Method for determining lime or cement mixing amount of high liquid limit soil and lime or cement modification method thereof

Abstract

The application discloses a method for determining the lime or cement mixing amount of high liquid limit soil, which proposes a consistency model, a CBR value model and a CBR expansion model of high liquid limit soil after mixing with lime or cement, and the above models are fitted through different lime or cement mixing amount experiments, the lime or cement mixing amount when the consistency, CBR value and CBR expansion limit are satisfied is calculated by using the fitted models, and the maximum value is selected as the final lime or cement mixing amount of high liquid limit soil. The application also discloses a lime or cement modification method of high liquid limit soil, which proposes that the final lime or cement mixing amount cannot exceed the lime or cement mixing amount X0 corresponding to the consistency of 1.3 as a constraint condition after the final lime or cement mixing amount is determined, and when the final lime or cement mixing amount does not exceed X0, the modified high liquid limit soil is directly filled to form a roadbed, and when the final lime or cement mixing amount exceeds X0, water is added to the modified soil for filling, and the water adding amount is controlled to make the consistency of the modified soil controlled in [1.0, 1.3].

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of geotechnical engineering, and particularly relates to a method for determining the lime or cement content of high liquid limit soil and a lime or cement modification method of high liquid limit soil. BACKGROUND

[0002] High liquid limit soil refers to fine-grained soil with a liquid limit exceeding 50%. Such soil has high clay content, a large pore ratio, and strong hydrophilicity, and has strong water absorption and storage capacity. When used for embankment filling, it often has problems such as difficulty in compaction, low bearing capacity, and poor stability, and cannot form a stable foundation, which seriously affects the construction progress and service performance of roads. In southern China such as western Guangdong, Guangxi, and Yunnan, high liquid limit soil is widely distributed and other soil resources are scarce, and the source of filling material for roadbed filling has become a major challenge. People improve high liquid limit soil by adding lime or cement to it to make the high liquid limit soil meet the quality requirements of embankment filling. For example, the Chinese patent application with the application number CN201010019479.5, "Method for improving high liquid limit soil in roadbed engineering", uses unslaked lime for treatment. This invention can significantly reduce the water content of high liquid limit soil, reduce the liquid limit value and plasticity index, and thus improve the engineering quality of the roadbed. This patent gives the unslaked lime content as 5%, but does not involve a method for determining the lime content. The Chinese patent application with the application number CN201910000788.9, "Method for improving high liquid limit soil for roadbed filling", uses cement as the main solidifying material, and gypsum and UEA expanding agent to generate ettringite to provide expansion source and fill pores. This patent determines the solidifying agent content ratio through a series of steps: ordinary Portland cement 75%, gypsum 20%, and UEA expanding agent 5%. This patent determines the content ratio of the improved material according to experiments, and does not give the determination process. Yang and others in "Experimental study on road use characteristics of high liquid limit soil treated with lime" studied the strength change and physical and mechanical properties of high liquid limit soil treated with different doses of lime, and recommended the lime content with a certain degree of empiricism, but did not give a clear method for determining the lime content, and did not consider the compaction performance of the filling material after adding lime. When lime or cement is used to treat high liquid limit soil, the determination of the lime or cement content is an important technical link. If the lime or cement content is too large, the soil may be too dry and difficult to compact. If the content is too small, the CBR value (California Bearing Ratio) and CBR expansion of the soil may not meet the requirements, and the soil may be too wet and difficult to compact. Therefore, reasonably determining the lime or cement content is crucial for ensuring the treatment effect of high liquid limit soil, saving engineering cost, and improving the service level of roadbeds. However, there is currently a lack of a better method for reasonably determining the lime or cement content. SUMMARY

[0003] In order to solve the problems in the background art, the present application provides a method for determining the mixing amount of lime or cement for high liquid limit soil and a method for modifying the high liquid limit soil with lime or cement, so as to better guide the engineering application of lime or cement in treating high liquid limit soil.

