Loess improvement filling material for collapse treatment as well as preparation method and application of loess improvement filling material

Abstract

The invention provides a loess improved filling material for collapse treatment. The loess improved filling material is prepared from the following raw materials in parts by weight: 2 parts of cement, 3 parts of bentonite and 100 parts of air-dried loess crushed materials. The preparation method comprises the following steps: naturally air-drying the building waste loess, crushing, sieving with a sieve with the aperture of 2mm, adding the cement and the bentonite, and stirring and mixing. The loess improved filling material is used for collapse filling engineering. The problems of environmental pollution and water and soil loss caused by resource utilization of the building waste loess and accumulation of the waste loess can be solved; the problem of high cement dosage in the existing loess modification technology is solved, carbon emission can be reduced, and pollution to environments such as underground water is reduced; the cement and the bentonite are mixed to modify the loess, so that the problem of material and construction technical cost caused by overhigh cement addition amount in the prior art is effectively reduced, and the problems of low water stability, long-term attenuation of strength and deformation, lack of coordination with surrounding soil and the like of the improved loess with low cement content are solved.

Description

Technical Field

[0001] The invention belongs to the technical field of filling materials, and in particular relates to a loess improved filling material for collapse control, a preparation method and an application thereof. Background Art

[0002] The random stacking and extensive filling of construction waste soil not only causes environmental pollution and soil erosion, but also causes harm to existing buildings. The resource utilization of construction waste soil is the fundamental way to solve the problem of construction waste soil. On the one hand, the resource utilization of construction waste soil can replace high-energy-consuming materials such as cement, sand and gravel, reduce carbon emissions, and on the other hand, it can reduce filling costs after scientific treatment, providing green, low-carbon and environmentally friendly material guarantees for the treatment of special soil foundation engineering diseases.

[0003] At present, the treatment of construction waste loess at home and abroad generally adopts the form of extensive filling. After filling, the soil body suffers from serious soil erosion, the slope becomes unstable and damaged, and the surrounding buildings are affected. Some research has been conducted on the use of modified loess as filling materials. Generally, physical, chemical and biological treatment methods are used for modification. Adding cement and lime is a common modification method. At present, when filling the modified loess materials, in order to pursue the strength of the soil body after filling, the proportion of cement and lime added is relatively high; small-scale filling projects generally use cement mortar, concrete and other materials for filling, without considering the coordination of filling materials or filling materials with the surrounding soil.

[0004] Based on the above analysis, it is necessary to utilize construction waste loess as a resource and conduct comprehensive and systematic modification research on it to obtain new loess filling materials that are low-carbon, environmentally friendly, have mechanical properties that meet engineering requirements, have good coordination and consistency with the surrounding soil, and have lower costs. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a loess improved filling material for collapse control and a preparation method and application thereof in view of the deficiencies of the above-mentioned prior art. The filling material solves the environmental pollution and soil erosion problems caused by the resource utilization of waste loess from construction and the accumulation of waste loess; it solves the problem of high cement addition in the existing loess modification technology, and can effectively reduce carbon emissions and reduce pollution to the environment such as groundwater; the present invention mixes cement and bentonite to modify the loess, effectively reducing the material and construction technology cost problems caused by excessive cement addition in the prior art, and solves the problems of weak water stability of loess after modification with low cement content, long-term attenuation of strength and deformation, and lack of coordination with the surrounding soil.

[0006] To solve the above technical problems, the technical solution adopted by the present invention is: a loess improved filling material for collapse control, which is made from the following raw materials in different weight portions and then optimized through experiments: 1 to 7 parts of cement, 1 to 5 parts of bentonite, and 100 parts of loess crushed material.

[0007] According to the test conclusion, preferably, a loess improved filling material for collapse control is made of the following raw materials in parts by weight: 2 parts of cement, 3 parts of bentonite, and 100 parts of loess crushed material.

[0008] The invention adopts cement and bentonite to improve loess. The addition of cement can improve the gelling property between particles, and the addition of bentonite can improve the particle grading and the bonding property between particles, thereby improving its engineering properties.

[0009] Preferably, the cement is ordinary Portland cement, and the bentonite is sodium bentonite.

[0010] The present invention also provides a method for preparing the above-mentioned loess improved filling material for collapse control, which method comprises:

[0011] S1. Naturally air-dry the construction waste loess, crush it, and pass it through a sieve with a pore size of 2 mm to obtain air-dried loess crushed material;

[0012] S2, adding cement and bentonite to the air-dried loess crushed material obtained in S1, stirring and mixing, to obtain loess improved filling material for collapse control.

