Method for improving strength of collapsible loess roadbed and inhibiting fracture development

Abstract

The invention relates to a method for improving the strength of a collapsible loess roadbed and inhibiting fracture development, which comprises the following steps: S1, crushing loess, sieving, and drying to constant weight to obtain dried loess; s2, adding xanthan gum accounting for 1.5%-2.0% of the mass of the dried loess or guar gum accounting for 1.0%-1.5% of the mass of the dried loess into the dried loess, and uniformly stirring to obtain a dry glue-soil mixed material; s3, uniformly spraying water accounting for 14.0% of the mass of the dry gel-soil mixture into the dry gel-soil mixture, and uniformly stirring to obtain a wet gel-soil mixture; and S4, preparing the improved loess subgrade filler from the rubber-soil mixed wet material by adopting a static pressure method, wherein the improved loess subgrade filler is cured for not less than 7 days under a standard curing condition. The technology is simple, the requirement for construction equipment is not high, environment friendliness is achieved, the adopted green renewable biopolymer is used for improving loess, the strength of the loess roadbed can be effectively improved, and cracks generated due to the humidifying-dehumidifying influence are reduced.

Description

Technical Field

[0001] The invention relates to the technical field of road materials for civil engineering, and in particular to a method for improving the strength of collapsible loess roadbed and inhibiting the development of cracks. Background Art

[0002] Loess is a silty sediment formed by the Quaternary wind deposition. It is widely distributed in Northwest my country and the middle and upper reaches of the Yellow River. It has a special apparent structure and material composition with large pores, developed vertical joints, and high soluble salt content. Its physical and mechanical properties show significant water sensitivity, which is specifically manifested as a sudden drop in strength when softened by water and cracking of the structure when dehydrated and dried. When loess is in an environment of repeated humidification and dehumidification, cracks will be generated inside the soil, gradually evolving and developing into cracking. The soil will inevitably suffer from stress damage, posing a serious safety hazard to the roadbed construction and slope stability in the loess area. Therefore, collapsible loess is difficult to be directly used as roadbed filler in road engineering, and high-quality civil engineering raw materials such as high-strength hardened sand and gravel have become increasingly scarce. In order to achieve local materials for engineering construction, in recent years, the problem of loess improvement has become a hot spot in loess foundation treatment, with the aim of inhibiting the expansion of cracks caused by moisture changes, reducing soil erosion and improving the strength characteristics of loess.

[0003] At present, the research on loess improvement mainly includes the following types of improvement materials: (1) using traditional inorganic materials such as cement and lime to improve loess; (2) using flexible materials such as fibers and geogrids to improve loess; and (3) using industrial solid wastes such as steel slag, fly ash, and slag to improve loess. Existing studies have shown that using traditional inorganic materials to improve loess can significantly improve the engineering properties of loess, but the high addition of cement, lime and other materials to improve the soil will lead to salinization of soil and groundwater, aggravating the formation of soil desertification in the northwest region. At the same time, cement raw materials will emit a large amount of carbon and nitrogen oxides during the calcination process, causing serious damage to the soil ecological environment. Using fiber and other grid nets to anchor loess in a regional and deep level can enhance the shear strength of loess and inhibit the development of microcracks, but its water resistance and compressive strength are not high. Using industrial solid waste to improve loess can effectively improve the strength of loess and take into account the concept of saving resources and turning waste into treasure, but it requires crushing and heavy metal digestion. This process is prone to produce a lot of dust and wastewater, and the process is complicated and increases costs. Therefore, exploring low-carbon, environmentally friendly and green economic foundation treatment materials is an effective way to achieve sustainable development.

[0004] Biopolymers are environmentally friendly materials. With good hydrophilic adhesion, high strength after drying and harmless degradation, they are rich in raw materials, simple in process, low in price and environmentally friendly. Compared with ordinary cement materials, biopolymers have good corrosion resistance and durability.

[0005] Studies have shown that biopolymers can form a highly cohesive "bridge" structure around soil particles through the bond energy strengthening and hydration cementation of the hydrophilic groups in the biopolymer molecules, which can effectively limit the lateral deformation and longitudinal settlement of the soil; on the other hand, by filling the large pores between soil particles and forming a film to isolate water, it can slow down the rapid formation of the water content gradient difference inside the soil. The most common biopolymers are xanthan gum and guar gum. There have been studies on the use of these two gums to solidify sand, laterite, expansive soil, silt and dispersed soil, but there have been no reports on the use of xanthan gum or guar gum to improve the strength of loess roadbed fillers and inhibit the development of cracks. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a method for improving the strength of collapsible loess roadbed and inhibiting the development of cracks, which has simple process and is green and environmentally friendly.

