An apparatus for determining the dynamic moisture content of coarse-grained soils

Abstract

The present application relates to a kind of device for determining the dynamic water content of coarse-grained soil, comprising: water inlet unit for simulating the water inlet condition of coarse-grained soil layer;Coarse-grained soil container (2) for loading coarse-grained soil;Percolation unit for filtering out the water flowing through coarse-grained soil without being able to adhere to its surface and fine particles in coarse-grained soil;Mass measurement unit;For measuring the mass of filtered fine particles, container mass and total mass of the device;The water inlet unit is arranged at the top of the coarse-grained soil container (2);The percolation unit is arranged at the bottom of the coarse-grained soil container (2);The mass measurement unit includes fine particle mass detection scale (7), container mass detection scale (8) and total mass detection scale (9) of the device.Compared with the prior art, the present application can meet the needs of different soil and climate conditions, and help to provide more detailed parameter basis for the macroscopic and microscopic mechanical behavior analysis of coarse-grained soil under extreme conditions such as heavy rain, mountain flood, etc.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of civil engineering design, and particularly relates to a device for measuring dynamic water content of coarse-grained soil. BACKGROUND

[0002] Coarse-grained soil is widely used in the construction of railway and highway subgrades, such as subgrade and ballast bed. Previous studies have shown that the water content of coarse-grained soil has a significant impact on its mechanical behavior, and further affects the service performance of the soil structure. When subjected to sudden natural disasters such as heavy rainfall and flash floods, the water content in the coarse-grained soil is in a complex dynamic change, and is affected by many factors such as the amount of infiltrating water, gradation, and burial depth. In previous studies, the water content in the soil was considered as a static constant to analyze its influence, especially for coarse-grained soil, which has good permeability. Usually, only the mechanical properties under the final stable water content state or saturated state are analyzed, and the dynamic change of water content caused by water is not fully considered. Therefore, there is a lack of devices for measuring the dynamic water content of coarse-grained soil.

[0003] The influence of water infiltration on coarse-grained soil mainly reflects in two aspects: stable attached water on the particle surface and flowing water film. The stable attached water refers to the water attached to the particle surface when the particle is completely wetted at the end of the infiltration and drainage process. However, due to the large pores and poor water storage capacity of coarse-grained soil, the stable attached water on the particle surface is relatively small. The flowing water film is a layer of water film temporarily formed on the particle surface when the water infiltration intensity is large, because the water attached to the particle surface is less than the water infiltration speed. This layer of water film will gradually disappear as the drainage process ends. Since the flowing water film is closely related to the water infiltration intensity and will gradually disappear over time after the end of the infiltration process, the water storage capacity of the soil body will also change continuously. The dynamic water storage capacity of coarse-grained soil is directly related to the water content of the flowing water film on the particle surface, which in turn affects the cohesion between particles, and thus affects the particle contact behavior of coarse-grained soil under dynamic action, and further affects the shear strength and dynamic stability of the soil body. Taking the ballast bed as an example, the water accumulation phenomenon caused by long-term rainfall will reduce the frictional resistance between the ballast particles, thereby reducing the resistance of the ballast bed and affecting the service performance of the ballast bed. Therefore, it is necessary to further study the influence of water infiltration on the change of water content of coarse-grained soil.

[0004] In addition, for most coarse-grained soils, the smaller particles inside are unstable due to the meso-mechanism of structure and stress. The small particles can be eroded at a lower hydraulic gradient than predicted by classical hydraulics theory. Therefore, it is necessary to measure the degree of loss of small particles in coarse-grained soil under different water infiltration conditions, which has reference value for the internal stability analysis of coarse-grained soil of embankments and flood protection dikes.

[0005] It should be noted that the particle size of the coarse-grained soil in soil mechanics is usually not greater than 60mm, and the coarse-grained soil in the present project refers to sand, gravel, pebble and the like widely used in railway engineering, and the upper limit of the particle size can be greater than the particle size range of the coarse-grained soil in soil mechanics. SUMMARY

[0006] The purpose of the present application is to provide a device for measuring the dynamic water content of coarse-grained soil, which overcomes at least one of the above-mentioned defects of the prior art.

