A device and method for testing a hydraulic jacking failure model of a clay layer

Abstract

The present application relates to a kind of hydraulic jacking destruction model test device and test method of clay layer, the device includes: multilayer soil body support device, inside from bottom to top is laid with sandy soil layer and clay layer;Flow guide pipe, from the bottom of multilayer soil body support device is inserted, inside is filled with the sandy soil flush with top end;Water level control system, connect with flow guide pipe;Cylinder loading system, with the controllable load applied to the soil in multilayer soil body support device;Servo system, connect with water level control system and cylinder loading system;Data acquisition system, including pore water pressure sensor, water pressure sensor, displacement sensor and soil pressure sensor;Data processing terminal, respectively with cylinder loading system, water level control system, data acquisition system connection.Compared with prior art, the present application can accurately experiment on the instability and failure of clay layer under high water head, and has the advantages of easy operation, high precision, easy to observe.

Description

Technical Field

[0001] This invention relates to the field of indoor physical test simulation technology in geotechnical engineering, and in particular to a test device for a hydraulic jacking failure model of cohesive soil layers. Background Technology

[0002] Rapid urban development has placed new demands on underground space development, leading to a surge in ultra-large and ultra-deep foundation pit projects. Since developed cities are mainly concentrated in coastal and riverside areas, where geological conditions are complex and abundant confined water is present, confined water has a significant impact on the safety and stability of deep foundation pit projects. It is a key factor in the deformation and instability of deep foundation pits, and sudden instability caused by confined water at the bottom of the pit has become a hot topic in foundation pit engineering.

[0003] Traditional 1g indoor model tests in geotechnical engineering are conducted under constant gravity conditions. Due to the large size of actual engineering projects, indoor tests are often scaled-down models. Based on the soil's self-weight stress, these scaled-down models result in a reduction in soil depth, thus altering the soil's self-weight stress field and failing to reflect the actual stress state on site. This leads to significant difficulties in simulating actual engineering projects. Furthermore, model tests coupled with foundation pit excavation struggle to quantify the impact of the weakly permeable layer at the pit bottom on the stability of the pit bottom under confined water. Additionally, existing tests simulate uniform and continuous distribution of confined aquifers, while in actual strata, the thickness of confined aquifers is uneven, sometimes even lenticular, all of which contribute to localized instability and heave at the pit bottom. Existing standard calculation formulas only apply to ideal, simplified soil layer forms and do not consider the influence of soil shear strength, resulting in overly conservative results. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a test device and method for hydraulic jacking failure model of cohesive soil layer with higher accuracy of experimental results. It can simulate the original ground stress state of the foundation pit, the different thicknesses and shear strengths of the weak permeable layer at the bottom of the foundation pit, and the conditions of different water heads of the confined aquifer. It has a wide range of applications and high simulation accuracy.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] According to a first aspect of the present invention, a test apparatus for a hydraulic jacking failure model of cohesive soil layers is provided, the apparatus comprising:

[0007] The multi-layered soil support device has sandy soil layers and clay soil layers laid from bottom to top inside.

[0008] A diversion pipe is inserted from the bottom of the multi-layer soil support device, and the inside of the diversion pipe is filled with sand that is level with the top.

[0009] A water level control system is connected to the guide pipe and controls the test water level in the guide pipe to simulate the pressure head.

[0010] A cylinder loading system is used to apply a controllable load to the soil in a multi-layer soil support device.

[0011] The servo system is connected to the water level control system and the cylinder loading system, respectively.

[0012] The data acquisition system includes a pore water pressure sensor installed at the top of the diversion pipe, a water pressure sensor installed on the water inlet pipe of the diversion pipe, and a displacement sensor and an earth pressure sensor used to measure the displacement of the soil and the load on the multi-layer soil support device when the cylinder is loaded.

[0013] The data processing terminal is connected to the cylinder loading system, the water level control system, and the data acquisition system, respectively.

[0014] Preferably, the multi-layer soil support device includes multiple hollow glass cylinders with independently adjustable heights, a metal ring, and a support disc at the bottom.

[0015] The plurality of hollow glass cylinders are assembled together by locking screws and metal rings and fixed to the supporting disc; the guide pipe is inserted from the bottom of the multi-layer soil support device and extends beyond the set height of the supporting disc; the connection between the guide pipe and the supporting disc is sealed.

