Research on the Mechanism and Prevention Methods of the Drying Shrinkage Effect of Earthen Sites

The Impact of Microwave Drying on the Structure of Exemplary Soils-Insights Using X-ray Microtomography

In the field of soil drying methods, rapid microwave heating is progressively replacing conventional techniques. Due to the specific heat transport caused by microwaves, the drying process can significantly modify soil structure, which, in turn, can influence mechanical and filtration characteristics. In this study, we compared structural changes of exemplary non-cohesive (medium quartz sand (MSa)) and cohesive soil (silty clay mainly composed of kaolinite (siCl)). The sample materials were subjected to three different drying methods: air-drying, conventional oven (CO) drying, and microwave oven (MO) drying (MO). Soil structure was studied using X-ray microtomography (XµCT) and described in detail by image analysis methods. The study showed that the analyzed types of heating had a negligible effect on the structure of the sands, but a significant impact in the case of silty clay. Such a phenomenon is discussed and explained in this paper. The study advances the testing of soils microwave drying in a geotechnical laboratory.

Experimental Study on the Cracking and Mechanical Properties of Lime Soil with Different Slaking Conditions of Newly Repaired Earthen City Walls

In this paper, a method to control the lime reaction by different slaking conditions is proposed to reduce the occurrence of cracks in newly repaired earthen city walls. The effects and mechanisms of the slaking time (0 h, 12 h, 24 h, 48 h and 72 h), lime content (10%, 15% and 20%), and moisture content (14%, 18% and 22%) on the cracking and mechanical properties of lime soil were analyzed by the test results of surface cracks, triaxial compression, particle gradation, pH value, X-ray diffraction and scanning electron microscope. The results show that proper slaking of lime soil specimens can reduce surface cracks and improve mechanical properties. After 12 h of appropriate slaking, the crack rate of the lime soil with 20% content decreased by 97.13%, the cohesion increased by 20.27%, and the internal friction angle decreased by 11.27%. However, the mechanical properties decreased when the slaking time was too long. After 72 h of slaking, the cohesion of 20% lime soil decreased by 8.21% and the internal friction angle increased by 2.82%. Further analysis shows that the appropriate slaking conditions can regulate the reaction rate and alkali environment, control the lime produced cementitious substances, improve the particle gradation and further reduce the occurrence of surface cracks. These results provide a basis for the restoration technology of newly repaired earthen city walls.

Experimental Study on the Effect of Carbonation Reaction on the Properties of Imitation Site Soil

In this study, sodium methylsilicate and lime were selected to prepare the same proportion of Imitation Site Soil, and according to the principle of carbonation reaction of restoration materials, the effect of carbonation reaction on the performance of restoration soil of earthen sites was studied. The study has good significance for the conservation and restoration of earthen sites. The samples were cured with CO₂ concentration and curing age as variables. After curing, the samples were tested to determine their water-resistant properties, uniaxial compressive strength, and pH value and a micro scanning electron microscope was used. The results indicated that the carbonation reaction can quickly improve the water resistance and compressive strength of imitation site soil, and reduced the water absorption by 16.67% compared to the specimens conditioned at 0.03% CO₂ concentration. The UCS of specimens at 5%, 10%, and 15% CO₂ concentrations increased by 72.22%, 131.19%, and 219.27%, respectively, compared with those at 0.03% CO₂ concentration after the specimens were environmentally maintained in the carbonation chamber at 0.03%, 5%, 10%, and 15% CO₂ concentrations for 120 h, respectively. The internal particle gradation of the imitation site soil improved after carbonation. These results provide a basis for improving the restoration technology of earthen sites.