A foundation bearing capacity test method and device based on centrifugal simulation

Abstract

The present invention discloses a foundation bearing capacity test method and device based on centrifugal simulation, which belongs to the field of foundation bearing capacity test. The method includes: S1, taking foundation soil and measuring instruments; S2, preparing a foundation structure in a model box and fixing the measuring instrument at a predetermined position; S3, setting a strip foundation on the surface or inside of the foundation structure; S4, setting a load applying device in the model box and rigidly connecting it to the strip foundation to apply the load; S5, hoisting and fixing the model box in a centrifuge and applying centrifugal force according to a predetermined process, collecting the measurement results of each measuring instrument; after the preset conditions are met, applying the load to the foundation structure until the target termination conditions are reached, and collecting relevant data; S6, the test ends. The present invention can use the centrifugal simulation test method to achieve similar mechanical characteristics of the scaled physical model, providing a unique and effective foundation bearing capacity model test method, thereby effectively improving the reliability of the foundation bearing capacity model test results.

Description

Technical Field

[0001] The present 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 issue 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. Therefore, physical model tests play an irreplaceable role in the field of foundation bearing capacity research. Commonly used scaled physical model tests are limited by size effects and are often unable to simulate the actual stress state of the actual foundation, thereby failing to 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 foundation bearing capacity test by centrifuge simulation, provide a unique and effective testing process, and effectively improve the accuracy of foundation bearing capacity test results.

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

[0006] An 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. preparing a foundation structure to be measured in a model box using the foundation soil material; fixing each measuring device at a predetermined position in or near the foundation structure during the preparation of the foundation structure;

[0009] S3. Arranging 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. Hanging and fixing the model box in the hanging basket of the centrifuge, 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 a predetermined condition is met, applying a load to the foundation structure through the bearing capacity pressure device until a target termination condition is reached, and automatically recording relevant data such as the load;

[0012] S6. The centrifuge stops, the test ends, and 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 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, so as to simulate different groundwater level conditions.

[0016] In some 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 displacement data of the surface of the foundation structure;

[0018] The particle image velocimetry device is placed facing the foundation structure, collects image data of the foundation structure through the observation window of the model box and identifies color line marks to measure the displacement velocity of the soil 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 changes in pore water pressure during the process of increasing centrifugal acceleration and the process of pressure loading by the bearing force pressure applying device.

[0021] In some embodiments, in step S5, operating the centrifuge to apply centrifugal force to the model box according to a predetermined process includes: at the beginning of the test, gradually increasing the centrifugal acceleration by n times the acceleration of gravity, loading the centrifugal acceleration in multiple steps until a preset target value is reached, where n is a positive integer; after each acceleration step reaches the set value, reading and analyzing the earth pressure gauge in the measuring device; after the earth pressure gauge reading stabilizes, and after continuing to operate 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. The above steps are repeated until the preset centrifugal acceleration target value is reached.

[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 adopts an intermittent graded loading method to perform pressure operation. 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. The pressure operation ends.

[0024] An 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 located in the 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, serving as a test model for a foundation bearing capacity test;

[0027] A strip foundation is provided on the upper surface of the foundation structure or at a certain buried depth and is in contact with the foundation structure, and is used to bear the load applied by the pressure device and transmit 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 testing;

[0029] a centrifuge, used to fix the model box and apply centrifugal force to the foundation structure therein, so as to simulate a measurement environment of a prototype foundation that is 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 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 embodiments, the foundation structure is prepared in layers, and dyed sand marking strips 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 clay soil foundation under a saturated working condition, or the foundation structure is a sandy soil foundation or a clay 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, where:

[0038] N means that the preset target value of centrifugal acceleration is N times the acceleration due to 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 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 displacement data of the surface of the foundation structure;

[0044] The particle image velocimetry device is placed facing the foundation structure, collects image data of the foundation structure through the observation window of the model box and identifies color line marks to measure the displacement velocity of the soil 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 changes in pore water pressure during the process of increasing centrifugal acceleration and 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] The centrifugal simulation-based foundation bearing capacity test method provided in the embodiments of the present invention provides a complete and reliable foundation bearing capacity test method, which can accurately measure the bearing capacity of sandy soil foundations or clay soil foundations under saturated and unsaturated working conditions, and provide reliable experimental data for determining the bearing capacity of prototype foundations under different strata and groundwater levels.

