Compression testing instrument considering the true lateral confinement conditions around the underlying soil mass and its application

Abstract

The present invention provides a compression tester and its application that consider the true lateral confinement conditions around the underlying soil mass of a foundation. The compression tester includes a main test chamber, a loading pressure plate, a hydraulic loading system, and a monitoring and control system. In the main test chamber, a permeable stone and a soil sample are arranged from top to bottom. The permeable stone includes a central permeable stone and a surrounding permeable stone, and there is a certain annular gap between them. Correspondingly, the soil sample includes a central soil sample and a surrounding soil sample, which correspond to the central permeable stone and the surrounding permeable stone respectively. The loading pressure plate includes a central main pressure plate and a surrounding pressure plate. The hydraulic loading system is used to apply pressure to the central soil sample. The monitoring and control system is used to monitor the original settlement of the overall soil sample under the action of the overlying soil pressure and the additional settlement of the central soil sample under the action of the additional pressure. The present invention can consider the true lateral confinement conditions that change with depth around the underlying soil mass of the foundation, and solves the inherent defect of the conventional compression test that infinitely magnifies the lateral confinement conditions of the soil mass.

Description

Technical Field

[0001] The present invention belongs to the technical field of geotechnical engineering tests, and particularly relates to a compression tester and its application that consider the true lateral confinement conditions around the underlying soil of the foundation. Technical Background

[0002] Foundation settlement has always been an important topic that has received much attention in the field of geotechnical engineering. Pre-determining the settlement value of the foundation under the action load of the upper building is of great significance for the entire project and is also the key to determining the success or failure of the project. How to select a reasonable method to quantitatively calculate the foundation settlement is a problem that geotechnical engineering technicians have been concerned about for a long time.

[0003] Currently, the main method in the industry is to obtain the e-p (void ratio - vertical stress) compression curve based on the conventional soil compression test, and then calculate the foundation settlement amount by combining the layer-wise summation method. Finally, the calculated settlement amount needs to be multiplied by an empirical amplification factor greater than 1 to be regarded as the true settlement amount of the foundation. Obviously, the settlement amount calculated by the conventional compression test is smaller than the actual settlement. Therefore, it is necessary to multiply the calculated value by an empirical coefficient to amplify it. The main reason for the smaller calculated value is the defect of the conventional compression test itself. The pressure plate of its compression tester almost covers the entire surface of the cutting ring, placing all the soil samples in the cutting ring under the pressure plate. Therefore, the soil sample has almost no room for lateral deformation and can only undergo restricted vertical deformation under the vertical pressure. In fact, although the soil directly below the underlying foundation is also restricted by the surrounding soil, this kind of restriction has a depth effect, that is, in the shallower part, due to the small earth pressure of the surrounding soil above, the lateral confinement effect is very weak, while in the deeper part, the surrounding soil is suppressed by the larger earth pressure above, making its deformation restriction effect on the soil directly below the foundation gradually increase. The conventional compression test is equivalent to infinitely amplifying the lateral deformation restriction of the underlying soil of the foundation, resulting in a smaller deformation value of the tested sample and further leading to an inaccurate calculated value of the foundation settlement amount. Summary of the Invention

[0004] The first object of the present invention is to provide a compression tester that considers the true lateral confinement conditions around the underlying soil of the foundation based on the universality and important influence of the foundation settlement problem in geotechnical engineering and the defects of the current conventional compression test, so as to ensure the rationality of the deformation data measured in the test and fully simulate the true mechanical conditions of the underlying soil of the foundation.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A compression tester that considers the true lateral confinement conditions around the underlying soil of the foundation, characterized in that: the compression tester includes a main test chamber, a loading pressure plate, a hydraulic loading system, a monitoring and control system, and a frame;

[0007] The main test chamber is located in the center of the compression tester. The main test chamber is surrounded by a barrel-shaped test chamber steel wall. In the main test chamber, a permeable stone and a soil sample are arranged from top to bottom. The permeable stone includes a central permeable stone and a surrounding permeable stone surrounding the periphery of the central permeable stone. There is a certain annular gap between the central permeable stone and the surrounding permeable stone. Correspondingly, the soil sample includes a central soil sample and a surrounding soil sample. The central soil sample corresponds to the central permeable stone, and the surrounding soil sample corresponds to the surrounding permeable stone. The annular gap is to avoid friction between the central permeable stone and the surrounding permeable stone, and between the central main pressing plate and the surrounding pressing plates during the test. The central permeable stone and the surrounding permeable stone allow the water in the soil sample to drain during the compression test. The central soil sample represents the soil mass directly below the foundation in actual engineering, while the surrounding soil sample represents the peripheral soil mass outside the foundation range in actual engineering. The surrounding pressing plates are provided with permeable holes for the drainage of water during the compression test.

