巴基斯坦某黄土场地湿陷特性试验

Research on collapsibility of a loess site in Pakistan

巴基斯坦某地区的黄土为第四纪全新统冲洪积层,对该地区的研究和现有地质资料都比较少,需要做专门的研究。为了确定该区域的黄土地层分布情况及湿陷特性,根据工程场地建筑分布,分别选取典型位置的钻孔,取土样进行土工室内试验研究。利用构度指标定量描述黄土的结构特征,确定黄土的自重湿陷系数和湿陷系数,计算场地自重湿陷量和总湿陷量,并与规范方法进行比较。试验结果表明,该区域场地黄土的干密度和湿陷系数(上覆压力200 kPa)随深度几乎不变,天然含水率随深度整体呈增加的趋势。黄土的构度随综合物理特征量的增加而呈指数形式减小,压缩屈服应力psc随含水量的增加而减小,并且与构度呈线性关系。判定该区域黄土的场地为自重湿陷性场地,修正系数建议取小于1,地基湿陷等级为Ⅲ级严重。

The loess of an area in Pakistan is the Quaternary Holocene alluvium.The study and existing geological data in this area are relatively few,and special research is needed.In order to determine the distribution and collapsibility of the loess,based on the construction distribution of the loess site,undisturbed soil sample was selected at the typical location.The unconfined compression strength tests and compressive tests were carried out.The structural characteristics of loess were quantitatively described by structural index.The self-weight collapsible coefficient and collapsible coefficient of loess were determined,the self-weight settlement and the total settlement were calculated and compared with the standard method.The experimental results show that the dry density and the collapsible coefficient(p=200 kPa)of the loess are almost unchanged with the depth,and the natural moisture content increases as a whole.The structural index of loess decreases exponentially with the increase of comprehensive physical quantity.The compressive yield stress psc decreases with the increase of moisture content,and it has a linear relationship with the structural index.The loess site was determined as a self-weight collapsible site.The correction coefficient is suggested to be less than 1,and the grade of foundation collapsible is Ⅲ.