side of the model box 1 for controlling and observing the water level rise and fall in the soil; the aluminum plate 2-1 with water holes and the water tank bracket 2-3 are formed by the water tank The bracket fixing screw 2-4 is tightened and connected; the surface of the aluminum plate 2-1 with a water hole is pasted with a filter geotextile to prevent the loss of the test soil during the groundwater change process; the scale 2-5 is set on the toughened glass 1 -2 can be used to directly observe and record changes in the water level; the first water valve 2-6 connected to the water tank 2 is installed on the right side of the model box 1 to control the rise and fall of the water level in the water tank 2.

The symmetrical surface retaining unit 3 is a U-shaped stainless steel strip, which is fixed on the model box frame 1-1 by bolts 4; the U-shaped stainless steel strips are connected by an H-shaped water-stop rubber strip, and the U-shaped stainless steel strip is connected to the model box. The box frame 1-1 is connected by an S-shaped water-stop rubber strip;

The foundation pit support structure includes a retaining wall 5, a retaining wall support 6 and several support units 8; the retaining wall 3 is always kept perpendicular to the tempered glass 1-2 during the movement; One end has an internal threaded port, and the internal threaded port is threadedly connected with the support fixing bolt 8-7 to realize the installation of the support unit 8;

The pressure-bearing overhead layer 9 is composed of a stainless steel plate 9-1 with a water hole, a stainless steel short column 9-2 and a filter geotextile 9-3; the bottom of the stainless steel plate 9-1 with a water hole is fixed with stainless steel The short column 9-2 is placed on the bottom plate 1-3 of the model box 1 in the model box 1, and is sealed and connected with the four sides of the model box 1 through glass glue; the surface of the stainless steel plate 9-1 with a water hole is pasted Reverse filter geotextile 9-3, to prevent the loss of the test soil during the change of the confined water head;

The bottom of the right side of the model box 1 is installed with a second water valve 10 connected to the pressure-bearing overhead layer 9, which is used to connect the model box 1 and the pressure-bearing head adjustment system; the bottom test soil in the model box 1 is gravel sand 14 -1, to simulate the confined soil layer; the overlying test soil is weakly permeable soil, and clay silt 14-2 can be used, saturated with airless water;

The pressurized water head regulating system is composed of a water pressure gauge 11, a Marriott bottle 12 and a support 13; the water pressure gauge 11 is connected to the model box 1 and the Marriott bottle 12 through a three-way pipe; the Marriott bottle 12 is composed of organic glass cylinder 12-1, intake valve 12-2, third water valve 12-3, air outlet valve 12-4 and air bag 12-5; the liquid in the organic glass cylinder 12-1 It is anaerobic water 15; nitrogen gas of 1 atm is housed in the described air bag 12-5; fixed pulley 13-1 is installed on the described support 13, and steel wire rope 13-2 bypasses fixed pulley 13-1 to connect Marriott bottle 12 and hand The shaker 13-3 controls the lifting of the Marriott bottle 12 through the hand shaker 13-3 to adjust the size of the pressurized water head; the first water valve 2-6, the second water valve 10, and the intake valve 12 -2. The third water valve 12-3 and the air outlet valve 12-4 are copper core valves;

The measurement system includes a miniature pore water pressure sensor, a miniature earth pressure cell, a displacement sensor, a multi-channel data acquisition instrument and a digital camera; Data acquisition instrument; the digital camera is placed directly in front of the model box, and a light source can be added according to the shooting needs; the digital camera should eliminate interference during the test process, and its position cannot be moved;

As shown in Figure 3, the thickness of the symmetric surface retaining unit 3 is 10mm, and its width can be adjusted according to the thickness of the excavated soil layer to be simulated; the size of the bolt 4 of the fixed symmetric surface retaining unit 3 is M8 , welded and fixed on the model box frame 1-1.