[0004] The present application provides a method for determining the mixing amount of lime or cement for high liquid limit soil, comprising the following steps:

[0005] At least five different mixing amounts X of lime or cement are adopted 掺 The high liquid limit soil is mixed respectively to obtain modified soil samples, the liquid limit, plastic limit, and water content after mixing lime of the modified soil samples are measured respectively, and the consistency W of the modified soil samples is calculated respectively c ;

[0006] The modified soil samples are made into CBR test pieces, and the CBR value and CBR expansion amount of the CBR test pieces are obtained through testing;

[0007] The mixing amount X of lime or cement 掺 , the consistency W c , the CBR value and the CBR expansion amount are substituted into the consistency model: W c =a1X 掺 2 +b1X 掺 +c1, the CBR value model: CBR=a2X 掺 2 +b2X 掺 +c2, and the CBR expansion amount model: CBR expansion amount=a3X 掺 2 +b3X 掺 +c3, so as to fit the parameters a1, b1, c1, a2, b2, c2, a3, b3 and c3;

[0008] The consistency model, the CBR value model and the CBR expansion amount model after fitting are used to calculate the mixing amount X1 of lime or cement corresponding to W c =1.0, the mixing amount X2 of lime or cement corresponding to CBR value=3.9%, and the mixing amount X3 of lime or cement corresponding to CBR expansion amount=5.1%, and the maximum value X of X1, X2 and X3 is taken as the final mixing amount of lime or cement for the high liquid limit soil. max

[0009] Further, the natural consistency of the high liquid limit soil is [0.75, 1.0), or the CBR value is <3.9%, or the CBR expansion amount is >5.1%. The above indexes limit the selection criteria of the modifiable treated high liquid limit soil, so as to select the high liquid limit soil suitable for lime or cement modification treatment.

[0010] Further, the mixing amount X of lime or cement​掺 The value range is 0.5%-10%. This ensures that the lime or cement content can play a modifying role in high liquid limit soil while avoiding excessive lime or cement content that would lead to high costs and uneconomical practices.

[0011] Furthermore, the amount of lime or cement added X 掺 The values ​​of follow an arithmetic sequence.

[0012] Furthermore, the amount of lime or cement added X 掺 The values ​​of follow a geometric sequence.

[0013] Lime or cement content X 掺 The values ​​of follow an arithmetic or geometric sequence, which improves the accuracy of the model fitting process.

[0014] Furthermore, the liquid limit and plastic limit of the modified soil sample were obtained using a combined liquid and plastic limit determination method. Using the combined liquid and plastic limit determination method to determine the liquid phase and plastic limit of the modified soil sample is more efficient.

[0015] Furthermore, the moisture content of the modified soil sample was obtained by drying, resulting in high accuracy and reliable results.

[0016] The above-mentioned testing methods were used to conduct standardized tests on the modified soil samples to meet the roadbed construction standards.

[0017] On the other hand, the present invention also provides a method for modifying high liquid limit soil with lime or cement, wherein the final lime or cement content X of the high liquid limit soil is determined using the above-mentioned method for determining the lime or cement content of high liquid limit soil. max The final dosage of lime or cement is X. max After modification and treatment, the material is directly filled in.

[0018] Furthermore, it also includes the step of calculating W using the fitted consistency model. c =1.3 corresponds to the lime or cement dosage X0, when the final lime or cement dosage X max When the value exceeds X0, water is added to the modified soil before filling. The amount of water added is controlled so that the consistency of the modified soil with the final admixture Xmax is controlled within [1.0, 1.3].

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] The method for determining the lime or cement content of high liquid limit soil provided by the application proposes a consistency model, a CBR value model and a CBR expansion amount model of high liquid limit soil after mixing with lime or cement, the three models are fitted through different lime or cement content experiments, the lime or cement content when the consistency, CBR value and CBR expansion amount limits are met is calculated by using the three fitted models respectively, the maximum value is selected as the final lime or cement content of high liquid limit soil, the final lime or cement content obtained by the determining method comprehensively considers the strength, deformation characteristics and rolling construction performance of high liquid limit soil after modification, the final lime or cement content is more in line with the engineering practice of roadbed filling, the treatment effect of high liquid limit soil is ensured, the engineering cost is saved, and the service level of the roadbed is improved. Meanwhile, the classification index of high liquid limit soil that can be modified by using lime or cement is refined, so that it is more operable to judge whether the chemical modification treatment of lime or cement can be performed. In addition, the method for modifying high liquid limit soil by using lime or cement provided by the application proposes that the final lime or cement content cannot exceed the lime or cement content X0 corresponding to the consistency of 1.3 as a constraint condition, when the final lime or cement content does not exceed X0, the modified roadbed is directly filled after the modification treatment by using the final lime or cement content Xmax, when the final lime or cement content exceeds X0, the modified roadbed is filled after the modification treatment by using the lime or cement content X0 corresponding to the consistency of 1.3. max The modified soil is filled after adding water, and the amount of water is controlled to control the consistency of the modified soil in [1.0, 1.3] to adapt to the engineering standard of roadbed filling. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 is a curve graph of the consistency of the modified soil sample changing with the lime content;

