基于地下水位变化高层建筑群引起地层分层沉降规律研究

发布时间：2018-09-06 08:30

【摘要】：地面沉降已经使得世界上60多个国家和地区蒙受巨大的经济损失,仅上海一地即高达2900多亿元,平均每下降1mm造成的经济损失约1.53亿元。本文以上海地区地面沉降为研究背景,采用理论分析、数值模拟和室内试验等手段,对软土地区高层建筑荷载和地下水位变化联合作用引起的地面沉降进行研究,为软土地区地面沉降防治提供理论基础。(1)根据位移协调条件,建立承压完整井抽水引起地面沉降计算模型。以单层承压含水层抽水为例,不考虑上覆土层固结,地面最大水平位移与最大竖向位移相比,约小一个数量级,但其影响范围与竖向位移相当。含水层差异沉降显著时,上覆土层的存在使得地面沉降值小于含水层压缩量。差异沉降不显著时,二者基本一致;考虑上覆土层固结过程,假设上覆土层饱和度不变,土体分别采取弹性及Merchant粘弹性本构关系,固结初期,二者计算固结度大致相等,随着固结时间增加,土体本构关系取弹性时固结度大于取粘弹性时的固结度,二者计算固结度差值逐渐增大,按本文计算参数,最大差值达29.6%。(2)通过调整桩长、建筑间距、降深和抽水层次,对建筑荷载、抽水以及二者共同作用引起的地面沉降进行数值模拟。桩长增加,建筑物沉降量值降低,但沉降分布几乎不变;建筑间距增加,建筑物所处位置土体沉降最大,区域中心沉降随建筑物间距增加沉降量值迅速降低;降深相同,开采深部含水层引起的沉降远小于开采浅部含水层引起的沉降;抽水阶段,建筑物影响范围约为建筑物所处位置及附近0.5倍基础宽度。开采第一含水层,建筑物的存在降低了地面沉降,建筑物所在位置沉降减少约50%;降深每增加1m,角桩桩顶轴力约增加1%,中心位置桩顶轴力约增加1.5%,桩身轴力变化幅度大,建筑物对土体变形影响显著。开采第二含水层,建筑物对土体变形影响很小。桩基础受力状态的变化是建筑物及附近土体在抽水阶段沉降分布发生变化的主要原因。根据建筑物及抽水沿深度影响范围,结合上海中心城区地下水开采策略和分层沉降数据,上海中心城区地面沉降主要原因已逐渐由开采地下水转变为工程建设,工程建设引起的地面沉降约占地面总沉降的40%。(3)地面沉降模型试验。采用颗粒图像测速技术,研究建筑荷载和地下水开采引起土体分层变形规律。先建建筑使得后建建筑处土体发生固结,后建建筑累计沉降小于先建建筑沉降。后建建筑使得原有建筑附近地面沉降速率增加,建筑荷载引起的地面沉降存在叠加效应;建筑物内部区域因叠加效应的存在,沉降量增加。建筑物外围则沉降差较大;抽水时,建筑物桩基础的负摩擦作用降低了建筑物及建筑物周围土体的沉降,相应地增加了建筑物周围的差异沉降;相对于加载引起的沉降,抽水引起的沉降发展较为缓慢,但持续时间长。加载和抽取地下水引起的地面沉降,都是软土层的变形占整个地面沉降的比例很大;地下水回灌抑制地面沉降效果显著,但引起地面回弹量值甚微,地面沉降几乎是不可逆的。(4)对比室内模型试验与数值模拟结果。高层建筑荷载引起的地面沉降,建筑范围内部因叠加效应存在,沉降量值增加,但差异沉降相对降低。在已有建筑物的影响下,抽水引起的地面沉降,因桩土间相互作用,建筑物附近沉降值降低,但差异沉降增加。在建筑加载阶段因叠加效应沉降值增加、沉降差值相对降低的地区,在抽水阶段受建筑物影响依然较大,但沉降差值增加,沉降值相对降低;建筑荷载及抽水共同作用,使得建筑物附近沉降差变小,沉降趋于平缓。但若抽水量过大,则会引起沉降差反向增加。
[Abstract]:Land subsidence has caused enormous economic losses to more than 60 countries and regions in the world. Shanghai alone is as high as 29 billion yuan, with an average economic loss of about 153 million yuan per mm of decline. The study of ground subsidence caused by combined action of floor building load and groundwater level variation provides theoretical basis for prevention and control of ground subsidence in soft soil area. (1) According to displacement coordination conditions, a calculation model of ground subsidence caused by pumping of confined well is established. Taking pumping of single confined aquifer as an example, the ground is the largest without considering the consolidation of overlying soil layer. Compared with the maximum vertical displacement, the horizontal displacement is about one order of magnitude smaller, but its influence range is equivalent to the vertical displacement. When the differential settlement of the aquifer is significant, the ground settlement value of the overlying soil is smaller than the compression of the aquifer. When the differential settlement is not significant, the two are basically identical; considering the consolidation process of the overlying soil, the overlying soil is assumed to be saturated. At the initial stage of consolidation, the degree of consolidation calculated by the two methods is approximately equal. With the increase of consolidation time, the degree of consolidation calculated by the elastic constitutive relation is greater than that calculated by the viscoelastic constitutive relation, and the difference between the two methods increases gradually. According to the calculated parameters, the maximum difference is 29.6%. (2) By adjusting the pile length, building spacing, depth reduction and pumping level, the numerical simulation of the ground settlement caused by building load, pumping and their interaction is carried out. The settlement value decreases rapidly with the increase of spacing; the settlement caused by mining deep aquifer is much smaller than that caused by mining shallow aquifer; the influence range of buildings is about 0.5 times the width of foundation nearby and the location of buildings in pumping stage. The axial force on the top of the corner pile increases by 1%, and the axial force on the top of the pile increases by 1.5% with the increase of the depth by 1 m. According to the influence range of buildings and pumping along the depth, combined with the groundwater exploitation strategy and stratified subsidence data in the central area of Shanghai, the main cause of land subsidence in the central area of Shanghai has gradually changed from groundwater exploitation to engineering construction, and the land subsidence caused by engineering construction covers about land. (3) Land subsidence model test. Using particle image velocimetry technique, the soil layered deformation caused by building load and groundwater mining is studied. The soil consolidation occurs at the post-construction site and the accumulated settlement of the post-construction site is less than that of the pre-construction site. With the increase of building load, the ground subsidence caused by building load has superposition effect; the subsidence of building interior area increases because of superposition effect; the settlement difference of building exterior is larger; when pumping, the negative friction of building pile foundation reduces the subsidence of building and the soil around the building, and correspondingly increases the differential settlement around the building. Comparing with the settlement caused by loading, the subsidence caused by pumping develops slowly, but lasts for a long time. The subsidence caused by loading and pumping groundwater accounts for a large proportion of the total land subsidence. The effect of groundwater recharge on restraining land subsidence is remarkable, but the amount of ground rebound is very small, and the land subsidence is almost the same. (4) Comparing the results of indoor model test and numerical simulation, the ground subsidence caused by high-rise building load exists in the building area because of superposition effect, and the settlement value increases, but the differential settlement decreases relatively. In the area where the value of settlement increases due to superposition effect and the value of settlement difference decreases relatively, the value of settlement difference decreases relatively with the increase of the value of the building in the pumping stage, but the value of settlement difference decreases relatively with the increase of the value of the building in the pumping stage. However, if the pumping volume is too large, the differential settlement will increase.
【学位授予单位】：中国矿业大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P642.26

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