[0013] Preferably, the water content of the air-dried loess crushed material in S1 is ≤5%.

[0014] The present invention also provides an application of the above-mentioned loess improved filling material for subsidence control, characterized in that the loess improved filling material for subsidence control is used for subsidence filling engineering.

[0015] Preferably, water is added to the loess improved filling material for collapse control until the water content is 16.3%, and the material is stirred evenly and then compacted and filled.

[0016] Compared with the prior art, the present invention has the following advantages:

[0017] The present invention can solve the environmental pollution and soil erosion problems caused by the resource utilization of waste loess from construction and the accumulation of waste loess; it can solve the problem of high cement addition in the existing loess modification technology, and can effectively reduce carbon emissions and reduce pollution to the environment such as groundwater; the present invention mixes cement and bentonite to modify the loess, effectively reducing the material and construction technology cost problems caused by excessive cement addition in the existing technology, and solves the problems of weak water stability of loess after modification with low cement content, long-term attenuation of strength and deformation, lack of coordination with surrounding soil, etc.

[0018] The present invention is further described in detail below with reference to the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1It is a schematic diagram of the loess structure and bentonite and cement filling bonding of Example 1 of the present invention. DETAILED DESCRIPTION

[0020] Example 1

[0021] 1. Mechanism of cement and bentonite improving loess in this embodiment:

[0022] Loess is silt, and its single-grain structure provides good structural conditions for the addition and improvement of cement and bentonite. Figure 1 . Loess particles are mainly composed of quartz and feldspar minerals, which provide a good bonding object for cement and bentonite. Adding cement to loess will cause bonding between loess particles, and the single particle structure of loess will be transformed into a granular structure and a clot structure, and the bonding strength between soil particles will be improved; bentonite with fine particles (2μm~10μm) has a strong water absorption and expansion property, which is easy to fill in the pores between loess particles, which can not only improve the grading of loess and increase the bonding strength between soil particles, but also reduce the porosity of loess, further improve the compactness of loess, and improve the water stability of loess particles. The water adsorbed by bentonite plays a positive role in the gelation of cement.

[0023] 2. Technical solution for improving loess subsidence filling materials with cement and bentonite

[0024] Cement and bentonite improved loess is mainly based on the "Standard for Geotechnical Test Methods" (GB / T50123-2019). The experimental research method is used to prepare samples by mixing the reshaped loess before improvement and different cement, bentonite contents and loess. Compaction test, disintegration test, permeability test, direct shear test, unconfined uniaxial compressive strength test and medium pressure consolidation test are carried out to test the engineering properties of cement and bentonite improved loess filling materials.

[0025] 1. Sample preparation and curing

[0026] The loess samples used in the test were taken from the west of Zhengzhou City. The loess in this area belongs to Q3 loess, which is slightly wet and mainly composed of powder particles. The single particle has a large pore structure, and a small amount of calcium crystals can be seen on the broken surface. The average natural moisture content of the original loess is 14.00% and the average natural density is 1.61g / cm by indoor standard test. 3 The maximum dry density ρ obtained by compaction test d =1.76g / cm 3 , the optimum moisture content w = 15.7%. The specific physical properties of loess are shown in Table 1.

[0027] Table 1 Main physical properties of loess

[0028]

[0029] Preparation of reshaped samples: The loess samples obtained from the on-site soil layer were naturally air-dried, crushed with a rubber hammer, and then passed through a 1mm pore size sieve. The soil was mixed according to the optimal moisture content w=15.7%, and then sealed and placed for more than 48 hours to ensure uniform moisture distribution for the preparation of reshaped samples.

[0030] Cement and bentonite used in the experiment: ordinary Portland cement, PO42.5; sodium bentonite, purchased from Sichuan Renshou Xingda Industry and Trade Co., Ltd.

[0031] Preparation of loess improved samples: The proportions were made according to cement addition of 0, 1%, 2%, 3%, 5%, and 7%, and bentonite addition of 0, 1%, 3%, and 5%. Samples were prepared according to the optimal moisture content and maximum dry density of each mix determined by the compaction test. The specific steps were as follows: the air-dried disturbed soil sample was crushed and passed through a 2mm sieve, cement and bentonite were added, and stirred evenly. According to the controlled mass method, the uniaxial compressive strength sample (φ39.1×80mm), direct shear test ring knife sample (φ61.8×20mm), penetration sample (φ61.8×40mm), disintegration sample (φ61.8×20mm) and compression sample (φ61.8×20mm) were prepared by the sample striking method and compaction method respectively.

[0032] The prepared samples were cured for 5 days, 15 days and 28 days for relevant tests. To unify the comparability of the test results, the samples at each curing stage were vacuumed and saturated, and then placed in water for 2 days before testing.

