Method for preventing and treating collapsing and freeze-thaw deformation of loess roadbed in seasonal frozen area

Abstract

The invention relates to a method for preventing and treating collapsing and freeze-thaw deformation of a loess roadbed in a seasonal frozen area, which comprises the following step of: curing loess by using xanthan gum to obtain cured loess of which the compaction degree is 90% and the collapsing coefficient delta s is less than 0.015. The method has the advantages of easily available raw materials, ecological environmental protection, low cost and simple construction method, can effectively eliminate loess freeze thawing and collapsing deformation, and is used for reinforcing loess site soil bodies with different collapsing grades.

Description

Technical Field

[0001] The invention relates to the technical field of environmental geotechnical engineering, and in particular to a method for preventing and controlling loess roadbed collapse and freeze-thaw deformation in seasonally frozen areas. Background Art

[0002] Northwest my country belongs to the seasonal frozen soil zone, and loess is widely distributed. Collapsible loess has low compressibility and high strength at low water content, but it will collapse when the soil meets water, resulting in a sudden increase in compressibility and a sudden drop in strength. The periodic freeze-thaw cycle will also change the structure of loess. The temperature change during the freeze-thaw cycle causes water migration, which leads to changes in the internal pores and structure of the loess, and even the reorganization of the internal structure of the loess. In addition, the freeze-thaw cycle will cause secondary collapse of the compacted loess, or even multi-level collapse, which will pose a serious threat to the stability of the loess foundation of buildings, roads, channels and other projects in frozen soil areas. Therefore, the research on the freeze-thaw and collapsible deformation treatment of loess has been widely concerned in engineering applications.

[0003] There are many methods for curing or treating loess to eliminate its freeze-thaw and collapsible deformation, such as the following methods: replacement method, strong tamping method, compaction method, chemical method, pre-immersion method and composite foundation method, etc. Although these methods are effective in treating loess, they not only consume a lot of materials and are costly in actual application, but the construction is greatly restricted by the site and construction period, and the applicability is limited for deep frozen soil and complex geological conditions. In addition, the most common and simplest method in current engineering practice is to use traditional materials such as lime and cement to solidify loess, which has a good curing effect. However, cement and lime solidified soil bodies will aggravate the trend of soil desertification in the northwest region due to their high alkalinity. At the same time, the carbon emissions of cement and lime raw material production are huge, which will cause irreversible damage to the environment. The use of microorganisms, other curing agents and other materials to solidify loess often still needs to be combined with cement for good results, and the cost is relatively high.

[0004] In view of the fact that most of the current methods for preventing and controlling loess roadbed subsidence and methods for preventing and controlling freeze-thaw deformation of loess roadbed in seasonal frozen soil areas can only solve the problem of one of the deformations, either subsidence or freeze-thaw, and that low-carbon, environmentally friendly, economical and simple prevention and control methods are still insufficient, there is an urgent need to develop a new treatment method that meets the current low-carbon and environmental protection requirements while being economical and easy to construct.

[0005] Xanthan gum is currently the largest-scale natural colloidal biopolymer with superior performance and wide applications. It has strong thickening and coagulation properties. With its superior properties, xanthan gum has been used to solidify sandy soil, laterite, expansive soil, silt and other soils, but there has been no report on the use of xanthan gum to eliminate the freezing and thawing and collapsing deformation of loess. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a method for preventing and controlling loess roadbed subsidence and freeze-thaw deformation in seasonally frozen areas with low cost and simple construction.

[0007] In order to solve the above problems, the present invention discloses a method for preventing and controlling the collapse and freeze-thaw deformation of loess roadbed in seasonally frozen areas, characterized in that: the method refers to solidifying the loess with xanthan gum, that is, obtaining a compaction degree of 90% and a collapse coefficient of d s <0.015 of solidified loess.

[0008] The solidified loess is prepared by the following method: S1: crush the loess, pass it through a 2 mm sieve, and then dry it at 105°C to constant weight to obtain the dried loess; S2: Add 0.5%, 1.0%, 1.5%, and 2.0% xanthan gum by weight to the dried loess, and stir evenly to obtain a dry mix; Add 14.0% water by weight to the dry mixture in S3, stir evenly, put into a sealed bag and seal for 24 hours to obtain solidified loess.

[0009] The minimum water replenishment height of the solidified loess is 20 mm.

[0010] Compared with the prior art, the present invention has the following advantages: 1. The present invention adopts xanthan gum as a solidifying material, which has good environmental friendliness, does not pollute soil and water, and is beneficial to the protection of the ecological environment. In addition, the use of xanthan gum to solidify loess can also reduce engineering construction costs and improve engineering quality.

