Drainage boundary simulation device for soft soil foundation model test

Abstract

The soft soil foundation model test drainage boundary simulation device comprises a model box, a permeation pad, a pressurization force measuring mechanism, a vacuum machine, a water tank and a plurality of plastic drainage belts, the permeation pad comprises a permeable material and a plurality of steel plates, an annular cavity is defined by the outer surfaces of the steel plates and the inner side wall of the model box, and the permeable material is filled in the annular cavity; the plastic drainage belts are embedded in the permeable material, the top end of one plastic drainage belt is connected with the water tank, the water tank is arranged above the side of the model box, the top end of the other plastic drainage belt is connected with the vacuum machine, a plurality of permeable holes are formed in each steel plate, and the top of each steel plate is fixedly connected with the top of the model box through a clamping mechanism. The pressurization force measuring mechanism is used for applying pressure to the inner surfaces of the multiple steel plates and measuring the pressure. The device can simulate permeation of peripheral moisture of the foundation at different depths, and helps experimenters to obtain more accurate development rules of moisture content, pore pressure and consolidation settlement after a soft soil foundation model experiment is carried out.

Description

Technical Field

[0001] The invention relates to the field of geotechnical engineering model tests, and in particular to a drainage boundary simulation device for soft soil foundation model tests. Background Art

[0002] Soft soil foundations are widely distributed in coastal areas and inland lake areas. Soft soil foundations are an important part of construction projects, transportation projects, municipal projects, water conservancy projects, ports, docks, dams and airports. Due to the high moisture content, low strength and high compressibility of soft soil, various practical engineering constructions of soft soil foundations face many challenges. In order to study the key issues in soft soil foundation engineering, researchers usually use two common methods: theoretical analysis or experimental analysis. Among various experimental research methods, the scaled model test of soft soil foundation is one of the important means.

[0003] Soft soil foundation model tests are of great significance in geotechnical engineering design and construction guidance. They can provide key mechanical parameters and stress-deformation characteristics, thereby guiding engineering practice, such as evaluating foundation stability, studying foundation stress-deformation characteristics, verifying the reliability of theoretical methods, and guiding the development and application of new materials and new processes. In addition to the simulation of soft soil foundations, soft soil foundation model tests also involve the simulation of various boundary conditions, mainly including displacement boundary and seepage boundary simulation. Cai Jun studied the drainage decompression effect and bearing characteristics of permeable concrete pile foundations in a model box made of resin glass and steel plates; Sun Wentao used a polymethyl methacrylate (PMMA) cylindrical model barrel to study the reinforcement effect of blown-fill soft soil foundations under different heating and cooling cycle paths, revealing the consolidation evolution process of the blown-fill soft soil foundation model during repeated cold-heat changes. The above model tests considered the simulation of displacement boundary conditions, but the drainage boundary conditions were not fully considered.

[0004] As far as soft soil foundation is concerned, the groundwater replenishment of the site has a significant impact on the stress and deformation of the foundation. Ignoring the simulation of drainage boundary conditions will affect the changes in foundation soil saturation and pore water pressure, and thus affect the reliability of the model test results. In existing related studies, when considering the permeable boundary, the upper boundary of the model foundation is usually set as a permeable boundary, and the left and right sides and the bottom boundary are set as impermeable boundaries. In actual engineering, the seepage of water below the groundwater level in soft soil foundation is free, and its seepage rate is related to the permeability properties of the soil layer. In sandy soil layers, the groundwater seepage rate is fast, and the seepage boundary can be regarded as a drainage boundary; in clay soil layers, the groundwater seepage rate is slow, and the seepage boundary is a weakly permeable boundary. It can be seen that the current soft soil foundation model tests cannot consider the above situation.

[0005] To this end, it is necessary to invent a model test drainage boundary simulation device to simulate various seepage boundaries of actual soft soil foundations, thereby improving the reliability of soft soil foundation model tests and assisting the design and construction of soft soil projects in coastal areas. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a multifunctional drainage boundary simulation device for soft soil foundation model test in view of the deficiencies of the prior art. The simulation device can simulate the penetration of water in the periphery of the foundation at different depths, including the infiltration and drainage of groundwater, so as to solve the problem that the existing soft soil foundation model test does not reflect the groundwater recharge in the deep foundation soil, and help the experimenter to obtain more accurate development laws of water content, pore pressure and consolidation settlement after conducting the soft soil foundation model test, so as to provide more effective guidance for the field experiment.