[0007] In order to solve the above problems, a method for improving the strength of collapsible loess roadbed and inhibiting the development of cracks described in the present invention comprises the following steps: 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: adding 1.5% to 2.0% by weight of xanthan gum or 1.0% to 1.5% by weight of guar gum to the dried loess, and stirring evenly to obtain a mixed clay dry material; S3: evenly spraying 14.0% of the mass of the clay mixed dry material with water into the clay mixed dry material, stirring evenly to obtain the clay mixed wet material; S4: preparing the improved loess roadbed filler with the rubber-soil mixed wet material by static pressure method, and the improved loess roadbed filler is cured for no less than 7 days under standard curing conditions.

[0008] The compaction coefficient of the improved loess roadbed filler in step S4 is 95%.

[0009] The standard curing conditions in step S4 refer to using a standard curing box with a set temperature of 20±2° C. and a relative humidity of 50±5%.

[0010] Compared with the prior art, the present invention has the following advantages: 1. The improved material biopolymer xanthan gum or guar gum in the present invention forms a viscous colloid when combined with water, which can wrap and cement loess particles, effectively fill the pores between loess particles, and promote the connection of loess particles into a whole, which significantly improves the integrity and strength performance of the loess structure and effectively inhibits the development and expansion of loess cracks.

[0011] 2. The improved loess obtained by the present invention is used as a roadbed filler. Compared with the plain loess roadbed, the soil particles have a dense structure, which makes the improved loess high in strength and good in crack resistance. It can be applied to engineering practices such as road construction and slope protection to improve the durability of loess roadbed and slopes, and reduce the problems of roadbed softening and collapsing, water loss and shrinkage cracking caused by rainwater leaching. The strong bonding ability of biopolymers effectively limits the transverse and longitudinal deformation of the loess roadbed, promotes the bonding between loess particles, thereby enhancing the integrity of the connection between loess particles and inhibiting the development of loess cracks.

[0012] 3. The present invention adopts green renewable biopolymer to improve loess, which can effectively improve the strength of loess roadbed and reduce cracks caused by humidification and dehumidification.

[0013] 4. The biopolymer of the present invention has abundant raw materials, simple process, low requirements on construction equipment, and is green and environmentally friendly. After engineering practice, it is beneficial to the self-repair of the ecological environment. 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 The present invention is a flow chart for preparing the biopolymer-improved loess roadbed filler.

[0016] Figure 2 This is a graph showing the relationship between the xanthan gum dosage and the unconfined compressive strength during the unconfined compressive strength test of Example 1 of the present invention.

[0017] Figure 3 This is a graph showing the relationship between the guar gum dosage and the unconfined compressive strength during the unconfined compressive strength test of Example 1 of the present invention.

[0018] Figure 4 This is a graph showing the relationship between the crack rate of the xanthan gum-modified loess sample and the number of dry-wet cycles during the dry-wet cycle test of Example 2 of the present invention.

[0019] Figure 5 This is a graph showing the relationship between the crack rate of the guar gum modified loess sample and the number of dry-wet cycles during the dry-wet cycle test of Example 2 of the present invention. DETAILED DESCRIPTION

[0020] like Figure 1 As shown, a method for improving the strength of collapsible loess roadbed and inhibiting the development of cracks comprises the following steps: S1: Grind the loess, pass it through a 2mm sieve, and then dry it at 105℃ to constant weight to obtain the dried loess. The purpose of the drying process is to remove the heterogeneity of the soil's own moisture and unify the moisture content of the clay dry material.

[0021] S2: Add 1.5% to 2.0% by weight of xanthan gum or 1.0% to 1.5% by weight of guar gum to the dried loess and stir evenly to obtain the mixed clay dry material.

[0022] S3: Evenly spray 14.0% of the mass of the mixed clay dry material with water into the mixed clay dry material, stir evenly to avoid the agglomeration of particles in the clay wet material, and obtain the clay mixed wet material.

[0023] S4 uses static pressure method to make improved loess roadbed filling material from clay-soil mixed wet material, and the improved loess roadbed filling material is cured for no less than 7 days under standard curing conditions.

[0024] Among them: the compaction coefficient of improved loess roadbed filling is 95%.

[0025] Standard curing conditions refer to the use of a standard curing box with a set temperature of 20±2℃ and a relative humidity of 50±5%.

[0026] The unit of mass in the present invention is kg.

[0027] Example 1 In order to improve the strength of the roadbed and reduce the development of cracks under the influence of humidification and dehumidification, a method for improving the strength of the collapsible loess roadbed and inhibiting the development of cracks comprises the following steps: S1: Grind the loess, pass it through a 2 mm sieve, and then dry it at 105°C to constant weight to obtain the dried loess.

