CN116735325B - Sampling and shear strength testing methods for maintaining the original structure of spoil soil - Google Patents

Abstract

The invention provides a sampling and shear strength testing method for maintaining an original structure of a waste residue soil body, belongs to the technical field of waste residue soil tests in geological engineering, and aims to adopt a copolymer material as a sealing material in a sampling process, avoid disturbance of the original structure of the original soil in the sampling process and a transportation process, and enable a deblocking process to be simpler and easier, wherein the method comprises the following steps: preparing an acrylamide-acrylic acid copolymer from a mixture consisting of pure water, glycerol, acrylamide and acrylic acid in a mass ratio of 1:2:4-8:2-4 under the condition of heating in a water bath; selecting a waste residue soil plane with a preset size and shape for leveling at a gentle part of a waste residue soil slope surface; dividing an injection adhesive tape on the flattened waste residue soil plane, and uniformly injecting a copolymer material consisting of an acrylamide-acrylic acid copolymer into the injection adhesive tape until reaching a preset depth; and after the copolymerization material is solidified, removing waste residue soil at the periphery of the adhesive tape to obtain a sealed waste residue soil sample.

Description

Sampling and shear strength testing methods for maintaining the original structure of spoil soil

Technical field

The invention relates to the technical field of geological engineering spoil soil testing, and in particular to a sampling and shear strength testing method that maintains the original structure of the spoil soil body.

Background technique

In actual engineering projects, a large amount of engineering waste is caused by excavation during engineering construction. It is necessary to drain the waste soil and take appropriate measures to deal with it. Before disposing of the spoil soil, it is necessary to test the structure and mechanical properties of the spoil soil to select a reasonable disposal method. One of the most important mechanical parameters in geotechnical engineering is the shear strength of soil. Therefore, it is particularly necessary to test the shear strength of spoil soil.

Relevant studies have shown that the interaction and spatial arrangement between spoil soil particles have a significant impact on the shear strength characteristics of spoil soil. However, the accurate description of the mechanical properties of spoil soil will be affected by the complexity, uncertainty and complexity of the mesoscale between particles. Constraints on randomness. At present, the two conventional shear strength test methods are in-situ direct shear test and indoor direct shear test, but both have certain defects during the actual test process.

On-site in-situ direct shear tests need to be carried out at the engineering site. The test conditions are relatively complex and there are many environmental and geological factors that are difficult to control. In addition, the test equipment is bulky and complex to assemble, which will lead to a decrease in the accuracy of the test results.

The indoor direct shear test obtains the shear strength parameters of the spoil soil mainly through reshaped soil. Compared with the original soil, although the physical indicators of the reshaped soil will not change, the particle skeleton arrangement and particle contact of the reshaped soil will not change. The form and pore distribution characteristics have changed, destroying the initial structure of the spoil soil. This will lead to obvious differences in the mechanical parameters of the reshaped soil obtained from the test and the original soil, making the reshaped soil unable to truly reproduce the original soil. The strength and deformation characteristics of the soil, that is, the shear strength obtained by reshaping the soil, are difficult to characterize the mechanical properties of the spoil site.

Contents of the invention

In view of this, the present invention aims to propose a sampling and shear strength testing method that maintains the original structure of the spoil soil, so as to solve the problem that it is difficult to characterize the mechanical properties of the spoil site in tests using reshaped soil.

A first aspect of the embodiment of the present invention provides a sampling method for maintaining the original structure of spoil soil, including:

Preparing a mixture of pure water, glycerin, acrylamide and acrylic acid with a mass ratio of 1:2:4-8:2-4 under water bath heating conditions to prepare an acrylamide-acrylic acid copolymer;

In the gentle part of the spoil slope, select a spoil plane with a preset size and shape for smoothing to facilitate sampling; wherein the preset size and shape are determined based on the testing requirements for the spoil sample;

An injection tape is defined on the leveled spoil soil plane, and a copolymer material composed of the acrylamide-acrylic acid copolymer is evenly injected into the injection tape until a preset depth is reached;

After the copolymer material solidifies, dig out the spoil soil around the injection tape to obtain a sealed spoil soil sample.

Further, the preset depth is 1.1-1.2 times the height of the spoil soil sample; the width of the injection tape is 1/10-1/6 of the width of the spoil soil sample.

Further, the mixture of pure water, glycerol, acrylamide and acrylic acid with a mass ratio of 1:2:4-8:2-4 is prepared into an acrylamide-acrylic acid copolymer under water bath heating conditions, including :

Add the glycerol, the acrylic acid and the acrylamide to the pure water in sequence, stir and mix to obtain a mixed liquid; wherein the pure water, the glycerol, the acrylamide and the acrylic acid The mass ratio is 1:2:4-8:2-4;

An initiator is added to the mixed liquid, and after stirring, the water bath is heated at a temperature of 50 to 70°C for 10 to 20 minutes to obtain the acrylamide-acrylic acid copolymer; wherein the initiator includes persulfate and azo compounds. one of them.

Further, the mass ratio of the pure water, the glycerin, the acrylamide and the acrylic acid is 1:2:6:3.

