Foundation bearing capacity test method and device based on centrifugal simulation

Abstract

The invention discloses a foundation bearing capacity test method and device based on centrifugal simulation, and belongs to the field of foundation bearing capacity tests. The method comprises the following steps: S1, taking a foundation soil material and a measurer; s2, preparing a foundation structure in the model box and fixing a measurer at a preset position; s3, a strip-shaped foundation is arranged on the surface or in the foundation structure; s4, arranging a load applying device in the model box and rigidly connecting the load applying device with the strip-shaped foundation so as to apply a load; s5, the model box is hoisted and fixed in a centrifugal machine, centrifugal force is applied according to a preset process, and the measurement result of each measurer is collected; after a preset condition is met, applying a load to the foundation structure until a target termination condition is reached, and collecting related data; and S6, ending the test. According to the method, the mechanical characteristics of the reduced-scale physical model can be similar by utilizing a centrifugal simulation test mode, and a unique and effective foundation bearing capacity model test method is provided, so that the reliability of a foundation bearing capacity model test result is effectively improved.

Description

Technical Field

[0001] The invention belongs to the technical field of foundation bearing capacity testing, and in particular relates to a foundation bearing capacity testing method and device based on centrifugal simulation. Background Art

[0002] With the continuous improvement of the requirements for foundation evaluation and treatment technology in engineering construction, accurately determining the foundation bearing capacity of different geotechnical materials has become a key technical problem that urgently needs to be solved. The existing mathematical model for calculating foundation bearing capacity needs to be verified by the results of physical model tests, so physical model tests play an irreplaceable role in the field of foundation bearing capacity research. The commonly used scaled physical model tests are limited by the size effect and are often unable to simulate the actual stress state of the actual foundation, and thus cannot accurately reflect the actual foundation bearing capacity level, resulting in errors in the test results. There are also methods in the prior art that use artificial centrifugal force to simulate the actual foundation gravity, but they have failed to provide a set of effective test methods for determining foundation bearing capacity under complex geological and groundwater level conditions, resulting in the inability to obtain accurate and reliable results in existing foundation bearing capacity tests. Summary of the invention

[0003] The present invention aims to solve one of the technical problems in the above-mentioned related art at least to a certain extent.

[0004] To this end, the purpose of the present invention is to provide a foundation bearing capacity test method and device based on centrifugal simulation, which can realize the foundation bearing capacity test by centrifuge simulation, provide a unique and effective test process, and effectively improve the accuracy of the foundation bearing capacity test results.

[0005] In order to solve the above-mentioned technical problems, the present invention is achieved as follows:

[0006] The embodiment of the present invention provides a foundation bearing capacity test method based on centrifugal simulation, the method comprising the following steps:

[0007] S1. Take a certain amount of foundation soil and a measuring device for testing;

[0008] S2, using the foundation soil material to prepare a foundation structure to be measured in a model box; during the process of preparing the foundation structure, fixing each measuring device at a predetermined position in or near the foundation structure;

[0009] S3, providing a strip foundation on the surface of the foundation structure or at a certain buried depth;

[0010] S4, arranging a bearing force pressure device in the model box, wherein a pressure head of the bearing force pressure device is rigidly connected to the strip foundation, so as to apply a load to the foundation structure through the strip foundation during the test;

[0011] S5, hoisting and fixing the model box in the hanging basket of the centrifuge, and operating the centrifuge according to a predetermined process to apply centrifugal force to the model box, and recording the measurement results of each relevant measuring device through an automatic data acquisition system; after reaching a predetermined condition, applying a load to the foundation structure through the bearing force pressure device until a target termination condition is reached, and automatically recording relevant data such as the load;

[0012] S6. The centrifuge stops and the test ends. The relevant data recorded during the test are analyzed to determine the bearing capacity of the foundation structure.

[0013] In addition, the foundation bearing capacity test method based on centrifugal simulation according to the present invention may also have the following additional technical features:

[0014] In some of the embodiments, when preparing the foundation structure in step S2, the foundation structure is divided into several layers and filled and prepared in sequence from bottom to top, and after each layer is filled and leveled, a corner of the surface of the layer close to the observation window is dug out to form a groove with a depth of about 5 mm, and then uniform fine sand dyed white is filled into the groove to form a color line mark that is convenient for observing the deformation of the foundation structure.