[0028] S2: Add xanthan gum or guar gum to 1 kg of dried loess, the specific dosage is shown in Table 1~2. Stir evenly to obtain the mixed clay dry material.

[0029] S3: Evenly spray 14.0% of the mass of the mixed clay dry material with water into the mixed clay dry material, stir evenly to avoid the agglomeration of particles in the clay wet material, and obtain the clay mixed wet material.

[0030] S4 Based on the relationship between the maximum dry density of plain loess and the target compaction coefficient of 95%, the rubber-soil mixed wet material is weighed, filled into a standard mold in two layers and compacted. The fillers between the layers are flattened and then scraped to make the soil particles between the layers tightly embedded without any fault phenomenon.

[0031] After the unconfined compressive strength specimens were prepared, they were placed in a standard curing box with a set temperature of 20±2℃ and a humidity of 50±5%. The curing ages were 1, 7, 14, and 28 days, respectively.

[0032] Take out the sample that has been cured to the set age and place it at room temperature to eliminate the surface fog. Use the YAW-300D microcomputer-controlled electronic pressure testing machine to start the unconfined compressive strength test, control the loading rate to 1mm / min, and stop loading when large cracks appear on the sample surface or the axial pressure drops to 1 / 3 of the maximum pressure.

[0033] The relationship between the unconfined compressive strength of plain loess and loess modified by biopolymer xanthan gum or guar gum and the amount of biopolymer added is as follows Figure 2~3 As shown in the figure, it can be seen that the unconfined compressive strength of the improved loess sample gradually increases with the increase of curing age, and the strength growth rate slows down after 14 days. In addition, the unconfined compressive strength of the improved loess sample increases first and then decreases with the increase of the bio-glue content. When the xanthan gum and guar gum content are 1.5% and 1.0% respectively, the unconfined compressive strength of the improved loess is most significantly improved.

[0034] The unconfined compressive strength results of xanthan gum and guar gum improved loess at curing ages of 1d, 7d, 14d, and 28d are shown in Tables 1 and 2.

[0035] Table 1 Table 2 It can be found from Table 1 and Table 2 that different amounts of xanthan gum and guar gum with biopolymers have different degrees of improvement on the unconfined compressive strength of improved loess. For example, when the amount of xanthan gum and guar gum is 1.5% and 1.0 respectively, the unconfined compressive strength of improved loess can reach 416.14kPa and 383.86kPa after curing for 7 days, while the strength of plain loess is 207.22kPa. The strength of improved loess is 100.8% and 85.2% higher than that of plain loess of the same age. It is worth noting that the unconfined compressive strength of improved loess does not gradually increase with the increase of the amount of addition. In other words, the larger the amount of addition, the more significant the effect of improved loess strength is, which is more conducive to reducing the construction cost of actual projects.

[0036] Example 2 A method for improving the strength of collapsible loess roadbed and inhibiting the development of cracks, comprising the following steps: S1: Grind the loess, pass it through a 2 mm sieve, and then dry it at 105°C to constant weight to obtain the dried loess.

[0037] S2: Add xanthan gum or guar gum to 1 kg of dried loess, the specific dosage is shown in Table 3~4. After stirring evenly, the mixed clay dry material is obtained.

[0038] S3: Evenly spray 14.0% of the mass of the mixed clay dry material with water into the mixed clay dry material, stir evenly to avoid the agglomeration of particles in the clay wet material, and obtain the clay mixed wet material.

[0039] S4 Considering that the crack development caused by radial shrinkage due to water loss in the soil is difficult to fully reflect from the boundary, and the crack development of small-sized specimens is restricted by the boundary and cannot be extended, considering that the crack development is affected by boundary constraints and size effects, a larger-sized (30cm×30cm×4cm) acrylic transparent uncovered mold is made to prepare the specimen. At the same time, the specimen thickness has a deeper impact on the surface cracking, so the specimen thickness is set to 2cm to reduce the test error. The mixed wet material is loaded into the mold, the surface is flattened, and the soil sample is pressed to the specified thickness using the static pressure method.

[0040] The specimens were placed in a standard curing box with a set temperature of 20±2°C, a humidity of 50±5%, and a curing period of 7 days.

[0041] Take out the sample that has been cured to the set age, place it at room temperature to eliminate surface fog, and prepare for the dry-wet cycle test.

[0042] In order to simulate the natural state, the repeated rainfall and high-temperature evaporation of loess caused the internal water migration and microcrack evolution of the soil. In this test, the plastic wrap was removed from the cured samples, and then placed in a 18±2℃ normal temperature water tank. Geotextile absorbent filter paper and permeable stone were laid on the top of the samples. The water level was always 10mm above the permeable stone. The samples were immersed in water for 12 hours. At this time, the pores inside the sample particles reached water saturation.