[0008] The loading pressing plate is arranged on the permeable stone. The loading pressing plate includes a central main pressing plate and surrounding pressing plates. The central main pressing plate is arranged on the central permeable stone, and the surrounding pressing plates are arranged on the surrounding permeable stones.

[0009] The hydraulic loading system is used to apply pressure loading to the central main pressing plate above the central soil sample and the central permeable stone.

[0010] The monitoring and control system is used to control the up and down movement of the hydraulic loading system for servo control of the hydraulic loading system, monitor the pressure of the hydraulic loading system, and monitor the original settlement of the overall soil sample under the action of the overburden pressure and the additional settlement of the central soil sample under the action of the additional pressure.

[0011] While adopting the above technical solutions, the present invention can also adopt or combine the following technical solutions:

[0012] As a preferred technical solution of the present invention: The loading pressing plate is equipped with a standard weight and is equipped with multiple pressing plate kits of the same weight and the same size to simulate the overburden pressure of the soil sample under different depth conditions, including: respectively used to simulate different degrees of soil pressure above the central soil sample and different degrees of soil pressure above the surrounding soil sample.

[0013] As a preferred technical solution of the present invention: The central permeable stone is integrally in a disc shape, and the surrounding permeable stone is integrally in an annular shape.

[0014] As a preferred technical solution of the present invention: There is a certain annular gap between the surrounding permeable stone and the test chamber steel wall.

[0015] As a preferred technical solution of the present invention: the hydraulic loading system includes a hydraulic lift, a lifting platform, a controller, a pressure application shaft, and a bearing groove. The lifting platform is designed in a stepped shape;

[0016] The hydraulic lift is fixed to the frame columns of the frame;

[0017] The controller is connected to the monitoring and control system and is controlled by the monitoring and control system to drive the lifting platform to move up and down along the hydraulic lift, so as to drive the pressure application shaft to push into the bearing groove below the pressure application shaft;

[0018] The pressure application shaft is fixed to the central position of the bottom surface of the lifting platform, and the bearing groove is fixed to the central position of the top of the central main pressing plate. The inner side of the bearing groove is used to accommodate the lower end of the pressure application shaft, and is used to support the additional pressure of the pressure application shaft, that is, to simulate the additional pressure of the building transmitted from the foundation to the foundation soil. The bearing groove is made of light material, and its weight can be ignored.

[0019] As a preferred technical solution of the present invention: the pressure application shaft is integrally in the shape of a long cylinder, and the lower end is in the shape of a hemisphere to make smooth contact with the inner side of the bearing groove and apply additional pressure.

[0020] As a preferred technical solution of the present invention: the monitoring and control system includes a pressure sensor. The pressure sensor is arranged at the position on the central main pressing plate in contact with the hydraulic loading system. Specifically, the pressure sensor is arranged on the inner side of the bearing groove, and is used to monitor the additional pressure applied when the pressure application shaft moves down, and is fed back to the computer through a data transmission cable. The computer then judges it according to the preset additional pressure value, and issues an instruction to the controller to servo-control the lifting of the lifting platform to ensure that the applied additional pressure value is the target value.

[0021] As a preferred technical solution of the present invention: the monitoring and control system includes a first displacement sensor and a second displacement sensor. The first displacement sensor and the second displacement sensor are both arranged on the bottom surface of the stepped part of the lifting platform in the hydraulic loading system. The first displacement sensor is used to monitor the original settlement of the overall soil sample under the action of overburden pressure, and the second displacement sensor is used to monitor the additional settlement of the central soil sample under the action of additional pressure.