[0015] In some of the embodiments, after the foundation structure is prepared, water is evenly supplied from the bottom of the foundation structure through a water supply system until the water level in the foundation structure reaches a predetermined water level to simulate different groundwater level conditions.

[0016] In some of the embodiments, the measuring device includes a plurality of laser ranging displacement sensors, a set of particle image velocimetry equipment, a plurality of earth pressure gauges and a plurality of pore water pressure gauges;

[0017] The laser ranging displacement sensor is arranged above the foundation structure and is used to measure the displacement data of the surface of the foundation structure;

[0018] The particle image velocimetry device is arranged facing the foundation structure, collects image data of the foundation structure through the observation window of the model box and identifies color line marks, thereby realizing the measurement of soil displacement velocity at different locations of the foundation structure;

[0019] The soil pressure gauge is arranged at the bottom of the foundation structure and is used to measure the pressure of the foundation structure under the corresponding environment;

[0020] The pore water pressure gauge is arranged inside the foundation structure, and is used to monitor the change of the pore water pressure during the process of increasing centrifugal acceleration and during the process of pressure loading by the bearing force pressure applying device.

[0021] In some embodiments, the content of running the centrifuge to apply centrifugal force to the model box according to a predetermined process in step S5 includes: at the beginning of the test, increasing the centrifugal acceleration step by step according to the increment of n times the gravitational acceleration, loading in several times until the preset target value, n is a positive integer; after each level of acceleration is loaded to the set value, the earth pressure gauge in the measuring device is read and analyzed; after the reading of the earth pressure gauge is stable, after continuing to run for a predetermined period of time, the reading of the laser ranging displacement sensor in the measuring device is read to determine the surface displacement of the foundation structure in the vertical direction. The above steps are repeated until the preset centrifugal acceleration target value is loaded.

[0022] In some embodiments, in step S5, applying a load to the foundation structure by the bearing force applying device includes:

[0023] The bearing capacity pressure device applies pressure in an intermittent graded loading manner. Each time pressure is applied, pressure is applied to the strip foundation arranged on the foundation structure at a first downward pressure speed. When the pressure reaches the first pressure threshold, the pressure head stops pressing until the vertical settlement displacement of the strip foundation reaches a relative stability and the measured value of the pore water pressure meter returns to the value before loading. Then the next level of loading is continued in the above manner until the vertical displacement of the strip foundation reaches the first displacement threshold, and the pressure operation ends.

[0024] The embodiment of the present invention further provides a foundation bearing capacity test device based on centrifugal simulation, the test device comprising:

[0025] The model box is arranged in the hanging basket of the centrifuge and is used to provide a model space and measurement space for several measuring instruments for the foundation bearing capacity test;

[0026] A foundation structure, arranged inside the model box, and used as a model to be tested for foundation bearing capacity testing;

[0027] A strip foundation is arranged on the upper surface of the foundation structure or at a certain buried depth and is in contact with and connected to the foundation structure, and is used to carry the load applied by the pressure device and transfer it to the foundation structure, thereby realizing the foundation bearing capacity test;

[0028] A bearing capacity pressure device, rigidly connected to the strip foundation, for providing load for foundation bearing capacity test;

[0029] A centrifuge, used to fix the model box and apply centrifugal force to the foundation structure therein, so as to simulate the measurement environment of a prototype foundation equivalent to several times the dead weight of the foundation structure;

[0030] A plurality of measuring devices are respectively arranged inside or around the foundation structure and are used to measure various parameters of the foundation structure before, during and after the test.

[0031] In some of the embodiments, the load-bearing pressure device is a hydraulic device.

[0032] In addition, the foundation bearing capacity test device based on centrifugal simulation according to the present invention may also have the following additional technical features:

[0033] In some of the embodiments, the foundation structure is prepared in layers, and dyed sand marking belts are provided between each layer;

[0034] According to different water level control conditions in the foundation structure, the foundation structure is a sandy soil foundation or a clayey soil foundation under a saturated working condition, or the foundation structure is a sandy soil foundation or a clayey soil foundation under an unsaturated working condition.

[0035] In some embodiments, the relationship between the preset target centrifugal acceleration of the centrifuge and the parameters of the foundation structure includes:

[0036]

[0037] Among them, in the formula:

[0038] N means that the preset target value of centrifugal acceleration is N times the acceleration of gravity;

[0039] L p , L m are the foundation width of the prototype foundation and the foundation width of the foundation structure respectively;

[0040] H p , H m are the foundation depth of the prototype foundation and the foundation depth of the foundation structure respectively;

[0041] σ p , σ m They are respectively the foundation soil pressure of the prototype foundation and the foundation soil pressure of the foundation structure.

