【作者】 秦晓艳；

【导师】 介玉新；

【作者基本信息】 清华大学 ， 岩土工程， 2010， 硕士

【摘要】 在西部山区,削山填沟既是防灾减灾的需要,也有利于缓解用地矛盾。结合略阳县凤凰山区综合治理工程,论文对土桥沟和罗家沟填方工程进行了有限元应力应变计算和稳定性分析。论文主要进行以下工作:(1)针对土桥沟和罗家沟填方工程下部的堆石混凝土挡土坝,研究下游面坡度、上游面倾角、坝后土体内摩擦角、地震烈度等对挡土坝抗滑稳定性的影响。计算表明:减缓下游面坡度、增大上游面倾角或墙后土体内摩擦角,均能增大堆石混凝土挡土坝的抗滑稳定性;坡度为1:0.8的土桥沟堆石混凝土挡土坝和1:0.7的罗家沟堆石混凝土挡土坝能够满足正常使用和抗震要求。(2)采用有限元方法,研究堆填土变形模量、泊松比以及土工格栅变形模量对填方工程应力应变的影响。计算结果表明,随着堆填土变形模量的增大,水平位移和竖向沉降均减小;随着泊松比增大,水平位移增大,竖向沉降减小;当土工格栅变形模量增大时,水平位移减小,但竖向沉降基本不变。(3)对加筋边坡进行正常使用和地震荷载下瑞典条分法和毕肖普法稳定分析,计算表明两边坡均满足抗滑要求。(4)对加筋边坡进行有限元强度折减法稳定分析,并对边坡失稳三种判据进行了研究。计算结果表明三种不同的判据对应着不同的安全系数,采用某种单一判据来判断边坡是否失稳是不可靠的。在加筋土边坡中应当考虑筋材抗拉强度不足而引起的边坡失稳。结合加筋边坡破坏机理和失稳的具体体现,建议综合考虑塑性区贯穿、特征点位移拐点和数值计算收敛性,并将筋材受力情况作为边坡失稳的辅助判据。数值计算表明,边坡坡脚的筋材往往首先达到抗拉强度,加筋高边坡中局部破坏很可能成为控制因素。(5)依据边坡滑动的矢量特征,假定筋材和土体具有相同安全系数,构造了加筋边坡“矢量和”法安全系数求解公式,将基于有限元真实应力场的素土边坡抗滑稳定分析的“矢量和”法应用于加筋边坡。计算结果表明,不管是素土边坡还是加筋边坡,“矢量和”法计算结果均与极限平衡法相近,且能克服有限元强度折减法安全系数依赖于边坡失稳判据的缺点。更多还原

【Abstract】 In the western mountains, cutting hills to backfill ditchs not only meets the needs of disaster prevention and mitigation, but also contributes to ease the shortage of land. With Lueyang comprehensive treatment project in the Phoenix Mountains, FEM calculation of stress and strain field and stability analysis to Tuqiaogou and Luojiagou Embankment are done in the paper. The following is the main contents in the paper:(1) The stability of the concrete retaining wall located in the lower embankmen is analysed. The influence of the downstream face slope, the upstream face angle, friction angle of soil behind the wall and seismic intensity is studied. The calculation results show that: reducing the downstream slope or increasing the upstream face angle and internal friction angle can increase the stability of the concrete retaining wall; When the downstream face slope is 1:0.8, the the concrete retaining wall of Tuqiaogou Embankmen meets the normal use and seismic requirements; to the concrete retaining wall of Luojiagou Embankmen, the downstream face slope of 1:0.8 can meet the normal use and seismic requirements.(2) Using the FEM softward ABAQUS, stress and strain fields in Tuqiaogou Embankment and Luojiagou Embankment are calculated and the influence of soil deformation modulus, Poisson’s ratio and deformation modulus of geogrid is studied. The results show that: increasing deformation modulus of soil, horizontal displacement and vertical settlement are reduced at the same time; increasing Poisson’s ratio, the horizontal displacement increases, but the vertical settlement decreases; increasing deformation modulus of geogrid, the horizontal displacement decreases, but the vertical settlement remains unchanged.(3)Using the software STAB developed by Chen Zuyu Academician, the reinforced slope stability under normal use and seismic load conditions is calculated. The calculation results of Swedish circle method and simplified Bishop method show that: the reinforced slopes of Tuqiaogou Embankment and Luojiagou Embankment meet the normal use and seismic requirements. (4) Using ABAQUS software, the reinforced slope stability is analysed by FEM strength reduction, and three slope failure criteria are studied. When the equivalent plastic strain zone with a given value develops from the toe and the top, the displacement occurrs mutation or calculation fails to converge, we think the slope becomes instable. The calculation results show that the safety factor of slopes under different criteria is different. The safety fator is not reliable if single criterion is used to judge whether the slope is safe or not was used. So the three slope failure criteria should be all considered. If the tensile force of geogrid is beyond tensile strength, the slope may slide. So the tensile forces of geogrid should be considered as a secondary criterion of slope failure and the criterion for reinforcement design rationality. Studies show that: the stress of the geogrid in toe of the slope often firstly reaches its tensile strength, and local instability in reinforced slope may be control factors.(5)Based on the vector characteristics of slope sliding, safety factor formula of vector sum method is constructed. It assumes that the geigrid has the same safety factor with soil, and vector sum method in natural slope is introduced to the reinforced slope safety analysis. The results show that whether it is natrual slope or reinfored, the results of vector sum method were similar with the limit equilibrium method. It overcomes shortcomings of FEM strength reduction-the safety fator is subjected to failure cateria and stress field is unreal.更多还原