[0022] As a preferred technical solution of the present invention: the monitoring and control system includes a computer. The computer is the core of the monitoring and control system. It is connected with a signal data transmission cable, can receive real-time data fed back from all sensing and monitoring devices, and can issue real-time instructions to corresponding functional components in a timely manner, especially by issuing an instruction to the controller, so as to realize the servo control of the hydraulic loading system.

[0023] As a preferred technical solution of the present invention: The base of the frame is fixed to a firm special cement floor by screws, mainly playing the role of protecting the test equipment and providing a supporting reaction force.

[0024] The second object of the present invention is to provide the application of the compression tester considering the true lateral confinement conditions around the underlying soil of the foundation in the compression test of soil samples under different depth conditions.

[0025] Another object of the present invention is to provide the application of the vertical strain - additional compressive stress curve of the central soil sample under different depth conditions obtained in the application of the compression tester in the compression test of soil samples under different depth conditions in the calculation of foundation settlement.

[0026] The present invention provides a compression tester considering the true lateral confinement conditions around the underlying soil of the foundation and its application. Compared with the prior art, it has the following beneficial effects:

[0027] (1) Compared with the conventional compression test, the present invention can highly restore the lateral confinement conditions that vary with depth around the underlying soil of the foundation, rather than infinitely magnifying the lateral confinement conditions. By considering the true lateral confinement conditions that vary with depth around the underlying soil of the foundation, it solves the inherent defect of the conventional compression test of infinitely magnifying the lateral confinement conditions of the soil, thus successfully avoiding the problem of the measured value of soil sample deformation being too small caused by the infinite magnification of the lateral confinement conditions;

[0028] (2) The present invention distinguishes the central soil sample and the surrounding soil samples under the foundation and applies different vertical loads to them, which can more clearly distinguish the effects of overlying soil pressure and building additional pressure;

[0029] (3) The present invention uses double displacement gauges to monitor different functions. One first monitors the original settlement of the overall soil sample under the action of overlying soil pressure, and the other then monitors the settlement of the central soil sample under the main pressure plate under the action of the additional pressure of the building foundation, which can effectively distinguish the effects of two different pressures;

[0030] (4) The present invention uses the ε1 - Δp (vertical strain - additional compressive stress) curve representing the central soil sample at different depths to replace the e - p (void ratio - vertical compressive stress) curve of the conventional compression test, making it more convenient to calculate the foundation settlement by the layer - sum method;

[0031] (5) The present invention adopts a computer servo control system, which can receive and process the data fed back by the sensing monitoring equipment and automatically perform servo control on the functional components of the instrument through transmission signals. Description of the Drawings

[0032] Figure 1 It is a diagram of the compression tester considering the true lateral confinement conditions around the underlying soil of the foundation provided by the present invention;

[0033] Figure 2 is Figure 1 the view in the A-A direction in

[0034] Figure 3 is Figure 1 the view in the B-B direction in

[0035] Figures 4a - 4g are respectively the schematic diagrams of compression simulating different depth conditions ( Figures 4a to 4g simulating in sequence from the surface layer to the deep layer in terms of depth);

[0036] Figure 5 corresponds to Figures 4a - 4g the s-p (settlement - compressive stress) curves of the central specimen under each depth condition in

[0037] Figure 6 is the schematic diagram of the compression of the central specimen in the compression test;

[0038] Figure 7 corresponds to Figure 5 the ε1-Δp (vertical strain - additional compressive stress) curves of the central specimen under each depth condition in

[0039] Figure 8 is the typical sectional view for calculating foundation settlement;

[0040] In the figure: 1 - frame column; 2 - hydraulic lift; 2a - controller; 3 - displacement sensor ②; 4 - load-bearing groove; 5 - surrounding pressing plate; 6 - water-permeable hole; 7 - surrounding water-permeable stone; 8 - central water-permeable stone; 9 - surrounding soil sample; 9a - central soil sample; 10 - screw; 11 - frame base; 12 - pressurizing shaft; 13 - displacement sensor ①; 14 - lifting platform; 14a - first step of the lifting platform ladder; 14b - second step of the lifting platform ladder; 14c - third step of the lifting platform ladder; 15 - test computer; 16 - data transmission cable; 17 - central main pressing plate; 17a - special light pressing plate; 18 - pressure sensor; 19 - steel wall of the test chamber; 20 - special cement floor; 21 - first annular gap; 22 - second annular gap; 23 - additional compressive stress; 24 - settlement amount; 25 - compressive stress; 26 - additional compressive stress Δp1 applied after compressive stress p1; 27 - additional settlement Δs1 generated under additional compressive stress Δp1; 28 - settlement s1 corresponding to compressive stress p1; 29 - original height of the central soil sample; 30 - height of the central soil sample after compression under compressive stress p1; 31 - height of the central soil sample after compression under compressive stress p1 and additional compressive stress Δp1; 32 - diameter of the central soil sample (central main pressing plate); 33 - vertical strain ε1 of the central soil sample after applying additional compressive stress Δp. Specific implementation manners