[0007] The purpose of the present application can be achieved by the following technical solutions:

[0008] A device for measuring the dynamic water content of coarse-grained soil, characterized in that it comprises:

[0009] a water inlet unit for simulating the water inlet condition of the coarse-grained soil layer;

[0010] a coarse-grained soil container for loading coarse-grained soil;

[0011] a filtration unit for filtering out water that flows through the coarse-grained soil without being attached to its surface and fine particles in the coarse-grained soil;

[0012] a mass measurement unit for measuring the mass of the filtered fine particles, the mass of the container and the total mass of the device;

[0013] The water inlet unit is arranged at the top of the coarse-grained soil container; the filtration unit is arranged at the bottom of the coarse-grained soil container; and the mass measurement unit comprises a fine particle mass detection scale, a container mass detection scale and a total device mass detection scale.

[0014] Further, the water inlet unit comprises a surface water inlet assembly and / or a deep water inlet assembly; wherein the surface water inlet assembly and the deep water inlet assembly are not simultaneously installed at the top of the coarse-grained soil container.

[0015] Preferably, the surface layer is a coarse-grained soil layer with a thickness less than or equal to 100cm.

[0016] Further, the water inlet unit of the coarse-grained soil comprises a surface water inlet assembly and / or a deep water inlet assembly.

[0017] More specifically, when the device designed according to the application is used to measure the dynamic water content of a special geometric coarse-grained soil layer, the surface soil and deep soil need to be divided according to the soil quality, particle size gradation, density and other factors of the coarse-grained soil. If only the surface soil is divided, the dynamic water content of the coarse-grained soil layer only needs the surface water inlet assembly. If the surface soil and deep soil are both divided, the whole test needs to be divided into two steps. In the first step, the dynamic water content of the coarse-grained soil of the surface soil is obtained by using the surface water inlet assembly. In the second step, the surface water inlet assembly is replaced by the deep water inlet assembly, the water inlet condition is adjusted based on the data of the first step, and the dynamic water content of the coarse-grained soil of the deep soil is obtained.

[0018] This is because the height of the container is limited by the measurement environment. If the deep water inlet assembly is not used, when the height of the container is lower than the depth of the soil to be measured, the measurement target cannot be met. At the same time, a too high container height is not realistic, which will complicate the measurement process, reduce the measurement efficiency and consume a lot of cost.

[0019] Further, the surface water inlet assembly comprises a water pump for controlling the water inlet intensity and a water inlet device for spraying water; the water pump is in communication with the water inlet device; the spraying radius of the water inlet device is equal to the inner diameter of the coarse-grained soil container, so as to better simulate the rainfall process under natural conditions.

[0020] Specifically, the surface water inlet assembly comprises a water pump for adjusting the water inlet amount and a water inlet device. The water pump for adjusting the water inlet amount is used to control the size of the water inlet intensity. According to the different dynamic water contents of the coarse-grained soil under different water inlet intensities, the water inlet intensity is divided into a certain number of levels, and the change of each level is realized by adjusting the water pump. The water inlet amount L per unit time is calculated by the inner diameter D of the cross section of the cylindrical coarse-grained soil container and the water inlet intensity P, and the calculation expression is:

[0021]

[0022] Among them, the spraying radius of the water inlet device is the same as the inner diameter D of the coarse-grained soil container under each level of water inlet intensity.

[0023] Further, the deep water inlet assembly comprises a flow control valve and a flow buffer; the top of the flow buffer is provided with a water inlet pipe for water inlet; the flow control valve is arranged on the water inlet pipe. Among them, the flow control of the flow control valve in the deep water inlet assembly in the above-mentioned second step experiment is determined according to the dynamic change of the filtered water quality in the above-mentioned first step experiment, and the flow buffer is connected below the flow control valve to control the flow rate of the water flow and simulate the flow of the water flow in the deep ballast.

