Drainage boundary simulation device for soft soil foundation model test

Abstract

The soft soil foundation model test drainage boundary simulation device disclosed by the application comprises a model box, a permeable pad, a pressurized force measuring mechanism, a vacuum machine, a water tank and a plurality of plastic drainage belts. The permeable pad comprises water permeable material and a plurality of steel plates. The outer surfaces of the plurality of steel plates and the inner side walls of the model box enclose a ring cavity. The water permeable material is filled in the ring cavity. The plurality of plastic drainage belts are embedded in the water permeable material. The top end of one of the plastic drainage belts is connected with the water tank. The water tank is arranged above the side of the model box. The top end of another plastic drainage belt is connected with the vacuum machine. A plurality of water permeable holes are formed in each steel plate. The top of each steel plate is fixedly connected with the top of the model box through a clamping mechanism. The pressurized force measuring mechanism is used for applying pressure to the inner surfaces of the plurality of steel plates and measuring the pressure. The device can simulate the penetration of peripheral moisture at different depths of the foundation, and help experimenters to obtain more accurate development rules of water content, pore pressure and consolidation settlement after the soft soil foundation model experiment.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of geotechnical engineering model test, in particular to a soft soil foundation model test drainage boundary simulation device. BACKGROUND

[0002] Soft soil foundation is widely distributed in coastal areas and inland lake areas. Soft soil foundation is an important part of building engineering, traffic engineering, municipal engineering, water conservancy engineering, port, wharf, dam and airport, etc. Due to the high water content, low strength and large compressibility of soft soil, various types of actual engineering construction of soft soil foundation are faced with various challenges. In order to study the key problems in soft soil foundation engineering, researchers usually adopt two common methods of theoretical analysis or experimental analysis. Among various types of experimental research methods, soft soil foundation scale model test is an important means.

[0003] Soft soil foundation model test has important significance in geotechnical engineering design and construction guidance, which can provide key mechanical parameters and stress and deformation characteristics, thereby guiding engineering practice, such as evaluating foundation stability, studying foundation stress and deformation characteristics, testing the reliability of theoretical methods, guiding the development and application of new materials and new technologies, etc. In addition to the simulation of soft soil foundation, soft soil foundation model test also involves the simulation of various types of boundary conditions, mainly including displacement boundary and water seepage boundary simulation. Cai Jun made a study on the drainage pressure relief effect and bearing characteristics of pervious concrete pile foundation in a model box made of resin glass and steel plate; Sun Wentao studied the reinforcement effect of dredger fill soft soil foundation under different temperature rise and fall cycle paths by using a polymethyl methacrylate (PMMA) cylindrical model barrel, and revealed the consolidation evolution process of the dredger fill soft soil foundation model in the process of cold-heat repeated changes. The above model tests consider the simulation of displacement boundary conditions, but the simulation of drainage boundary conditions is not sufficient.

[0004] As for soft soil foundation, the groundwater recharge 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 saturation and pore water pressure change of the foundation soil, and further affect the reliability of the test results of the model test. In the existing related research, when considering the seepage 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. However, in actual engineering, the seepage of water below the groundwater level of soft soil foundation is free, and its seepage velocity is related to the permeability of the soil layer. In sandy soil layer, the seepage velocity of groundwater is fast, and the seepage boundary can be regarded as a drainage boundary; in clay soil layer, the seepage velocity of groundwater is slow, and the seepage boundary is a weak permeable boundary. It can be seen that the current soft soil foundation model test cannot consider the above conditions.

[0005] Therefore, it is necessary to invent a model test drainage boundary simulation device to simulate various types of seepage boundaries of actual soft soil foundation, thereby improving the reliability of soft soil foundation model test and assisting the design and construction of soft soil engineering in coastal areas. SUMMARY

[0006] The technical problem solved by the present application is to provide a multifunctional soft soil foundation model test drainage boundary simulation device to solve the problems of the prior art.

