To address environmental concerns related to cement-stabilized expansive soil and the safety risks of caustic-activated blast furnace slag, this study explores the use of lime-activated blast furnace slag as an alternative stabilizer in northern Hebei, China. The effects of slag dosage, curing time, and osmotic pressure on the expansion, osmotic properties, and strength of the improved soil were evaluated through free expansion rate, permeability coefficient, and unconfined compressive strength tests. Results show that adding slag-lime significantly reduces soil expansion. As slag content increases, the free expansion rate decreases exponentially. During the curing period of 3-7 days, expansion declines and stabilizes between 7-14 days. Similarly, the permeability coefficient permeability coefficient decreases with higher slag content, following a quadratic trend. Under osmotic pressures of 0.1-0.2 MPa, the permeability coefficient permeability coefficient increases but stabilizes between 0.2-0.4 MPa.Furthermore, slag-lime significantly enhances unconfined compressive strength, which increases linearly with slag content. The stress-strain curve follows a logistic function in the rising stage and a rational fractional equation in the descending stage.This study demonstrates that lime-activated blast furnace slag is a sustainable and effective alternative for stabilizing expansive soils while reducing dependence on cement.

The low-velocity penetrator (LVP) is a planetary penetration device that can drive itself to a target depth through its internal periodic impacts. When LVP generates impact energy, it inevitably produces a recoil that can only be counteracted by friction with the soil, if there is no other auxiliary device. Unfortunately, LVP is extraordinarily sensitive to the recoil during the initial stage since the small contact area with the soil results in minor friction between them. Significantly, once the recoil exceeds the friction, LVP cannot work properly and may even retreat, inducing mission failure. In this paper, we develop an optimized LVP with an auxiliary device for lower recoil and higher performance. Specifically, we establish a dynamic model to analyze the single-cycle motion of LVP and provide essential support for its optimization and design. Meanwhile, an integration method is proposed to calculate the friction between LVP and the soil reasonably and accurately. On the basis of these, we obtain the optimal mass and stiffness parameters of LVP that meet both high penetration efficiency and low recoil. Furthermore, only relying on the parameter optimization is insufficient to eliminate the recoil, and an auxiliary penetration scheme is proposed to provide an external force counteracting the recoil until LVP arrives at a certain depth. Through multiple comparative penetration experiments, we validate the effectiveness of our approaches in promoting penetration ability, stability, and restraining the recoil of LVP. This work provides two novel approaches for solving the contradiction of efficient penetration while reducing the recoil for LVP.

Ground improvement is necessary in many flat areas and landfill sites in Japan because these areas have soft ground and are highly susceptible to serious damage such as long-term consolidation settlement and liquefaction. The deep mixing method (DMM) is an in-situ soil treatment in which native soils or fills are blended with cementitious and/or other materials. Ground treated by DMM has higher strength and lower compressibility than untreated ground. However, there are quality problems in this method due to a condition in which a mixture of soil and materials adheres to and rotates along with the stirring blades without performing efficient mixing. Therefore, our purpose is to improve quality of improved columns produced by the mechanical mixing method using vertical rotary shafts and mixing blades. In this study, five cases of small-scale model experiments were conducted with changing in the blade rotation number, the incident angle of agitating blades, and the agitating blade angle. Strength tests were conducted using unconsolidated samples at different depths to investigate strength distribution, and needle penetration tests were also conducted. From the results, the effects of the blade rotation number, the incident angle, and the agitating blade angle on improvement quality were discussed.