[0016] Preferably, the hollow glass tube is a cylindrical hollow glass tube;

[0017] The cohesive soil layer and the sandy soil layer are laid in a combination of a cohesive, weakly permeable layer in the upper part and a confined aquifer in the lower part of the confined aquifer.

[0018] Preferably, the multi-layer soil support device is a detachable multi-layer soil support device, used to remove the top model glass tube in actual tests for subsequent confining pressure loading tests.

[0019] Preferably, a perforated plexiglass plate is placed horizontally at the same height as the supporting disc; the bottom of the supporting disc has several small holes, each with a valve, and is connected to a water level control system via a drain hose.

[0020] Preferably, the water level control system includes a water tank, a water pump, and a valve connected in sequence by pipes, and connected to a diversion pipe;

[0021] The water pressure sensor is installed on the connecting pipe between the valve and the guide pipe to measure the water pressure entering the guide pipe.

[0022] Preferably, the cylinder loading system includes a loading reaction frame, a cylinder loading device, and a loading plate for consolidation loading or a loading ring for confining pressure loading, which are in contact with the soil in the multi-layer soil support device.

[0023] The cylinder loading device is fixed on the loading reaction frame. The cylinder loading system is connected to the loading plate or loading ring through an extension rod to apply load to the soil in the multi-layer soil support device. The earth pressure sensor is installed at the top of the extension rod.

[0024] Preferably, the bottom of the loading reaction frame is provided with pulleys.

[0025] Preferably, the data acquisition system further includes a digital imaging recording device; the data processing terminal is also equipped with a dynamic signal testing and analysis device.

[0026] According to a second aspect of the present invention, a simulation test method is provided for the instability and failure of a weakly permeable layer at the bottom of a foundation pit caused by confined water, using any of the apparatuses described in the present invention, the method comprising the following steps:

[0027] Step S1: The cohesive soil layer and sandy soil layer required for the test are prepared by clay and sand respectively. The clay is mixed with water according to the actual moisture content to make remolded soil to obtain the cohesive soil sample. The sandy soil is removed of particulate impurities and dried to obtain the sandy soil sample.

[0028] Step S2: Sand is placed on the supporting disc and inside the guide pipe. The sand in the guide pipe is arranged to be level with the top of the guide pipe. A pore water pressure sensor is placed at the top of the guide pipe. Then the prepared clay slurry is added.

[0029] Step S3: Start the cylinder loading system through the servo system to perform consolidation loading, adjust the loading pressure step by step to the preset value, and collect loading pressure and displacement data in real time.

[0030] Step S4: After consolidation loading is completed, confining pressure loading is performed to apply overburden pressure to the cohesive soil layer. Earth pressure data is collected in real time. When the preset pressure is reached, the cylinder loading system is controlled by the servo system to maintain the confining pressure stability.

[0031] Step S5: Control the water level control system through the servo system to pump water to the top of the guide pipe and collect pore water pressure data in real time;

[0032] Step S6: Gradually increase the water pressure, maintaining a stable water pressure for a set duration at each level;

[0033] Step S7: Repeat step S6 until the cohesive soil layer becomes unstable and fails.

[0034] Compared with the prior art, the present invention has the following advantages:

[0035] 1) Under 1g conditions, this invention can simulate the original ground stress state of the foundation pit, the thickness and shear strength of the weak permeable layer at the bottom of the foundation pit, and the water head of different confined aquifers to address the stability problem of sudden heave at the bottom of the foundation pit. It has a wide range of applications, high simulation accuracy, small overall size of the test device, simple and clear principle, and convenient operation. Through experimental research and analysis, it can solve the problem of design waste caused by the inability to consider the beneficial effect of clay shear strength on resisting the heave of confined water in existing design theories.

[0036] 2) This invention can achieve continuous and precise changes in consolidation loading and hydraulic loading by adjusting the cylinder loading system and the water level control system; at the same time, the cylinder loading device can achieve a large loading pressure with a small equipment volume; by connecting the guide pipe to the water level control system through the water pipe, the size of the test water level can be precisely adjusted to simulate the pressure head.

[0037] 3) By adopting a multi-layer model glass cylinder design with different heights, the thickness of the solidified cohesive soil layer can be precisely controlled to simulate the thickness of the clay layer from the bottom of the foundation pit to the top of the confined water layer.