[0024] Further, the percolation unit comprises a first filter screen and a second filter screen arranged in parallel, the first filter screen is used to filter out the water flowing through the coarse soil and not attached to the surface of the coarse soil and to carry the coarse soil in the container, and the second filter screen is used to filter out the fine particles in the coarse soil, and the second filter screen is arranged on the side of the first filter screen away from the coarse soil container. The pore size of the filter screen is determined by the particle size gradation of the ballast.

[0025] Further, the contact angle of the surface material of the first filter screen and the second filter screen is greater than 90°. The material of the first filter screen and the second filter screen is a water-repellent nano material.

[0026] Preferably, the contact angle of the surface material of the filter screen is greater than 150°, i.e. a super-hydrophobic material, at which time it is difficult for the liquid to form a film on the surface of the material, and the wettability is poor. The nano material includes nano silicon dioxide material, bismuth sulfide nano material, and polymer nano composite material, etc. At the same time, high polymer waterproof paint can also be used, such as polysiloxane paint, polyurethane waterproof paint, etc. If the contact angle of the listed materials cannot reach greater than 150°, the hydrophobicity of the existing materials can be further improved by adding other materials to modify or process the existing materials.

[0027] Preferably, the percolation unit mainly comprises two layers of filter screens arranged in parallel at the bottom of the coarse soil container, the first filter screen is mainly used for water permeation and carries the measured object in the upper container, and therefore the pore size of the first filter screen is suggested to be set as D3 of the measured object; the second filter screen is mainly used for filtering out fine particles and preventing the fine particles from flowing out through the screen holes, and therefore the pore size of the second filter screen is suggested to be set as 1‰ of D of the measured object. Since the particle size of the coarse soil varies in a large range, the second filter screen is arranged in a detachable form to meet the gradation requirements of different measured objects. 50

[0028] Further, the device further comprises a support frame for supporting the coarse soil container and a water storage container for collecting the effluent; the support frame and the water storage container are arranged on the device total mass detection scale; and the support frame is arranged on the container mass detection scale.

[0029] Preferably, the fine particle mass detection scale is a cantilever beam weighing scale; and the cantilever beam weighing scale is connected with the second filter screen.

[0030] Further, the device further comprises a data post-processing platform; and the data post-processing platform is connected with the output ends of the fine particle mass detection scale, the container mass detection scale, and the device total mass detection scale.

[0031] ​Specifically, the real-time measurement data of the fine particle quality detection scale, the container quality detection scale and the device total quality detection scale are transmitted to the data post-processing platform through the data transmission line for storage. The data post-processing platform is obtained by calculating and converting the data obtained by the quality measurement unit. According to the quality measured by the quality measurement unit, the following formula is used for calculation:

[0032]

[0033] In the formula, m 容0 represents the mass of the coarse-grained soil container before water is added after the container quality measurement system is reset, that is, the mass of the measured coarse-grained soil, m 容 represents the mass of the coarse-grained soil container during the measurement process, ω 细 represents the water content of the fine particles on the secondary filter screen obtained by the drying test after each test, and the dynamic water content ω of the measured coarse-grained soil is finally obtained; similarly, according to

[0034]

[0035] and m 储 = m 总 -m 容 -m 细 , the dynamic change rule of the fine particle loss rate and the mass of water in the water storage container (the mass of the filtered water) during the measurement process can be obtained, m 储 represents the mass of water in the water storage container, m 总0 represents the total mass of the device when the measured coarse-grained soil is filled.

[0036] Compared with the prior art, the present application combines the correlation between the dynamic water content of coarse-grained soil and different water inlet intensities, and proposes a device for measuring the dynamic water content of coarse-grained soil from the perspective of adjustable water inlet intensity, which has the following beneficial effects:

[0037] (1) The water inlet unit can consider both surface water inlet and deep water inlet, and through the water pump with adjustable water inlet amount, the difference in the dynamic water content of coarse-grained soil caused by the flowing water film under different water inlet intensities can be considered.

[0038] (2) The filtration unit uses a secondary filter screen to collect fine particles, which can prevent the loss of fine particles from affecting the measurement results; the secondary filter screen is in a detachable form to meet the needs of different particle size gradations of the measured objects.

