| Collapsible loess is a kind of soil whose structure is destroyed and whose soil body is obviously deformed after immersion under the action of self-weight stress or additional stress plus self-weight stress of overlying soil.When there is collapsible loess in engineering construction,it is necessary to consider the influences of collapsibility on foundation and buildings,otherwise it will cause damage and loss in engineering.The surrounding areas of Lanzhou city is a typical large thickness collapsible loess area.The collapsible soil layer has a large thickness and a high collapsibility level.It is of great significance to study the engineering characteristics of loess in this area,especially the collapsible characteristics for engineering construction.Based on the newly built Pengjiaping Water Treatment Plant and Evergrande Feicui Huating Project,this paper studies the engineering characteristics of collapsible loess in Lanzhou.The main research contents and achievements are as follows:(1)This paper analyzes the collapsibility mechanism of loess and analyzes the physical and mechanical factors that influence collapsibility of loess.(2)The thickness of loess layer in Pengjiaping is about 50 meters,and there are silt and gravel interbeds in the lower part.The density of loess is relatively dense,and the collapsibility coefficient is positively related to the void ratio,and negatively related to the dry density.The soil samples that determine the degree of collapsibility are those with void ratio greater than 0.8 and dry density less than 1.35.(3)The water content of soil samples with slight to medium degree of collapse is mainly in the range of 7%-17%.When the water content is greater than 17.5%,the collapsibility coefficient of soil samples of both projects is less than 0.015,and when the water content is high,the soil samples certainly have no collapsibility,but when the water content is low,the soil samples do not necessarily have collapsibility,so thewater content is not the most important factor affecting the collapsibility.(4)The collapsibility level is an important index to evaluate the collapsibility of loess layer,and the collapsibility depth is an important index of foundation treatment,but the area with high collapsibility depth may not have high collapsibility level.The distribution of the collapsibility of Evergrande Feicui Huating is different from Pengjiaping Water Treatment Plant.Although the thickness of the soil layer is large,the thickness of the collapsible soil layer is not large,and the collapsibility of the upper soil layer is strong,so the collapsibility level is very high.It can be seen that it is not comprehensive to evaluate the collapsibility of soil samples only by sampling depth,and other physical indexes need to be analyzed.(5)Pengjiaping area is a large thickness collapsible loess site,but the thickness of collapsible soil layer is about 20 meters,so it is feasible to use compaction pile to treat the foundation.(6)This paper further analyzes the data of Pengjiaping area by multiple regression analysis.After the collinearity test,since the void ratio index is calculated according to the density index,the paper conducted multiple regression analysis with the collapsibility coefficient as the dependent variable and the water content,depth and dry density as the independent variables.The results show that the void ratio has the greatest influence on the collapsibility coefficient.At the same time,to verify whether this conclusion is applicable to other areas of Lanzhou city,this paper compares the soil samples of Evergrande Shanshuicheng area,which is far away from Pengjiaping area.The regression results show that the void ratio also has the greatest impact on the collapsibility coefficient of Evergrande Shanshuicheng area. |
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