[0041] The present invention will be further described in detail with reference to the accompanying drawings and specific embodiments.

[0042] A compression tester that takes into account the actual lateral confinement conditions around the underlying soil has a structure as Figure 1 shown, mainly including five functional parts: a main test chamber, a loading platen, a hydraulic loading system, a monitoring and control system, and a frame.

[0043] In the upper part, a hydraulic elevator 2 is installed on the frame column 1, and a lifting platform 14 is mounted on the hydraulic elevator 2 and can be adjusted by the controller 2a to move up and down along the hydraulic elevator 2. The lifting platform 14 is designed in a stepped shape, and displacement sensor ①13 and displacement sensor ②3 are respectively installed on the bottom surfaces of the steps. The displacement monitoring data can be fed back to the computer 15 through the data transmission cable 16. A pressure application shaft 12 is provided at the center of the bottom of the lifting platform 14, and the bottom of the pressure application shaft 12 is hemispherical and can be in smooth contact with and apply pressure to the bearing groove 4 below it. The bearing groove 4 is fixed at the center of the top surface of the central main platen 17, and a pressure sensor 18 is installed on its surface to monitor the additional pressure applied when the pressure application shaft 12 moves down, and is fed back to the computer 15 through the data transmission cable 16.

[0044] In the middle part, the test chamber steel wall 19 is fixed to the frame base 11 in a barrel shape and forms a filling space for the soil sample together with the central permeable stone 8 and the surrounding permeable stones 7. Among them, the part along the edge of the central permeable stone 8 downward is denoted as the central soil sample 9a, and correspondingly, the part along the contour of the surrounding permeable stone 7 downward is denoted as the surrounding soil sample 9. Similarly, a central main platen 17 is stacked above the central permeable stone 8, and a surrounding platen 5 is stacked above the surrounding permeable stones 7. Among them, a bearing groove 4 is provided at the center of the top surface of the central main platen 17, and the surrounding platen 5 is provided with permeable holes 6 to allow the water body to drain out during the compression test.

[0045] In the lower part, screws 10 fix the frame base 11 to the special cement floor 20 to fix the whole frame.

[0046] Figure 2 For Figure 1 the view in the A-A direction in, it shows the spatial relationship among the pressure application shaft 12, the bearing groove 4, the central main platen 17, the surrounding platen 5, the main test chamber steel wall 19, and the surrounding permeable stones 7. It can be seen that the pressure application shaft 12 abuts against the bearing groove 4, and the bearing groove 4 is fixedly connected to the center of the top surface of the central main platen 17. An annular gap ①21 is controlled between the central main platen 17 and the surrounding platen 5, that is, the annular gap between the central permeable stone and the surrounding permeable stones 7. The surrounding platen 5 is provided with permeable holes 6 to allow the water body in the soil sample to flow out. An annular gap ②22 is controlled between the surrounding permeable stones 7 and the test chamber steel wall 19. The design of the annular gap can avoid friction between components during the test.

[0047] Figure 3 For Figure 1View B-B shows the stepped design of the lifting platform and the positions of the displacement sensors. It can be seen that the lifting platform is divided into three layers. Displacement sensor ①13 is installed on the bottom surface of the stepped part ①14a of the lifting platform, and displacement sensor ②3 is installed on the bottom surface of the stepped part ③14c of the lifting platform. At the same time, it can be seen that the pressure shaft 12 is fixedly connected to the bottom surface of the stepped part ③14c of the lifting platform.

