Upper bound analysis of ultimate pullout capacity of shallow 3-D circular plate anchors based on nonlinear Mohr-Coulomb failure criterion

Based on the nonlinear Mohr-Coulomb failure criterion and the associated flow rules,the three-dimensional(3-D)axisymmetric failure mechanism of shallow horizontal circular plate anchors that are subjected to the ultimate pullout capacity(UPC)is determined.A derivative function of the projection function for projecting the 3-D axisymmetric failure surface on plane is deduced using the variation theory.By using difference principle,the primitive function of failure surface satisfying boundary condition and numerical solution to its corresponding ultimate pullout capacity function are obtained.The influences of nonlinear Mohr-Coulomb parameters on UPC and failure mechanism are studied.The result shows that UPC decreases with dimensionless parameter m and uniaxial tensile strength increases but increases when depth and radius of plate anchor,surface overload,initial cohesion,geomaterial density and friction angle increase.The failure surface is similar to a symmetrical spatial funnel,and its shape is mainly determined by dimensionless parameter m;the surface damage range expands with the increase of radius and depth of the plate anchor as well as initial cohesion but decreases with the increase of dimensionless parameter m and uniaxial tensile strength as well as geomaterial density.As the dimensionless parameter m=2.0,the numerical solution of UPC based on the difference principle is proved to be feasible and effective through the comparison with the exact solution.In addition,the comparison between solutions of UPC computed by variation method and those computed by upper bound method indicate that variation method outperforms upper bound method.

Variation analysis of ultimate pullout capacity of shallow horizontal strip anchor plate with 2-layer overlying soil based on nonlinear M-C failure criterion

Based on the nonlinear Mohr-Coulomb failure criterion and an associated flow rule,a kinematic admissible velocity field of failure mechanism of the 2-layer soil above a shallow horizontal strip anchor plate is constructed.The ultimate pull-out force and its corresponding failure mechanism through the upper bound limit analysis according to a variation principle are deduced.When the 2-layer overlying soil is degraded into single-layer soil,the model of ultimate pullout force could also be degraded into the model of single-layer soil.And the comparison between results of single-layer soil variation method and those calculated by rigid limit analysis method proves the correctness of our method.Based on that,the influence of changes of geotechnical parameters on ultimate pullout forces and failure mechanism of a shallow horizontal strip anchor with the 2-layer soil above are analyzed.The results show that the ultimate pull-out force and failure mechanism of a shallow horizontal strip anchor with the 2-layer soil above are affected by the nonlinear geotechnical parameters greatly.Thus,it is very important to obtain the accurate geotechnical parameters of 2-layer soil for the evaluation of the ultimate pullout capacity of the anchor plate.

浅埋小断面隧洞开挖技术在白乃水库中的应用

为了保证浅埋隧洞开挖的安全性,提高开挖施工质量,加快施工进度,通过对白乃水库输水导流隧洞浅埋小断面洞段开挖施工工艺的研究,确定了以保证施工安全为约束条件的浅埋小断面隧洞开挖方法,施工过程中严格按照“管超前、严注浆、短进尺、强支护、早封闭、勤量测”的原则施工,采用超前小导管、工字钢支撑、挂网锚喷等支护形式进行隧洞全断面开挖,有效解决了浅埋小断面隧洞开挖过程中围岩不稳定、施工速度慢等问题。

浅埋平板圆锚竖向拉拔极限承载力计算方法

采用自制可视化试验装置开展了平板圆锚的拉拔模型试验,基于数字照相测量技术对极限拉拔下锚周土体的位移变形场进行了量化分析。在本次试验的埋深比范围内,极限承载力随埋深比增加而非线性增大,但增长速率逐渐减缓;观测到的锚周土体滑动面与地面、锚板所围区域整体呈现出“底大、顶小、径长”的倒喇叭形状;滑动面可用两条直线段来近似描述;极限拉拔力学模型由一个截面直径上小下大的倒圆台和一个等截面圆柱体组成。根据极限平衡条件推导建立了砂土中浅埋平板圆锚竖向拉拔极限承载力的计算方法,该方法对4组试验数据的计算较其他4种方法与试验实测值更为接近,且离散性更小,效果较好。