[0007] The technical solution adopted by the present application to solve the above technical problem is: a soft soil foundation model test drainage boundary simulation device, comprising a model box, a permeable pad, a pressure measuring mechanism, a vacuum machine, a water tank and a plurality of plastic drainage belts, the permeable pad comprises a water permeable material and a plurality of steel plates, the plurality of steel plates are arranged along the inner side wall of the model box in sequence, the outer surface of the plurality of steel plates and the inner side wall of the model box form an annular cavity, the water permeable material is filled in the annular cavity, the permeation coefficient of the water permeable material is inversely proportional to the pressure it bears, the plurality of plastic drainage belts are respectively vertically buried in the water permeable material, the top end of one of the plastic drainage belts is connected to the water tank through a water delivery pipe, a valve is installed on the water delivery pipe, the water tank is arranged above the side of the model box, the top end of another plastic drainage belt is connected to the vacuum machine through a water pumping pipe, a plurality of water permeable holes are formed in each steel plate, the top of each steel plate is fixedly connected to the top of the model box through a clamping mechanism, the pressure measuring mechanism is arranged on the inner side of the plurality of steel plates, and the pressure measuring mechanism is used to apply pressure to the inner surface of the plurality of steel plates and measure the size of the applied pressure.

[0008] The technical principle of the soft soil foundation model test drainage boundary simulation device of the present application is that the pressure measuring mechanism and the clamping mechanism jointly apply a specific pressure to the permeable pad to compact the water permeable material, the greater the pressure, the smaller the permeation coefficient of the water permeable material, and vice versa, by changing the permeation coefficient of the water permeable material, the speed of water flow in the permeable pad to the soft soil foundation is changed. For example, soft soil is filled in the model box of the simulation device to simulate the soft soil foundation, when vacuum preloading is performed on the soft soil foundation in the model box, the permeation coefficient of the water permeable material can be changed to change the speed of water flow in the permeable pad to the soft soil foundation, so as to adjust the water supply and simulate the water level change of the soft soil foundation, which is more in line with the actual situation on site.

[0009] In the model experiment, the valve on the water delivery pipe is twisted to change the speed of water flow from the water tank to the water permeable material, so that the saturation of the water permeable material is maintained within a certain range, neither overflowing nor lacking. The water tank can also be raised or lowered, or the water level in the water tank can be changed, so that the water head of the permeable pad is increased or decreased, simulating the water head around the foundation soil at different depths. The vacuum machine can use different vacuum degrees to extract water from the water permeable material to different degrees.

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

[0011] As a preferred embodiment, the water permeable material is white sandstone or a mixture of white sandstone and bentonite. White sandstone is the most widely used stone material by humans and is a high-quality sandstone with a very tight structure, uniform sandstone particles, delicate texture, and loose structure, so it has a high water absorption rate. The main component of white sandstone 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, i.e. the permeability gradually decreases with the increase of dry density (compaction degree). The permeability coefficient of white sandstone decreases after the addition of bentonite, and the permeability coefficient can be changed by changing the proportion of bentonite, thereby changing the speed of water flow from the permeable pad to the soft soil foundation and expanding the adjustment range of the permeability coefficient.

[0012] As a preferred embodiment, the model tank is a square model tank, the number of steel plates is four, and the number of plastic drainage belts is four, with each of the four plastic drainage belts arranged at a corner of the model tank.

[0013] As a preferred embodiment, the clamping mechanism is a plurality of sets of vices, and the pressure measuring mechanism is four sets of pressure measuring rods. The two steel plates opposite to each other are clamped by two sets of pressure measuring rods, and the two steel plates opposite to each other are clamped by the other two sets of pressure measuring rods. The pressure measuring rods of the present application adopt existing technology. In addition to pressure measuring rods, other pressure measuring mechanisms in existing technology can also be used, as long as they can apply pressure and measure the pressure

[0014] Compared with the prior art, the present application has the following advantages: the simulation device of the present application can simulate the penetration of water around the foundation at different depths, including penetration into the foundation and foundation drainage, to solve the problem that the existing soft soil foundation model test does not reflect the recharge of groundwater in deep foundation soil, helping experimenters to obtain more accurate development rules of water content, pore pressure and consolidation settlement after the soft soil foundation model test, thereby providing more effective guidance for on-site experiments. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 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 the model box in the 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 will be described in further detail below with reference to the accompanying drawings and embodiments. All devices or components not limited in the present invention are conventional technical means in the art.