As shown in Figure 4, the water tank 2 is composed of an aluminum plate 2-1 with water holes, a strip aluminum plate 2-2, a water tank bracket 2-3, a water tank bracket fixing screw 2-4, a scale 2-5 and a first The water valve 2-6 is composed of; the surface of the aluminum plate 2-1 with water holes is arranged with a large number of water holes to ensure that the water level in the water tank is connected and consistent with the water level of the test soil during the test, so as to realize the Adjust the water level in the water tank to control the rise and fall of the phreatic level of the test soil.

As shown in Figure 5(a) and Figure 5(b), the stainless steel plate 9-1 with a water hole makes the airless water in the pressure-bearing overhead layer 9 and the gravel sand 14-1 pressure-bearing layer hydraulically communicated, Provide the confined water head pressure of the gravel sand 14-1 containment layer; the thickness of the stainless steel plate 9-1 with water holes, the arrangement of the water holes and the arrangement of the stainless steel short columns 9-2 should meet the force requirements. Calculation requirements, so that the pressure-bearing overhead layer 9 is sufficient to bear the weight of the test soil.

As shown in Figure 6, the retaining wall 5 is an aluminum plate, and its thickness is calculated by the stiffness of the retaining wall simulated by the test; the retaining wall support 6 is a 20mm thick strip aluminum plate; the upper part of the retaining wall 5 is The retaining wall bracket 6 is fixed by the bracket fixing bolt 7, and a threaded hole is opened in the middle, and the supporting fixing bolt 8-7 required for installing the supporting unit 8 is threaded through the threaded hole, and the water-stop rubber strip 5-1 is fixed by slotting on both sides; The water-stop rubber strip 5-1 ensures that no water leakage occurs on the contact surface with the model box 1 during the movement of the retaining wall 5; the size of the bracket fixing bolt 7 and the support fixing bolt 8-7 is M8.

As shown in Fig. 7(a) and Fig. 7(b), the support fixing bolts 8-7 pass through the threaded holes on the retaining wall 5, and are screwed and fixed on the retaining wall 5. The supporting unit 8 can adopt the following two forms:

1. The support unit 8 includes a solid aluminum rod 8-1, a telescopic rod 8-2 and a support connecting bolt 8-3; the solid aluminum rod 8-1 has several grooves, and one end has an internal thread; The telescopic rod 8-2 is a hollow aluminum tube, and there are several threaded holes on the telescopic rod 8-2; the support connecting bolt 8-3 passes through the threaded holes on the telescopic rod 8-2 to resist the solid aluminum rod 8-1 The grooves make the solid aluminum rod 8-1 and the telescopic rod 8-2 tightly connected, and no sliding occurs during the test. The diameter of the solid aluminum rod 8-1 and the thickness of the hollow aluminum rod 8-2 are calculated from the supporting stiffness of the test simulation; the size of the supporting connecting bolt 8-3 can be selected as M6.

Two, the support unit 8 includes a first support rod 8-4, a second support rod 8-5 and a sleeve 8-6; one end of the first support rod 8-4 has an external thread; the second support rod One end of the rod 8-5 has an internal thread, and the other end has an external thread; the sleeve 8-6 has an internal thread channel, one end is threaded to the first support rod 8-4, and the other end is threaded to the second support rod 8- 5. The diameter of the first support rod 8-4, the diameter of the second support rod 8-5 and the wall thickness of the sleeve 8-6 are calculated from the stiffness of the inner support simulated by the test.

The working process of the present invention is as follows: first, the retaining wall 5 and the retaining wall bracket 6 are connected and assembled through the bracket fixing bolt 7; then the earth pressure box is installed on the retaining wall 5, and the notches on both sides are embedded with water-stop rubber strips 5-1, and apply epoxy resin in the gap between the notch and the water-stop rubber strip 5-1; the assembled retaining wall 5 is erected in the model box 1 through the retaining wall bracket 6 to ensure that the retaining wall 5 and The tempered glass 1-2 on both sides of the model box 1 is vertical; the symmetrical plane soil retaining unit 3 is installed at the symmetrical plane of the excavation model of the foundation pit, and is fixed on the model box frame 1-1 by the bolt 4 fixing the symmetrical plane soil retaining unit ; Fill the gravel sand 14-1 layer by layer in the model box 1 and compact it, and fill it to the specified height; fill it with clay silt 14-2 layer by layer, and compact it until the filling is completed, and the second water valve 10 will use 50L Pass the airless water saturated test soil gravel sand 14-1 and clayey silt 14-2 to the model box 1 at a speed of / day, and close the second water valve 10 after the soil is completely saturated; drill holes to bury the pores A water pressure sensor is used to backfill the borehole soil; displacement sensors are installed on the retaining wall 5 and the inner and outer soil surfaces of the foundation pit to monitor the displacement of the retaining wall 5 and the deformation of the foundation pit soil respectively;

