The reciprocating action of the external environment gradually reduces the mechanical properties and water stability of original heritage buildings, resulting in the gradual loss of their cultural value. In this paper, the adobe for the construction of raw soil and cultural relics in western Henan is taken as the research object. The local plain soil is used as the raw material, and the adobe samples are prepared with modified materials such as quicklime and sodium methyl silicate, in order to improve its mechanical properties and water stability. The degree of correlation between the compressive strength, capillary water absorption, pH value, particle size distribution, and the electrical conductivity of modified raw adobe, as well as the modification mechanism of the microstructure, was studied. The results show that the addition of quicklime and sodium methyl silicate can enhance the compressive strength and water resistance of the modified raw adobe, and the optimum dosage is 1.5% sodium methyl silicate; with the increase of the curing age, the compressive strength of the single-mixed quicklime sample, the single mixed sodium methyl silicate samples, and the composite sample were increased by 1.94 times, 12.6 times and 2.61 times, respectively, compared with the plain soil samples, and with the increase of compressive strength, the pH, conductivity and capillary water absorption of the samples decreased continuously. It is evident from the particle gradation test and SEM images that the internal pores of the samples in the modified group become smaller, and the particle structure of the sample doped with sodium methyl silicate is the densest. The results of the study provide support for the restoration of the soil and cultural-relic buildings.

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.

The calibration of material mechanical parameters and deformation and failure mechanism of earthen soil have always been difficult problems in the field of cultural relics protection. How to establish a relationship between physical and mechanical properties of soil at macro and micro scales is the focus of the research. The nanostructure model of earthen soil composed of many atoms was established by molecular dynamics (MD) method. The stress-strain relationship of different moisture content was obtained by uniaxial compression simulation. Based on the electron micrograph image (magnification ×500) and the image reconstruction method, a micromodel composed of particles and pores was constructed. Furthermore, using the displacement loading method, we obtained the stress-strain relationship of the earthen soil with different moisture contents. Our results showed that the displacement of the left and right boundaries of the circular pore model is 1.26 times more than that of the polygonal pore model, and the displacement of the polygonal pore model is 1.28 times more than that of the circular pore model. The stress-strain curve simulated by the polygonal pore model is consistent with the experimental results. The results of the numerical analysis are in good agreement with those of the macro test, which indicates that the research ideas and the methods used for earthen soil exploration in this work are feasible. Our present findings provide reference for deterioration research and safety evaluation of cultural relic buildings such as earthen sites.