[0042] In some of the embodiments, the measuring device includes a plurality of laser ranging displacement sensors, a set of particle image velocimetry equipment, a plurality of earth pressure gauges and a plurality of pore water pressure gauges;

[0043] The laser ranging displacement sensor is arranged above the foundation structure and is used to measure the displacement data of the surface of the foundation structure;

[0044] The particle image velocimetry device is arranged facing the foundation structure, collects image data of the foundation structure through the observation window of the model box and identifies color line marks, thereby realizing the measurement of soil displacement velocity at different locations of the foundation structure;

[0045] The soil pressure gauge is arranged at the bottom of the foundation structure and is used to measure the pressure of the foundation structure under the corresponding environment;

[0046] The pore water pressure gauge is arranged inside the foundation structure, and is used to monitor the change of the pore water pressure during the process of increasing centrifugal acceleration and during the process of pressure loading by the bearing force pressure applying device.

[0047] Compared with the prior art, the present invention has at least the following beneficial effects:

[0048] In the embodiment of the present invention, the foundation bearing capacity test method based on centrifugal simulation is provided, which provides a complete and reliable foundation bearing capacity test method, and can accurately measure the bearing capacity of sandy soil foundation or clay soil foundation under saturated working conditions and unsaturated working conditions, and provide reliable experimental data for determining the bearing capacity of prototype foundation under different strata and groundwater level conditions;

[0049] In the embodiment of the present invention, a foundation bearing capacity test method based on centrifugal simulation is provided, which uses a particle image velocimetry device and a color line marker to realize the displacement information of soil at different depths in the foundation structure during the foundation bearing capacity test; at the same time, a laser ranging displacement sensor is arranged above the foundation structure to realize more accurate measurement of the surface displacement data of the foundation structure; the combination of the two measurement methods can obtain more reliable foundation structure displacement data, thereby improving the accuracy of the foundation bearing capacity test;

[0050] In an embodiment of the present invention, a foundation bearing capacity test method based on centrifugal simulation is provided, which simulates the natural sedimentation and self-weight consolidation process of foundation rock and soil materials by applying centrifugal acceleration step by step to a preset target value. The load is applied in stages by a pressure head, and each level of load is maintained for a period of time after application until the vertical settlement displacement of the strip foundation reaches a relative stability before applying the next level of load, and the change of the pore water pressure measurement value during the loading process is confirmed to eliminate the influence of excess pore water pressure on the foundation bearing capacity test results of the foundation structure. The above-mentioned loading method provides a set of reliable and effective test methods for the foundation bearing capacity test of the present invention, and compared with other loading methods, more accurate and effective measurement data can be obtained.

[0051] The foundation bearing capacity test device based on centrifugal simulation of the present invention is used to implement the foundation bearing capacity test method based on centrifugal simulation, and thus at least has all the features and advantages of the foundation bearing capacity test method based on centrifugal simulation, which will not be described in detail here. Additional aspects and advantages of the present invention will be partially given in the following description, partially become obvious from the following description, or be understood through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1A flow chart of a foundation bearing capacity test method based on centrifugal simulation disclosed in one embodiment of the present invention;

[0053] Figure 2 A physical picture of a 450g-ton large geotechnical centrifuge disclosed in one embodiment of the present invention;

[0054] Figure 3 A schematic diagram of the structure of a centrifuge model box disclosed in one embodiment of the present invention;

[0055] Figure 4 This is a structural diagram of a foundation structure model disclosed in one embodiment of the present invention; wherein (a) is a front view, and (b) is a top view;

[0056] Figure 5 A diagram of a bar-shaped basic structure disclosed in one embodiment of the present invention; wherein (a) is a front view, and (b) is a top view;

[0057] Figure 6 A schematic diagram of hydraulic loading disclosed in one embodiment of the present invention;

[0058] Figure 7 This is an exploded schematic diagram of the connection parts of a hydraulic loading device disclosed in one embodiment of the present invention;

[0059] Figure 8 A schematic diagram of the plan structure of a hydraulic loading device disclosed in one embodiment of the present invention;

[0060] Fig. 9 A state diagram after hydraulic loading is completed disclosed in one embodiment of the present invention;

[0061] Fig.10 A front view of a measuring device arrangement disclosed in one embodiment of the present invention;

[0062] Fig.11 A top view of a measuring device arrangement disclosed in one embodiment of the present invention; DETAILED DESCRIPTION

[0063] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0064] The embodiments of the present invention are described in detail below through specific embodiments and application scenarios in conjunction with the accompanying drawings.