[0039] (3) Considering the influence of different water inlet intensities and different particle size gradations on the device for measuring the dynamic water content of coarse-grained soil, the device can meet the needs of different soil and climate conditions, and can help to provide more detailed parameter basis for the macroscopic and microscopic mechanical behavior analysis of coarse-grained soil under extreme conditions such as heavy rain and mountain torrents. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 Fig. 1 is a schematic diagram of the device structure for measuring the dynamic water content of the surface layer of coarse-grained soil in the embodiment;

[0041] Figure 2 Fig. 2 is a schematic diagram of the device structure for measuring the dynamic water content of the deep layer of coarse-grained soil in the embodiment;

[0042] Figure 3 Fig. 3 is a schematic diagram of the device structure from the top for measuring the dynamic water content of coarse-grained soil in the embodiment;

[0043] Figure 4 Fig. 4 is a schematic diagram of the primary filter screen in the embodiment;

[0044] Figure 5 Fig. 5 is a schematic diagram of the secondary filter screen in the embodiment;

[0045] Reference signs in the figure: 1 - water inlet, 2 - coarse-grained soil container, 3 - coarse-grained soil sample, 4 - primary filter screen, 5 - secondary filter screen, 6 - water storage container, 7 - fine particle mass detection scale, 8 - container mass detection scale, 9 - device total mass detection scale, 10 - data transmission line, 11 - real-time display and control terminal, 12 - flow control valve, 13 - flow buffer, 14 - support frame. DETAILED DESCRIPTION

[0046] The present application will be described in detail below with reference to the accompanying drawings and specific embodiments. The present embodiment is implemented on the premise of the technical solution of the present application, and gives a detailed implementation and specific operation process, but the protection scope of the present application is not limited to the following embodiments.

[0047] EMBODIMENT

[0048] The present embodiment provides a device for measuring the dynamic water content of coarse-grained soil, which can be used to test the dynamic water storage capacity of ballast for railway track bed, as shown in Figures 1-3 The device mainly includes a water inlet unit, a filtration unit, a mass measurement unit, and a data post-processing platform. By measuring the dynamic changes in the mass of different parts of the device, the changes in the mass of filtered water, the dynamic water content of the ballast, and the dynamic loss rate of fine particles can be obtained.

[0049] The inventor found the correlation between the dynamic water content of the ballast bed and the rainfall intensity by analyzing the response of the water content of the ballast bed under different rainfall intensities. The dynamic water content of the ballast bed is closely related to the contact behavior of the ballast particles under dynamic action, which further affects the analysis of dynamic stability. The present application can measure the changes in the water content of the ballast bed at different rainfall intensities and different track bed thicknesses over time, which provides an important basis for analyzing the cohesion between ballast particles under rainfall conditions and the contact behavior of ballast particles under dynamic action, and further analyzing the shear strength and dynamic stability of the overall track bed.

[0050] For the determination of the dynamic water content of the ballast, it is recommended that the cross-sectional diameter of the coarse-grained soil container 2 be 60 cm, the overall height of the coarse-grained soil container 2 be 100 cm, and the diameter of the base of the total mass detection scale 9 of the lowermost layer be 100 cm.

[0051] The water inlet unit of the device is divided into a surface water inlet assembly and a deep water inlet assembly. The surface water inlet assembly divides the water inlet intensity into 7 levels according to the different dynamic water contents of the coarse-grained soil sample 3 under different conditions. The change of each level is realized by adjusting the water pump. According to the recommended size of the coarse-grained soil container and the rainfall intensity range specified in the specification, the water inlet intensity is recommended to be set to the values shown in Table 1. In order to meet the needs of different tests, the rainfall level can be adjusted and designed as needed on the basis of the original level through linear interpolation and other methods.

