Leaning pagodas in China: laboratory test and analysis of subsidence under frequent earthquakes

Abstract

The inclination of ancient pagodas leads to a non-uniform stress distribution on the soil below. This non-uniform stress threatens the structural stability of the ancient pagodas, and the degree of damage depends on the soil properties. This paper researches the residual strain under the ancient pagodas in China to simulate the non-uniform stress state under frequent earthquake conditions using a dynamic triaxial test apparatus. The non-uniform stress state was expressed by the consolidation stress ratio. The frequent earthquakes were indicated by the dynamic stress ratio and cyclic interval vibration loading. To describe the foundations of the ancient pagodas in China, two types of soil, the mucky clay (Q4) and the paleo-clay ( $${\text{Q}}_{3}^{\text{al}}$$ ), were tested. The relationship between the two different soils and the consolidation and dynamic stress ratios were determined by measuring the deformation and accumulated deformation. Additionally, mathematical models to estimate the residual strains of the soils were established and verified. The results indicate that the soil strain increment of mucky clay, which increases with the consolidation stress ratio and dynamic stress ratio, is an important parameter for evaluating the leaning pagodas’ stability in soft soil regions when subjected to frequent earthquake. The soil strain increment of paleo-clay, however, is inversely proportional to the consolidation stress ratio and no apparent relationship is found with the dynamic stress ratio. More research needs to be done on the subsidence of paleo-clay.