[0065] See also Figure 1As shown, in some embodiments of the present invention, a foundation bearing capacity test method based on centrifugal simulation is provided, which uses a centrifuge to apply centrifugal acceleration to a foundation structure prepared with a limited amount of geotechnical materials, thereby realizing loading of the foundation structure measurement environment, so that it can simulate the real foundation stress state, thereby accurately determining the foundation bearing capacity. The use of the centrifugal simulation test method for determining the foundation bearing capacity test process is the innovation of the present invention. Below, the specific content of the foundation bearing capacity test method based on centrifugal simulation of the present invention is described.

[0066] 1 Experimental design description

[0067] 1.1 Test Principle

[0068] The centrifugal model test method uses the centrifugal field to increase the volume force of the model and form artificial gravity. When the ratio of the prototype size to the model size is n, the centrifugal acceleration preset target value a m for:

[0069]

[0070] Where: L p is the prototype size; L m is the model size; g is the gravitational acceleration.

[0071] When a prototype size 1 / n test model is placed in a centrifugal gravity field of ng, the weight of the test model increases by n times, and the stress on each point in the model is the same as the stress on the corresponding point in the prototype. This is the similarity law of centrifugal model test. Table 1 lists the similarity laws of relevant parameters of centrifugal model test.

[0072] Table 1 Similarity law of relevant parameters of centrifuge model test

[0073]

[0074]

[0075] 1.2 Purpose of the experiment

[0076] The purpose of this test is to comprehensively evaluate the impact of groundwater level fluctuations on the bearing capacity and settlement behavior of foundation structures. By simulating groundwater level changes and applying loads to foundation structures through centrifuge model tests, the mechanical response of foundation structures under different water level conditions is explored, providing important theoretical and data support for the design and maintenance of urban infrastructure such as subways.

[0077] 1.3 Working conditions

[0078] The test uses a LXJ-4-450 large geotechnical centrifuge, with a maximum rotation radius of 5.03m, a maximum acceleration of 300g, a payload of 1.5ton, a payload capacity of 450g-ton, and a DC motor drive with a motor power of 700kW. The centrifuge basket has a size of 1.5m×1.0m×1.5m. The performance indicators of the centrifuge are shown in Table 2.

[0079] Table 2 Performance indicators of LXJ-4-450 large geotechnical centrifuge

[0080]

[0081]

[0082] 1.4 Test equipment preparation

[0083] 1.4.1 Centrifuge test model size

[0084] The preset target centrifugal acceleration of the centrifugal model is 50g, the dimensions of the experimental model box are 850mm (inner length) × 305mm (inner width) × 573mm (inner height), and the total mass of the model box is 108kg. The experiment is planned to be equipped with a set of hydraulic loading devices and a strip foundation, please refer to Figure 2 , Figure 3 shown.

[0085] 1.4.2 Total mass of soil

[0086] See also Figure 4 As shown, the area of ​​the foundation structure model can be calculated to be 2592.5cm 2 , taking the width of the model as 305mm, we can calculate the volume of the model to be 77775cm 3 The foundation material of this test is Fujian standard sand. The dry density of this sand under the condition of 75% relative dry density is 1584kg / m 3 , the total mass of the excavated soil is calculated to be 125.25kg.

[0087] 1.4.3 Total mass of strip foundation

[0088] See also Figure 5 As shown, the dimensions of the strip foundation are 305mm (length) × 100mm (width) × 150mm (height), and the depth of the strip foundation in the soil is 50mm. The volume of the strip foundation is 4575cm 3 The density of concrete is 2400kg / m 3 , the mass of the strip foundation is calculated to be 10.98kg.

[0089] 2 Centrifugal model test method for foundation bearing capacity

[0090] 2.1 Total mass of the test model

[0091] The total mass of the test model = mass of the model box (108kg) + mass of the soil (125.25kg) + mass of the strip foundation (10.98kg) + weight of the reaction frame and beam (500.33kg) = 744.56kg.

