【作者】 张正；

【导师】 杨建民； 韩俊杰；

【作者基本信息】 天津大学 ， 建筑与土木工程， 2019， 硕士

【摘要】 按照经典土压力理论进行基坑支护设计,非饱和土地区基坑支护结构实测位移通常远小于设计值,其中一个重要原因是未考虑非饱和土基质吸力影响而导致抗剪强度指标偏小。本文针对山西盂县某基坑工程实例,基于文献数据推算其非饱和黄土水-土特征关系曲线,并将得到曲线与63条黄土水-土特征关系曲线所形成的数据库曲线进行比对以验证其正确性。应用非饱和土理论,考虑基质吸力对非饱和土抗剪强度值的影响,沿用规范方法计算支护结构主动和被动土压力,并比较选用两种非饱和土处理方法进行计算比对,对设计结果进行校核。为验证理论的正确性及对不同施工方法的通用性,依据河道两岸荷载分布情况选取坑边超载较小的两工段,设计并施工灌注桩和SMW工法桩进行试验,并连续监测位移控制点位移情况。经比对:采用非饱和土抗剪强度设计所得支护结构受力和变形远小于规范方法计算结果,且更接近于实测值;进一步分析了非饱和土饱和度变化对本工程支护结构受力和变形的影响,得到饱和度与弯矩及位移的拟合曲线;在实际工程分析及整理过程中发现两种非饱和土处理方法的内在联系,严格证明了总粘聚力法非饱和土处理方法与卢宁吸应力法非饱和土处理方法完全等效。并提出基于现行规范应用非饱和土抗剪强度值进行基坑设计的流程供参考。基于部分试验段中基坑上侧存在土坡情况而造成理论分析与实际位移有出入的问题;更进一步分析了坑边非饱和土坡对支护结构土压力的影响;建模分析了坡壁挖槽状态下土坡最大自平衡宽度并与估算公式进行对比,提出3种理论工况并应用PLAXIS 3D进行有限元模拟,通过有限元模拟与理论结果的对比,验证理论正确性的同时证明了采用此理论可进一步降低支护结构的内力及位移。更多还原

【Abstract】 The measured internal force and displacement for supporting structure of deep excavation are usually much smaller than those calculated with classic earth pressure theories.One of the important reasons is the matrix suction of unsaturated soil is not taken into account which reduces the shear force index.In this paper,a project is made in Yu County,Shanxi Province,the presumed loess soil-water characteristic curve is get based on the literature data.The curves obtained are compared with the database curves formed by 63 soil-water characteristic curve of loess to verify their correctness.The unsaturated soil theory is applied and the matric suction effect on shear strength of unsaturated soils is considered.Based on the technical specification for retaining and protection of building foundation excavations to calculate active and passive earth pressures,two methods of unsaturated soil treatment are compared and a check of design results is made.In order to verify the correctness of the theory and the universality of different construction methods,according to the load distribution on both sides of the river,two sections are selected to carry out the test of the bored piles and the Soil Mixing Wall(SMW)piles,respectively,and the displacement of the displacement control point is continuously monitored.It is found that the force and deformation of the supporting structure obtained by the shear strength of unsaturated soil is much smaller than that of the design by technical specification for retaining and protection of building foundation excavations,which is closer to the measured value.The influence of saturation changes in unsaturated soil to the supporting structure force and deformation is analysed,in the process of practical engineering analysis and consolidation,the internal relationship between the two methods of unsaturated soil treatment is found,we also strictly prove that the total cohesion method is equivalent to the Ning Lu suction stress method.The process of supporting structure design based on current specifications using the application of unsaturated soil shear strength values is proposed for reference.Based on the existence of soil slope on the upper side of the supported excavation in some test sections where the theoretical analysis and the actual displacement are different.The influence of the unsaturated slope on the soil pressure of the supporting structure is further analyzed.The modeling of the slope wall is analyzed.The maximum self-balancing width of the soil slope is compared with the estimation formula.Three theoretical conditions are proposed and the finite element simulation is carried out by using PLAXIS 3D.The comparison between the finite element simulation and the theoretical results verifies the theoretical correctness and proves the adoption of this.The theory can further reduce the internal force and displacement of the supporting structure.更多还原