Further, the mass ratio of the initiator to the acrylamide is 1:5-10.

Further, the glycerol, the acrylic acid and the acrylamide are sequentially added to the pure water, and stirred and mixed to obtain a mixed liquid, including:

After adding the glycerin and the acrylic acid to the pure water, stir the pure water;

While stirring, add the acrylamide to obtain the mixed liquid.

Further, the purity of the acrylamide is above 99%, the purity of the acrylic acid is above 99%, and the purity of the glycerol is above 95%.

Further, the copolymer material composed of the acrylamide-acrylic acid copolymer is uniformly injected into the injection tape until a preset depth is reached, including:

Glue injection equipment with a pore pressure probe is used to evenly inject the copolymer material into the injection tape. The injection amount and depth of the copolymer material are controlled by the pore pressure probe; during the glue injection process, the The glue injection equipment is heated to maintain the fluidity of the copolymer material.

A second aspect of the embodiment of the present invention provides a shear strength testing method, which method includes:

Use a hot air dryer to degumm the sealed spoil soil sample obtained by the sampling method described in the first aspect;

After the part of the degummed spoil soil sample containing the copolymer material is cut off, it is placed in a direct shear instrument to perform a direct shear test to test the shear strength of the spoil soil sample.

Further, the use of a hot air dryer for degumming includes:

Run the hot air dryer clockwise around the sealed spoil soil sample to heat and dry each part of the copolymer material so that the copolymer material loses strength.

The sampling method provided by the invention to maintain the original structure of the spoil soil body includes: heating a mixture composed of pure water, glycerol, acrylamide and acrylic acid with a mass ratio of 1:2:4-8:2-4 in a water bath Preparation of acrylamide-acrylic acid copolymer under the conditions; in the gentle part of the spoil slope, select a spoil plane with a preset size and shape for smoothing to facilitate sampling; wherein, the preset size and shape are based on the spoil The test requirements for the soil sample are determined; an injection tape is defined on the flattened spoil soil plane, and the copolymer material composed of the acrylamide-acrylic acid copolymer is evenly injected into the injection tape until the predetermined level is reached. Set the depth; after the copolymer material is solidified, dig out the spoil soil around the injection tape to obtain a sealed spoil soil sample; thus, the present invention uses acrylamide-acrylic acid copolymer in the sample The spoil soil is sealed during the process. The copolymer material formed by acrylamide-acrylic acid copolymer has high shear strength. Therefore, it is not easy to be damaged during transportation, which avoids the waste soil sample being damaged during transportation. At the same time, since the copolymer material forms flakes that are easy to fall off after drying and dehydration, the copolymer material can be directly heated and dried when testing the spoil soil sample to separate the spoil soil sample and the copolymer material. This makes it simple and easy to separate the spoil soil sample and the sealing material during testing, and also avoids the problem of liquid carrying part of the spoil soil sample after heating and drying, causing the waste soil sample to be lost.

Description of the drawings

The drawings forming a part of the present invention are used to provide a further understanding of the present invention. The illustrative embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the attached picture:

Figure 1 shows a step flow chart of a sampling method for maintaining the original structure of spoil soil provided by an embodiment of the present invention;

Figure 2 shows a step flow chart of a sampling method for maintaining the original structure of spoil soil provided by yet another embodiment of the present invention;

Figure 3 shows a step flow chart of a shear strength testing method provided by an embodiment of the present invention;

Figure 4 shows a schematic structural diagram of a direct shear instrument provided by an embodiment of the present invention;

Figure 5 shows the shear strength test effect diagram of the spoil soil sample obtained by the copolymer material sampling method and the spoil soil sample obtained by the wax sealing method provided by the embodiment of the present invention;

Figure 6 shows the shear strength test effect diagram of the spoil soil sample and the remolded soil sample obtained in the embodiment of the present invention;

Figure 7 shows the shear strength relationship curve of the spoil soil sample obtained by the embodiment of the present invention, the spoil soil sample obtained by the wax sealing method, and the reshaped sample;

Explanation of reference signs: 100. Lower shear box of the sample; 110. Lower ball bearing; 200. Horizontal loading device; 210. Pull rod; 220. First pull ring; 230. Second pull ring; 240. Horizontal drive motor; 300. Upper sample shear box; 310. Upper bottom plate; 320. Upper sample shear box enclosure; 330. Upper sample shear box side plate; 400. Sample upper shear box connection structure; 410. Bearing ; 500, vertical loading device; 510, ball head; 520, loading plate; 530, upper ball bearing; 540, vertical drive motor.

Detailed ways

It should be noted that, as long as there is no conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.

At present, during the construction process of geotechnical engineering projects, it is easy to cause a large amount of engineering waste. In order to achieve scientific disposal of waste soil, the structure and mechanical properties of the waste soil are tested, and the structural and mechanical properties of the waste soil are tested to achieve the desired results. The purpose of scientific disposal of waste soil. In geotechnical engineering, the shear strength of soil is one of the most important mechanical parameters.