[0052] Table 1 Recommended values of water inlet rate

[0053]

[0054] In the deep water inlet assembly, there is a flow control valve 12 and a flow buffer 13, which are used to simulate and realize the measurement of the dynamic water content of the deeper coarse-grained soil 3. Generally speaking, a 100 cm coarse-grained soil container 2 can meet the maximum depth of the ballast corresponding to the standard track bed. If it is used to measure the dynamic water content of a special geometric track bed, such as a track bed with a thickness of 120 cm, the overall test needs to be divided into two steps. In the first step, the surface water inlet system is used to obtain the dynamic water content of the ballast in the upper 100 cm of the track bed. In the second step, the surface water inlet assembly is replaced by the deep water inlet assembly, the water inlet is adjusted based on the data of the first step, and the dynamic water content of the ballast with a depth of 100 cm to 120 cm is obtained.

[0055] The spray radius of the water inlet device 1 in the surface water inlet assembly under each intensity is consistent with the inner diameter (60 cm) of the cross section of the cylindrical coarse-grained soil container 2 of the device, so as to better simulate the rainfall process under natural conditions.

[0056] The flow control of the flow control valve 12 in the deep water inlet assembly in the second step is determined according to the dynamic change of the filtered water quality in the first step. The flow buffer 13 is connected to the flow control valve 12 to control the flow rate of the water flow, simulating the flow of water in the deep ballast.

[0057] The two-stage filter in the device filters out the water that flows through the coarse-grained soil but fails to adhere to its surface and the fine particles in the coarse-grained soil. The aperture of the filter screen is determined by the particle size gradation of the ballast.

[0058] For the first-stage filter 4 that filters out the water and carries the upper coarse-grained soil, see Figure 4, in order to prevent coarse soil through the first filter screen 4, the screen size is D3 of the standard special ballast gradation, 22.4mm according to TB / T2140-2008 "Railway Ballast", for the second filter screen 5 filtering out fine particles, see Figure 5 , set in a detachable form to meet the different levels of ballast particle size distribution requirements, the screen size can be taken as the standard special ballast gradation D 50 (40mm) of 1‰, about 0.04mm.

[0059] The mass measurement unit includes three measurement modules to measure the mass of the filtered fine particles m 细 , the mass of the coarse soil container m 容 and the total mass of the device m 总 , wherein the mass of the fine particles may be smaller due to changes, the fine particle mass detection scale 7 uses a cantilever scale, the container mass measurement scale 8 and the device total mass measurement scale 9 are ordinary laboratory high-precision electronic scales, and real-time measurement data is input into a computer for storage through a data transmission line 10.

[0060] The real-time mass data obtained in the experiment includes the mass of the fine particle solid and the fine particle surface attached water in m 细 , so the dynamic water content change cannot be directly obtained, and the water content ω 细 of the fine particles needs to be obtained through drying experiments after the test, and then the dynamic changes of the coarse soil dynamic water content ω 储 , the mass of water in the water storage container m 储 and the fine particle loss rate ρ at the sampling frequency are obtained through the following formula:

[0061] The mass of water in the water storage container: m 总 = m 容 -m 细

[0062] The dynamic water content of the coarse soil:

[0063] The fine particle loss rate:

[0064] Compared with the prior art, the device for measuring the dynamic water content of the coarse soil in the embodiment considers the influence of different water inflow intensities and different particle size distributions, can meet the needs of different soil and climate conditions, and helps to provide more detailed parameter basis for the macroscopic and microscopic mechanical behavior analysis of the coarse soil under extreme conditions such as heavy rain and mountain torrents.

[0065] The above merely describes preferred embodiments of the present application, but is not intended to limit the present application to other forms, and any person skilled in the art can make changes or modifications to the above disclosed technical contents into equivalent embodiments with equivalent changes. However, any simple modification, equivalent change and modification made to the above embodiments without departing from the technical solution content of the present application and according to the technical essence of the present application still belongs to the protection scope of the technical solution of the present application.