[0092] 2.2 Similarity Criteria

[0093] Assuming that the preset target value of centrifugal acceleration is N times the acceleration of gravity, that is, N = prototype size / model size, the model scale relationship is as follows:

[0094]

[0095] L p , L m ——Prototype foundation width, model foundation width, m;

[0096] H p , H m ——Prototype foundation depth, model foundation depth, m;

[0097] σ p , σ m ——Prototype foundation soil pressure, model foundation soil pressure, kPa;

[0098] T p 、T m ——Prototype consolidation time, model consolidation time, s.

[0099] 2.3 Foundation structure preparation

[0100] Apply an even amount of oil lubricant, such as synthetic grease or industrial butter, to the four walls of the model box. Prepare the sand foundation structure model in 6 layers, with each layer 50 mm thick. In order to ensure the uniformity of the sand density, the sand rain method is used to prepare the model, that is, the dry density is determined to be 1548 kg / m according to the pre-calibrated sand rain method dry density-drop distance relationship curve. 3 The corresponding drop distance is then used to make the sand and soil fall evenly from the sand rain method device into the model box. After each layer is filled, three points are randomly selected to sample and test the dry density of the model, and compared with the preset dry density of 1548kg / m 3 For comparison, if the error exceeds 100kg / m 3, then refill the model of this layer. After each layer of the model is filled and leveled, a corner of the surface of the layer near the observation window is dug to form a groove about 5 mm deep, and then the uniform fine sand dyed white is filled into the groove to form a color line mark for easy observation of foundation structure deformation. For more information about the color line, please refer to the following 2.5.2. During the filling process of the sand model, a specific measuring device needs to be placed at the preset position. For more information about the location of the measuring device, please refer to the following 2.5.

[0101] The water supply system at the bottom of the model is used to evenly supply water to the foundation structure soil until the preset water level is reached and the water supply is stopped. When the water level in the foundation structure model is lower than the model surface, it is an unsaturated working condition; when the water level in the foundation structure model is at the same height as the model surface, it is a saturated working condition. After the water supply operation is completed, it is necessary to observe whether there are bubbles inside the model through the observation window of the model box. If bubbles are generated, the model box should be slightly vibrated or knocked to discharge the bubbles.

[0102] 2.4 Experimental process

[0103] 2.4.1 Applying centrifugal acceleration to the test model

[0104] After the test model is prepared, the model box is hoisted and fixed in the centrifuge basket, and each measuring device is installed and tested. After the test starts, the centrifugal acceleration is increased step by step by 5g per level, and increased in 10 times until the centrifugal acceleration increases to the preset target value. The increase of centrifugal acceleration is carried out step by step, with an increase of 5g each time, to simulate the natural deposition of actual foundation materials and the consolidation process under deadweight conditions. This graded loading method is conducive to more accurately simulating the real stress level in the prototype foundation structure. When each level of acceleration is loaded to the set value, the earth pressure gauge is read and analyzed. After the earth pressure gauge reading is stable, it will continue to run for 10 minutes before entering the next level of loading process. After the centrifugal acceleration reaches the preset target value of 50g, the laser sensor reading is measured to determine the vertical displacement of the foundation structure. Then, a hydraulic device is used to apply vertical loads to the strip foundation in stages.

[0105] 2.4.2 Applying vertical loads to strip foundations

[0106] Connection between hydraulic device and strip foundation Figure 6 As shown, the hydraulic rod of the hydraulic device is connected to the connecting rod through four bolt holes, and the connecting rod is connected to the hydraulic head through a large bolt. The hydraulic head and the strip foundation are also rigidly connected by bolts. The connection method and the structure of the hydraulic device and the hydraulic head are shown in Figure 7 , 8 shown.

[0107] The strip foundation is rigidly connected to the loading device through loading screws. The loading device presses down the strip foundation at a speed of 0.1mm / s. The vertical load provided by the hydraulic device is loaded in stages, with each load being 5kPa. After each load is pressurized, the load is maintained for a period of time until the vertical settlement displacement of the strip foundation reaches a relative stability before applying the next load and observing the pore water pressure gauge reading. The relative stability standard of the strip foundation settlement under each load is that the hourly settlement is less than 0.1mm for two consecutive hours. If the pore water pressure gauge reading exceeds the theoretical value of the hydrostatic pressure, the pore water pressure gauge reading should be waited for to fall back to the vicinity of the theoretical value of the hydrostatic pressure. When the pore water pressure exceeds the theoretical value of the hydrostatic pressure, it means that the vertical loading causes excess pore water pressure to be generated inside the soil. Maintaining the load and waiting for the settlement displacement of the strip foundation to stabilize and the pore water pressure value to fall back is to ensure the accuracy of the test results. After the vertical displacement of the strip foundation reaches 50mm, stop loading and unloading. During the loading process, if the strip foundation is found to be tilted and cannot continue to move in the vertical direction, the downward loading should be stopped immediately and the test should be repeated. Fig. 9 shown.