[0049] In an embodiment of the present invention, a centrifugal simulation-based foundation bearing capacity test method is provided. A particle image velocimetry device and color line markings are used to obtain displacement information of soil at different depths in a foundation structure during the foundation bearing capacity test. Furthermore, a laser ranging displacement sensor disposed above the foundation structure is used to achieve more accurate measurement of surface displacement data of the foundation structure. The combination of these two measurement methods can yield 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. 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, which can obtain more accurate and effective measurement data compared with other loading methods.

[0051] The centrifugal simulation-based foundation bearing capacity testing device of the present invention is used to implement the aforementioned centrifugal simulation-based foundation bearing capacity testing method, and thus has at least all the features and advantages of the aforementioned centrifugal simulation-based foundation bearing capacity testing method, which are not further described herein. Additional aspects and advantages of the present invention will be described in part in the following description and will become apparent from the following description or learned through 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 centrifuge model box structure 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 This is a schematic diagram of the planar structure of a hydraulic loading device disclosed in one embodiment of the present invention;

[0060] Figure 9 This is a state diagram after the hydraulic loading is completed disclosed in one embodiment of the present invention;

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

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

[0063] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall 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 with reference to the accompanying drawings.

[0065] See also Figure 1As shown, some embodiments of the present invention provide a foundation bearing capacity testing method based on centrifugal simulation. This method uses a centrifuge to apply centrifugal acceleration to a foundation structure made of a limited amount of geotechnical material, thereby loading the foundation structure measurement environment and simulating the actual foundation stress state, thereby accurately determining the foundation bearing capacity. The use of the centrifugal simulation test method for determining foundation bearing capacity is an innovative feature of the present invention. The specific content of the foundation bearing capacity testing method based on centrifugal simulation of the present invention is described below.

[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 acceleration due to gravity.

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

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

[0073]

[0074]

[0075] 1.2 Purpose of the Test

[0076] The purpose of this experiment is to comprehensively evaluate the impact of groundwater level fluctuations on the bearing capacity and settlement behavior of foundation structures. By simulating groundwater level fluctuations 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 used a large geotechnical centrifuge, model LXJ-4-450. It has a maximum rotation radius of 5.03 m, a maximum acceleration of 300 g, a payload of 1.5 tonnes, and a payload capacity of 450 g-tons. It is driven by a 700 kW DC motor. The centrifuge basket measures 1.5 m × 1.0 m × 1.5 m. Table 2 shows the performance of this centrifuge.

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

[0080]

[0081]

[0082] 1.4 Preparation of test equipment

[0083] 1.4.1 Centrifuge test model size

[0084] The target centrifugal acceleration of the centrifugal model is preset to 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 to be equipped with a hydraulic loading device 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, the volume of the model can be calculated to be 77775cm 3 The foundation material of this test is Fujian standard sand, and the dry density of this sand at 75% relative dry density is 1584kg / m 3 The total mass of the excavated remains is calculated to be 125.25 kg.

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

[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 oily 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, each 50 mm thick. In order to ensure the uniformity of the sand density, the sand rain method was used to prepare the model. The dry density was determined to be 1548 kg / m based on the pre-calibrated sand rain method dry density-drop distance relationship curve. 3 The corresponding drop distance is set, and then the sand is evenly dropped from the sand rain method device into the model box according to this drop distance. After each layer is filled, 3 points are randomly selected to sample and test the dry density of the model, and the dry density is compared with the preset dry density of 1548kg / m 3 For comparison, if the error exceeds 100kg / m 3, then refill that layer of the model. After each layer of the model is filled and leveled, a corner of the layer's surface, near the observation window, is excavated to form a groove approximately 5 mm deep. Fine, uniformly dyed white sand is then filled into the groove to form a color line marking for observing foundation structure deformation. For more information on color lines, see 2.5.2 below. During the sand and soil model filling process, specific measuring devices must be placed at pre-set locations. For more information on measuring device locations, see 2.5 below.

[0101] A water supply system at the bottom of the model is used to evenly supply water to the foundation soil until the preset water level is reached. When the water level in the foundation structure model is lower than the model surface, it is considered unsaturated; when the water level is equal to the model surface, it is considered saturated. After the water supply operation is completed, the model box should be inspected for bubbles through the observation window. If bubbles are present, gently vibrate or tap the model box to dislodge them.

