巴东组压实黏性土湿化变形特性试验研究

Experimental study on wetting deformation characteristics of compacted cohesive soil of Badong formation

巫山县污水处理厂高填方工程场坪高程为179 m,最大填方高度为75 m。当三峡水库蓄水至175 m高程时,填方体绝大部分位于库水位以下,必须考虑填料湿化变形引起的沉降和不均匀沉降。土体浸水湿化不仅可引起湿化体积变形,而且还会引起剪切变形和土体强度降低,从而影响土工建筑物的安全。对巴东组土料进行颗粒分析和重型击实试验,得到了填料的可压实性、最优含水率和最大干密度指标;选择巴东组二段土料进行不同压实度、不同围压下的三轴湿化变形试验,得到了湿化应力-应变关系和附加湿化应变与应力水平、围压的关系。结果表明:湿化变形随湿化点偏应力增大而增大,附加轴向应变随围压增大而减小,随着应力水平增大而增大;当轴向应变超过某特征值时,其偏差应力与轴向应变由幂函数关系变为双曲线关系,特征值约为1.2%;围压较小时,附加体积应变随着湿化点应力水平增大而增大,当围压较大时,附加体积应变随应力水平增大先增大,然后趋于稳定,最后再减小。巫山县污水处理厂高填方工程采用“碾压+强夯”控制干密度和“湿法填筑”控制施工含水量,高填方的最大总沉降为69.85 mm,小于限定值100 mm,取得了较好的工程效果。

The elevation of the site-formation works for the high earthfill project of Wushan County Sewage Treatment Plant is 179m with the maximum filling height of 75m.When the impoundment of the Three Gorges Reservoir reaches the elevation of 175m,most of the filling body is located below the reservoir water level,thus the settlement and uneven settlement caused by the wetting deformation of the filling material must be considered.The wetting of soil mass caused by water-immersion can not only lead to wetting volume deformation,but also cause shear deformation and the decrease of the strength of the soil mass,thus impact the safety of the relevant hydraulic structure.Both the particle size analysis and heavy compaction test are made on the earth material of Badong Formation,and then the compactibility,the optimal water content and the index of the maximum dry density of the filling material are obtained,while the experiments of the triaxial wetting deformations under different compactnesses and different confining pressures are made on the earth material from the second member of Badong Formation;from which the wetting stress-strain relationship and the relationship between the additional wetting strain and stress level as well as the confining pressure are obtained.The wetting deformation increases along with the increase of the deviatoric stress at the wetting point,while the additional axial strain decreases along with the increase of the confining pressure and increases along with the increase of the stress level.When the axial strain exceeds a certain characteristic value,the relationship between its deviatoric stress and axial strain changes from a power function relationship into a hyperbolic relationship,of which the characteristic value is about 1.2%.When the confining pressure is lower,the additional volume strain increases along with the increase of the stress level at the wetting point,while the additional volume strain increases at first,and then tends to stable and finally decreases along with the increase of the stress level under a higher confining pressure.For the high earthfill project of Wushan County Sewage Treatment Plant,the method of controlling the dry density with roller-compaction+dynamic compaction and the method of wet-filling for controlling the construction water content are adopted,and then the maximum total settlement of the high earthfill body is 69.85 mm,which is less than the limit value of 100 mm,thus a better engineering effect is achieved.