In related technologies, the shear strength testing methods of waste soil include in-situ direct shear tests and indoor direct shear tests. Among them, on-site direct shear tests need to be conducted at the engineering site. The test conditions are relatively complex and environmental and geological factors are difficult to control, which affects the accuracy of the test results. Therefore, indoor direct shear tests are usually used to obtain the shear strength parameters of spoil soil.

However, the indoor direct shear test is used to obtain the shear strength parameters of the spoil soil through reshaped soil. The reshaped soil is the shape of the original soil that has been dried and crushed, and then remade according to the density and moisture content of the original soil. It is a kind of test soil that imitates the original soil. Therefore, although the physical indicators of the reshaped soil have not changed, the particle skeleton arrangement, particle contact form, and pore distribution characteristics of the reshaped soil have all changed, destroying the spoil soil body. The initial structure of the reshaped soil results in obvious differences between the mechanical parameters of the reshaped soil and the original soil, and the obtained shear strength is difficult to characterize the mechanical properties of the abandoned slag site.

Currently, in order to obtain undisturbed soil for sampling, paraffin is usually used as a sealing material during the sampling process to maintain the stability of the undisturbed soil and the initial structure of the particle skeleton. However, the strength of paraffin is low and cannot withstand the disturbance during transportation, and it is easily damaged. damage, resulting in the loss of the original soil during transportation; at the same time, during the unsealing process of paraffin, the paraffin is usually hot-melted into liquid wax to separate it from the original soil. However, because the wax liquid has a certain viscosity and the wax liquid is extremely It is easy to solidify, making the separation process complicated and the undisturbed soil easy to lose.

In view of this, the present invention proposes a sampling and shear strength testing method that maintains the original structure of the spoil soil. During the sampling process, the copolymer material prepared on site is used to seal the sampling site. Therefore, during the sampling process, The copolymer material is used for sealing to obtain the spoil soil sample. Since the copolymer material has high shear strength after solidification, it is not easily damaged during transportation and avoids the loss of the original sample. At the same time, due to the preparation of the copolymer material in the present invention Pure water is added in the process. During the drying process, the water in the copolymer material is taken away, causing the copolymer material to form flakes after drying. The separation process is simple and avoids the loss of the original soil.

The sampling and shear strength testing method of maintaining the original structure of the spoil soil mass according to the present invention will be described in detail below with reference to the accompanying drawings and examples.

Referring to Figure 1, Figure 1 shows a step flow chart of a sampling method for maintaining the original structure of spoil soil provided by an embodiment of the present invention. As shown in Figure 1, the method includes:

S101, prepare an acrylamide-acrylic acid copolymer from a mixture of pure water, glycerin, acrylamide and acrylic acid with a mass ratio of 1:2:4-8:2-4 under water bath heating conditions.

Among them, acrylamide-acrylic acid copolymer is a copolymer material. The copolymer material is a type of gel with strong hydrophilicity and a three-dimensional network structure. Therefore, based on the strong hydrophilicity of the copolymer material, adding pure water during the preparation process can make the copolymer material in a swollen state; heating and drying the copolymer material can dehydrate the copolymer material that was originally in a swollen state, causing the copolymer material to dry out. Forming flakes, the copolymer material can be easily separated from the soil sample; in addition, the copolymer material in the swollen state still has high shear strength and is not easily damaged during the transportation of the undisturbed soil. Therefore, the copolymer material is more convenient during the undisturbed soil sampling process. The best sealing material.

In the embodiment of the present invention, considering the real-time nature of sampling spoil soil at the project site, acrylamide-acrylic acid copolymer is selected as the sealing material of the undisturbed soil. This is because acrylamide-acrylic acid can be prepared quickly and the reaction conditions are not strict. Usually, the copolymerization process of acrylamide and acrylic acid can be completed by heating in a water bath at a temperature of 50 to 70°C for 10 to 20 minutes to obtain acrylamide. -Acrylic copolymer, fast reaction and low temperature, suitable for on-site operations.

At the same time, in order to avoid the loss of spoil soil samples during transportation, it is necessary to prepare copolymer materials with higher shear strength. Therefore, the mass ratio of pure water, glycerol, acrylamide and acrylic acid is controlled at 1: Between 2:4-8:2-4, an acrylamide-acrylic acid copolymer material with higher strength is obtained.

Preferably, pure water, glycerol, acrylamide and acrylic acid with a mass ratio of 1:2:6:3 are used to prepare the copolymer material. Under this mass ratio, the strength of the prepared copolymer material is 8MPa, which can effectively Avoid damage during transportation.

In the embodiments of the present invention, there are no specific requirements for the molecular weight of the prepared acrylamide-acrylic acid copolymer, as long as it can form a copolymer material with a certain strength, wherein the strength of the copolymer material is above 3 MPa, and above this strength, the copolymer material is It is not easy to be damaged during transportation, which will lead to the loss of spoil soil samples.

S102. In the gentle part of the spoil slope, select a spoil plane with a preset size and shape for smoothing to facilitate sampling.

Wherein, the preset size and shape are determined according to the testing requirements for the spoil soil sample.

