中国南海吹填岛礁钙质砂动力特性试验研究

Experimental investigation on the dynamic characteristics of calcareous sand from the reclaimed coral reef islands in the South China Sea

南海对我国经济发展、资源开发与运输、维护国土完整具有战略性意义。目前我国已在南海海域以吹填方式建设了一系列的岛礁,并在其上修建了一系列的结构物(房屋、防波堤、机场等)。作为这些重要结构物的地基材料,珊瑚钙质砂在极端波浪、海底地震等环境荷载作用下的动态响应特性对评价其上结构物的安全稳定性具有重要的意义。以我国南海珊瑚岛礁吹填工程为背景,对取自岛礁吹填体现场的钙质砂样品,以吹填现场实测的颗粒级配和干密度为依据,开展动态三轴循环试验,研究我国南海珊瑚岛礁吹填体钙质砂地基土的动力特性。试验结果表明:岛礁钙质砂受动态循环荷载作用,在排水不通畅的条件下可以达到部分液化状态,在排水通畅的条件下不发生液化;在不排水条件下,岛礁钙质砂归一化的累积孔压u/σ0’与振次比N/Nf符合Seed提出的反正弦孔压发展模式;在不排水条件下,所有岛礁钙质砂样品的动态变形模量Ed/E0与归一化应变εm/εr之间全部重合在一条双曲线上,表明不排水条件下岛礁钙质砂的Ed/E0与εm/εr化之间的关系不受干密度和颗粒级配的影响,具有很好的统一性。

The South China Sea shows strategic significance for China’s economic development,resource exploitation,and maintenance of national land integrity.At present,China has built a series of coral reef islands in the South China Sea by the means of reclamation.A number of structures,such as buildings,breakwaters and airports etc.,have been built on these reclaimed coral reef islands.As the foundation materials,calcareous sand’s response to extreme ocean wave and strong seismic wave play an important role in evaluating the stability of these structures on these reclaimed islands.In this study,taking the coral reef island reclamation project in the South China Sea as the engineering background,a series of tri-axial cyclic tests is performed for the calcareous sands sampled from reclaimed islands,to investigate their dynamic mechanical properties.The experimental results show that the calcareous could become partially liquefied under cyclic loading in undrained condition.While they can’t become liquefied in drained condition.In undrained condition,the relationship between normalized residual pore pressure u/σ0’and cycle times ratio N/Nfis found in accordance with the inverse sine development model proposed by Seed.Furthermore,the relationship curves between the dynamic deformation modulus of all calcareous sand samples and their corresponding normalized strainεm/εr all overlap on one hyperbolic line,indicating that the relationship between the dynamic deformation modulus and normalized strainεm/εr of calcareous sand is independent on dry density,particles size gradation.