[0108] The rigid connection between the strip foundation and the loading device ensures that the load can be accurately transferred from the loading device to the strip foundation, and further to the foundation structure. The rigid connection means that during the loading process, the relative displacement between the strip foundation and the loading device is very small and can be ignored, which ensures the accuracy of the vertical displacement data of the strip foundation. After trying different loading speeds, it was found that 0.1mm / s is a relatively reasonable loading speed, which helps to more accurately control the loading process and monitor the changes in the readings of various measuring instruments; in addition, the relatively slow loading speed can also reduce the test errors caused by inertia effects. These two points are very beneficial to the test method of the present invention.

[0109] 2.5 Monitoring plan

[0110] A total of 8 laser ranging displacement sensors were used to monitor the vertical displacement of the foundation structure surface and strip foundation from above the foundation structure. A particle image velocimetry (PIV) instrument was used to monitor the internal displacement of the foundation structure from the side of the model box observation window. A soil pressure gauge was used to monitor the change of soil pressure in the foundation structure during the increase of centrifugal acceleration. A total of 2 were deployed. A pore water pressure gauge was used to monitor the change of pore water pressure during the increase of centrifugal acceleration and the vertical loading of the strip foundation. A total of 2 were deployed.

[0111] 2.5.1 Installation of laser ranging displacement sensor

[0112] The specific location of the laser ranging displacement sensor is shown in Table 3 and Fig.10 and Fig.11 shown.

[0113] Table 3 Laser ranging displacement sensor position table

[0114]

[0115]

[0116] 2.5.2 Installation of PIV equipment

[0117] The camera of the particle image velocimetry (PIV) equipment is 32cm away from the model box horizontally, and the height rises 15cm from the bottom of the model box. According to the light environment and the focal length of the camera, the camera is debugged to achieve a clear and complete camera image of the test model, including the foundation structure, strip foundation and part of the hydraulic rod. Color lines are used as markers. The color lines are located at depths of 50mm, 100mm, 150mm, 200mm and 250mm from the surface of the foundation structure, respectively, and are completed in the layered filling stage of the foundation structure. The color line marker color is selected as white, but other colors can also be selected according to the sensitive hue of the particle image velocimetry (PIV) camera, so as to enable accurate identification. The color line dye should be a low water-soluble dye to prevent the dye from flowing and diffusing with the pore water during the rising water level.

[0118] 2.5.3 Installation of earth pressure gauge

[0119] The location of the earth pressure gauge is shown in Table 4 and Fig.10 and Fig.11 shown.

[0120] Table 4 Earth pressure gauge location table

[0121]

[0122] 2.5.4 Installation of pore water pressure gauge

[0123] The locations of pore water pressure gauges are shown in Table 5 and Fig.10 and Fig.11 shown.

[0124] Table 5 Pore water pressure gauge location table

[0125]

[0126] 2.6 Recording and use of monitoring data

[0127] At the beginning of the test, all measuring devices should be turned on at the same time to ensure that the time zero point of the readings of each measuring device is the same. The readings of the earth pressure gauge during the increase of centrifugal acceleration are recorded in Table 6. The readings of the laser ranging displacement sensor after the foundation structure model reaches the target acceleration and stabilizes before the hydraulic device applies the load are recorded in Table 7. The readings of the single laser ranging displacement sensor during loading of the hydraulic device and loading are recorded in Table 8.

[0128] The load-settlement curve of the strip foundation is obtained by the data recorded in Table 8. In the load-displacement curve, the load is expressed by the settlement q, which is obtained by dividing the output of the hydraulic device by the bottom area of ​​the strip foundation; the displacement is expressed by s / B, which is the ratio of the actual settlement s of the strip foundation to the foundation width B. Referring to the Technical Specifications for Building Foundation Testing (JGJ 340-2015), the method for determining the bearing capacity of the foundation structure based on the load-settlement curve is as follows:

[0129] If the soil around the strip foundation shows obvious lateral extrusion and the surrounding soil shows obvious uplift, the load value of the previous level where this phenomenon occurs shall be taken as the ultimate bearing capacity of the foundation structure;

