Physical States and Strength Parameters of Low-Compacted Garden Hill Fill in Shanghai

Abstract

The physical states of two artificially constructed garden hills in Chenshan Garden in Shanghai were investigated in field. It was found that in the warm and humid climate of Shanghai city, the unsaturated fills have high water contents (mostly between 25% and 30%), high saturation degrees (mostly between 88% and 98%), and low compaction degrees (mostly between 83% and 91%). Direct shear tests were conducted on two kinds samples to investigate the influence of saturation degree and compaction degree on the shear strengths of the fill, laboratory compacted samples prepared with four compaction degrees and four saturation degrees, and in-situ samples boring from the two hills. Based on the test results, strength parameter values of the fills considering the physical states were given for the stability analysis of the soft ground and hill slope. INTRODUCTION Shanghai is located in the Yangtze River delta of China and the ground surface is flat. Artificially filled hills are often constructed in gardens on the soft ground of the city. Silty clay is usually used for the fill material. Height of the artificially constructed hills increased rapidly in recent years, from 5m up to over 20m. Stability control of the soft ground and the hill slope are very important in this kind of project, and the strengths of the fill material need to be determined properly for a reliable stability analysis. The fills of the garden hills are usually unsaturated in natural condition. It is well known the shear strength and strength parameters of unsaturated soil highly depends on the physical states, such as compaction degree, water content, and saturation degree (Fredlund and Rahardjo, 1997). The physical properties of the fills relate to not only the condition under construction, but also the climate conditions after construction. The natural silty clay used is mostly below the groundwater level and saturated. After excavated and transported to the construction site, although it is dried by exposing in atmosphere, the silty clay still has high water content when used for construction. The compaction is usually conducted by driving the truck on the fill for several rounds. Thus, the compaction degree is usually much lower than the fills in embankments. The climate in Shanghai is warm and wet, and the average yearly rainfall is about 1200mm. This kind climate condition may also impact the water content of the fills strongly. The most field investigations of the effect of climate conditions on the physical states and strengths of compacted fills focus on the road embankment fills. For 164 Soil Behavior and Geomechanics GSP 236 © ASCE 2014