Experimental Study on the Comprehensive Identification and Improvement of Dispersive Soil in Western Jilin Province, China

In this study, physical experiments, clay mineral determination, and pH testing were performed to examine the basic properties of soil samples from a soil material yard selected for dam construction at Hua’ao Lake, Qian’an County, Jilin Province, China. The results show that the soil in the study area is cohesive, the mineral content of illite in the illite/montmorillonite mixed layer is approximately 50%, and the pH value of the environment from which the soil samples were taken is 8.43-8.91. These factors enable the soil in this area to be dispersed. The dispersibility of the soil sampled from this area was evaluated by a double hydrometer test, a pinhole test, a fragmentation test, a sodium adsorption ratio test, and determination of the percentage of exchangeable sodium ions. Because these test methods had inconsistent results, the test methods in combination with the typical geomorphic conditions of the sampling points were ultimately used to comprehensively evaluate the soil dispersion. The results demonstrate that the cohesive soil sampled from the soil material yard is dispersible and must be treated with improvement measures before it can be used as a filling material for the dam. To improve the dispersive and transitional soil, 2%, 3%, 4%, 5%, and 6% L1Fa2 (a 1 : 2 ratio of lime and fly ash) and C1L1Fa4 (a 1 : 1 : 4 ratio of cement, lime, and fly ash) were used to perform improvement tests on 10 groups of dispersive soil samples and 10 groups of transitional soil samples. The results reveal that the addition of 4% L1Fa2 best improves the dispersive soil in this area. Therefore, the soil intended for this project should be used as a dam-building material after improvement with the 4% addition of L1Fa2.

A Study on the Durability of Dispersive Soils Improved by Alum in Western Jilin Province of China

Dispersive soil, which has the characteristics of low erosion resistance and high dispersibility in water, is the main reason for the channel slope failure that happened in the planning area of the Western Alkaline Treatment project in Jilin Province. Therefore, the study focused on the improvement of dispersive soil. In this research, pinhole test and crumb test were conducted on the soil under varying percentages of alum (1%, 1.5%, 2%, 2.5%, and 3%). Results indicated that alum can reduce the dispersivity of soil distinctly, and the optimal content of alum was 2.5%. This research also investigated the durability of 2.5%-alum-improved dispersive soil for dispersibility under the condition of freeze-thaw cycle. The soil samples with 2.5% alum content were subjected to pinhole test, crumb test, double hydrometer test, and percentage of exchangeable sodium ion test under the different number of freeze-thaw cycles. The results showed that the 2.5%-alum-improved soil was unaffected by the number of freeze-thaw cycles, which illustrated that alum can be used to improve soil dispersivity in engineering practice.

Physical, chemical and microstructural characterization of two problematic soils from the Paraguayan Chaco

It is not uncommon for Geotechnical Engineering works to be carried out under unfavorable conditions that compromise the earth-stability. In this context, the Paraguayan Region of Chaco is notably known owing to the presence of problematic soils that possess dispersive characteristics and/or present high amounts of soluble-sulfates content. Geomaterials of such nature affect mainly the road infrastructure earthworks due to, respectively, their promptness to erosive phenomena when in contact with water and swelling owing to the grown and hydration of expansive minerals such as ettringite and thaumasite, when treated with calcium-based materials. Therefore, present research presents a detailed characterization of a dispersive soil and a sulfate-rich dispersive soil, both collected in the Western Region of Paraguay. Physical, chemical and microstructure tests were carried out in order to verify and explain the deleterious behavior observed in both soils.

Landslide Failure Mechanisms of Dispersive Soil Slopes in Seasonally Frozen Regions

Hydraulic projects with dispersive soil in seasonally frozen regions are susceptible to landslide failures. The mechanism of such landslide failures has not been fully understood thus far; therefore, it was investigated in this study by using on-site surveys, laboratory tests, and theoretical calculations. The results showed that the landslides of dispersive soil in seasonally frozen regions could be categorized as shallow-seated landslides and deep-seated landslides. The preconditions for landslide occurrence were soil mass looseness and cracks, caused by freeze-thawing. The degradation of dispersive soil led to a rapid influx of water into the soil. The reason for shallow-seated landslides was that the numerous sodium ions present in the soil mass dissolved in water and damaged the soil structure, resulting in a substantial reduction in shear strength. The reason for deep-seated landslides, however, was the erosion due to rainfall infiltration after the shallow-seated landslides caused tensile cracks at the top of the slope, leading to soil instability. Landslide failures occurred when the dispersing soil slope underwent freeze-thawing and saturated soaking. The sliding surface was initiated at the top of the slope and gradually progressed to the bottom along the interface between the soil layers.

Nanometer Montmorillonite Modified Fly Ash Ecological Slope Protection Material and Its Preparation and Application

In order to scientifically and reasonably evaluate and select the quality and effect of ecological slope protection construction project and the structural form of ecological slope protection, this paper mainly studies nanomontmorillonite modified fly ash ecological slope protection material and its preparation method and related applications. The nanomontmorillonite modified fly ash ecological slope protection material and its application in this paper are based on nanomontmorillonite modified fly ash as the basic carrier, and the pore structure is used to plant grass for slope protection to achieve the purpose of ecological slope protection. Firstly, the nanomontmorillonite modified fly ash ecological slope protection material was prepared through the selection of raw materials, the mix ratio design, and the reasonable selection of the preparation process, and the range analysis method was used to optimize the mix ratio of nanomontmorillonite modified fly ash. By reasonable selection of alkali-reducing measures, selection of slope protection vegetation, preparation of planting substrates, and research on phytobiology, through experimental analysis, we obtained nanomontmorillonite modified fly ash with high strength and good water permeability and alkalinity in the pores to meet the requirements of plant growth ecological slope protection materials. Finally, through engineering practice, we explored the construction method of nanomontmorillonite modified fly ash ecological slope protection material and obtained good ecological slope protection benefits. The experimental data show that, for dispersive soil, when the degree of compaction is 80%, the compressive modulus of the soil is 3.46 MPa; when the degree of compaction is 86%, the compressive modulus of the soil becomes 4.51 MPa, an increase of 46.57%. The experimental results show that the nanomontmorillonite modified fly ash ecological slope protection material can help the soil become more compact.