[0033] 2. Test results and analysis

[0034] (1) Optimal moisture content and maximum dry density

[0035] According to the standard compaction test method of the "Standard for Geotechnical Test Methods" (GB / T50123-2019), an electric compactor was used to compact soil samples with different proportions of loess, cement, and bentonite to determine the optimal moisture content and maximum dry density of each proportion. The results are shown in Table 2.

[0036] Table 2 Compaction test results of different cements and bentonites

[0037]

[0038] It can be concluded from Table 2 that with the increase of cement addition, the optimal moisture content of the soil gradually increases and the maximum dry density gradually decreases; under the same bentonite content conditions, with the increase of cement addition, the optimal moisture content of the soil gradually increases and the maximum dry density gradually decreases; under the same cement addition conditions, with the increase of bentonite addition, the optimal moisture content of the soil gradually increases and the maximum dry density gradually increases.

[0039] (2) Disintegration

[0040] According to the disintegration test method of the "Standard for Geotechnical Test Methods" (GB / T50123-2019), disintegration tests were carried out on loess improved by cement and bentonite at different curing times. The results are shown in Table 3.

[0041] Table 3 Disintegration of loess after being improved by different ratios of cement and bentonite

[0042]

[0043]

[0044] It can be concluded from Table 3 that with the increase of cement addition, the disintegration of the modified loess decreases. The loess with a ratio of 1% cement + 1% bentonite still has obvious disintegration, and the disintegration rate is above 19%. With the increase of bentonite addition, the disintegration rate increases, reaching 29.84% at 5% bentonite. When the cement content reaches 2%, the disintegration rate of the sample decreases significantly, falling below 3%. With the continued increase of cement addition, the disintegration rate of the sample decreases to below 1%, and the sample still maintains its integrity after being immersed in water for 30 minutes.

[0045] (3) Permeability

[0046] The permeability test was conducted according to the method of variable head permeability test in the Geotechnical Test Method Standard (GB / T50123-2019), and the instrument used was the TST-55 permeameter. The variable head permeability test was conducted on the samples of loess with different proportions of cement and bentonite added and cured for 28 days. The results are shown in Table 4.

[0047] Table 4 Permeability coefficient of loess improved by different ratios of cement and bentonite (d = 28)

[0048]

[0049]

[0050] It can be seen from Table 4 that the permeability coefficient of the soil decreases significantly with the increase of cement content, especially when the cement content is 2%, indicating that the addition of cement has a significant effect on reducing the permeability coefficient of the soil. Compared with the permeability coefficient of loess without cement and bentonite, the permeability coefficients of the soil with 1%, 2%, 3%, 5%, and 7% cement content are reduced by 6.9 times, 60.3 times, 157.1 times, 373.1 times, and 817.8 times, respectively, when 1% bentonite is added. The permeability coefficient of the soil decreases significantly with the increase of bentonite content. Compared with the permeability coefficient of loess without cement and bentonite, the permeability coefficients of the soil with 0%, 1%, 3%, and 5% bentonite content are reduced by 36.9 times, 60.3 times, 621.9 times, and 1456.1 times, respectively, when 2% cement is added. Adding bentonite can effectively reduce the permeability of loess.

[0051] (4) Shear strength

[0052] According to the direct shear test method in the Geotechnical Test Method Standard (GB / T50123-2019), the strain-controlled direct shear test was carried out on the improved loess after uniform saturation, and the shear strength index of loess with different proportions was obtained and shown in Table 5. It can be concluded from Table 5 that with the increase of cement content, the cohesion of loess with different proportions increases significantly, and with the increase of bentonite content, the internal friction angle of loess with different proportions is relatively maximum at 3%.

[0053] Table 5 Shear strength index of loess improved by different ratios of cement and bentonite (d=28)

[0054]

[0055]

[0056] (5) Unconfined uniaxial compressive strength

[0057] According to the method of unconfined uniaxial compressive strength test in the Geotechnical Test Method Standard (GB / T50123-2019), the unconfined uniaxial compressive strength test of the improved loess was carried out using a pressure testing machine, and the test results are summarized in Table 6. It can be clearly seen from Table 6 that adding cement and bentonite to loess can effectively improve its unconfined compressive strength. When the cement content is greater than 1, the compressive strength increases significantly. After the curing is completed, the compressive strength of 2% cement content + 3% bentonite content reaches 1069.5kPa.

