天津滨海地区深部黏土层弹塑性变形特征与地面沉降关系研究

利用在滨海新区施工的2眼全取芯钻孔（G2和G3），通过原状土样工程特性指标测试、固结压力试验、0-P0反复加、卸荷试验及地面沉降分层标监测数据分析等，系统阐述了滨海地区深部黏性土层弹塑性变形特征与地面沉降的关系。结果表明：天津滨海地区100 m以浅主要为欠固结土层；100～400 m土层处于超固结和微超固结状态，主要是由过去地下水超量开采造成的；400 m以下土层以正常固结为主。G2和G3孔不同层位黏性土层在反复加、卸荷试验过程中表现出塑性变形量逐渐减小，而弹性变形量几乎不变，与反复加、卸荷次数无关，表明黏性土层在水位反复升降条件下，逐渐变为以弹性变形为主。黏性土层这种特性显示，在地下水位反复升降多次后，黏性土层将会逐渐变成弹性体，在水位恢复时，将产生同步回弹，对防治地面沉降具有重要意义。分析弹塑性变形与黏性土层深度、天然含水率和黏粒含量的相关性发现：弹性变形量与黏性土层深度、天然含水率及黏粒含量呈正相关性；塑性变形量与深度相关性不明显，与天然含水率和黏粒含量呈负相关性。

Relationship between elastoplastic deformation of deep clay and land subsidence in Tianjin coastal area

Two boreholes of G2 and G3 were drilled at Tanggu and Dagang in Tianjin, and undisturbed samples were extracted at various depths. Through laboratory test of all soil samples, this study measured the physical and mechanical properties and conducted consolidation test and repeated loading and unloading tests for clayey soils. By analyzing the test results, this study delineated the characteristics and influence factors of elastic-plastic deformation. Study results indicate that clayey soils in depth less than 100 m are under-consolidated soft soil. Clayey soils in depth from 100 m to 400 m are in the states of over-consolidated or slightly over-consolidated, which causes by long-term over-exploitation of groundwater in the past. Deep clayey soils in depth more than 400 m show the state of normal consolidated. Based on the repeated loading and unloading tests of clayey soils in boreholes G2 and G3, it is found that plastic deformation decreases gradually and elastic deformation remains unchanged, independent on repeating times. The test results also suggest that clayey soils will gradually become an elastic body in the process of groundwater fluctuation, and deformation will rebound when groundwater recovers. By analyzing correlation between elastic-plastic deformation and depth, natural moisture content and clay content of clayey soil, it is found that elastic deformation shows positive correlation with depth, natural moisture content and clay content, and plastic deformation shows negative correlation with natural moisture content and clay content and no obvious correlation with depth.