[0011] 2. The present invention adopts the method of eliminating the collapsibility of loess by using xanthan gum, which solves the problem that collapsible loess will collapse when it encounters water and thus produce settlement. The indoor test results show that the collapsibility coefficient of solidified loess decreases with the increase of xanthan gum dosage (in the range of 0.5% to 2.0%). When the dosage of biopolymer is 0.5%, the collapsibility coefficient of solidified loess is d s is 0.011( d s <0.015), the collapsibility is eliminated.

[0012] 3. The present invention significantly reduces the temperature difference between the cold and warm peaks during the freeze-thaw cycle, with the temperature difference reduced by 24.4%, wherein the highest positive temperature remains consistent with that of unsolidified loess, and the lowest negative temperature increases by 3.5°C; the solidified loess after adding xanthan gum is 13.3% deeper than the loess freezing depth, and the freeze-thaw deformation of the loess caused by temperature change is eliminated after adding xanthan gum. The frost heave rate of solidified loess with a xanthan gum content of 0.5% is reduced by 25%, and the thaw settlement coefficient is reduced by 91.6%; during the freeze-thaw cycle, the moisture migration of the solidified loess after adding xanthan gum is significantly reduced, and the moisture migration at H=140mm is reduced from 10% to 0.5%, and the moisture remains basically unchanged before and after freeze-thaw.

[0013] 4. The present invention has the advantages of easy availability of raw materials, environmental protection, low cost and simple construction method, and can reinforce loess soil in different collapsible grades. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The specific implementation modes of the present invention are further described in detail below in conjunction with the accompanying drawings.

[0015] Figure 1 This is a graph showing the relationship between the xanthan gum dosage and the collapsibility coefficient in the comparative example and the examples of the present invention.

[0016] Figure 2 The figure is a graph showing the relationship between the xanthan gum dosage and the frost heave rate (a) and thaw settlement coefficient (b) in the comparative example and the example of the present invention.

[0017] Figure 3 This is a graph showing the relative height changes of freeze-thaw cycle samples with different xanthan gum dosages in the comparative examples and embodiments of the present invention. DETAILED DESCRIPTION

[0018] A method for preventing and controlling loess roadbed subsidence and freeze-thaw deformation in seasonally frozen areas, the method comprising solidifying the loess with xanthan gum to obtain a compaction degree of 90% and a subsidence coefficient of 90%. d s <0.015 of solidified loess.

[0019] Solidified loess is prepared by the following method: S1: crush the loess, pass it through a 2 mm sieve, and then dry it at 105°C to constant weight to obtain the dried loess; S2: Add 0.5%, 1.0%, 1.5%, and 2.0% of xanthan gum by weight to the dried loess, and stir evenly to obtain a dry mix; Add 14.0% water by weight to the S3 dry mix, stir evenly, and place in a sealed bag for 24 hours to ensure uniform distribution of water, thus obtaining solidified loess. The amount of water added is calculated based on the optimal moisture content of loess.

[0020] Loess will collapse when it comes into contact with water and during freeze-thaw periods. After being solidified by xanthan gum, the collapsibility and freeze-thaw properties of the loess are eliminated, and the minimum water replenishment height of the solidified loess is 20mm.

[0021] The loess selected in the following case is collapsible loess, which was taken from the soil site in Tongxin County, Ningxia Hui Autonomous Region. It is light yellow in color, has a low natural moisture content, is uniform in texture, has large pores, and has a small amount of plant roots. The sampling depth is 1.5m. By conducting indoor geotechnical experiments on loess, its basic physical parameters were obtained, including the optimal moisture content ω=14.0%, the maximum dry density r max =1.741 g / cm 3 .

[0022] Example 1 Add 0.5% of xanthan gum to 1kg of dried loess at a rate of 0.5% by mass of the loess, stir evenly for 5 minutes and bag for later use. Then weigh out 14.0% of the mass of the dry mixture of water, stir the dry mixture and water evenly, put them into a sealed bag and seal for 24 hours to obtain solidified loess.

[0023] Example 2 Add xanthan gum at 1.0% of the mass of loess to 1kg of dried loess, stir evenly for 5 minutes and bag for later use. Then weigh out water that accounts for 14.0% of the mass of the dry mixture, stir the dry mixture and water evenly, and after stirring, put them in a sealed bag and seal them for 24 hours to obtain solidified loess.