[0130] If the settlement during a certain load level is greater than 5 times the settlement of the previous load level, and the load-settlement curve shows a significant steep drop, the previous load value is taken as the ultimate bearing capacity of the foundation structure;

[0131] If the settlement during a certain level of load cannot reach the relatively stable standard within 24 hours (i.e. the settlement per hour is less than 0.1 mm for two consecutive hours), the load value of the previous level shall be taken as the ultimate bearing capacity of the foundation structure;

[0132] If there is a proportional limit on the load-settlement curve, the load value corresponding to the proportional limit is taken as the ultimate bearing capacity of the foundation structure;

[0133] If there is a proportional limit on the load-settlement curve and when the ultimate load is reached, if the ultimate load value is less than twice the load value corresponding to the proportional limit, half of the ultimate load value is taken as the ultimate bearing capacity of the foundation structure;

[0134] If after loading is completed, the settlement displacement value of the foundation structure reaches a relatively stable standard, the proportional limit cannot be determined on the load-settlement curve, and the ultimate load has not been reached, then half of the corresponding load value when loading is completed is taken as the ultimate bearing capacity of the foundation structure.

[0135] Table 6 Model soil pressure record table before strip foundation loading

[0136]

[0137] Table 7 Model surface displacement record table before strip foundation loading

[0138]

[0139] Table 8 Pressure and displacement records of strip foundation during loading stage

[0140]

[0141] For parts of the present invention that are not described in detail, reference may be made to the prior art in the art or technologies known to those skilled in the art.

[0142] The embodiments of the present invention are described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned specific implementation modes, which are merely illustrative rather than restrictive. Under the guidance of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the present invention and the claims, all of which are within the protection of the present invention.

Claims

1. A foundation bearing capacity test method based on centrifugal simulation, characterized in that: The steps of the method include: S1. Take a certain amount of foundation soil and a measuring device for testing; S2, using the foundation soil material to prepare a foundation structure to be measured in a model box; during the process of preparing the foundation structure, fixing each measuring device at a predetermined position in or near the foundation structure; S3, providing a strip foundation on the surface of the foundation structure or at a certain buried depth; S4, arranging a bearing force pressure device in the model box, wherein a pressure head of the bearing force pressure device is rigidly connected to the strip foundation, so as to apply a load to the foundation structure through the strip foundation during the test; S5, hoisting and fixing the model box in the hanging basket of the centrifuge, and operating the centrifuge according to a predetermined process to apply centrifugal force to the model box, and recording the measurement results of each relevant measuring device through an automatic data acquisition system; after reaching a predetermined condition, applying a load to the foundation structure through the bearing force pressure device until a target termination condition is reached, and automatically recording relevant data such as the load; S6. The centrifuge stops and the test ends. The relevant data recorded during the test are analyzed to determine the bearing capacity of the foundation structure.

2. The foundation bearing capacity test method based on centrifugal simulation according to claim 1 is characterized in that: When preparing the foundation structure in step S2, the foundation structure is divided into several layers and filled and prepared in sequence from bottom to top, and after each layer is filled and leveled, a corner of the surface of the layer close to the observation window is dug out to form a 5 mm deep groove, and then uniform fine sand dyed white is filled into the groove to form a color line mark that is convenient for observing the deformation of the foundation structure.

3. The foundation bearing capacity test method based on centrifugal simulation according to claim 2 is characterized in that: After the foundation structure is prepared, water is evenly supplied from the bottom of the foundation structure through a water supply system until the water level in the foundation structure reaches a predetermined water level to simulate different groundwater level conditions.

4. The foundation bearing capacity test method based on centrifugal simulation according to claim 1 is characterized in that: The measuring device includes a plurality of laser ranging displacement sensors, a set of particle image velocimetry equipment, a plurality of soil pressure gauges and a plurality of pore water pressure gauges; The laser ranging displacement sensor is arranged above the foundation structure and is used to measure the displacement data of the surface of the foundation structure; The particle image velocimetry device is arranged facing the foundation structure, collects image data of the foundation structure through the observation window of the model box and identifies color line marks, thereby realizing the measurement of soil displacement velocity at different locations of the foundation structure; The soil pressure gauge is arranged at the bottom of the foundation structure and is used to measure the soil pressure of the foundation structure under corresponding test conditions; The pore water pressure gauge is arranged inside the foundation structure, and is used to monitor the change of the pore water pressure during the process of increasing centrifugal acceleration and during the process of pressure loading by the bearing force pressure applying device.