[0007] The technical solution adopted by the present invention to solve the above technical problems is: a drainage boundary simulation device for a model test of a soft soil foundation, comprising a model box, a permeable pad, a pressure measuring mechanism, a vacuum machine, a water tank and a plurality of plastic drainage belts, wherein the permeable pad comprises a water-permeable material and a plurality of steel plates, wherein the plurality of steel plates are arranged in sequence along the inner wall of the model box, wherein the outer surfaces of the plurality of steel plates and the inner wall of the model box form an annular cavity, wherein the water-permeable material is filled in the annular cavity, wherein the permeability coefficient of the water-permeable material is inversely proportional to the pressure it is subjected to, and wherein the plurality of plastic drainage belts are respectively vertically buried in the water-permeable material. The material, the top of one of the plastic drainage belts is connected to the water tank via a water pipe, a valve is installed on the water pipe, the water tank is arranged on the upper side of the model box, the top of the other plastic drainage belt is connected to the vacuum machine via a suction pipe, a plurality of water holes are opened on each of the steel plates, the top of each of the steel plates is fixedly connected to the top of the model box through a clamping mechanism, the pressure-applying force-measuring mechanism is arranged on the inner side of the multiple steel plates, and the pressure-applying force-measuring mechanism is used to apply pressure to the inner surface of the multiple steel plates and measure the magnitude of the applied pressure.

[0008] The technical principle of the drainage boundary simulation device for the soft soil foundation model test of the present invention is: a specific pressure is applied to the permeable pad by a pressure measuring mechanism and a clamping mechanism to compact the permeable material. The greater the pressure, the smaller the permeability coefficient of the permeable material. Vice versa, by changing the permeability coefficient of the permeable material, the speed at which the water in the permeable pad flows to the soft soil foundation is changed. For example, when soft soil is filled in the model box of the simulation device of the present invention to simulate the soft soil foundation and the soft soil foundation is vacuum pre-pressed in the model box, the speed at which the water in the permeable pad flows to the soft soil foundation can be changed by changing the permeability coefficient of the permeable material, thereby adjusting the water source replenishment and simulating the water level change of the soft soil foundation, which is more in line with the actual situation on site.

[0009] When conducting a model experiment, by twisting the valve on the water pipe, the speed at which the water in the water tank flows to the permeable material is changed, so that the saturation of the permeable material is kept within a certain range, neither overflowing nor too lacking. The water tank can also be raised or lowered, or the height of the water in the water tank can be changed to increase or decrease the water head of the permeable pad, simulating the water head around the foundation soil at different depths, and it can also be replenished with water. The vacuum machine can use different vacuum levels to pump water from the permeable material to different degrees.

[0010] Before the water-permeable material is filled into the annular cavity, the initial compaction degree of the water-permeable material should be tested to determine the permeability coefficient of the water-permeable material. The present invention buries the plastic drainage belt in the water-permeable material to form a channel for water replenishment or vacuum drainage.

[0011] Preferably, the permeable material is white sandstone or a mixture of white sandstone and bentonite. White sandstone is the most widely used stone material by humans. It is a high-quality sandstone with a very tight structure, uniform sand and gravel particles, fine texture, and loose structure. Therefore, it has a high water absorption rate. Its main component is quartz. The permeability coefficient of white sandstone is generally on the order of 10 -6 cm / s, and the permeability coefficient of white sandstone is inversely proportional to the dry density, that is, as the dry density (compaction degree) increases, its permeability gradually decreases. After the addition of bentonite, the permeability coefficient of white sandstone will decrease. By changing the proportion of bentonite components, the permeability coefficient can also be changed, thereby changing the speed at which water in the permeable pad flows to the soft soil foundation and expanding the adjustment range of the permeability coefficient.

[0012] Preferably, the model box is a square model box, the number of the steel plates is four, the number of the plastic drainage belts is four, and the four plastic drainage belts are respectively arranged at the four corners of the model box.