[0043] After the immersion test, each sample was placed in a constant temperature drying oven at 50°C, and the samples were taken out and weighed every 4 hours. When the difference in mass of two consecutive samples was about 2g, the sample was considered to have reached a constant weight state, and the test was stopped. During the test, photos were taken at fixed points and the time when the cracks first appeared was recorded.

[0044] This test considers that the sample is saturated with water until it loses water and dries up, and the mass reaches a constant weight state, which is a dry-wet cycle. Repeat the above immersion saturation and drying dehumidification process, and set up 6 dry-wet cycle tests in total.

[0045] After 6 dry-wet cycle tests, the relationship between the total crack area (pixel) of the biopolymer xanthan gum and guar gum improved loess and the number of dry-wet cycles is shown in Tables 3 and 4.

[0046] Table 3 Table 4 After 6 dry-wet cycle tests, the relationship between the crack rate (%) of loess improved by biopolymer xanthan gum and guar gum and the number of dry-wet cycles is shown in Tables 5 and 6.

[0047] Table 5 Table 6 It can be seen from Tables 5 and 6 that after 6 dry-wet cycles, the total crack area of ​​the plain loess sample with a dosage of 0% is 53193 pixels and the crack rate is 4.86%. The total crack areas of the improved soil with xanthan gum and guar gum dosages of 2.0% and 1.5% are 40496 pixels and 23828 pixels, respectively, and the crack rates are 3.78% and 1.36%, respectively. Compared with the plain loess, the total crack area is reduced by 23.9% and 55.2%, and the crack rate is reduced by 22.3% and 72.0%.

[0048] Therefore, when the dosage of xanthan gum and guar gum was 2.0% and 1.5% respectively, the crack development of the improved loess sample was significantly inhibited, and the crack rate of the plain loess sample was greatly reduced. In addition, guar gum has a very significant effect on improving the crack resistance of the improved loess.

[0049] In summary, the biopolymers xanthan gum and guar gum of the present invention can significantly improve the unconfined compressive strength of the improved loess and inhibit the development and expansion of cracks in the loess under the influence of humidification and dehumidification, which means that under the action of additional pressure and self-weight pressure and under the influence of special climatic environment, the bearing capacity of the road base and the crack resistance of the pavement will be improved simultaneously. When the optimal amount of xanthan gum (1.5%~2.0%) or guar gum (1.0%~1.5%) is used to improve the loess sample, when the curing age is 7d, the unconfined compressive strength value is increased by 100.8% and 85.2% compared with the strength of the plain loess of the same age; the crack rate is reduced by 22.3% and 72.0%. At the same time, as a natural high molecular polysaccharide compound produced by plants and fungi, the biopolymer has good hydrophilic adhesion, high strength after dehydration and degradability, and is harmless to degradation. It is applied to the fields of loess roadbed improvement and slope protection, and has almost no impact on the surrounding ecological environment, and has good economic value and social benefits.

[0050] It should be emphasized that the implementation cases provided by the present invention include but are not limited to the above two categories. The above embodiments only illustrate the preparation method of the present invention and the strengthening effect of improved loess, which can be applied to the field of civil engineering roadbed filling construction. For relevant technical researchers engaged in this field, the aforementioned invention implementation cases or technical routes can still be modified or replaced in accordance with regulations. However, these modifications or replacement technical essences, without departing from the core technical content of the present invention, are all within the scope of protection of the claims and description of the present invention.

Claims

1. A method for improving the strength of collapsible loess roadbed and inhibiting the development of cracks, comprising the following steps: 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: adding 1.5% to 2.0% by weight of xanthan gum or 1.0% to 1.5% by weight of guar gum to the dried loess, and stirring evenly to obtain a mixed dry material of clay; S3: evenly spraying 14.0% of the mass of the clay mixed dry material with water into the clay mixed dry material, stirring evenly to obtain the clay mixed wet material; S4: preparing the improved loess roadbed filler with the rubber-soil mixed wet material by static pressure method, and the improved loess roadbed filler is cured for no less than 7 days under standard curing conditions.

2. A method for improving the strength of collapsible loess roadbed and inhibiting the development of cracks as claimed in claim 1, characterized in that: The compaction coefficient of the improved loess roadbed filler in step S4 is 95%.

3. A method for improving the strength of collapsible loess roadbed and inhibiting the development of cracks as claimed in claim 1, characterized in that: The standard curing conditions in step S4 refer to using a standard curing box with a set temperature of 20±2° C. and a relative humidity of 50±5%.

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