戈壁碎石土浅基础抗拔性能研究

发布时间：2018-03-13 10:10

本文选题：戈壁　切入点：抗拔　出处：《中国地质大学（北京）》2013年博士论文　论文类型：学位论文

【摘要】：戈壁是我国西北地区广泛分布的一种特殊地基，随着疆电外送等电网工程建设，越来越多输电线路杆塔基础工程需经过戈壁地区。抗拔性能通常是杆塔基础设计的控制条件，为充分利用天然戈壁地基抗拔性能，掏挖扩底基础在该地区输电线路工程中广泛应用。目前，基础抗拔承载性能研究多集中于桩基及回填土扩展基础，而戈壁碎石土掏挖扩底基础抗拔性能研究较少。本研究根据新疆和甘肃地区7个地点46个戈壁碎石土浅埋掏挖扩底基础抗拔现场试验成果，采用4种典型方法评价了戈壁碎石土扩底掏挖浅基础抗拔性能，给出了戈壁碎石土扩底掏挖浅基础抗拔归一化荷载－位移特征曲线，提出了基础抗拔极限承载力确定方法及其计算理论。基于归一化荷载－位移双曲线模型及可靠度分析方法，建立了戈壁碎石土扩底掏挖浅基础抗拔荷载与位移的预测计算方法。主要创新性研究结论及成果如下：（1）戈壁碎石土为级配不均匀土，但级配连续性好，，且因含可溶盐而具有显著的盐份胶结作用，其工程性质不同于一般“土石混合体”，抗剪性能较好。（2）戈壁碎石土掏挖扩底浅基础抗拔极限承载力影响因素敏感性由大到小顺序为：深径比、基底扩展角和立柱直径。上拔荷载作用下，戈壁碎石土掏挖扩底浅基础抗拔荷载－位移曲线呈初始弹性直线段、弹塑性曲线过渡段和直线破坏3阶段“缓变型”规律。（3）初始直线斜率法和Chin数学模型法确定的基础极限承载力和位移分别代表了戈壁碎石土浅基础抗拔承载性能上、下限，双直线交点法确定的极限承载力和位移位于荷载－位移曲线弹塑性过渡段，宜采用L1－L2方法确定其抗拔极限承载力和位移。（4）极限平衡承状态下，戈壁碎石土浅基础抗拔极限承载力由基础混凝土自重、滑动面旋转体内土体重量、滑动面剪切阻力垂直分量3部分组成。由此建立了戈壁碎石土掏挖扩底浅基础抗拔极限承载力计算的理论方法，并通过变量分离和归一化处理，给出了抗拔极限承载力计算参数随基础尺寸和土体抗剪强度参数变化的规律。（5）归一化荷载－位移双曲线模型可较好拟合戈壁碎石土掏挖扩底基础抗拔荷载－位移实测曲线并减小其离散性。按归一化荷载－位移双曲线模型参数均值所确定的荷载－位移拟合曲线代表了试验数据的平均值，而荷载－位移试验曲线刚度均大于95％保证率双曲线模型参数所确定的荷载－位移拟合曲线刚度。（6）提出的戈壁碎石土抗拔浅基础正常使用极限状态下允许位移和允许荷载的计算方法，可作为基于强度和变形统一的基础工程设计依据。
[Abstract]:Gobi is a special foundation widely distributed in the northwest of China. With the construction of power transmission and other power grid projects in Xinjiang, more and more transmission line tower foundations need to pass through the Gobi area. The anti-drawing performance is usually the control condition of tower foundation design. In order to make full use of the uplift resistance of the natural Gobi foundation, the excavated foundation is widely used in the transmission line engineering in this area. At present, the research on the uplift bearing capacity of the foundation is mainly focused on the pile foundation and the backfill foundation. However, there is little research on the pullout resistance of Gobi gravel foundation. Based on the field test results of 46 Gobi gravel soils in 7 locations in Xinjiang and Gansu, In this paper, four typical methods are used to evaluate the pullout performance of the shallow foundation of the Gobi gravel soil, and the characteristic curves of the uplift load and displacement of the foundation are given. A method for determining the ultimate bearing capacity of the foundation under pull-out and its calculation theory are proposed, based on the normalized load-displacement hyperbolic model and the reliability analysis method. The prediction method of uplift load and displacement of Gobi gravel soil is established. The main innovative research conclusions and results are as follows:. 1) Gobi macadam is non-uniform gradation soil, but the gradation continuity is good, and it has remarkable salt cementation function because of the soluble salt, its engineering property is different from the common "soil-rock mixture", and its shearing property is better. (2) the sensitivity of uplift ultimate bearing capacity of excavated and expanded shallow foundation of Gobi macadam is as follows: ratio of depth to diameter, expansion angle of base and diameter of column. The drawing load-displacement curve of Gobi gravel soil with excavated and expanded shallow foundation shows the initial elastic straight line section, the elastic-plastic curve transition section and the "slow deformation" law in three stages of straight line failure. 3) the ultimate bearing capacity and displacement determined by the initial linear slope method and Chin mathematical model method represent the upper and lower limit of uplift bearing capacity of shallow foundation of Gobi gravel soil, respectively. The ultimate bearing capacity and displacement determined by the double linear intersection method are located in the elastic-plastic transition section of the load-displacement curve. L1-L2 method should be used to determine the ultimate bearing capacity and displacement of the load-displacement curve. (4) under the condition of ultimate equilibrium bearing, the ultimate bearing capacity of shallow foundation of Gobi gravel soil is the weight of foundation concrete, and the weight of soil body of sliding surface rotates. The vertical component of shear resistance of sliding surface is composed of three parts. A theoretical method for calculating the ultimate uplift bearing capacity of shallow foundation with excavated and expanded base of Gobi gravel is established, which is treated with variable separation and normalization. The variation of ultimate bearing capacity parameters with foundation size and shear strength parameters is given. (5) the normalized load-displacement hyperbolic model can better fit the measured curves of uplift load-displacement of excavated and expanded foundation of Gobi gravel soil and reduce its discreteness. Determined by the parametric mean value of the normalized load-displacement hyperbolic model. The load-displacement fitting curve represents the average value of the test data. The stiffness of load-displacement test curve is larger than that of load-displacement fitting curve determined by hyperbolic model parameters of 95% guarantee rate. 6) the calculation method of allowable displacement and allowable load under normal service limit state of uplift shallow foundation of Gobi crushed stone soil can be used as the basis of foundation engineering design based on unified strength and deformation.
【学位授予单位】：中国地质大学（北京）
【学位级别】：博士
【学位授予年份】：2013
【分类号】：TU471

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