[0013] Preferably, the clamping mechanism is a plurality of sets of vises, and the pressure force measuring mechanism is four sets of pressure force measuring rods. The two front and rear opposite steel plates are tightened by two sets of the pressure force measuring rods, and the two left and right opposite steel plates are tightened by the other two sets of the pressure force measuring rods. The pressure force measuring rod of the present invention adopts the existing technology. In addition to the pressure force measuring rod, other pressure force measuring mechanisms in the existing technology can also be adopted, as long as they can apply pressure and measure the pressure.

[0014] Compared with the prior art, the present invention has the following advantages: the simulation device of the present invention can simulate the penetration of peripheral water at different depths of the foundation, including infiltration into the foundation and foundation drainage, so as to solve the problem that the existing soft soil foundation model test does not reflect the recharge of groundwater in the deep foundation soil, and help experimenters obtain more accurate development laws of water content, pore pressure and consolidation settlement after conducting soft soil foundation model experiments, thereby providing more effective guidance for field experiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic diagram (perspective view) of the appearance of the drainage boundary simulation device for the soft soil foundation model test in the embodiment;

[0016] Figure 2 is a cross-sectional view of a model box in an embodiment;

[0017] Figure 3 for Figure 2 Enlarged view of point A in the middle;

[0018] Figure 4 is a front view of a steel plate in the embodiment;

[0019] Figure 5 This is the relationship between the permeability coefficient and pressure of the permeable material when the bentonite content is 25%. DETAILED DESCRIPTION

[0020] The present invention is further described in detail below in conjunction with the embodiments of the drawings. All devices or components not limited in the present invention adopt conventional technical means in the art.

[0021] The soft soil foundation model test drainage boundary simulation device of the embodiment is as follows Figure 1 to Figure 3 As shown, it includes a model box 1, a permeable pad, a pressure measuring mechanism 4, a vacuum machine 5, a water tank 6 and a plurality of plastic drainage belts 7. The permeable pad includes a water-permeable material 2 and a plurality of steel plates 3. The plurality of steel plates 3 are arranged in sequence along the inner wall of the model box 1. The outer surfaces of the plurality of steel plates 3 and the inner wall of the model box 1 form an annular cavity. The water-permeable material 2 is filled in the annular cavity. The permeability coefficient of the water-permeable material 2 is inversely proportional to the pressure it is subjected to. A plurality of plastic drainage belts 7 are vertically buried in the water-permeable material 2, respectively. The top end of one of the plastic drainage belts 7 is connected to the water tank 6 via a water pipe 61. A valve 62 is installed on the water pipe 61. The water tank 6 is arranged on the upper side of the model box 1. The top end of another plastic drainage belt 7 is connected to the vacuum machine 5 via a pumping pipe 51. Figure 4 As shown, each steel plate 3 is provided with a plurality of water-permeable holes 31 ( Figure 1 (not shown in the figure), the top of each steel plate 3 is fixedly connected to the top of the model box 1 through a clamping mechanism 8, and a pressure-applying force-measuring mechanism 4 is arranged on the inner side of the plurality of steel plates 3. The pressure-applying force-measuring mechanism 4 is used to apply pressure to the inner surfaces of the plurality of steel plates 3 and measure the magnitude of the applied pressure.

[0022] In this embodiment, the model box 1 is a square model box 1, the number of steel plates 3 is four, the number of plastic drainage belts 7 is four, and the four plastic drainage belts 7 are arranged at the four corners of the model box 1 respectively. The clamping mechanism 8 is a plurality of sets of vises, and the pressure force measuring mechanism 4 is four sets of pressure force measuring rods. The two steel plates 3 facing each other front and back are tightened by two sets of pressure force measuring rods, and the two steel plates 3 facing each other left and right are tightened by the other two sets of pressure force measuring rods. The pressure force measuring rod adopts the existing technology. In addition to the pressure force measuring rod, other pressure force measuring mechanisms in the existing technology can also be adopted, as long as they can apply pressure and measure the pressure.

[0023] White sandstone and white sandstone and bentonite with different proportions were used as different permeable materials to test the permeability coefficients of different permeable materials at different compaction degrees, and the results are shown in Table 1. The compaction degree was measured by applying a specific pressure to the permeable pad through the pressure measuring mechanism 4 and the clamping mechanism 8, compacting the permeable material 2 to different degrees, and measuring the corresponding compaction degree by the ring knife method.