Specifically, when obtaining the spoil soil sample, the sampling is carried out according to the size of the required sample, that is, the sampling size is determined based on the size of the sample required for the original spoil soil sample test. At the same time, since it is necessary to use copolymerization on the surface of the sample The material is sealed, so a part of the size needs to be reserved as a filling tape. Therefore, when selecting the spoil soil plane for sampling, it is necessary to delineate a slightly larger range of the spoil soil sample for sampling. Among them, the shape of the sample is also determined according to the test needs. If the test needs to be cylindrical, cylindrical spoil soil is dug out. If a rectangular parallelepiped is required, rectangular parallelepiped spoil soil is dug out. There is no specific limit in the present invention. For example, when performing a direct shear test on a spoil soil sample, the size of the excavated spoil soil sample is determined based on the size of the shear box in the direct shear instrument used to test the spoil soil sample, and then the test is carried out based on this size. When collecting waste soil samples, the width of the injection tape is not specifically limited in the present invention, as long as the waste soil samples can be wrapped.

S103, define an injection tape on the leveled spoil soil plane, and evenly inject a copolymer material composed of the acrylamide-acrylic acid copolymer into the injection tape until a preset depth is reached.

In the embodiment of the present invention, after selecting the spoil soil plane for sampling, a certain range of injection tape is defined on the spoil soil plane to increase the strength of the spoil soil in the injection tape through the injected copolymer material, thereby achieving Sealing effect on the specimen.

A certain width range of the outer surface of the spoil soil sample is used as an injection tape, and the liquid copolymer material is evenly injected onto the surface of the spoil soil. Since the spoil soil has a porous structure with accumulation of particles, the acrylamide-acrylic acid copolymer can penetrate from the pores. Enter to harden part of the spoil soil to seal the internal spoil soil and prevent the internal spoil soil from being disturbed. Among them, the preset depth is the depth required for glue injection. In order to achieve the sealing effect of the spoil soil, the preset depth is generally set to 1.1-1.2 times the height of the spoil soil sample, so that the spoil soil test The sample side surface is completely covered.

S104: After the copolymer material solidifies, dig out the spoil soil around the injection tape to obtain a sealed spoil soil sample.

Specifically, acrylamide-acrylic acid copolymer forms a gel-like substance after cooling, that is, it forms a solid copolymer material. Therefore, when acrylamide-acrylic acid is not cooled and solidified, it needs to be injected into the injection tape so that it can be solidified as a fluid. The form is filled into the set outer layer of the injection tape of the spoil soil sample, and then after the acrylamide-acrylic acid is cooled, the outer layer of the injection tape is hardened to seal the spoil soil sample.

After the copolymer material solidifies, a spoil soil sample with a certain strength on the surface is formed. At this time, the spoil soil on the periphery of the injection tape is dug out to obtain a sealed spoil soil sample.

In some embodiments, considering that sealing only the side of the spoil soil may still be disturbed during transportation, after digging out the spoil soil around the injection tape, part of the copolymer material at the bottom of the spoil soil sample is cut off , to inject copolymer material into the bottom surface of the spoil soil sample. After the copolymer material solidifies, the bottom surface is smoothed to reinforce the bottom surface of the spoil soil sample.

The sampling method provided by the embodiment of the present invention to maintain the original structure of the spoil soil body is to prepare a copolymer material, and before it is cooled, inject the copolymer material into the injection tape demarcated by the sample, so that the solid formed after cooling can The original sample is completely wrapped to form a sealed spoil soil sample. Therefore, the original sample is wrapped with a higher-strength copolymer material as the sealing material to avoid the loss of the original sample due to insufficient strength during transportation. , at the same time, since the copolymer material after absorbing water can be directly dehydrated by drying it, and then form shriveled flakes, since the shriveled flakes are weak in strength, at this time, just dig out the original part of the adhesive tape to obtain the remaining waste. For samples with the original structure of the spoil, the method of removing the sealing material is simple and easy. Therefore, using the sampling method provided by the embodiment of the present invention can maintain the original structure of the spoil and avoid the original sample being transported during transportation. loss and easy separation of the mounting material and the original sample during the testing stage.

Referring to Figure 2, Figure 2 shows a step flow chart of a sampling method for maintaining the original structure of spoil soil provided by yet another embodiment of the present invention. As shown in Figure 2, the method includes:

S201: Add the glycerin, the acrylic acid and the acrylamide to the pure water in sequence, stir and mix to obtain a mixed liquid.

Specifically, in order to fully dissolve various components, after adding pure water, glycerol and acrylic acid, the mixture is continuously stirred, and acrylamide is added while stirring, so that acrylic acid and acrylamide are fully mixed. In the embodiments of the present invention, the purity of the acrylamide is above 99%, the purity of the acrylic acid is above 99%, and the purity of the glycerol is above 95%.

S202, add an initiator to the mixed solution, stir and heat in a water bath maintaining a temperature of 50 to 70°C for 10 to 20 minutes, to obtain the acrylamide-acrylic acid copolymer.

In the embodiment of the present invention, the mass ratio of initiator to acrylamide is 1:5-1:10, and the initiator includes any one of persulfate and azo compound.