[0048] The following combines Figures 4a - 4g to Figure 6 , and the basic steps for the compression test and foundation settlement calculation of the present invention are as follows:

[0049] I. Obtaining the s-p compression curve of the central soil sample

[0050] As shown in Figures 4a - 4g , compression tests of soil samples under different depths are carried out ( Figures 4a to 4g simulating in turn from the surface layer to the deep layer, the greater the buried depth of the soil sample, the greater the overburden pressure stress, indicating that the lateral deformation restriction of the surrounding soil sample 9 on the central soil sample 9a is also stronger), for example Figure 4a simulating the compression of the central soil sample after receiving the additional compressive stress 23 under the surface layer conditions, while Figures 4b to 4g respectively represent the compression of the central soil sample 9a after applying different magnitudes of overburden pressures p1, p2, p3, p4, p5, and p6 and then applying the additional compressive stress 23. It should be noted that the overburden pressure stress is achieved by the weight of the pressing plate, and increasing the overburden pressure stress is achieved by increasing the number of layers of the pressing plate. The central main pressing plate 17 and the surrounding pressing plates 5 both adopt standard counterweights and are each equipped with multiple pressing plate kits of the same weight and the same size. As Figures 4a - 4g shown, it is necessary to ensure that the compressive stress applied by the central main pressing plate 17 and the surrounding pressing plates 5 to the soil samples (9, 9a) in each layer is equal everywhere, that is, the overburden pressure stress represented by one layer of pressing plate is p1, and that of two layers is p2, and so on. In addition, Figure 4a when simulating the condition of no overburden pressure stress on the surface layer, the central pressing plate 17 should not be added above the central soil sample 9a, but in order to avoid damaging the central permeable stone, a very thin special light pressing plate 17a is used to cover the central permeable stone, so that both the damage of the permeable stone can be avoided and the condition of no overburden pressure stress on the surface layer in this situation can be simulated.

[0051] According to Figures 4a - 4g the compression test shown, obtain Figure 5The s-p compression curve shown. It can be seen that when the overburden stress is continuously and uniformly applied to the central soil sample 9a and the surrounding soil sample 9 simultaneously (i.e., in a conventional compression test, the surrounding soil sample 9 is compressed synchronously, meaning non-open type), as the compressive stress p increases, a conventional compression curve 0 can be obtained, and the greater the compressive stress, the more difficult the compression becomes. After applying a certain magnitude of overburden stress and then applying an additional compressive stress to the central soil sample 9a, the s-p curve of the central soil sample 9a shows a downward development trend at the overburden stress point (the surrounding soil sample is no longer subject to the additional compressive stress, meaning open type), that is, the settlement becomes larger and larger. This increasing trend is also related to the overburden stress. The greater the overburden stress, the less obvious the increasing trend of the settlement generated after applying the additional compressive stress to the central soil sample. For example, when the overburden stress increases to p6 and then the central soil sample is pressurized, its open-type compression curve 1 has gradually approached the conventional compression curve. In the figure, the overburden stress p1 is taken as an example. After applying the overburden stress p1, the soil sample first undergoes a primary settlement s128, and then an additional compressive stress Δp126 is applied to the central soil sample, and then the central soil sample generates a corresponding additional settlement Δs127. Correspondingly, after applying the overburden stresses p2, p3, p4, p5, or p6, the primary settlements generated by the soil sample can be recorded as s2, s3, s4, s5, and s6 in turn (not repeated in the figure).

[0052] II. Conversion of the ε1-Δp Compression Curve of the Central Soil Sample

[0053] Taking the example of applying the overburden stress p1 and then applying an additional compressive stress to the central soil sample 9a, the compression process of the central soil sample 9a is shown as Figure 6 , the height of the central soil sample 9a during filling is h29, and the diameter is denoted as D32. Under the condition of applying the overburden stress p1, the surrounding soil sample 9 and the central soil sample 9a are first compressed simultaneously, and a primary settlement s1 occurs. This settlement is completely caused by the compressive stress of the upper soil mass and is realized by applying the weight of the pressing plate in the experiment. During this process, the lifting platform is fixed at a certain position, and this primary settlement s1 is monitored by the displacement sensor ②3. The height of the central soil sample 9a is compressed from the filling height h29 to h-s130.