Open the third water valve 12-3 and the air outlet valve 12-4, inject airless water 15 into the plexiglass cylinder 12-1 of the Marriott bottle 12 by the third water valve 12-3, and the air outlet valve 12 -4 discharge the gas in the plexiglass cylinder 12-1; to be filled with anaerobic water in the plexiglass cylinder 12-1, close the third water valve 12-3 and the air outlet valve 12-4; through the intake valve 12 -2 connects the air bag 12-5 equipped with 1atm nitrogen; then connects the model box 1 and the pressurized water head regulating system through the second water valve 10 through water.

Place the digital camera directly in front of the model box (it cannot be moved during the test), adjust the camera parameters, and set the automatic shooting time interval of the digital camera to 20s; if the light in the laboratory is insufficient, add LED light sources on both sides of the digital camera; Use the data acquisition instrument to collect and record the readings of the micro-pore water pressure sensor, the micro-earth pressure cell and the displacement sensor in the initial state of the test, and use a digital camera to take photos of the test soil in the initial state of the test;

After the above-mentioned test preparations are completed, open the first water valve 2-6 to adjust the water level in the water tank 2 to simulate the rise and fall of the test soil in the model box 1; open the second water valve 10 and the third water valve The water valve 12-3 and the air intake valve 12-2 are kept open during the entire foundation pit soil excavation and support installation process, so as to realize the continuous supply of the pressure-bearing water head adjustment system to the pressure-bearing overhead layer 9 required for the test. Pressure water head; adjust the height of the Marriott bottle 12 through the hand crank 13-3, and use the self-locking function of the hand crank 13-3 to fix the height of the Marriott bottle 12 to control the size of the pressurized water head. Measure 11 to read the size of the confined water head; remove the retaining unit on the symmetrical plane of the first section, and slowly excavate the soil on the left side of the retaining wall 5 by excavating the symmetrical plane to the foundation pit; excavate to the first When the support design position is below, the first support is installed, and the internal thread at one end of the support 8 is connected with the support fixing bolt 8-7 on the retaining wall 5, and the length of the support 8 is adjusted to tighten the reaction frame 1-5 , complete the installation of support 8. After the installation of the first support is completed, continue to excavate the soil, and install the support in the same way until the excavation of the foundation pit is completed.

During the whole foundation pit excavation test process, the water tank 2 is used to apply the water level corresponding to each working condition of the foundation pit excavation, and the pressure water head corresponding to each working condition of the foundation pit excavation is applied through the pressure head adjustment system; through the data The acquisition instrument continuously collects and records the readings of the miniature pore water pressure sensor, miniature earth pressure cell and displacement sensor during the test, and triggers the digital camera to take pictures of the deformation of the test soil during the whole test.

By analyzing the readings of the micro-pore water pressure sensor and the micro-earth pressure cell collected and recorded by the data acquisition instrument, the water and soil pressure response law caused by the coordinated rise and fall of the phreatic level and the confined water head during the entire excavation process of the foundation pit is obtained; through the analysis of the data acquisition instrument The readings of the recorded displacement sensor and the PIV image analysis of the photos taken by the digital camera can be used to obtain the displacement field of the soil, so as to know the deformation law of the excavation soil with the coordinated rise and fall of the phreatic level and the confined water head.

The above embodiment is a preferred implementation mode of the present invention, and is a further description of the content of the present invention and its application, and it should not be understood that the present invention is only applicable to the above embodiment. All technologies implemented based on the principles and contents of the present invention belong to the scope of the present invention.