Preferably, the mass ratio of initiator to acrylamide is 1:5, which can obtain a copolymer material with higher strength and save materials at the same time.

Preferably, the temperature is controlled at 60°C, and the water bath heating time is preferably 10 minutes. The water bath heating time can be appropriately increased according to the acrylamide content, but it should not exceed 20 minutes. In order to sample the on-site spoil soil in a timely manner, the temperature can be controlled slightly higher during the preparation process to obtain copolymer materials quickly to meet on-site needs.

Among them, the main process of generating copolymer material-acrylamide-acrylic acid copolymer, acrylic acid and acrylamide/> Copolymerization reaction:

.

S203. In the gentle part of the spoil slope, select a spoil plane with a preset size and shape for smoothing to facilitate sampling.

Wherein, the preset size and shape are determined according to the testing requirements for the spoil soil sample.

S204, define an injection tape on the leveled spoil soil plane, and evenly inject a copolymer material composed of the acrylamide-acrylic acid copolymer into the injection tape until a preset depth is reached.

In the embodiment of the present invention, the preset depth is the depth required for glue injection. In order to achieve the sealing effect of the spoil soil, the preset depth is generally even 1.1-1.2 times the height of the spoil soil sample, so as to achieve the sealing effect of the spoil soil. The side surface of the spoil soil sample is completely covered; the width of the injection tape is generally 1/10-1/6 of the width of the spoil soil sample; within this range, the copolymer material used as the sealing material will not be too thin, so that The spoil soil sample is disturbed during transportation, which causes the initial structure of the particle skeleton of the spoil soil sample to change. It will not be too thick, resulting in material waste or a long solidification time of the copolymer material.

Since the excavated spoil soil sample and the injection tape are related to the size of the sample required for the test, the size of the excavated spoil soil sample and the injection of acrylamide-acrylic acid copolymer were confirmed based on the size of the test instrument. The width of the tape, such as when performing a direct shear test, is determined based on the size of the sample that the direct shear instrument can hold.

For example, if the direct shear box is a 17cm × 18cm × 20cm rectangular parallelepiped, then when sampling, select a spoil soil slope with a height of more than 20cm, and its top area is more than 20cm × 20cm. At this time, the slope should be flattened first. The flat surface of the top surface of the sample is used for glue injection. The specific size of the flat plane used for glue injection is determined according to the size of the injection tape. If the required width of the injection tape is 3cm, the length and width of the flat plane should be larger than that of the undisturbed soil sample. The extra 3cm in width will be used as an injection tape from the outer surface to a depth of 3cm to inject acrylamide-acrylic acid copolymer. As a result, the surface strength of the spoil soil sample was increased by injecting acrylamide-acrylic acid copolymer onto the surface to prevent the internal spoil soil from being disturbed.

Specifically, the process of uniformly injecting liquid acrylamide-acrylic acid copolymer into the spoil soil sample is: using a glue injection equipment with a pore pressure probe, uniformly injecting the copolymer material into the injection tape. The injection amount and depth of material are controlled by the pore pressure probe; during the glue injection process, the glue injection equipment is heated to maintain the fluidity of the acrylamide-acrylic acid copolymer.

For example, when injecting glue into the injection tape, the reaction-completed acrylamide-acrylic acid copolymer is first injected into the glue injection equipment with a pore pressure probe; at this time, the acrylamide-acrylic acid copolymer has not yet cooled down to allow it to It can be injected into glue injection equipment in liquid state.

Then, the glue injection equipment with a pore pressure probe is used to evenly inject the copolymer material into the injection tape. During the injection process, the pore pressure changes of the injection tape are monitored through the pore pressure probe, and the copolymer material is adjusted based on the changes. The injection amount; and, the injection depth of the copolymer material is controlled through the pore pressure value, so that the copolymer material can be evenly injected into the injection tape and reach the preset depth.

In the specific implementation, the horizontal and vertical pore pressure probes are moved in the injection tape to enable the copolymer material to diffuse in the injection tape. It should be noted that since the copolymer material will solidify and lose fluidity after cooling, the glue injection equipment needs to be kept heated during the glue injection process so that the copolymer material can be injected into the pores of the spoil soil in the form of liquid.

S205: After the copolymer material solidifies, dig out the spoil soil around the injection tape to obtain a sealed spoil soil sample.

After the acrylamide-acrylic acid copolymer is cooled, the copolymer material formed - acrylamide-acrylic acid copolymer supports the voids of the surface spoil soil and improves its surface strength. Therefore, the acrylamide-acrylic acid copolymer improves the strength and avoids spoilage. The soil sample is disturbed so that the original sample can be obtained.