[0102] 2.4 Experimental process

[0103] 2.4.1 Applying centrifugal acceleration to the test model

[0104] After the test model was prepared, the model box was hoisted and secured in the centrifuge basket, and the measuring devices were installed and tested. After the test began, the centrifugal acceleration was increased in 5g increments, repeated 10 times, until the centrifugal acceleration reached the preset target value. The centrifugal acceleration was increased gradually, by 5g each time, to simulate the natural deposition and consolidation of actual foundation materials under their own weight. This graded loading method facilitates a more accurate simulation of the actual stress levels in the prototype foundation structure. At each acceleration level, the earth pressure gauge was read and analyzed. After the earth pressure gauge reading stabilized, the system continued to operate for another 10 minutes before moving on to the next loading level. After the centrifugal acceleration reached the preset target value of 50g, the laser sensor reading was measured to determine the vertical displacement of the foundation structure. Next, a hydraulic system was used to apply graded vertical loads to the strip foundation.

[0105] 2.4.2 Applying vertical load to strip foundation

[0106] The connection between the hydraulic device and the strip foundation is as follows 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 with 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 via loading screws. The loading device applies pressure to the strip foundation at a rate of 0.1 mm / s. The vertical load provided by the hydraulic device is applied in stages, with each stage being 5 kPa. After each stage is applied, the load is maintained for a period of time until the vertical displacement of the strip foundation reaches relative stability before the next stage is applied. The pore water pressure gauge reading is then observed. The standard for relatively stable settlement of the strip foundation under each stage of load is a settlement of less than 0.1 mm per hour for two consecutive hours. If the pore water pressure gauge reading exceeds the theoretical value of hydrostatic pressure, the pore water pressure gauge reading should be allowed to return to near the theoretical value. When the pore water pressure exceeds the theoretical value of hydrostatic pressure, this indicates that the vertical loading has generated excess pore water pressure within the soil. Maintaining the load until the strip foundation settlement reaches stability and the pore water pressure value returns is necessary to ensure the accuracy of the test results. After the vertical displacement of the strip foundation reaches 50 mm, loading is stopped and unloading is initiated. During the loading process, if the strip foundation is found to be tilted or unable to move vertically, the downward loading should be stopped immediately and the test should be repeated. Figure 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 changes in the readings of various measuring instruments; in addition, the relatively slow loading speed can also reduce the test error caused by inertia effects. These two points are very beneficial to the test method of the present invention.

[0109] 2.5 Monitoring plan

[0110] Eight laser ranging displacement sensors were deployed from above the foundation structure to monitor the vertical displacement of the foundation surface and strip foundations. Particle image velocimetry (PIV) was used to monitor the internal displacement of the foundation structure from the side of the model box observation window. Two soil pressure gauges were deployed to monitor changes in soil pressure during centrifugal acceleration. Two pore water pressure gauges were deployed to monitor changes in pore water pressure during centrifugal acceleration and during vertical loading of the strip foundations.

[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 Figure 10 and Figure 11 shown.

[0113] Table 3 Laser ranging displacement sensor position table

[0114]

[0115]

[0116] 2.5.2 Installation of Particle Image Velocimetry (PIV) Equipment

[0117] The camera of the particle image velocimetry (PIV) equipment is 32 cm horizontally away from the model box and 15 cm higher than the bottom of the model box. The camera is debugged according to the lighting environment and the focal length of the camera so that the camera image can clearly and completely capture 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 50 mm, 100 mm, 150 mm, 200 mm and 250 mm from the surface of the foundation structure, and are completed respectively during the layered filling stage of the foundation structure. The color of the color line marker is 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 water level rise.

[0118] 2.5.3 Installation of earth pressure gauge

[0119] The locations of the earth pressure gauges are shown in Table 4 and Figure 10 and Figure 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 Figure 10 and Figure 11 shown.

[0124] Table 5. Pore water pressure gauge location table

[0125]

[0126] 2.6 Recording and use of monitoring data

[0127] At the start of the test, all measuring devices should be powered on simultaneously to ensure that the zero readings for each device are consistent. See Table 6 for the earth pressure gauge readings during the increasing centrifugal acceleration. See Table 7 for the laser ranging displacement sensor readings after the foundation structure model reaches the target acceleration and stabilizes before the hydraulic device applies the load. See Table 8 for the readings of the individual laser ranging displacement sensors during and after the hydraulic device is loaded.

