| Shanghai is one of the most famous soft soil regions in the world. Its poor geological condition brings many difficulties to the development of Shanghai's underground space. Artificial Ground Freezing Method (AGFM) is widely used in subway projects in Shanghai for it can discard disadvantages of soft soil. AGFM is usually treated as a technique with high safety factor. But the geological disaster happened in 2003 on Line 4 of Shanghai metro warned us once again. It is necessary for us to carry out more study on artificial frozen soil.So far, there is no full study on engineering properties of Shanghai soft soils under secondary freeze-thaw action. This study is based on the restoration project of the Line 4 of Shanghai metro. Reviewing the researches on effects on mechanical properties of frozen soil under freeze-thaw action, the research methods of frozen soil and the status of research on frozen soil's structural characteristics, this study is to make systematic advanced development on engineering properties of layer ⑥, layer ⑦1 and layer ⑦2 soils in Shanghai. The research work involves several aspects as following:(1) To investigate status of researches on soil under freeze-thaw action, and summarize results of experimental research on this area.(2) To find out the differences of these three different layers of soil. These different properties are the key factor to their different engineering properties under freeze-thaw action.(3) To do systematic advanced developments, including mechanics test, thermodynamic test, frost heave test, thawing settlement test. Analyze the different factors of each parameter, and find out the rules on how these properties of different soils change under cyclic freeze-thaw action. Give reasons to the results. Find out the key different properties of layer ⑥, layer ⑦1 and layer ⑦2 soil broadways, find out the key different properties of each layer of soil lengthways.(4) To find out several measures that can improve the safety performance of...
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