The sampling method provided by the embodiment of the present invention to maintain the original structure of the spoil soil body is to prepare a copolymer material and inject the copolymer material into the surface injection tape of the spoil soil before it is cooled, so that the solid formed after cooling can be filled The pores in the tape are filled to form a spoil soil sample sealed with a copolymer material. Therefore, the spoil soil sample is hardened and wrapped by using a higher-strength copolymer material as the sealing material to avoid damage caused by insufficient strength during transportation. In the case of loss of the original sample, at the same time, drying the copolymer material after absorbing water can directly dehydrate it, thereby forming shriveled flakes. Since the dried flakes are weak in strength, the original sample of the tape-injected part is directly cut off at this time. A test sample that maintains the original structure of the spoil soil can be obtained, and the method of removing the sealing material is simple and easy. Therefore, by using the sampling method provided by the embodiment of the present invention, while maintaining the original structure of the spoil soil, it can also avoid The original sample is lost during transportation and it is easy to separate the sealing material and the original sample during the testing stage.

Referring to Figure 3, Figure 3 shows a step flow chart of a shear strength testing method provided by an embodiment of the present invention. As shown in Figure 3, the method includes:

S301, prepare an acrylamide-acrylic acid copolymer from a mixture of pure water, glycerin, acrylamide and acrylic acid with a mass ratio of 1:2:4-8:2-4 under water bath heating conditions.

Preferably, an acrylamide-acrylic acid copolymer is prepared from a mixture of pure water, glycerol, acrylamide and acrylic acid with a mass ratio of 1:2:6:3, and the strength of the acrylamide-acrylic acid copolymer obtained can be Reach 8MPa.

S302. In the gentle part of the spoil slope, select a spoil plane with a preset size and shape for smoothing to facilitate sampling.

Wherein, the preset size and shape are determined according to the testing requirements for the spoil soil sample.

S303, define an injection tape on the leveled spoil soil plane, and evenly inject a copolymer material composed of the acrylamide-acrylic acid copolymer into the injection tape until a preset depth is reached.

S304: After the copolymer material solidifies, dig out the spoil soil around the injection tape to obtain a sealed spoil soil sample.

S305, use a hot air dryer to degumm the sealed spoil soil sample.

In the embodiment of the present invention, since the indoor direct shear test method is used to test the shear strength of the undisturbed soil, after the spoil soil sample sealed with the copolymer material is obtained, the spoil soil sample is transported to the laboratory for direct shearing. During the test, specifically, when loading the spoil soil sample into the transport box, a cushioning air bag was filled in the gap between the original soil and the transport box to reduce disturbance to the original soil during transportation.

When conducting the test, the original sample is first degummed; specifically, the hot air dryer is run clockwise around the spoil soil sample sealed with the copolymer material to heat and dry each part of the copolymer material. Dry so that the copolymer material loses strength.

Since pure water is added during the preparation of the copolymer material, the copolymer material actually used as a sealing material is in a swollen state. Therefore, when the copolymer material is heated and dried, the copolymer material will form dry flakes due to the loss of water. When the waste material is mixed with the copolymer material, the part of the waste soil mixed with the copolymer material can be cut off to obtain the waste soil that maintains the original structure, that is, the waste soil remains in its original shape. Therefore, the degumming process is simple and easy. Among them, since the copolymer material is a flammable material, when heating and drying the copolymer material, be careful to keep a certain distance between the hot air dryer and the copolymer material to prevent the copolymer material from igniting. In the embodiment of the present invention, the surface of the spoil soil sealed with the copolymer material is kept at a distance of 15 cm from the hot air dryer for heating and drying.

S306. After cutting off the part containing the copolymer material from the degummed spoil soil sample, place it in a direct shear instrument to perform a direct shear test to test the shear strength of the spoil soil sample. .

In the embodiment of the present invention, after cutting off the part containing the copolymer material in the spoil soil sample, a complete spoil soil sample without impurities can be obtained for shear strength testing.

In some embodiments, in order to study the structure of the spoil soil sample, before performing a shear strength test on the spoil soil sample, a geotechnical CT scan can be performed after degumming to obtain the spoil soil sample. The parameters such as initial pore parameters, particle morphology and particle contact relationship are then conducted, and then a direct shear test is conducted to test the shear strength of the spoil soil sample.

Specifically, a direct shear test was performed on the spoil soil sample. The direct shear test was performed in a direct shear instrument. The specific method includes:

Place the degummed spoil soil sample in a direct shear shear box so that the bottom of the spoil soil sample is located in the lower shear box of the specimen. Install the upper shear box, upper shear cover plate, and Ball bearings, loading plates, jack piston, load-bearing top plate and horizontal loading device;

Conduct a direct shear test, start loading normal force and tangential force, and record the tangential force and tangential displacement during the loading process;

Based on the tangential force and tangential displacement, the shear strength of the spoil soil specimen was determined.

For example, referring to Figure 4, Figure 4 shows a schematic structural diagram of a direct shear instrument used for a direct shear test in an embodiment of the present invention. As shown in Figure 4, the direct shear instrument consists of a sample lower shear box 100, and a test It consists of a horizontal loading device 200 connected to the lower shear box 100, an upper shear box 300 corresponding to the lower shear box 100, a connection structure 400 for the upper shear box and a vertical loading device 500.