[0022] Figure 2 is a curve graph of the CBR value of the CBR test piece changing with the lime content;

[0023] Figure 3 is a curve graph of the CBR expansion amount of the CBR test piece changing with the lime content. DETAILED DESCRIPTION

[0024] In order to more clearly and completely describe the technical solutions of the application, the application is further described in detail through specific embodiments below, unless otherwise defined, all technical and scientific terms used in the present application have the same meanings as those commonly understood by the person skilled in the technical field to which the application belongs.

[0025] A representative high liquid limit soil is taken from a highway construction site in a certain place in China. According to the Highway Soil Test Regulations (JTG3430-2020), the natural moisture content of the taken high liquid limit soil is obtained by using the drying method. The liquid limit and plastic limit of the taken high liquid limit soil are obtained by using the liquid-plastic limit combined determination method. The consistency of the taken high liquid limit soil is calculated. The optimum moisture content of the taken high liquid limit soil is obtained by using the wet heavy compaction method. According to the obtained optimum moisture content, the soil sample is prepared, and the CBR value and CBR expansion of the taken high liquid limit soil are obtained by using the CBR cylinder, immersion method and CBR test method in CBRTube, Immersion Method and CBR Test Method of Yang and Ping et al. in Classification Index System Research of Expansive Soil Used as Roadbed Filling, and the results are shown in Table 1.

[0026] Table 1 Physical properties and mechanical properties of the taken high liquid limit soil

[0027]

[0028] The present application proposes a high liquid limit soil filler classification index system as shown in Table 2. According to the test results, the natural consistency, CBR value and CBR expansion of the modified soil are determined, and the soil classification and treatment method are determined. When the natural consistency of the high liquid limit soil is [0.75, 1.0], or the CBR value is <3.9%, or the CBR expansion is >5.1%, the taken high liquid limit soil needs to be modified.

[0029] Table 2 Classification index of high liquid limit soil filler

[0030]

[0031] For the high liquid limit soil taken from the above-mentioned highway construction site in a certain place in China, the natural consistency is [0.75, 1.0], or the CBR value is <3.9%, or the CBR expansion is >5.1%, and the modified treatment needs to be carried out. Five kinds of lime content X 掺 : 2%, 4%, 6%, 8%, 10% are prepared, and modified soil samples are obtained. The modified soil samples are sealed and soaked for 24 hours, and the moisture content of the five kinds of modified soil samples is obtained by using the drying method according to the Highway Soil Test Regulations (JTG3430-2020). The liquid limit and plastic limit of the five kinds of lime content modified soil are obtained by using the liquid-plastic limit combined determination method, and the consistency W c of the five kinds of modified soil samples is calculated. The CBR value and CBR expansion of the CBR test piece are obtained by testing. The test results are shown in Table 3.

[0032] Table 3 Parameters of modified soil samples

[0033]

[0034] The lime content X 掺 , consistency Wc , CBR value and CBR expansion amount are substituted into the consistency model: W c =a1X 掺 2 +b1X 掺 +c1, CBR value model: CBR=a2X 掺 2 +b2X 掺 +c2, CBR expansion amount model: CBR expansion amount=a3X 掺 2 +b3X 掺 +c3, parameters a1, b1, c1, a2, b2, c2, a3, b3 and c3 are fitted, and the fitted models are as follows:

[0035] W c =0.0091X 掺 2 -0.0128X 掺 +0.954,

[0036] CBR=0.0673X 掺 2 +0.9796X 掺 +0.456,

[0037] CBR expansion amount=0.1155X 掺 2 -1.9329X 掺 +8.492.

[0038] The consistency curve of the modified soil sample with the change of lime content is shown in Figure 1 , the CBR value curve of the CBR test piece with the change of lime content is shown in Figure 2 , and the CBR expansion amount curve of the CBR test piece with the change of lime content is shown in Figure 3 .