[0038] 4) By using a guide pipe with a diameter smaller than that of multiple model glass cylinders, and with the height of the sandy soil layer outside the guide pipe lower than the part of the guide pipe that is higher than the supporting disc, this invention can prevent the formation of a crack surface extending to the wall of multiple model glass cylinders and prevent water from seeping through the cylinder wall of multiple model glass cylinders to the top of the cohesive soil layer, so as not to obtain the expected test results.

[0039] 5) By replacing the loading plate with a loading ring, overburden pressure can be applied to the cohesive soil layer to simulate the effect of the unexcavated soil on the stability of the soil layer at the bottom of the pit. Attached Figure Description

[0040] Figure 1 This is a three-dimensional diagram of the present invention;

[0041] Figure 2 This is a side view of the model box of the present invention.

[0042] Figure 3 This is a schematic diagram illustrating the consolidation loading principle of the present invention.

[0043] Figure 4 This is a schematic diagram illustrating the confining pressure loading principle of the present invention.

[0044] Reference numerals: 1-Model glass cylinder; 2-Metal ring; 3-Supporting disc; 4-Guide pipe; 5-Cylinder loading device; 6-Servo system; 7-Loading reaction frame; 8-Water pump; 9-Water tank; 10-Water pressure sensor; 11-Valve; 12-Cohesive soil layer; 13-Sandy soil layer; 14-Loading plate; 15-Loading ring. Detailed Implementation

[0045] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0046] Example

[0047] like Figures 1-4 As shown in the figure, this embodiment provides a test apparatus for a hydraulic jacking failure model of cohesive soil layers. The apparatus includes:

[0048] The multi-layered soil support device has sandy soil layers and clay soil layers laid from bottom to top inside.

[0049] The diversion pipe 4 is inserted from the bottom of the multi-layer soil support device, and the inside of the diversion pipe 4 is filled with sand that is level with the top.

[0050] A water level control system is connected to the guide pipe 4 and controls the test water level in the guide pipe 4 to simulate the pressure head.

[0051] A cylinder loading system is used to apply a controllable load to the soil in a multi-layer soil support device.

[0052] Servo system 6 is connected to the water level control system and cylinder loading system 5 respectively;

[0053] The data acquisition system includes a pore water pressure sensor installed at the top of the diversion pipe 4, a water pressure sensor 10 installed on the water inlet pipe of the diversion pipe 4, a displacement sensor and a soil pressure sensor installed on the multi-layer soil support device for measuring the displacement of the soil and the load it receives when the cylinder is loaded, and a digital imaging recording device.

[0054] The data processing terminal is connected to the cylinder loading system, the water level control system, and the data acquisition system, and is equipped with a dynamic signal testing and analysis device.

[0055] The specific settings are as follows:

[0056] The multi-layer soil support device includes multiple hollow glass cylinders 1 with adjustable heights, metal rings 2, and a support disc 3 at the bottom. The multiple hollow glass cylinders 1 are assembled together by locking screws and metal rings 2 and fixed to the support disc 3, with rubber sealing rings at the joints. A guide pipe 4 is inserted from the bottom of the multi-layer soil support device and extends beyond the set height of the support disc 3. The joint between the guide pipe 4 and the support disc 3 is sealed.

[0057] In this embodiment, a three-layer soil support device is used, such as Figure 1 As shown, hollow glass cylinders 1-1, 1-2, and 1-3 are assembled together and fixed to the supporting disc 3 by locking screws and metal rings 2-1, 2-2, and 2-3; wherein, hollow glass cylinders 1-1, 1-2, and 1-3 can be made with glass cylinders of different vertical heights according to the thickness of the cohesive soil layer. Further, in this embodiment, hollow glass cylinder 1 is a cylindrical hollow glass cylinder;

[0058] A perforated plexiglass plate is placed horizontally at the same height as the supporting disc 3. Several small holes are opened at the bottom of the supporting disc 3, and valves are installed at the small holes. The plate is connected to the water level control system through a drainage hose.

[0059] The cohesive soil layer 12 and the sandy soil layer 13 are laid in a combination of a cohesive weakly permeable layer in the upper part of the confined aquifer and a confined aquifer in the lower part.

[0060] The multi-layer soil support device is a detachable multi-layer soil support device used in actual tests to remove the top hollow glass cylinder 1 for subsequent confining pressure loading tests.