Claims

1. An apparatus for determining the dynamic moisture content of coarse-grained soils, characterized by, The utility model relates to a device for measuring the water content of coarse-grained soil, comprising: a water inlet unit for simulating the water inlet condition of coarse-grained soil; a coarse-grained soil container (2) for loading coarse-grained soil; a percolation unit for filtering out water that flows through the coarse-grained soil and fails to adhere to the surface of the coarse-grained soil and fine particles in the coarse-grained soil; a mass measurement unit for measuring the mass of filtered fine particles, the mass of the container, and the total mass of the device; the water inlet unit is arranged at the top of the coarse-grained soil container (2); and the percolation unit is arranged at the bottom of the coarse-grained soil container (2); the percolation unit comprises: a primary filter screen (4) for filtering out water that flows through the coarse-grained soil and fails to adhere to the surface of the coarse-grained soil and carrying the coarse-grained soil in the coarse-grained soil container (2); and a secondary filter screen (5) for filtering out fine particles in the coarse-grained soil; the secondary filter screen (5) is arranged on the side of the primary filter screen (4) away from the coarse-grained soil container (2); the mass measurement unit comprises a fine particle mass detection scale (7), a container mass detection scale (8), and a total device mass detection scale (9); the device further comprises a data post-processing platform; the data post-processing platform is connected to the output ends of the fine particle mass detection scale (7), the container mass detection scale (8), and the total device mass detection scale (9); the real-time measurement data of the fine particle mass detection scale (7), the container mass detection scale (8), and the total device mass detection scale (9) are transmitted to the data post-processing platform through a data transmission line for storage; the data post-processing platform converts the data obtained by the mass measurement unit through calculation; and the mass of the coarse-grained soil is calculated according to the mass measured by the mass measurement unit by using the following formula: ； wherein m 容0 M0represents the mass of the coarse-grained soil container before water is added after the container mass measurement system is zeroed, i.e. the mass of the coarse-grained soil being measured, m 容 M1represents the mass of the coarse-grained soil container during the measurement, m 细 M2represents the mass of the fine particles filtered out during the measurement, ω 细 M3represents the water content of the fine particles on the second filter obtained by drying the test at the end of each test, from which the dynamic water content of the coarse-grained soil being measured is ultimately derived ω .

2. The apparatus for determining the dynamic water content of coarse-grained soils according to claim 1, characterized in that, the water inlet unit comprises a surface water inlet assembly.

3. The apparatus for determining the dynamic moisture content of coarse-grained soils according to claim 2, characterized in that the surface is a coarse-grained soil layer with a thickness less than or equal to 100 cm.

4. The apparatus for determining the dynamic water content of coarse-grained soils according to claim 1, characterized in that, the water inlet unit comprises a surface water inlet assembly and a deep water inlet assembly; the surface water inlet assembly and the deep water inlet assembly are not simultaneously arranged at the top of the coarse-grained soil container (2).

5. The apparatus for determining the dynamic water content of coarse-grained soils according to claim 2 or 4, characterized in that the surface water inlet assembly comprises a water pump for controlling the water inlet intensity and a water inlet device (1) for spraying water; the water pump is in communication with the water inlet device (1); and the spraying radius of the water inlet device (1) is equal to the inner diameter of the coarse-grained soil container (2).

6. The apparatus for determining the dynamic moisture content of coarse-grained soils according to claim 4, wherein, the deep water inlet assembly comprises a flow control valve (12) and a flow buffer (13); the flow buffer (13) is provided with a water inlet pipe at the top for water inlet; and the flow control valve (12) is arranged on the water inlet pipe.

7. The apparatus for determining the dynamic moisture content of coarse-grained soils according to claim 1, wherein, the contact angle between the surface materials of the primary filter screen (4) and the secondary filter screen is greater than 90°.

8. The apparatus for determining the dynamic water content of coarse-grained soils according to claim 1, wherein, the device further comprises a support frame (14) for supporting the coarse-grained soil container (2) and a water storage container (6) for collecting effluent; the support frame (14) and the water storage container (6) are arranged on the total device mass detection scale (9); the support frame (14) is arranged on the container mass detection scale (8).

9. The apparatus for determining the dynamic water content of coarse-grained soils according to claim 1, wherein, the fine particle mass detection scale (7) is a cantilever beam scale; and the cantilever beam scale is connected to the secondary filter screen (5).

Images