[0039] The CBR value and CBR expansion amount of the high liquid limit soil after mixing with lime need to meet the index range of CBR value≥3.9% and CBR expansion amount≤5.1%, and at the same time, the consistency of the soil mixed with lime should meet consistency≥1. If the consistency of the modified high liquid limit soil is more than 1.3 due to too much lime content, the soil is too dry to be compacted, and cannot be directly used for filling, but can be filled after adding water.

[0040] The consistency model, CBR value model and CBR expansion amount model after fitting are used to calculate W cThe lime mixing amount X1 corresponding to CBR value =1.0 is 3.23%, the lime mixing amount X2 corresponding to CBR value =3.9% is 2.93%, the lime mixing amount X3 corresponding to CBR expansion value =5.1% is 1.99%, and the maximum value 3.23% among X1, X2 and X3 is taken as the final lime mixing amount X of the high liquid limit soil max And W c The lime mixing amount X0 corresponding to CBR value =1.3 is 6.91%, and the final lime mixing amount X of the high liquid limit soil is 3.23% max The final lime mixing amount 3.23% is less than 6.91%, so the high liquid limit soil can be modified and treated by the final lime mixing amount 3.23% and then used for embankment filling.

[0041] The cement modified and treated high liquid limit soil can also be operated by the above process.

[0042] The embodiments of the present application are described above in combination with the drawings, and the above specific embodiments are only illustrative but not restrictive, and those skilled in the art can make many forms under the inspiration of the present application without departing from the purpose of the present application and the scope protected by the claims, which all belong to the protection scope of the present application.

Claims

1. A method for determining the lime or cement content of high liquid limit soil, comprising the following steps: adopting at least five different lime or cement dosages X 掺 The high liquid limit soil is respectively mixed to obtain modified soil samples, the liquid limit, plastic limit, water content after mixing lime of the modified soil samples are respectively determined, and the consistency W of the modified soil samples is respectively calculated c ; CBR test pieces are made from the modified soil sample, and the CBR value and CBR expansion amount of the CBR test pieces are obtained through testing; the cement dosage X 掺 , the consistency W c , the CBR value and the CBR expansion amount are substituted into the consistency model respectively: W c =a1X 掺 2 +b1X 掺 +c1, the CBR value model: CBR=a2X 掺 2 +b2X 掺 +c2, the CBR expansion amount model: CBR expansion amount=a3X 掺 2 +b3X 掺 +c3, parameters a1, b1, c1, a2, b2, c2, a3, b3 and c3 are fitted; The W is calculated by using the fitted consistency model, CBR value model and CBR expansion model c X1 corresponding to the lime or cement content when the value of =1.0, X2 corresponding to the lime or cement content when the value of CBR=3.9%, X3 corresponding to the lime or cement content when the value of CBR expansion=5.1%, and X is the maximum value among X1, X2 and X3 max is the final lime or cement content of the high liquid limit soil.

2. The method of claim 1, wherein the method is characterized by: The natural consistency range of the high liquid limit soil is [0.75, 1.0), or the CBR value is < 3.9%, or the CBR expansion amount is > 5.1%.

3. The method of claim 1, wherein the method is characterized by: The lime or cement content X 掺 is in the range of 0.5-10%.

4. The method of claim 1, wherein the method is characterized by: The lime or cement content X 掺 is an arithmetic progression.

5. The method of claim 1, wherein the method is characterized by: The lime or cement content X 掺 The values of X form a geometric progression.

6. The method of claim 1, wherein the method is characterized by: The liquid limit and plastic limit of the modified soil sample are obtained by using a combined liquid and plastic limit determination method.

7. The method of claim 1, wherein the method is characterized by: The moisture content of the modified soil sample is obtained by using a drying method.

8. A method of lime or cement modification of high liquid limit soil, characterized by, The final lime or cement mixing amount X of the high liquid limit soil is determined by the method according to any one of claims 1-7 max The final lime or cement mixing amount X is determined by the method according to any one of claims 1-7 max The modified soil is directly filled.

9. The method of claim 8, wherein the high liquid limit soil is a clay soil. Further comprising the step of calculating W c =1.3, and when the final dosage X max maxof lime or cement exceeds X0, water is added to the modified soil for filling, and the amount of water is controlled so that the consistency of the modified soil with the final dosage X

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