The horizontal loading device 200 includes a pull rod 210, a first pull ring 220, a second pull ring 230 and a horizontal drive motor 240. One end of the horizontal drive motor 240 is connected to the support surface, and the other end is connected to the pull rod 210 through the first pull ring 220. , the other end of the pull rod 210 is fixed to the second pull ring 230, and the pull rod 210 is connected to the outer wall of the lower shear box 100 of the sample through the second pull ring 230. The transmission system composed of the pull rod and the pull ring is relatively flexible and can reduce test errors.

The vertical loading device 500 includes a ball head 510, a loading plate 520, an upper ball bearing 530 and a vertical drive motor 540. The upper side of the vertical drive motor 540 is fixed to the supporting surface, and the lower output end is connected to the ball head 510 and can rotate. The ball head 510 The other side is connected to the top surface of the loading plate 520, and the bottom surface of the loading plate 520 is connected to the upper bottom plate 310 of the sample upper shear box 300 through the upper ball bearing 530.

During the specific implementation, the degummed undisturbed soil sample is loaded into the installed lower sample shearing box 100, and then the upper sample shearing box 300, the upper sample shearing box enclosure 320, and the sample are assembled. Upper shear box side plate 330, and coat the inner wall of the shear box with a layer of petrolatum on the sample. Place the upper shearing box 300 on the sample with the open end of the upper shearing box side plate 330 facing downward, place the lower shearing box 100 on the sample and the surface of the original sample, and then install the upper shearing box 300 on the sample. Upper base plate 310.

Place the sample lower shear box 100 and the sample upper shear box 300 filled with the original sample on the lower ball bearing 110. At this time, it should be ensured that the sample lower shear box 100 and the sample upper shear box 300 are aligned. Place it on the lower ball bearing 110 to avoid eccentric stress due to position error.

The lower shear box 100 of the sample is connected to the horizontal loading device 200 , and the upper shear box 300 of the sample is connected to the upper shear box connection structure 400 of the sample through the bearing 410 . A loading plate 520 and an upper ball bearing 530 are provided on the outside of the bottom of the upper shear box 300 on the sample, and then the vertical loading device 500 is connected.

After installing the equipment, start the direct shear test. First, remove the upper sample shearing box side plate 330 of the sample upper shearing box 300, then load the vertical drive motor 540, and load the horizontal drive motor 240, so that the sample lowers the shear box. 100 is displaced in a second direction at a preset speed, wherein the second direction is a direction approaching the horizontal driving motor 240 .

Record the power of the vertical drive motor 540 and the horizontal drive motor 240. The power can be used to calculate the stress of the shear box and calculate the shear strength of the original sample.

In the embodiment of the present invention, paraffin is also used to obtain the spoil soil sample. After the paraffin-sealed spoil soil sample is unsealed, the obtained undisturbed soil is subjected to a direct shear test using the same direct shear instrument. The test results are as follows As shown in Figure 5, the figure shows the shear strength curves of samples obtained by sealing with paraffin and sealing with copolymer materials; among them, the curve corresponding to the hydrogel method is provided for the embodiment of the present invention. The shear strength curve corresponding to the original sample obtained using the copolymer material sampling method.

Judging from the test results, although the original sample of spoil soil obtained by wax sealing method maintains most of the original structure of the original sample, the direct shear test results are affected by the damage of part of the initial structure. Under high shear stress, that is, In the case of 300KPa and 400KPa, the shear strength is slightly lower than the original sample obtained by the copolymer material method. At the same time, because the wax sealing method cannot completely remove the wax liquid during the degumming process, it will eventually cause the melted wax liquid to re-solidify. In the later stage of shearing, there will be a sudden increase and decrease in stress. This is because the sheared part at this time It is the cement of paraffin undisturbed soil.

In the embodiment of the present invention, the direct shear test of the reshaped sample was also compared. The test results are shown in Figure 6, which shows the shear strength curve of the sample sealed with copolymer material and the reshaped sample. Among them, the curve corresponding to the hydrogel method is the shear strength curve corresponding to the original sample obtained by the sampling method of the copolymer material provided in the embodiment of the present invention. Judging from the test results, the reshaped sample of spoil soil completely destroyed the initial structure of the spoil soil during the sampling and sample preparation process. The regularity during the shearing process was poor, and the peak stress was generally lower than the test results of the original sample. .

Taking shear strength (peak stress) as the ordinate and vertical pressure (normal pressure) as the abscissa, draw the relationship curve between shear strength and vertical pressure. The angle between the straight line and the abscissa is the internal friction angle of the spoil soil, and the intercept of the straight line on the ordinate axis is the cohesion of the spoil soil. The plotted shear strength relationship curve is shown in Figure 7, in which the curve corresponding to the hydrogel method is the shear strength curve corresponding to the original sample obtained by the sampling method using the copolymer material provided in the embodiment of the present invention. The figure shows the shear strength relationship curve of the specimens sealed with copolymer materials and the reshaped specimens. Judging from the results, the spoil soil obtained by the copolymer material method maintains the original structure of the original sample, the cohesion obtained is lower than that of the wax sealing method but higher than that of the reshaped sample, and the internal friction angle is higher than that of the wax sealing method and the reshaped sample. This allows us to clearly understand the mechanical properties of the soil sample by using the copolymer material method to obtain the original sample in actual engineering.

