Highway, road, and airfield construction on weak soils is costly endeavor. Re-use of agricultural waste is widely employed as a stabilizing agent to improve engineering properties of these soils. In this study, rice husk ash (RHA), a by-product of incineration of husk from rice production, was used as a potential stabilizer. The water absorption and retention rate of the stabilizer, denoted as W-ab, is determined by measuring the amount of water that is absorbed and retained by the stabilizer in relation to its initial dry mass. The study involved treatingAo clay, imitating a dredged soil with highwater content, at various addition ratios (ARHA). Diverse curing periods were applied to assess the liquid limits (w(L)), plastic limits (w(P)), and cone index (q(c)) of the treated clays. Compaction characteristics were also determined for several ARHA and different curing periods. The test results show an increase in both w(L) and w(P) with decrease in plastic index (I-p) with increase in ARHA, but no remarkable change in w(L) and w(P) associated with curing. Compaction characteristics show a decline in rho(dmax) and increase in wopt with increase in ARHA, but no notable changes in rho(dmax) and wopt with cured samples. Increase in q(c) with ARHA, but no noteworthy change in q(c) with curing was discerned through cone index test. The trends for curing observed in the above test results were consistent with that observed for W-ab. The results were then modified based on the W-ab of stabilizer. The measured water content (w) and liquidity index (IL) were modified to account for absorbed water (w*), which gave a better correlation with q(c) than w. The compaction characteristics were also modified based on Wab, ARHA and the results suggest that treated clays were able to achieve modified dry density (rho(dmax)*) at the same values of modified water content (w(opt)*).

Broken coal and rock (BCR) are an important component medium of the caving zone in the goaf (or gob), as well as the main filling material of fault fracture zone and collapse column. The compaction seepage characteristics of BCR directly affect the safe and efficient mining of coal mines. Thus, numerous laboratory studies have focused on the compaction seepage characteristics of BCR. This paper first outlines the engineering problems involved in the BCR during coal mining including the air leakage, the spontaneous combustion, the gas drainage, and the underground reservoirs in the goaf. Water inrush related to tectonics such as faults and collapse columns and surface subsidence related to coal gangue filling and mining also involve the compaction seepage characteristics of BCR. Based on the field problems of BCR, many attempts have been made to mimic field environments in laboratory tests. The experimental equipment (cavity size and shape, acoustic emission, CT, etc.) and experimental design for the BCR were firstly reviewed. The main objects of laboratory analysis can be divided into compression tests and seepage test. During the compaction test, the main research focuses on the bearing deformation characteristics (stress-strain curve), pore evolution characteristics, and re-crushing characteristics of BCR. The seepage test mainly uses gas or water as the main medium to study the evolution characteristics of permeability under different compaction stress conditions. In the laboratory tests, factors such as the type of coal and rock mass, particle size, particle shape, water pressure, temperature, and stress path are usually considered. The lateral compression test of BCR can be divided into three stages, including the self-adjustment stage, the broken stage, and the elastic stage or stable stage. At each stage, stress, deformation, porosity, energy, particle size and breakage rate all have their own characteristics. Seepage test regarding the water permeability experiment of BCR is actually belong to variable mass seepage. While the experimental test still focuses on the influence of stress on the pore structure of BCR in terms of gas permeability. Finally, future laboratory tests focus on the BCR related coal mining including scaling up, long term loading and water immersion, mining stress path matching were discussed.

The compaction characteristics of gravelly soil are affected by gravel hardness. To investigate the evolution and influencing mechanism of different gravel hardness on the compaction characteristics of gravelly soil, heavy compaction tests and crushing tests were conducted on gravelly soils with gravels originated from hard, soft and extremely soft rocks. According to orthogonal experiments and variance analysis, it was found that hardness has a significant impact on the maximum dry density of gravelly soil, followed by gravel content, and lastly, moisture content. For gravel compositions with an average saturated uniaxial compressive strength less than 60 MPa, the order of compacted maximum dry density is soft gravels > hard gravels > extremely soft gravels. Each type of gravelly soil has a threshold for gravel content, with 60% for hard and soft gravels and 50% for extremely soft gravels. Beyond these thresholds, the compacted dry density decreases significantly. There is a certain interaction between hardness, gravel content, and moisture content. Higher hardness increases the influence of gravel content, whereas lower hardness increases the influence of moisture content. Gravelly soils with the coarse aggregate (CA) between 0.7 and 0.8 typically achieve higher dry densities after compaction. In addition, the prediction equations for the particle breakage rate and CA ratio in the Bailey method were proposed to estimate the compaction performance of gravelly soil preliminarily. The results further revealed the compaction mechanism of different gravelly soils and can provide reference for subgrade filling construction.

Expansive soils pose a serious challenge to civil engineering constructions due to their ability to swell and shrink upon wetting and drying. This phenomenon usually leads to damage of the structure when the soil is not treated properly. Moreover, the disposal and utilization of fly ash (FA) in both economical and eco-friendly ways has received high attention in the world. Thus, this study focuses on the improvement of the geotechnical properties of expansive soils stabilized with varying percentages of fly ash as an admixture. In the present study, low calcium fly ash in different proportions by weight (0%, 10%, 20%, 30%, and 40%) was added to a moderately expansive soil collected from Doharramafi Village, India. Laboratory tests performed on the prepared mixtures included the determination of moisture-density relationships, California bearing ratio (CBR), and shear strength parameters. Test results show that moisture-density relationships, CBR values, and shear strength parameters of fly ash-treated soil are significantly modified and improved compared to control specimens. Furthermore, based on all laboratory tests, 30% fly ash content is observed to be the optimum fly ash quantity required to improve the geotechnical properties of soil stabilized with fly ash.