[0054] After the primary settlement is stable, slowly lower the lifting platform. When the bottom of the pressure application shaft just touches the pressure sensor in the bearing groove and the sensor reacts, start the loading under the target additional compressive stress value (such as Δp1), and synchronously monitor the displacement of the lifting platform during the loading process using the displacement sensor ①13. The loading process adopts servo control, that is, the pressure sensor transmits the measured pressure P to the computer, and then the computer checks Δp = 4P / (πD 2)Is it the target value Δp1? If it deviates from this value, an instruction is sent to the controller in a timely manner to servo-control the lifting platform to move up and down, ensuring that the pressure measured by the sensor always meets the target value requirements. During this loading process, the displacement sensor ①13 continuously monitors the displacement of the lifting platform until the displacement value stabilizes. This displacement is the additional settlement Δs127 generated by the central soil sample 9a under the additional compressive stress Δp1. During this process, the height of the central soil sample changes from h - s130 to h - s1 - Δs131. The vertical strain generated by the additional compressive stress Δp1 is (ε1) Δp1 = Δs1 / (h - s1). It should be noted that h - s130 is the true initial height of the central soil sample under the overburden pressure p1 (i.e., at the corresponding burial depth). Similarly, by conducting compression tests on the central soil sample under different additional compressive stresses under different magnitudes of overburden pressure conditions, the Figure 7 shown ε1-Δp curves representing the central specimen under different overburden pressures (p1, p2, p3, p4, p5, and p6) can be obtained.

[0055] III. Foundation settlement calculation

[0056] According to the test results as Figure 7 shown, the settlement of the foundation soil under the condition of the additional total load ΔP of the building in Figure 8 is calculated. First, the total calculation depth affected by the additional compressive stress below the foundation is denoted as H, and the foundation burial depth is H / 12. Then, H is divided into 6 calculation layers, each layer with a thickness of H / 6 (this thickness is the true initial thickness after being compressed by the overburden pressure before the additional compressive stress is applied). The average overburden pressure received by each layer is assumed to be p1, p2, p3, p4, p5, and p6 from top to bottom in turn, and the average additional compressive stress transmitted by the foundation is denoted as Δp1, Δp2, Δp3, Δp4, Δp5, and Δp6 respectively. Combining with the Figure 7 shown ε1-Δp curves of the central specimen under different burial depth conditions, the calculation formula for the foundation settlement can be obtained according to the concept of vertical strain as follows:

[0057]

[0058] In the formula, represents Figure 7 the vertical strain corresponding to the ε1-Δp curve 6 after p1 in under the additional compressive stress Δp1; Figure 7 represents the vertical strain corresponding to the ε1-Δp curve 5 after p2 in Figure 7 under the additional compressive stress Δp2; representsFigure 7 The vertical strain corresponding to the open ε1-Δp curve 3 after p4 under the additional compressive stress Δp4; Denote Figure 7 The vertical strain corresponding to the open ε1-Δp curve 2 after p5 under the additional compressive stress Δp5; Denote Figure 7 The vertical strain corresponding to the open ε1-Δp curve 1 after p6 under the additional compressive stress Δp6.

[0059] If the calculation depth is divided into n layers, the calculation formula for the foundation settlement can be written as:

[0060]

[0061] The above specific implementation manners are used to explain and illustrate the present invention, and are only the preferred embodiments of the present invention, rather than limiting the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and protection scope of the claims of the present invention fall within the protection scope of the present invention.

