Abstract: Combined with an engineering survey example under a weathered and eroded landform in Qionghai City, Hainan Province, the geotechnical engineering conditions of the site were identified by using a variety of investigation methods. There are different types of bedrocks with different degrees of weathering at the site. The sandstones and granites formed in the early period and the basalts formed in the Early Pleistocene of the Quaternary are filled with cohesive soil and sandy soil of marine and terrestrial deposits, forming a complex spatial distribution. Uneven hardness within the rock mass, large difference in shear strength, weak interlayer and other characteristics of the bedrock and soil layers. According to the investigation results, the complexity and uniformity of the proposed foundation under such geotechnical conditions are evaluated, and the influence of the characteristics of the large undulations of the bedrock surface, the soft interlayer between the bedrock and the hard interlayer of volcanic rock on the construction of the project is analyzed. For the individual building structures with different dimensions in the residential complex, potential geotechnical engineering problems, and the treatment measures and suggestions are presented in the paper.

Key words: safe thickness of foundation bedrock, hard interlayer of volcanic rock, weak substratum, ground uniformity