[0058] Table 6 Unconfined compressive strength of loess samples improved by cement and bentonite

[0059]

[0060] (6) Compressibility

[0061] According to the consolidation test method in the "Standard for Geotechnical Test Methods" (GB / T50123-2019), a medium-pressure consolidation test was carried out on the samples cured for 28 days using a medium-pressure consolidation instrument. The compressibility index of the soil is shown in Table 7. It can be concluded from Table 7 that with the increase of cement and bentonite content in loess, the deformation of the improved loess gradually decreases, the compression coefficient decreases, and the compression modulus increases significantly.

[0062] Table 7 Compressibility of loess improved by different ratios of cement and bentonite (d=28)

[0063]

[0064] 3. Optimal solution for collapse filling materials

[0065] Through the test and analysis of the engineering properties of loess mixed materials improved by cement and bentonite, loess composite materials with different mix ratios show different engineering properties. As the filling requirement for the collapse pit after the collapse disaster occurs, on the one hand, it can ensure that the soil after filling meets the requirements of foundation soil water stability, bearing capacity and deformation, and on the other hand, it must maintain a certain coordination with the surrounding soil. In addition, as a large-volume filling material, its easy construction, low cost, and low carbon properties must also be considered. Based on this, through a comprehensive analysis of the test results of loess engineering property indicators with different mix ratios of cement and bentonite, the loess mixture formed by mixing the loess with a cement content of 2% and a bentonite content of 3% under the corresponding optimal moisture content conditions is finally selected as the filling material for collapse disasters. Its engineering property indicators are shown in Table 8.

[0066] Table 8 Engineering properties of collapse filling materials

[0067]

[0068] 4. Cement and bentonite improved loess collapse filling material preparation technology

[0069] Air-dry the abandoned loess from construction naturally until the moisture content is less than 5%. Crush (grind) it and pass it through a sieve with a pore size of 2 mm. Add 2% ordinary Portland cement and 3% sodium bentonite, and stir evenly (i.e. 100 parts of air-dried loess crushed material, 2 parts of cement, and 3 parts of bentonite). Add water at the optimal moisture content of 16.3%, stir evenly, and compact and fill it within 1 hour for the best result. The time from preparation to filling should not exceed 3 hours, and the compaction degree should be controlled above 94%. The filling material can be directly pre-mixed and prepared according to the on-site conditions and then directly filled, or it can be prepared in a factory on the production line.

[0070] 5. Cement and bentonite improved loess material collapse filling technology

[0071] Conduct a detailed survey of the collapsed pits to find out the cause, scope, depth, scale, etc. of the collapse, and calculate the volume of filling materials required for collapse control. Clean the loose soil in the collapsed pits. If there is water, pump out the water first. After cleaning, fill the prepared filling materials in layers. Each layer must be compacted (compacted) evenly, and the layered compaction (compacting) thickness is not more than 100cm. After each layer is compacted (compacted), the surface is scraped, and the next layer is compacted (compacted). The compaction degree of each layer is controlled to be above 94%. The soil after filling and compaction (compacting) is tested according to the different foundation requirements within the collapse range. The testing standards are based on relevant national standards or technical regulations. The improved loess collapse control filling materials in the present invention are used for collapse filling projects.

[0072] The present invention uses cement and bentonite to improve loess. The addition of cement can improve the gelling property between particles and improve its engineering properties. The improved loess material is mainly used for collapse filling engineering. After the improvement, the engineering properties of the filling soil after compaction mainly include strength, compressibility, permeability and water stability.

[0073] The above is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent change made to the above embodiment according to the technical essence of the invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A loess improved filling material for subsidence control, characterized in that: The invention is prepared from the following raw materials in parts by weight: 2 parts of cement, 3 parts of bentonite and 100 parts of air-dried loess crushed material.

2. The loess improved filling material for collapse control according to claim 1, characterized in that: The cement is ordinary Portland cement, and the bentonite is sodium bentonite.

3. A method for preparing the loess improved filling material for collapse control as claimed in claim 1 or 2, characterized in that: The method is: S1. Naturally air-dry the construction waste loess, crush it, and pass it through a sieve with a pore size of 2 mm to obtain air-dried loess crushed material; S2. Add cement and bentonite to the air-dried loess crushed material obtained in S1, stir and mix, and obtain loess improved filling material for collapse control.

4. The method according to claim 3, characterized in that The water content of the air-dried loess crushed material in S1 is ≤5%.

5. An application of the loess improved filling material for collapse control as claimed in any one of claims 1 or 2 or 2, characterized in that: The improved loess filling material for subsidence treatment is used for subsidence filling engineering.

6. The use according to claim 5, characterized in that: Water is added to the loess improved filling material for collapse control until the water content is 16.3%, and the material is stirred evenly and then compacted and filled.

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