[0061] The cylinder loading system includes a cylinder loading device 5, a loading reaction frame with pulleys 7, a loading plate 14, and a loading ring 15.

[0062] The water level control system includes a water pump 8, a water tank 9, and a water pressure sensor 10. The water tank 9 is connected to a water pipe and a guide pipe 4. The water pressure sensor 10 is connected to the water pipe between the guide pipe 4 and the water pump 8 via a tee connector. Valves are provided between the guide pipe 4 and the water pump 8 and at the opening of the supporting disc.

[0063] The cylinder loading system includes a loading reaction frame 7, a cylinder loading device 5, and a loading plate 14 for consolidation loading or a loading ring 15 for confining pressure loading, which are in contact with the soil in the multi-layer soil support device. The cylinder loading device 5 is fixed on the loading reaction frame 7. The cylinder loading system 5 is connected to the loading plate 14 or the loading ring 15 through an extension rod to apply load to the soil in the multi-layer soil support device. A displacement sensor and a digital display are also provided. The top of the extension rod is connected to an earth pressure sensor.

[0064] Furthermore, the valve in this embodiment is a controllable valve.

[0065] Next, an embodiment of the method of the present invention is given, a simulation test method for the instability and failure of the weak permeable layer at the bottom of the foundation pit caused by confined water, the method comprising the following steps:

[0066] Step S1: The cohesive soil layer 12 and sandy soil layer 13 required for the test are prepared by clay and sand respectively. The clay soil is mixed with water according to the actual moisture content to make remolded soil to obtain the cohesive soil layer sample. The sandy soil layer sample is obtained by removing particulate impurities from the sandy soil and drying it.

[0067] Step S2: Sandy soil layer 13 is arranged on the supporting disc 3 and inside the guide pipe 4. The sand in the guide pipe 4 is arranged to be flush with the top of the guide pipe 4, and a pore water pressure sensor is installed at the top. Then the prepared clay slurry is added.

[0068] Step S3: Start the cylinder loading system through the servo system 6 to perform consolidation loading, and adjust the loading pressure step by step to the preset value. During the consolidation process, open the valve 11 at the support disc 3, and the drain hose will re-inject the drained water into the model glass tube. The loading pressure and displacement data of the loading plate 14 are collected in real time through the data acquisition system, and the data is analyzed by the computer.

[0069] Step S4: After consolidation is completed, remove the glass cylinder 1-1 and the metal ring 2-1, and scrape off the clay that protrudes above the glass cylinder 1-2. The height of the glass cylinder 1-2 is preset before consolidation to control the clay layer thickness under a given consolidation pressure, thus simulating the thickness of the clay layer at the bottom of the foundation pit. Replace the loading plate 14 with the loading ring 15 to simulate the pressure of the unexcavated overburden outside the foundation pit. Real-time soil pressure data is collected through a data acquisition system. When the preset pressure is reached, the servo system 6 controls the cylinder loading system to maintain stable consolidation pressure.

[0070] Step S5: Fill water into water tank 9, control valve 11 on water pipe through servo system 6, and start water pump 8 to pump water pump 8 to the top surface of guide pipe 4, and collect pore water pressure data in real time through data acquisition system.

[0071] Step S6: Gradually increase the water pressure, maintaining a stable water pressure for 5 minutes at each level;

[0072] Step S7: Repeat step S6 until the cohesive soil layer becomes unstable and fails. Compile a set of test data and digital images.

[0073] Step S8: Complete multiple sets of experiments under different preset conditions, use a computer to organize the experimental data, and combine theoretical methods and other means to study and analyze the data.