The shear strength testing method provided by the embodiment of the present invention uses copolymer material to seal the spoil soil obtained during the sampling process. Thanks to the higher strength of the copolymer material, the undisturbed soil can be prevented from being disturbed during transportation, thereby preventing The original soil is lost during transportation. At the same time, because the copolymer material can form brittle flakes after heating and drying, the unsealing process of the sealing material is simple and easy, and the original soil will not be lost during the unsealing process, which avoids The loss of the original sample leads to inaccurate shear strength testing, and the complicated unsealing process of the sealing material results in a complicated and long test process.

The above descriptions are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included in the present invention. within the scope of protection;

For the method embodiments, for the sake of simple description, they are all expressed as a series of action combinations. However, those skilled in the art should know that the present invention is not limited by the described action sequence, because according to the present invention, some steps Other orders or simultaneous steps are possible. Secondly, those skilled in the art should also know that the embodiments described in the specification are all preferred embodiments, and the actions and components involved are not necessarily necessary for the present invention.

The above is a detailed introduction to the sampling and shear strength testing methods for maintaining the original structure of the waste soil body provided by the present invention. Specific examples are used in this article to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only It is used to help understand the method and its core idea of the present invention; at the same time, for those of ordinary skill in the field, there will be changes in the specific implementation and application scope according to the idea of the present invention. In summary, this The content of the description should not be construed as limiting the invention.

Claims (9)

1. A sampling method that maintains the original structure of spoil soil, characterized in that the method includes: Preparing a mixture of pure water, glycerin, acrylamide and acrylic acid with a mass ratio of 1:2:4-8:2-4 under water bath heating conditions to prepare an acrylamide-acrylic acid copolymer; In the gentle part of the spoil slope, select a spoil plane with a preset size and shape for smoothing to facilitate sampling; wherein the preset size and shape are determined based on the testing requirements for the spoil sample; An injection tape is defined on the leveled spoil soil plane, and a copolymer material composed of the acrylamide-acrylic acid copolymer is evenly injected into the injection tape until a preset depth is reached; After the copolymer material solidifies, dig out the spoil soil around the injection tape to obtain a sealed spoil soil sample; wherein, the acrylamide-acrylic acid is uniformly injected into the injection tape. Copolymer materials composed of copolymers up to a preset depth including: Glue injection equipment with a pore pressure probe is used to evenly inject the copolymer material into the injection tape. The injection amount and depth of the copolymer material are controlled by the pore pressure probe; during the glue injection process, the The glue injection equipment is heated to maintain the fluidity of the copolymer material. 2. The sampling method for maintaining the original structure of the spoil soil according to claim 1, characterized in that the preset depth is 1.1-1.2 times the height of the spoil soil sample; the width of the injection tape is It is 1/10-1/6 of the width of the spoil soil sample. 3. The sampling method for maintaining the original structure of the waste soil body according to claim 1, characterized in that the mass ratio of pure water, glycerol, and propylene is 1:2:4-8:2-4. A mixture of amide and acrylic acid is prepared into an acrylamide-acrylic acid copolymer under water bath heating conditions, including: Add the glycerol, the acrylic acid and the acrylamide to the pure water in sequence, stir and mix to obtain a mixed liquid; wherein the pure water, the glycerol, the acrylamide and the acrylic acid The mass ratio is 1:2:4-8:2-4; An initiator is added to the mixed liquid, and after stirring, the water bath is heated at a temperature of 50 to 70°C for 10 to 20 minutes to obtain the acrylamide-acrylic acid copolymer; wherein the initiator includes persulfate and azo compounds. one of them. 4. The sampling method for maintaining the original structure of spoil soil according to claim 1 or 3, characterized in that the mass ratio of the pure water, the glycerol, the acrylamide and the acrylic acid is 1 :2:6:3. 5. The sampling method for maintaining the original structure of spoil soil according to claim 3, characterized in that the mass ratio of the initiator to the acrylamide is 1:5-10. 6. The sampling method for maintaining the original structure of the spoil soil according to claim 3, characterized in that the glycerin, the acrylic acid and the acrylamide are sequentially added to the pure water and stirred. Mix to obtain a mixture including: After adding the glycerol and the acrylic acid to the pure water, stir the pure water; While stirring, add the acrylamide to obtain the mixed liquid. 7. The sampling method for maintaining the original structure of the spoil soil according to claim 3, characterized in that the purity of the acrylamide is above 99%, the purity of the acrylic acid is above 99%, and the purity of the glycerol is above 99%. The purity is above 95%. 8. A shear strength testing method, characterized in that the method includes: The sealed spoil soil sample obtained by the sampling method described in any one of claims 1 to 7 is degummed using a hot air dryer; After the degummed spoil soil sample contains the part containing the copolymer material, it is placed in a direct shear instrument to perform a direct shear test to test the shear strength of the spoil soil sample. 9. The shear strength testing method according to claim 8, characterized in that the use of a hot air dryer for degumming includes: Run the hot air dryer clockwise around the sealed spoil soil sample to heat and dry each part of the copolymer material so that the copolymer material loses strength.