青藏高原冻土工程走廊场地地震动特征与路基动力响应分析

发布时间：2018-09-04 19:26

【摘要】：青藏高原冻土工程走廊内已建与拟建的国家重大基础工程密集分布。该区域地理位置重要、多年冻土工程力学性质特殊、地震活动频繁、全球气温变暖迅速以及人为扰动不断加剧,加快了多年冻土退化,使得宽度不足10公里的冻土工程走廊内构筑物稳定性问题与生态环境问题愈显突出。受多因素耦合作用以及各类构筑物之间相互影响,工程走廊内的生命线工程在地震动力荷载的叠加作用下将面临巨大的风险与挑战。因此,开展工程走廊沿线场地地震动特征探究与拟建高速公路路基动力响应分析,对于该区重大冻土工程的地震安全性评估具有迫切的现实和科学意义。本文旨在解决地震荷载作用下青藏高原冻土工程走廊沿线场地特征与路基动力响应机制问题,运用综合现场勘探测试资料、室内动三轴试验、数值模拟计算等方法,研究分析了工程走廊沿线冻土场地土体的波速特征、冻结青藏粉质粘土的动力学特性、场地地震动特征参数和路基动力响应。主要研究工作和所得结论归纳如下:(1)根据工程走廊场地波速钻孔资料,分析了冻土场地土体的波速变化特征。归纳资料可得出,冻土的波速值大于非冻土,其纵横波速比值近似为1.5;随着地温的降低和土体含冰量的增加,冻土波速随之增大。(2)通过对重塑冻结青藏粉质粘土在周期循环荷载作用下的动三轴试验,较为系统地研究了不同围压、不同负温、不同含水量和不同频率条件对冻土动力特性的影响。试验结果表明:随着冻土剪应变幅的增大,阻尼比均呈逐渐增大趋势,动剪模比呈逐渐减小趋势;阻尼比随着围压的减小、负温的降低、含水量的减小、频率的增大而减小;动剪模比随着围压的增大、负温的升高、含水量的减小、频率的增大而减小。(3)基于一维土层地震动反应分析理论,根据青藏高原内的地震地质条件、地球物理特征以及地震活动性,开展了冻土场地土层地震反应研究,得到了50年超越概率63%,10%和2%的基岩拟合地震动时程、设计场地地震动参数及反应谱。(4)采用二维非线性动力有限元分析方法,通过建立整体式和分离式典型高速公路路基横断面,对比分析了50年超越概率63%,10%和2%的青藏地震波作用下2种结构路基的加速度放大效应、应力响应特征和位移响应特征。同时,通过改变分离式路基的分幅间距,得到了不同分幅间距条件对分离式路基动力响应特征的影响。
[Abstract]:Intensive distribution of major national infrastructure projects in the frozen soil engineering corridor of the Qinghai-Xizang Plateau. The important geographical location of the region, the special mechanical properties of permafrost engineering, frequent seismic activity, rapid global warming and increasing anthropogenic disturbance have accelerated the permafrost degradation. The structural stability and ecological environment problems in the permafrost engineering corridor with width less than 10 km are more prominent. Due to the coupling of many factors and the interaction between various structures, lifeline engineering in the corridor will face great risks and challenges under the superposition of seismic dynamic loads. Therefore, it is of urgent practical and scientific significance to study the ground motion characteristics along the engineering corridor and to analyze the dynamic response of the proposed highway subgrade for the seismic safety assessment of the major frozen soil projects in this area. The purpose of this paper is to solve the problems of site characteristics and subgrade dynamic response mechanism along the corridor of frozen soil engineering in the Qinghai-Xizang Plateau under seismic loading, using comprehensive field exploration test data, indoor dynamic triaxial test, numerical simulation calculation and so on. The wave velocity characteristics of frozen soil, the dynamic characteristics of frozen Qinghai-Xizang silty clay, the characteristic parameters of ground motion and the dynamic response of roadbed are studied and analyzed. The main research work and conclusions are summarized as follows: (1) according to the data of wave velocity drilling in engineering corridor, the variation characteristics of wave velocity in frozen soil are analyzed. It can be concluded that the wave velocity of frozen soil is larger than that of non-frozen soil, and the ratio of longitudinal and transverse wave velocities is approximately 1.5. With the decrease of ground temperature and the increase of ice content in soil, The wave velocity of frozen soil increases with it. (2) through the dynamic triaxial test of remolded frozen Qinghai-Tibet silty clay under cyclic load, the different confining pressures and negative temperatures are systematically studied. The influence of different water content and different frequency on the dynamic characteristics of frozen soil. The results show that the damping ratio increases gradually and the dynamic shear die ratio decreases with the increase of shear strain amplitude of frozen soil, and the damping ratio decreases with the decrease of confining pressure, the decrease of negative temperature, the decrease of water content and the increase of frequency. The dynamic shear modulus ratio decreases with the increase of confining pressure, negative temperature, water content and frequency. (3) based on the theory of one-dimensional ground motion response, according to the seismic geological conditions in the Qinghai-Xizang Plateau, Based on the geophysical characteristics and seismic activity, the seismic response of permafrost soil layer is studied, and the 50 year surpassing probability of 63% and 2% of the bedrock is obtained to fit the time history of ground motion. Design site ground motion parameters and response spectrum. (4) by using two-dimensional nonlinear dynamic finite element analysis method, the subgrade cross-section of typical freeway subgrade is established. The acceleration amplification effect, stress response characteristics and displacement response characteristics of two kinds of structural subgrade under the action of Qinghai-Tibet seismic wave with 50 years transcendental probability of 6310% and 2% are compared and analyzed. At the same time, by changing the split-width spacing of the separated subgrade, the influence of the conditions of the split-width spacing on the dynamic response characteristics of the separated roadbed is obtained.
【学位授予单位】：兰州交通大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：U416.1

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