[0024] Table 1 Permeability coefficients of different permeable materials at different compaction degrees

[0025]

[0026] When the bentonite content n = 25%, the permeability coefficient of the permeable material under different pressures is shown in Table 2, and the relationship between the permeability coefficient of the permeable material and pressure is shown in Figure 5 Among them, the calculation formula of permeability coefficient is:

[0027]

[0028] Where: k is the permeability coefficient, in cm / s; a is the inner cross-sectional area of ​​the thin glass tube, in cm 2 ; L is the height of the permeable material sample, in cm; A is the cross-sectional area of ​​the permeable material sample, in cm 2 ; t2 and t1 are the moments, respectively, in seconds; h2 and h1 are the water levels corresponding to the moments t2 and t1, respectively, in cm.

[0029] Table 2 Permeability coefficient of permeable materials at different pressures when bentonite content is 25%

[0030]

[0031] The model box 1 of the simulation device is filled with soft soil to simulate a soft soil foundation. When the soft soil foundation is vacuum pre-pressed in the model box 1, the speed at which water in the permeable pad flows to the soft soil foundation can be changed by changing the permeability coefficient of the permeable material 2, thereby adjusting the water supply and simulating the water level change of the soft soil foundation, which is more in line with the actual situation on site.

[0032] When conducting a model experiment, by twisting the valve 62 on the water pipe 61, the speed at which the water in the water tank 6 flows to the water-permeable material 2 is changed, so that the saturation of the water-permeable material 2 is maintained within a certain range, neither overflowing nor being too lacking. The water tank 6 can also be raised or lowered, or the height of the water in the water tank 6 can be changed to increase or decrease the water head of the permeable pad, simulating the water head around the foundation soil at different depths, and water can also be replenished. The vacuum machine 5 can use different vacuum degrees to pump water from the water-permeable material 2 to different degrees.

[0033] The above-mentioned simulation device can simulate the penetration of peripheral water at different depths of the foundation, including the infiltration and discharge of groundwater, so as to solve the problem that the existing soft soil foundation model test does not reflect the groundwater recharge problem in the deep foundation soil, and help experimenters obtain more accurate development laws of water content, pore pressure and consolidation settlement after conducting soft soil foundation model experiments, so as to provide more effective guidance for field experiments.

Claims

1. Drainage boundary simulation device for soft soil foundation model test, characterized in that: It includes a model box, a permeable pad, a pressure force measuring mechanism, a vacuum machine, a water tank and a plurality of plastic drainage belts. The permeable pad includes a water-permeable material and a plurality of steel plates. The plurality of steel plates are arranged in sequence along the inner wall of the model box. The outer surfaces of the plurality of steel plates and the inner wall of the model box form an annular cavity. The water-permeable material is filled in the annular cavity. The permeability coefficient of the water-permeable material is inversely proportional to the pressure it is subjected to. The plurality of plastic drainage belts are vertically buried in the water-permeable material respectively. The top of one of the plastic drainage belts is connected to the water tank via a water pipe, a valve is installed on the water pipe, the water tank is arranged on the upper side of the model box, the top of another plastic drainage belt is connected to the vacuum machine via a pumping pipe, a plurality of water-permeable holes are opened on each of the steel plates, and the top of each of the steel plates is fixedly connected to the top of the model box through a clamping mechanism. The pressure force measuring mechanism is arranged on the inner side of the plurality of steel plates, and the pressure force measuring mechanism is used to apply pressure to the inner surface of the plurality of steel plates and measure the magnitude of the applied pressure.

2. The drainage boundary simulation device for soft soil foundation model test according to claim 1, characterized in that: The water-permeable material is white sandstone or a mixture of white sandstone and bentonite.

3. The drainage boundary simulation device for soft soil foundation model test according to claim 1, characterized in that: The model box is a square model box, the number of the steel plates is four, the number of the plastic drainage belts is four, and the four plastic drainage belts are respectively arranged at the four corners of the model box.

4. The drainage boundary simulation device for soft soil foundation model test according to claim 3 is characterized in that: The clamping mechanism is a plurality of sets of vises, and the pressure-applying force-measuring mechanism is four sets of pressure-applying force-measuring rods. The two front and rear opposite steel plates are tightened by two sets of the pressure-applying force-measuring rods, and the two left and right opposite steel plates are tightened by the other two sets of the pressure-applying force-measuring rods.

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