[0128] The load-settlement curve for the strip foundation is derived from the data recorded in Table 8. In the load-displacement curve, load is expressed as q, which is the hydraulic force divided by the strip foundation base area. Displacement is expressed as s / B, which is the ratio of the actual settlement s of the strip foundation to the foundation width B. Referring to the Technical Specification for Testing of Building Foundations (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 of a certain load level cannot reach the relatively stable standard within 24 hours (i.e. the settlement is less than 0.1 mm per hour 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 shall be 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 of strip foundation before loading

[0136]

[0137] Table 7 Surface displacement record of strip foundation model before 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 to 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 methods. The above-mentioned specific implementation methods are merely illustrative and not 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 protected by 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. preparing a foundation structure to be measured in a model box using the foundation soil material; fixing each measuring device at a predetermined position in or near the foundation structure during the preparation of the foundation structure; S3. Arranging 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. Hanging and fixing the model box in the hanging basket of the centrifuge, 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 a predetermined condition is met, applying a load to the foundation structure through the bearing capacity pressure device until a target termination condition is reached, and automatically recording load-related data; S6. The centrifuge stops, the test ends, and the relevant data recorded during the test are analyzed to determine the bearing capacity of the foundation structure; 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 displacement data of the surface of the foundation structure; The particle image velocimetry device is placed facing the foundation structure, collects image data of the foundation structure through the observation window of the model box and identifies color line marks to measure the displacement velocity of the soil 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 changes in pore water pressure during the process of increasing centrifugal acceleration and the process of pressure loading by the bearing capacity pressure applying device; In step S5, the centrifuge is operated according to a predetermined process to apply centrifugal force to the model box, including: at the beginning of the test, the centrifugal acceleration is increased step by step by n times the acceleration of gravity, and the centrifugal acceleration is loaded several times until a preset target value is reached, where n is a positive integer; after each acceleration level is loaded to the set value, the earth pressure gauge in the measuring device is read and analyzed; after the earth pressure gauge reading stabilizes, the centrifuge is continuously operated for a predetermined period of time, and 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; and the above steps are repeated until the preset centrifugal acceleration target value is reached.

2. The foundation bearing capacity test method based on centrifugal simulation according to claim 1, 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. 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 for convenient observation of foundation structure deformation.

3. The foundation bearing capacity test method based on centrifugal simulation according to claim 2, 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, so as to simulate different groundwater level conditions.

4. The foundation bearing capacity test method based on centrifugal simulation according to claim 1, characterized in that: In step S5, applying a load to the foundation structure by the bearing force pressure applying device includes: The bearing capacity pressure device performs pressure operation in an intermittent multiple pressure application manner, and each pressure application applies pressure 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 down until the measured value of the pore water pressure meter returns to the value before pressure application, and then continues to apply pressure in the above manner until the vertical displacement of the strip foundation reaches the first displacement threshold. The pressure operation ends.

5. A foundation bearing capacity test device based on centrifugal simulation, characterized in that: A method for testing foundation bearing capacity based on centrifugal simulation as described in any one of claims 1 to 4 can be realized; The test device comprises: The model box is located in the hanging basket of the centrifuge and is used to provide a model space for the foundation structure and measurement space for several measuring instruments for the foundation bearing capacity test; A foundation structure, arranged inside the model box, serving as a test model for a foundation bearing capacity test; A strip foundation is provided on the upper surface of the foundation structure or at a certain buried depth and is in contact with the foundation structure, and is used to bear the load applied by the pressure device and transmit 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 testing; a centrifuge, used to fix the model box and apply centrifugal force to the foundation structure therein, so as to simulate a measurement environment of a prototype foundation that is 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; The foundation structure is prepared in layers, with dyed sand marking strips set between each layer; According to different water level control conditions in the foundation structure, the foundation structure is a sandy soil foundation or a clay soil foundation under a saturated working condition, or the foundation structure is a sandy soil foundation or a clay soil foundation under an unsaturated working condition; The relationship between the preset target value of the centrifugal acceleration of the centrifuge and the parameters of the foundation structure includes: ， ， ； Among them, where: N Indicates that the preset target value of centrifugal acceleration is gravity acceleration. N times; 、 are the foundation width of the prototype foundation and the foundation width of the foundation structure respectively; 、 are the foundation depth of the prototype foundation and the foundation depth of the foundation structure respectively; 、 They are respectively the foundation soil pressure of the prototype foundation and the foundation soil pressure of the foundation structure.

6. The foundation bearing capacity test device based on centrifugal simulation according to claim 5, 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 displacement data of the surface of the foundation structure; The particle image velocimetry device is placed facing the foundation structure, collects image data of the foundation structure through the observation window of the model box and identifies color line marks to measure the displacement velocity of the soil 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 changes in pore water pressure during the process of increasing centrifugal acceleration and the process of pressure loading by the bearing force pressure applying device.

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