The effect of SH-lime composite material on capillary water rise resistance in the Great Wall

Abstract

Capillary rise of water leads to salt migration and accumulation, which is the main cause of erosion at the bottom of the Great Wall in Northwest China. In this study, we evaluated the effectiveness of SH (modified polyvinyl alcohol) and lime composite material against capillary water rise. We conducted comparative capillary rise cycle tests on two sample types: untreated Great Wall soil and soil treated with the SH-lime composite, using solutions of NaCl and Na2SO4 of specified concentrations. The surface hardness, strength, water-salt distribution, and pore size distribution of the samples were also evaluated. The results showed that: in the salt solution capillary rise cycle, the untreated soil samples quickly changed color and precipitated white crystals. As the test proceeded, the untreated soil samples developed cracks, followed by fragmentation at the corners, and finally collapsed. In contrast, the SH-lime solidified soil had less white crystal precipitation and no visible cracks after 7 cycles. This indicates that the overall integrity of the SH-lime solidified soil was higher. The capillary rise cycles also changed the pore size distribution of the samples. NaCl crystals tended to occupy and expand micropores and small pores, while Na2SO4 crystals tended to grow in large pores. In addition, Na2SO4 was more destructive to soil than NaCl. The SH-lime composite material reduced porosity and strengthened soil structure, which slowed down the expansion of large pores. The study concludes that SH-lime effectively inhibits capillary rise-induced water-salt migration and associated damage, making it a suitable choice for repairing capillary rise-prone Great Wall sites.