北京市山前缓倾台地黄土的湿陷性特征

Collapsible characteristics of loess on the piedmont dipping tableland in Beijing

通过室内试验和原位静载荷试验对工程经验和试验研究资料欠缺的北京市密云县浅山区薄层黄土的湿陷性特征进行了研究。根据室内试验成果,总结分析了研究区黄土物理指标与湿陷系数的关系。湿陷性终止含水量介于25%~30%;湿陷变形经历压密、稳定、破坏三个阶段;较小(50kPa)压力下黄土的湿陷敏感性弱,随着压力的增大敏感性增强,至100~150kPa时,敏感性达到峰值,随后逐渐减弱。选取研究区典型粉土层和粘土层进行了天然状态和浸水饱和后的原位静载荷试验,分析P-s曲线和s-lgt曲线认为,粉土层浸水饱和后的压缩变形经历四个阶段,湿陷性强烈,湿陷等级为II级,湿陷起始压力为50kPa;粘土层不湿陷,浸水饱和后应变硬化在0~25kPa阶段完成,此后沉降量基本随压力的增大呈线性增长,没有出现像粉土层浸水后在压力作用下结构性反复破坏的现象。

The characteristics of the piedmont thin collapsibility loess in Beijing Miyun County where the engineering experience and researching data are short are studied based on laboratory tests and in-situ static loading tests.Based on the results of the laboratory tests,the relationship between the coefficient of collapsibility and the physical indexes is analyzed.The collapsibility will disappear when the moisture content is over 25% to 30%.The collapse deformation will go through three stages：compaction,stability and destruction.The collapsible sensitivity is weak under lower pressure（50 kPa）.With the increase of pressure,the collapsible sensitivity increases.To 100~150 kPa,the collapsible sensitivity achieves to the peak,and then gradually weakens.Based on the natural state and after soaking in-situ static loading tests for the typical silt and clay layer,the P-s curves and s-lgt curves are analyzed.The silt layer deformation after soaking will go through four stages.The collapsibility is strong with class II grade,and then the initial collapse pressure is 50 kPa.Clay layer is not collapsible.After soaking,the strain hardening will be completed under the pressure of 0~25 kPa,and then the settlement has a linear growth with the pressure.There is no repeated structure damage under the pressure after soaking.