Claims

1. Application of a compression tester considering the true lateral confinement conditions around the underlying soil in the compression test of soil samples at different depths, characterized in that: The compression tester includes a main test chamber, a loading platen, a hydraulic loading system, a monitoring and control system, and a frame; The main test chamber is located at the center of the compression tester. The main test chamber is surrounded by a barrel-shaped test chamber steel wall. A permeable stone and a soil sample are arranged in the main test chamber from top to bottom. The permeable stone includes a central permeable stone and a peripheral permeable stone surrounding the periphery of the central permeable stone. There is a certain annular gap between the central permeable stone and the peripheral permeable stone; correspondingly, the soil sample includes a central soil sample and a peripheral soil sample. The central soil sample corresponds to the central permeable stone, and the peripheral soil sample corresponds to the peripheral permeable stone; The loading platen is arranged on the permeable stone. The loading platen includes a central main platen and a peripheral platen. The central main platen is arranged on the central permeable stone, and the peripheral platen is arranged on the peripheral permeable stone; The hydraulic loading system is used to apply pressure loading to the central main platen above the central soil sample and the central permeable stone; The monitoring and control system is used to control the up and down movement of the hydraulic loading system for servo control of the hydraulic loading system, monitor the pressure of the hydraulic loading system, and monitor the original settlement of the overall soil sample under the action of overburden pressure and the additional settlement of the central soil sample under the action of additional pressure; The loading platen is equipped with a standard weight and is equipped with multiple platen kits of the same weight and the same size to simulate the overburden pressure of the soil sample under different depth conditions; The hydraulic loading system includes a hydraulic elevator, a lifting platform, a controller, a pressure application shaft, and a bearing groove, The hydraulic elevator is fixed to the frame column of the frame; The controller is connected to the monitoring and control system and is controlled by the monitoring and control system to drive the lifting platform to move up and down along the hydraulic elevator to drive the pressure application shaft to push into the bearing groove below the pressure application shaft; The pressure application shaft is fixed to the central position of the bottom surface of the lifting platform, and the bearing groove is fixed to the central position of the top of the central main platen. The inner side of the bearing groove is used to accommodate the lower end of the pressure application shaft; The monitoring and control system includes a pressure sensor. The pressure sensor is arranged at the position on the central main platen in contact with the hydraulic loading system; The monitoring and control system includes a first displacement sensor and a second displacement sensor. Both the first displacement sensor and the second displacement sensor are arranged on the bottom surface of the step ladder part in the hydraulic loading system. The first displacement sensor is used to monitor the original settlement of the overall soil sample under the action of overburden pressure, and the second displacement sensor is used to monitor the additional settlement of the central soil sample under the action of additional pressure; The application includes the following steps: Conduct compression tests on soil samples under different depth conditions, successively simulating from the surface layer to the deep layer. The greater the burial depth of the soil sample, the greater the overburden pressure stress, indicating that the lateral deformation restriction of the surrounding soil sample on the central soil sample is also stronger. The overburden pressure stress is achieved by the weight of the pressing plate, and increasing the overburden pressure stress is achieved by increasing the number of layers of the pressing plate. Both the central main pressing plate and the surrounding pressing plates use standard counterweights and are each equipped with multiple pressing plate kits of the same weight and the same size. It is necessary to ensure that the compressive stress applied to the soil sample by the central main pressing plate and the surrounding pressing plates at each layer is equal everywhere. That is, the overburden pressure stress represented by one layer of pressing plate is p1, and for two layers it is p2, and so on. When simulating the condition of no overburden pressure stress on the surface layer, the central pressing plate should not be added above the central soil sample. However, to avoid damaging the central permeable stone, a very thin special lightweight pressing plate is used to cover the central permeable stone. In this way, both the damage to the permeable stone can be avoided and the condition of no overburden pressure stress on the surface layer can be simulated. According to the compression test, obtain the s-p compression curve. When a unified overburden pressure stress is continuously applied above both the central soil sample and the surrounding soil samples during the conventional compression test, that is, the surrounding soil samples are synchronously compressed, which means it is a non-open type. As the compressive stress p increases, a conventional compression curve can be obtained. The greater the compressive stress, the more difficult the compression becomes. After applying a certain magnitude of overburden pressure stress, when an additional compressive stress is applied to the central soil sample, the s-p curve of the central soil sample shows a downward development trend at the overburden pressure stress point, and the surrounding soil samples are no longer affected by the additional compressive stress, which means it is an open type, that is, the settlement becomes larger and larger. This increasing trend is also related to the overburden pressure stress. The greater the overburden pressure stress, the less obvious the increasing trend of the settlement generated after applying the additional compressive stress to the central soil sample. When the overburden pressure stress increases to p6 and then the central soil sample is pressurized, its open-type compression curve gradually approaches the conventional compression curve. Taking the overburden pressure stress p1 as an example, after applying the overburden pressure stress p1, the soil sample first generates a primary settlement s1, and then when an additional compressive stress Δp1 is applied to the central soil sample, the central soil sample generates a corresponding additional settlement Δs1. Correspondingly, after applying the overburden pressure stresses p2, p3, p4, p5, or p6, the primary settlements generated by the soil sample can be successively recorded as s2, s3, s4, s5, and s6.