[0024] Example 3 Add 1.5% of xanthan gum to 1kg of dried loess at a rate of 1.5% by mass of the loess, stir evenly for 5 minutes and bag for later use. Then weigh out 14% of the mass of the dry mixture of water, stir the dry mixture and water evenly, and after stirring, put them in a sealed bag and seal for 24 hours to obtain solidified loess.

[0025] Example 4 Add 2.0% of xanthan gum to 1kg of dried loess at a rate of 2.0% by mass of the loess, stir evenly for 5 minutes and bag for later use. Then weigh out 14.0% of the water by mass of the dry mixture, stir the dry mixture and water evenly, and after stirring, put them in a sealed bag and seal for 24 hours to obtain solidified loess.

[0026] Comparative Example 1 kg of dried loess was used as the control group to compare the curing effect of xanthan gum.

[0027] The solidified loess obtained in Examples 1 to 4 and the dried loess described in the comparative example were respectively pressed into a Φ100×200 mm soil column sample and a Φ79.8 m×20 mm ring knife sample by static pressing.

[0028] All soil column samples were controlled with a compaction coefficient of 0.9 and placed in a freeze-thaw box at a constant temperature of 1°C for 24 hours. The samples were then placed in a TMS9018 freeze-thaw cycle machine for freeze-thaw cycle tests.

[0029] The compaction coefficient of all ring knife specimens was controlled at 0.9. The prepared specimens were wrapped tightly with plastic wrap and placed in a sealed bag, and then placed in a standard curing box for curing for 24 hours.

[0030] The collapsibility test of the prepared ring cutter specimens was carried out using a WG single-lever consolidation instrument.

[0031]

Freeze-thaw cycle test

[0032]

Collapsibility test

[0033]

Test results

[0034] The collapsibility coefficient of plain loess d s 0.029 (0.015 < d s <0.03), the level of wetting is medium.

[0035] like Figure 2 As shown in the figure, the frost heave rate and thaw settlement coefficient of solidified loess first decrease and then increase with the addition of xanthan gum. The frost heave rate and thaw settlement coefficient are the smallest and most stable when the xanthan gum dosage is 0.5%. With the increase of freeze-thaw times, the frost heave rate and thaw settlement coefficient show a gradually decreasing trend. Comparing the frost heave rate and thaw settlement coefficient of each dosage, after the second freeze-thaw cycle, the frost heave rate of loess and xanthan gum dosage of 0.5%, 1.0%, 1.5%, and 2.0% are 0.16%, 0.11%, 0.19%, 0.19%, and 0.26%, respectively. When the xanthan gum content is 0.5%, the frost heave rate is reduced by 25% at most compared with the control loess; the thaw settlement coefficients after the second freeze-thaw cycle are 0.12%, 0.01%, 0.07%, 0.04%, and 0.04%, respectively. When the xanthan gum content is 0.5%, the thaw settlement coefficient is reduced by 91.6% at most compared with the control loess. It can be seen that the addition of xanthan gum can significantly reduce the freeze-thaw damage of loess.

[0036] like Figure 3 As shown in the figure, during the freeze-thaw cycle, after the second freeze-thaw cycle, the loess produced a phenomenon of internal soil collapse due to the influence of water migration from bottom to top, resulting in a decrease in the frost heave rate and a sudden increase in the thaw settlement coefficient; after the addition of xanthan gum, the xanthan gum inside the soil mixed with a part of the water to produce colloidal aggregates, which hindered the migration of water, resulting in a significant reduction in the amount of water migration inside the soil. It can also reduce the migration height of water in the soil, which was reduced from 180mm in loess to 20mm, a reduction of 88.9%.

Claims

1. A method for preventing and controlling loess roadbed collapse and freeze-thaw deformation in seasonally frozen areas, characterized in that: This method refers to the use of xanthan gum to solidify loess, that is, the compaction degree is 90% and the wetting coefficient is δ s <0.015 of solidified loess.

2. A method for preventing and controlling loess roadbed collapse and freeze-thaw deformation in seasonally frozen areas according to claim 1, characterized in that: The solidified loess is prepared by the following method: S1: crush the loess, pass it through a 2 mm sieve, and then dry it at 105°C to constant weight to obtain the dried loess; S2: Add 0.5%, 1.0%, 1.5%, and 2.0% xanthan gum by weight to the dried loess, and stir evenly to obtain a dry mix; Add 14.0% water by weight to the dry mixture in S3, stir evenly, put into a sealed bag and seal for 24 hours to obtain solidified loess.

3. The method for preventing and controlling loess roadbed collapse and freeze-thaw deformation in seasonally frozen areas according to claim 1, characterized in that: The minimum water replenishment height of the solidified loess is 20 mm.

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