Claims (10)

1. a phreatic table and artesian head work in coordination with the excavation of foundation pit model test apparatus of lifting, it is characterized in that, regulate system and seven parts of measurement system including model casing (1), water tank (2), some planes of symmetry gear soil unit (3), foundation pit supporting construction, pressure-bearing Stilt layer (9), artesian head; Described model casing (1) is made up of model casing framework (1-1), safety glass (1-2), model casing base plate (1-3), top frame (1-4), reaction plate (1-5) and model casing base (1-6); Bottom fixed model box plate (1-3) of described model casing framework (1-1), safety glass (1-2) is fixed in former and later two sides; Described model casing framework (1-1) and reaction plate (1-5) are each attached on model casing base (1-6), and top connects by pushing up frame (1-4); The bottom right side of described model casing (1) installs the second water flowing valve (10) of connection pressure-bearing Stilt layer (9), regulates system for connection mode molding box (1) and artesian head;

Described water tank (2) is made up of the aluminium sheet (2-1) with limbers, bar shaped aluminium sheet (2-2), tank bracket (2-3), tank bracket fixed screw (2-4), rule (2-5) and the first water flowing valve (2-6), it is erected at the upper right side in model casing (1), for the fluctuation in stage controlling and observing in the soil body by tank bracket (2-3); Described aluminium sheet (2-1) the surface mount anti-filter geotextile with limbers, it is prevented that test the loss of the soil body in groundwater change process; Described rule (2-5) is pasted onto on safety glass (1-2), can be used for directly observation and record phreatic table situation of change; Described first water flowing valve (2-6) is arranged on the right side of model casing (1) in order to joining water box (2);

Described plane of symmetry gear soil unit (3) is U-shaped stainless steel strip, is fixed on model casing framework (1-1) by bolt (4); Being connected by H type watertight rubber bar between described U-shaped stainless steel strip, U-shaped stainless steel strip is connected by S type watertight rubber bar with model casing framework (1-1);

Described foundation pit supporting construction includes retaining wall (5), retaining wall support (6) and some support units (8); Bracket fixing bolt (7) fixed retaining wall support (6) is passed through on described retaining wall (5) top, middle part has screwed hole, by the fixing bolt (8-7) of the support needed for the threaded installation support unit (8) of screwed hole, the fixing watertight rubber bar (5-1) of both sides fluting; Described watertight rubber bar (5-1) ensures not leak with model casing (1) contact surface in retaining wall (5) moving process; One end of described support unit (8) has inner thread mouth, and inner thread mouth is threadeded with supporting fixing bolt (8-7), it is achieved the installation of support unit (8);

Described pressure-bearing Stilt layer (9) is made up of the corrosion resistant plate (9-1) with limbers, rustless steel short column (9-2) and anti-filter geotextile (9-3); The described fixing rustless steel short column (9-2) in corrosion resistant plate (9-1) bottom with limbers, it is positioned on the model casing base plate (1-3) in model casing (1), and is connected with four side seals of model casing (1);Described corrosion resistant plate (9-1) surface mount anti-filter geotextile (9-3) with limbers;

Described artesian head regulates system and is made up of hydraulic pressure gauge (11), mariotte flask (12) and support (13); Described hydraulic pressure gauge (11) is by tee T connection mode molding box (1) and mariotte flask (12); Described support (13) is provided with fixed pulley (13-1), steel wire rope (13-2) is walked around fixed pulley (13-1) and is connected mariotte flask (12) and hand-operated device (13-3), is controlled the size of the lift adjustment artesian head of mariotte flask (12) by hand-operated device (13-3); Described mariotte flask (12) is made up of plexiglass cylinder (12-1), air intake valve (12-2), T-way water valve door (12-3), valve of giving vent to anger (12-4) and air bag (12-5); Described plexiglass cylinder (12-1) bottom arranges air intake valve (12-2) and T-way water valve door (12-3), and top arranges valve (12-4) of giving vent to anger; Described air intake valve (12-2) is connected with air bag (12-5);

Described measurement system includes miniature pore water pressure sensor, miniature soil pressure cell, displacement transducer, multi-Channels Data Acquisition and digital camera; Described miniature pore water pressure sensor, miniature soil pressure cell, displacement transducer pass through signal transmssion line connecting multi-channel data collecting instrument; Described digital camera is positioned over model casing dead ahead.

