Abstract:Considering some sinkholes found in loess area along the high speed railway(TGV) in France,which affect the foundations of TGV during the very rainy periods,the geological and geotechnical properties,especially the collapsibility of loess have been analyzed. Based on the geological presentation of loess deposits in northern France,tests on the collapsibility of loess located at the place 140 km north to Paris along the TGV have been carried out. The effects of initial water contents on the magnitude of collapse are also examined to find out the effects of seasonal change of water content on the loess collapsibility. Test results show that the effects of water content change on the magnitude of collapsibility are significant. The collapsibility linearly decreases with the increase of initial water content. So,the criteria for collapsibility should include the initial water content. The evaluation of various criteria for collapsibility are discussed according to the testing results obtained.