Rammed earth, a commonly used building material in ancient times, differs from natural sedimentary layers in that it is more compact. Buildings constructed from historical rammed earth sites frequently encounter the issue of rainwater erosion. Microbially induced calcium carbonate precipitation (MICP) is commonly applied to sand soil treatment, yet reports on its use for stabilizing rammed earth are scarce. This study focused on the rammed earth of the Shanhaiguan Great Wall and explored the efficacy of MICP in mitigating rain erosion through permeation tests, splash experiments, and scouring trials. The findings indicate that the forms of rain erosion damage under MICP treatment vary across different operational conditions. In laboratory experiments, as the concentration of the cementation solution increases, the amount of calcium carbonate crystals also increases. However, the permeability, splash resistance, and rain erosion resistance initially increase and then decrease. When the cementation solution concentration is 1.0 mol/L, the penetration rate is the highest, lasting 712.55 s. The splash pit rate is the lowest, at only 1.2 mm, and the soil erosion rate is the lowest, at only 4.13%. The rain erosion resistance in the field test exhibit the same trend, and the optimal concentration is 1.2 mol/L. The optimal concentration mechanism involves the aggregation of calcium carbonate crystals at suitable cementation solution concentrations, which begin to fill the soil particle pores, effectively resisting rainwater erosion. At lower concentrations of the cementation solution, calcium carbonate crystals are merely adsorbed by soil particles without blocking the pores. Due to the high compressibility of rammed earth, which results in lower porosity, a higher concentration of the cementation solution leads to rapid pore clogging by excessive calcium carbonate crystals, which accumulate on the surface to form a white crust layer. The MICP technique can effectively alleviate rainwater erosion in rammed earth, and the optimal concentration needs to be tailored to the porosity of the rammed earth. This mechanism was also validated in field scouring experiments on the Shanhaiguan Great Wall's rammed earth.

This research investigates the permeability and compressibility performance of aeolian-Na/Ca-bentonite mixtures (ANB/ACB) with varying bentonite contents, subjected to different freeze-thaw cycles, in which the particle size analysis, permeability tests, and compression tests are employed. The results indicate that: (1) with increasing bentonite content, ANB/ACB exhibits a gradual rise in uniformity coefficient, curvature coefficient, clay content, and compression index (Cc), accompanied by a decrease in permeability coefficient. Moreover, ACB's compression index gradually surpasses that of ANB. Under equivalent bentonite content, ACB demonstrates higher values for non-uniformity coefficient, curvature coefficient, and clay content than ANB; (2) experiencing freeze-thaw cycles, ANB exhibits an increasing permeability coefficient, whereas ACB, particularly at a high bentonite content, experiences a decreasing permeability coefficient with additional freeze-thaw cycles. Simultaneously, freeze-thaw effects degrade the compression indices of both ACB and ANB; and (3) increasing the normal stress leads to a rapid reduction in compression coefficients for ANB and ACB, with the rate of decrease gradually slowing down. Under constant normal stress, the compression coefficient ratio (ANB/ACB) decreases with rising bentonite content and increases with the number of freeze-thaw cycles. Additionally, electron microscope scans revealed that the freeze-thaw cycle effect influences the permeability and compressibility of the soil by altering the soil sample's pore structure and particle size.

Cement-based solidification/stabilization (S/S) techniques have been widely used to produce stable forms of contaminated soils and reduce the mobility of contaminants into the environment. However, information on the long-term performances of S/S under environmental conditions (i.e., variable loading and atmospheric carbon dioxide) remains sparse. In this study, a triaxial test setup was modified to simulate environmental conditions. The permeability and compressive strength of silica sand solidified with portland cement were measured at different stages of four scenarios involving carbonation only, axial strain only, carbonation followed by axial strain, and axial strain followed by carbonation. X-ray computed tomography (CT) was used to characterize the internal structure of the samples. Permeability and compressive strength results indicate that the axial strain accelerated the damage to the S/S specimens and increased their permeability. The deterioration due to the mechanical strain decreased in the presence of carbon dioxide. Consistent changes in microstructure were observed with the CT scan. The results indicate that the influence of stressors on the void size distribution, compressive strength, and permeability is complex and characterized by interactions between the stressors.

The authors conducted field permeability tests on numerous river embankments using a Marriott siphon in 30-cm test holes to obtain their saturated permeability coefficients. The results revealed that the field-obtained saturated permeability coefficients were larger than those obtained as a result of the laboratory permeability test conducted on the undisturbed specimens sampled from the same location. Regarding embankments constituted by fine-grained soils, there are cases in which the field-obtained coefficients are several orders of magnitude larger than those obtained under laboratory conditions. These results suggest that the field permeability coefficient obtained by the Marriott siphon with large-diameter test holes evaluates the macroscopic permeability, including in situ heterogeneity and anisotropy. In this study, the results of the field permeability tests at two embankments of the Oda and Kano Rivers are shown. In addition, the results of the laboratory permeability test for the undisturbed specimens sampled at each field site are shown. In each survey, the field permeability coefficients were larger than both the laboratory permeability coefficients and the estimated value from particle size, as in the case of other embankments investigated so far.