2. a kind of phreatic table according to claim 1 and artesian head work in coordination with the excavation of foundation pit model test apparatus of lifting, it is characterized in that, described support unit (8) includes solid aluminum bar (8-1), expansion link (8-2) and supports connecting bolt (8-3); Having some grooves on described solid aluminum bar (8-1), one end has inner thread mouth; Described expansion link (8-2) is hollow aluminum pipe, and expansion link (8-2) has some screwed holes; Described support connecting bolt (8-3) props up the groove of solid aluminum bar (8-1) through the screwed hole on expansion link (8-2).

3. a kind of phreatic table according to claim 1 and artesian head work in coordination with the excavation of foundation pit model test apparatus of lifting, it is characterized in that, described support unit (8) includes the first support bar (8-4), the second support bar (8-5) and sleeve (8-6); One end of described first support bar (8-4) has external screw thread; One end of described second support bar (8-5) has inner thread mouth, and the other end has external screw thread; Described sleeve (8-6) has female thread passage, and threaded one end connects the first support bar (8-4), threaded second support bar (8-5) of the other end.

4. a kind of phreatic table according to claim 1 and artesian head work in coordination with the excavation of foundation pit model test apparatus of lifting, it is characterised in that described digital camera answers exclusive PCR in process of the test, and its position can not be moved; Can need to set up light source according to shooting.

5. a kind of phreatic table according to claim 1 and artesian head work in coordination with the excavation of foundation pit model test apparatus of lifting, it is characterised in that described model casing framework (1-1) is welded by rustless steel steel bar thick for 10mm and stainless-steel sheet; Described safety glass (1-2) is arranged on model casing framework (1-1) inner side by building glue; Described model casing base plate (1-3) and reaction plate (1-4) are stainless-steel sheet thick for 10mm; Described top frame (1-5) is welded by the rustless steel steel bar that 20mm is thick; Described model casing main body and reaction plate (1-4) are fixed on model casing base (1-6) by surrounding spot welding; Described retaining wall (5) is aluminium sheet, and its thickness is obtained by the retaining wall Rigidity Calculation of test simulation; Described retaining wall support (6) is strip aluminum plate thick for 20mm;Described retaining wall (5) keeps vertical with safety glass (1-2) all the time in moving process; Described first water flowing valve (2-6), the second water flowing valve (10), air intake valve (12-2), T-way water valve door (12-3), valve of giving vent to anger (12-4) are copper core valve.

6. a kind of phreatic table according to claim 1 and artesian head work in coordination with the excavation of foundation pit model test apparatus of lifting, it is characterized in that, the diameter of described solid aluminum bar (8-1), the wall thickness of expansion link (8-2), the diameter of the first support bar (8-4), the diameter of the second support bar (8-5) and the wall thickness of sleeve (8-6) obtain by the Rigidity Calculation of the inner support of test simulation.

7. a kind of phreatic table according to claim 1 and artesian head work in coordination with the excavation of foundation pit model test apparatus of lifting, it is characterised in that described air bag (12-5) is built with the nitrogen of 1atm.

8. a kind of phreatic table according to claim 1 and artesian head work in coordination with the excavation of foundation pit model test apparatus of lifting, it is characterized in that, described water tank (2) and the liquid in plexiglass cylinder (12-1) are air free water (15).

9. a kind of phreatic table according to claim 1 and artesian head work in coordination with the excavation of foundation pit model test apparatus of lifting, it is characterised in that the bottom test soil body in model casing (1) is gravelly sand (14-1); The overlying test soil body is the weak water penetration soil body.

10. a kind of phreatic table according to claim 9 and artesian head work in coordination with the excavation of foundation pit model test apparatus of lifting, it is characterised in that the described weak water penetration soil body is clay silt (14-2); Described gravelly sand (14-1) and the weak water penetration soil body adopt air free water saturated.