[0021] The soft soil foundation model test drainage boundary simulation device of the embodiment is as follows Figures 1-3 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 several plastic drainage belts 7. The permeable pad includes a 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 surface of the plurality of steel plates 3 and the inner wall of the model box 1 form an annular cavity. The permeable material 2 is filled in the annular cavity. The permeability coefficient of the permeable material 2 is inversely proportional to the pressure it is subjected to. Several plastic drainage belts 7 are vertically buried in the permeable material 2. The top of one of the plastic drainage belts 7 is connected to the water tank 6 through 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 of the other plastic drainage belt 7 is connected to the vacuum machine 5 through a water 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 multiple steel plates 3. The pressure-applying force-measuring mechanism 4 is used to apply pressure to the inner surfaces of the multiple 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, the four plastic drainage belts 7 are respectively arranged at the four corners of the model box 1, the clamping mechanism 8 is a plurality of sets of vices, and the pressure measuring force mechanism 4 is four sets of pressure measuring force rods. The two steel plates 3 opposite to each other in front and back are tightly pressed by two sets of pressure measuring force rods, and the two steel plates 3 opposite to each other on the left and right are tightly pressed by the other two sets of pressure measuring force rods. The pressure measuring force rod adopts the prior art. In addition to the pressure measuring force rod, other pressure measuring force mechanisms in the prior art can also be used as long as they can exert pressure and measure the pressure size.

[0023] White sandstone, white sandstone and different proportions of bentonite were used as different permeable materials, and the permeability coefficients of different permeable materials under different compaction degrees were detected, and the results are shown in Table 1. Among them, the measurement method of compaction degree: through the joint action of the pressure measuring force mechanism 4 and the clamping mechanism 8 on the permeable pad, the permeable material 2 is compacted to different degrees, and the corresponding compaction degree is measured by the cutting ring method.

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

[0025]

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

[0027]

[0028] Among them, k is the permeability coefficient, the unit is cm / s; a is the inner cross-sectional area of the fine glass tube, the unit is cm 2 ; L is the height of the permeable material sample, the unit is cm; A is the cross-sectional area of the permeable material sample, the unit is cm 2 ; t2, t1 are respectively the time, the unit is s; h2, h1 are respectively the water level corresponding to time t2, t1, the unit is cm.

[0029] Table 2 Permeability coefficients of permeable material with 25% bentonite content under different pressures

[0030]

[0031] In the model box 1 of the above simulation device, soft soil is filled to simulate a soft soil foundation. When vacuum preloading is performed on the soft soil foundation in the model box 1, the speed of water flow from the permeable pad to the soft soil foundation can be changed by changing the permeability coefficient of the permeable material 2, so as to adjust the water supply and simulate the water level change of the soft soil foundation, which is more in line with the actual situation on site.

[0032] In the model experiment, the valve 62 on the water delivery pipe 61 is twisted to change the speed of water flow from the water tank 6 to the water permeable material 2, so that the saturation of the water permeable material 2 is kept within a certain range, neither overflowing nor lacking too much. The water tank 6 can also be raised or lowered, or the height of water in the water tank 6 can be changed, so that the water head of the permeable pad is increased or decreased, simulating the water head around the foundation soil at different depths in practice, and it can also be watered. The vacuum machine 5 can use different vacuum degrees to pump water from the water permeable material 2 to different degrees.

[0033] The above simulation device can simulate the penetration of water around the foundation at different depths, including the infiltration of groundwater and the discharge of groundwater, to solve the problem that the existing soft soil foundation model test does not reflect the recharge of groundwater in deep foundation soil, helping experimenters to obtain more accurate development rules of water content, pore pressure and consolidation settlement after the soft soil foundation model test, thereby providing more effective guidance for on-site experiments.

Claims

1. Soft soil foundation model test drainage boundary simulation device, characterized by: It includes a model box, a permeable pad, a pressure force measuring mechanism, a vacuum machine, a water tank and several plastic drainage belts. The permeable pad includes a permeable material and multiple steel plates. The multiple steel plates are arranged in sequence along the inner wall of the model box. The outer surfaces of the multiple steel plates and the inner wall of the model box form an annular cavity. The permeable material is filled in the annular cavity. The permeability coefficient of the permeable material is inversely proportional to the pressure it is subjected to. The several plastic drainage belts are vertically buried in the permeable material. The top of one of the plastic drainage belts is connected to the water tank through a water pipe. A valve is installed on the water pipe. The water tank is arranged on the side and above the model box. The top of another plastic drainage belt is connected to the vacuum machine through a water pumping pipe. Several permeable holes are opened on each steel plate. The top of each steel plate 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 multiple steel plates. The pressure 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.

2. The drainage boundary simulation device for soft soil foundation model test according to claim 1, characterized in that: The 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, 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 pressure-applying force-measuring rods, and the two left and right opposite steel plates are tightened by the other two sets of pressure-applying force-measuring rods.

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