5. The foundation bearing capacity test method based on centrifugal simulation according to claim 1, characterized in that: The contents of running the centrifuge to apply centrifugal force to the model box according to a predetermined process in step S5 include: at the beginning of the test, increasing the centrifugal acceleration step by step according to an increment of n times the gravitational acceleration, and loading it several times until a preset target value is reached, where n is a positive integer; after each level of acceleration is loaded to the set value, reading and analyzing the earth pressure gauge in the measuring device; after the reading of the earth pressure gauge is stable, after continuously running for a predetermined period of time, reading the reading of the laser ranging displacement sensor in the measuring device to determine the surface displacement of the foundation structure in the vertical direction; and repeating the above steps until the preset centrifugal acceleration target value is loaded.

6. The foundation bearing capacity test method based on centrifugal simulation according to claim 1, characterized in that: In step S5, the contents of applying a load to the foundation structure by the bearing force pressure applying device include: The bearing capacity pressure device applies pressure in an intermittent multiple-pressure manner, and each time the pressure is applied at a first downward pressure speed to the strip foundation arranged on the foundation structure. When the pressure reaches the first pressure threshold, the pressure head stops pressing until the measured value of the pore water pressure meter returns to the value before the pressure is applied, and then continues to apply pressure in the above manner until the vertical displacement of the strip foundation reaches the first displacement threshold, and the pressure operation ends.

7. A foundation bearing capacity test device based on centrifugal simulation, characterized in that: The test device comprises: The model box is arranged in the hanging basket of the centrifuge and is used to provide a model space of the foundation structure and a measuring space of several measuring instruments for the foundation bearing capacity test; A foundation structure, arranged inside the model box, and used as a model to be tested for foundation bearing capacity testing; A strip foundation is arranged on the upper surface of the foundation structure or at a certain buried depth and is in contact with and connected to the foundation structure, and is used to carry the load applied by the pressure device and transfer it to the foundation structure, thereby realizing the foundation bearing capacity test; A bearing capacity pressure device, rigidly connected to the strip foundation, for providing load for foundation bearing capacity test; A centrifuge, used to fix the model box and apply centrifugal force to the foundation structure therein, so as to simulate the measurement environment of a prototype foundation equivalent to several times the dead weight of the foundation structure; A plurality of measuring devices are respectively arranged inside or around the foundation structure and are used to measure various parameters of the foundation structure before, during and after the test.

8. The foundation bearing capacity test device based on centrifugal simulation according to claim 7, characterized in that: The foundation structure is prepared in layers, and dyed sand marking belts are provided between each layer; According to different water level control conditions in the foundation structure, the foundation structure is a sandy soil foundation or a clayey soil foundation under a saturated working condition, or the foundation structure is a sandy soil foundation or a clayey soil foundation under an unsaturated working condition.

9. The foundation bearing capacity test device based on centrifugal simulation according to claim 7, characterized in that: It is characterized in that The relationship between the preset target value of the centrifugal acceleration of the centrifuge and the parameters of the foundation structure includes: Among them, in the formula: N means that the preset target value of centrifugal acceleration is N times the acceleration of gravity; L p , L m are the foundation width of the prototype foundation and the foundation width of the foundation structure respectively; H p , H m are the foundation depth of the prototype foundation and the foundation depth of the foundation structure respectively; σ p , σ m They are respectively the foundation soil pressure of the prototype foundation and the foundation soil pressure of the foundation structure.

10. The foundation bearing capacity test device based on centrifugal simulation according to claim 7, characterized in that: The measuring device includes a plurality of laser ranging displacement sensors, a set of particle image velocimetry equipment, a plurality of soil pressure gauges and a plurality of pore water pressure gauges; The laser ranging displacement sensor is arranged above the foundation structure and is used to measure the displacement data of the surface of the foundation structure; The particle image velocimetry device is arranged facing the foundation structure, collects image data of the foundation structure through the observation window of the model box and identifies color line marks, thereby realizing the measurement of soil displacement velocity at different locations of the foundation structure; The soil pressure gauge is arranged at the bottom of the foundation structure and is used to measure the pressure of the foundation structure under the corresponding environment; The pore water pressure gauge is arranged inside the foundation structure, and is used to monitor the change of the pore water pressure during the process of increasing centrifugal acceleration and during the process of pressure loading by the bearing force pressure applying device.

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