[0074] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A test apparatus for hydraulic jacking failure model of cohesive soil layers, characterized in that, The device includes: The multi-layered soil support device has sandy soil layers and clay soil layers laid from bottom to top inside. The guide pipe (4) is inserted from the bottom of the multi-layer soil support device, and the inside of the guide pipe (4) is filled with sand that is level with the top. A water level control system is connected to the guide pipe (4) to simulate the pressure head by controlling the test water level in the guide pipe (4); A cylinder loading system is used to apply a controllable load to the soil in a multi-layer soil support device. The servo system (6) is connected to the water level control system and the cylinder loading system respectively; The data acquisition system includes a pore water pressure sensor installed at the top of the guide pipe (4), a water pressure sensor (10) installed on the water inlet pipe of the guide pipe (4), and a displacement sensor and a soil pressure sensor used to measure the displacement of the soil and the load on the multi-layer soil support device when the cylinder is loaded. The data processing terminal is connected to the cylinder loading system, the water level control system, and the data acquisition system, respectively. The multi-layer soil support device includes multiple hollow glass cylinders (1) with different heights, a metal ring (2), and a support disc (3) at the bottom. The plurality of hollow glass cylinders (1) are assembled together by locking screws and metal rings (2) and fixed on the supporting disc (3); the guide pipe (4) is inserted from the bottom of the multi-layer soil support device and extends beyond the set height of the supporting disc (3); the connection between the guide pipe (4) and the supporting disc (3) is sealed. The multi-layer soil support device is a detachable multi-layer soil support device, used to remove the top hollow glass tube (1) in actual tests to carry out subsequent confining pressure loading tests.

2. The hydraulic jacking failure model test device for cohesive soil layers according to claim 1, characterized in that, The hollow glass tube (1) is a cylindrical hollow glass tube; The cohesive soil layer and the sandy soil layer are laid in a combination of a cohesive, weakly permeable layer in the upper part and a confined aquifer in the lower part of the confined aquifer.

3. The hydraulic jacking failure model test device for cohesive soil layers according to claim 1, characterized in that, The supporting disc (3) is provided with a horizontally placed perforated organic glass plate at the same height; the bottom of the supporting disc (3) has several small holes, and valves are installed at the small holes, which are connected to the water level control system through drainage hoses.

4. The hydraulic jacking failure model test device for cohesive soil layers according to claim 1, characterized in that, The water level control system includes a water tank (9), a water pump (8) and a valve connected in sequence by pipes, and connected to a guide pipe (4). The water pressure sensor (10) is installed on the connecting pipe between the valve (11) and the guide pipe (4) to measure the water pressure entering the guide pipe (4).

5. The hydraulic jacking failure model test device for cohesive soil layers according to claim 1, characterized in that, The cylinder loading system includes a loading reaction frame (7), a cylinder loading device (5), and a loading plate (14) for consolidation loading or a loading ring (15) for confining pressure loading, which are in contact with the soil in the multi-layer soil support device. The cylinder loading device (5) is fixed on the loading reaction frame (7). The cylinder loading system is connected to the loading plate (14) or loading ring (15) through an extension rod to apply load to the soil in the multi-layer soil support device. The earth pressure sensor is set at the top of the extension rod.

6. The hydraulic jacking failure model test device for cohesive soil layers according to claim 5, characterized in that, The bottom of the loading reaction frame (7) is provided with pulleys.

7. The hydraulic jacking failure model test device for cohesive soil layers according to claim 1, characterized in that, The data acquisition system also includes a digital imaging recording device; the data processing terminal is also equipped with a dynamic signal testing and analysis device.

8. A simulation test method for the instability and failure of a weakly permeable layer at the bottom of a foundation pit caused by confined water, characterized in that, The method, employing the apparatus according to any one of claims 1 to 7, comprises the following steps: Step S1: The cohesive soil layer and sandy soil layer required for the test are prepared by clay and sand respectively. The clay is mixed with water according to the actual moisture content to make remolded soil to obtain the cohesive soil sample. The sandy soil is removed of particulate impurities and dried to obtain the sandy soil sample. Step S2: Sand is placed on the supporting disc (3) and inside the guide pipe (4). The sand inside the guide pipe (4) is arranged to be level with the top of the guide pipe (4). A pore water pressure sensor is placed on the top of the guide pipe (4). Then the prepared clay slurry is added. Step S3: Start the cylinder loading system through the servo system (6) to perform solidification loading, adjust the loading pressure step by step to the preset value, and collect loading pressure and displacement data in real time; Step S4: After the consolidation loading is completed, the confining pressure is applied to the cohesive soil layer. The soil pressure data is collected in real time. When the preset pressure is reached, the cylinder loading system is controlled by the servo system (6) to maintain the confining pressure stability. Step S5: Control the water level control system through the servo system (6) to pump water to the top surface of the guide pipe (4) and collect pore water pressure data in real time; Step S6: Gradually increase the water pressure, maintaining a stable water pressure for a set duration at each level; Step S7: Repeat step S6 until the cohesive soil layer becomes unstable and fails.

Images