三维圆形浅埋锚板极限抗拔力非线性上限解析

根据极限分析上限定理和非线性破坏准则,对水平圆形浅埋锚板上的填土建立2个机动容许的速度场,获得非线性破坏准则条件下的圆形浅埋锚板极限抗拔力上限解和破坏模式。通过"切线法"引进变量,将锚板上填土的非线性抗剪强度指标ct和φt作为变量参数,对锚板上部填土建立含有变量的速度场,根据外力功率与内部耗能相等原理求出极限抗拔力的目标函数与约束条件,最后根据"序列二次规划算法"对该问题进行优化。数值分析表明:当非线性破坏准则变为线性破坏准则时,结果与前人的成果一致,说明本文方法的正确性;非线性参数的变化对水平浅埋圆形锚板的破坏范围和极限抗拔力均有重要影响,且破坏范围与极限抗拔力具有显著的相关性。

斜坡浅埋水平条形锚板抗拔承载力的极限分析

针对山区和丘陵等复杂地形下浅埋锚板抗拔承载力计算问题,基于极限分析上限定理、非线性Mohr-Coulomb强度准则及其关联流动法则,构造了斜坡浅埋水平条形锚板的曲线型破裂机制和机动许可速度场,采用变分极值原理获得了其上方土体破裂面方程和抗拔承载力的上限解,分析了斜坡倾角和锚板埋深对锚板抗拔承载力的影响。结果表明:随着斜坡倾角的增大,锚板抗拔承载力逐渐减小,此时其上方两侧土体破裂面不再对称且整体向下坡侧偏移;锚板抗拔承载力及其上方两侧土体破裂面宽度均随着埋深增大而增加;锚板埋深越小,斜坡倾角对其抗拔承载力的影响越大,应在计算中予以考虑,以更合理地反映斜坡浅埋水平条形锚板的抗拔承载特性。

一种可考虑形状效应的浅埋板锚极限抗拔力计算方法

现有的板锚极限抗拔力计算方法只考虑了常规形状锚板的情况,不适用于特殊形状的锚板。为了更好地指导工程实践,在总结已有研究的基础上,研究了圆形、方形、正三角形和风筝形锚板,假定锚板的破坏面从锚板的侧面以膨胀角向上延伸,形成与锚板自身具有相同横截面形状的棱台,结合数学和力学理论分析,提出了一种可以考虑形状效应的浅埋板锚极限抗拔承载力计算方法,并将简化方法计算所得承载力和公开试验结果进行对比。结果表明,简化计算方法适用于埋深与板宽之比小于5的浅埋情况,且具有较高的精度,可以在初步工程设计中加以应用。研究结果为多种形态的浅埋锚板极限抗拔力计算提供了新的方法,可为类似工程项目的设计提供参考,具有一定的工程借鉴价值。

锚板抗拔理论在地下储气洞室中的应用

针对地下储气洞室稳定性要求,在分析总结现有锚板抗拔承载力研究成果基础上,指出水平抗拔锚板的受力机理与地下高压储气洞室顶部受力基本类似,尝试将成熟的水平圆形锚板抗拔承载力理论应用到地下高压储气洞室的岩石覆盖层厚度设计计算中,提出了确定地下高压储气洞室岩石覆盖最小厚度的新方法,通过对某地下储气库工程案例进行计算分析,并与现有确定水工隧洞最小覆盖厚度的上抬准则计算结果进行对比,表明本文采用的水平锚板理论确定高压储气洞室岩石覆盖层厚度更为合理适用。

基于离散元方法的锚板形状对极限抗拔力影响研究

考虑到现有的板锚极限抗拔力计算方法多只考虑了常规形状锚板的情况,结合离散元计算方法,定量化研究锚板形状对极限抗拔承载力的影响。结合函数拟合手段,在圆形锚板极限承载力计算基础上,提出了一种可以考虑形状效应的便于工程应用的简化计算公式。结果表明,在面积不变的情况下,将锚板设计成狭长形状时承载力更高,简化计算公式可以在具体的初步工程设计工作中加以应用。