2. The application according to claim 1, wherein: The central permeable stone is integrally disc-shaped, and the surrounding permeable stones are integrally annular.

3. The application according to claim 1, characterized in that: There is a certain annular gap between the surrounding permeable stone and the steel wall of the test chamber.

4. The application according to claim 1, characterized in that: The pressurizing shaft is integrally long cylindrical, and the lower end is hemispherical to smoothly contact the inner side of the bearing groove.

5. The application of the vertical strain - additional compressive stress curve of the central soil sample under different depth conditions obtained in the application of the compression tester for soil samples under different depth conditions in the calculation of foundation settlement, includes the following steps: After applying the overburden pressure stress p1, an additional stress is applied to the central soil sample. The height of the central soil sample (9a) during filling is h, and the diameter is denoted as D. Under the condition of applying the overburden pressure stress p1, the surrounding soil sample and the central soil sample are compressed simultaneously, and the primary settlement of s1 occurs. This settlement is completely caused by the pressure stress of the overlying soil mass and is achieved by applying the weight of the pressure plate in the experiment. During this process, the lifting platform is fixed at a certain position, and the primary settlement s1 is monitored by the first displacement sensor. The height of the central soil sample is compressed from the filling height h to h - s1; After the initial settlement stabilizes, slowly lower the lifting platform. When the bottom of the pressure application shaft just touches the pressure sensor in the bearing groove and the sensor reacts, start the loading under the target additional compressive stress value Δp1, and simultaneously use the second displacement sensor to monitor the displacement of the lifting platform during the loading process. The loading process adopts servo control, that is, the pressure sensor transmits the measured pressure P to the computer, and then the computer checks whether Δp = 4P / (πD 2 ) is the target value Δp1. If it deviates from this value, promptly issue an instruction to the controller to servo-control the up and down movement of the lifting platform to ensure that the pressure measured by the sensor always meets the target value requirements; during this loading process, the second displacement sensor continuously monitors the displacement of the lifting platform until the displacement value remains stable. This displacement is the additional settlement Δs1 generated by the central soil sample under the additional compressive stress Δp1. During this process, the height of the central soil sample changes from h - s1 to h - s1 - Δs1; the vertical strain generated by the additional compressive stress Δp1 is h - s1 is the true initial height of the central soil sample under the overburden pressure stress p1; Similarly, compression tests under different additional stresses are carried out on the central soil sample under different magnitudes of overburden pressure stresses, and the ε1-Δp curves representing the central samples under different overburden pressure stress conditions can be obtained; For calculating the settlement of the foundation ground under the condition of bearing the total additional load ΔP of the building, first, the total calculation depth affected by the additional stress below the foundation is H in total, and the foundation burial depth is H / 12. Then, H is stratified, and a total of 6 calculation layers are divided, with each layer having a thickness of H / 6. The average overburden pressure stress received by each layer is assumed to be p1, p2, p3, p4, p5, and p6 in sequence from top to bottom, and the average additional stress transmitted by the foundation is denoted as Δp1, Δp2, Δp3, Δp4, Δp5, and Δp6 respectively. Combining the ε1-Δp curves of the central samples under different burial depth conditions, the calculation formula for the ground settlement can be obtained according to the concept of vertical strain as follows: In the formula, represents the vertical strain corresponding to the open ε1-Δp curve after p1 under the additional compressive stress Δp1; represents the vertical strain corresponding to the open ε1-Δp curve after p2 under the additional compressive stress Δp2; represents the vertical strain corresponding to the open ε1-Δp curve after p3 under the additional compressive stress Δp3; represents the vertical strain corresponding to the open ε1-Δp curve after p4 under the additional compressive stress Δp4; represents the vertical strain corresponding to the open ε1-Δp curve after p5 under the additional compressive stress Δp5; represents the vertical strain corresponding to the open ε1-Δp curve after p6 under the additional compressive stress Δp6; If the calculation depth is divided into n layers, the calculation formula for the ground settlement is:

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