基坑降水引起的沉降变形时空规律及降水控制研究

【作者】 张莲花；

【导师】 孔德坊； 李荣强；

【作者基本信息】 成都理工学院 ， 地质工程， 2001， 博士

【摘要】 本文首先对基坑工程的研究现状以及引起的对周围环境的影响作了较为详细的论述，并着重对基坑工程降水产生的不良现象进行分析。总结了基坑降水引起沉降常用的计算方法。 针对基坑降水引起沉降的原因是水头降低导致有效应力增加的客观事实，对基坑降水的水位动态进行了模拟研究。特别对不同于供水水文的有隔水帷幕的基坑降水水位动态模拟进行分析，提出利用虚拟井点通过统流量耦合的水位计算数学模型。并引用Forchheimer公式推导出，有隔水帷幕时降水水位影响半径的估算公式。 针对降水引起沉降计算时，普遍采用总应力不变的观点计算有效应力增量的现状，提出总应力变化前提下潜水和承压含水层水位降低产生地层有效应力增量的计算公式。并进一步提出降水后土层持水密度的概念，利用水文中给水度的概念，推导出持水密度与给水度及工程常用土的物理力学指标之间的函数关系，运用到降水引起的固结沉降计算中。 由于沉降观测资料是基坑降水和支护结构变形两者引起沉降的总和，为估算支护结构变形产生的地面沉降，本文还对支护结构变形产生沉降的估算方法进行了总结，并运用灰色理论预测支护结构变形的发展。 对降水过程中的回灌措施的效果和影响范围进行了讨论，提出回灌作为防止措施的效果比作为治理措施的效果要好得多的观点，并对水位自然回升时基础和地下室进行抗浮验算。 本文提出了沉降变形控制的降水最优化设计的概念，即以周围环境对降水引发沉降的最低要求为约束，同时又满足工程施工和工程安全的需要，进行降水设计。这将改变过去人们仅从工程安全和施工条件的角度去进行降水设计的传统观点，而是把环境的因素考虑进来进行降水设计。 最后通过工程实例计算与实测值比较，验证了本文的降水和沉降的计算方法是较为准确而有效的．更多还原

【Abstract】 The foundation pit effects on the surroundings is firstly discussed in detail, and the bad phenomena caused by pit dewatering is emphatically analyzed in this paper. Summarization of the settlement induced by dewatering is also displayed. Because that the dewatering ground settlement is the result of the drawdown and soil effective stress increase, this paper gives the water lever dynamic simulation of foundation pit. The math model of groundwater flow of foundation pit with water- resistance curtains is put forward especially with the by-pass seepage coupling of virtual wells. Referring to the Forchheimer’s discharge formula, it is deduced and proposed that the formula for radius of drawdown influence with water-resistance curtains. Aiming at the matter of fact that the total stress is deemed changeless as calculating effective stress, the formula for effective stress with changeable total stress is proposed in soils of the confined and unconfined aquifers. The concept of holding water density of soil is brought forward to donate the soil density after dewatering. The function between soil holding water density and hydrogeology concept: specific yield, soil physical mechanics index is deduced, and applied to the FEM calculation of consolidation settlement. As the observed settlement data is the sum value caused by drawdown and bracing structure displacement, the settlement evaluating method is summed up. The gray theory is applied to the evaluating the displacement of bracing structure. It is discussed that the effects and influence of injection wells and is believed that the injection wells effects is better as preventing settlement measure than as harnessing settlement measure. When water levels recover naturally, the checking computations of the groundwork floating resistance should be taken. The concept of dewatering optimum design controlled by surroundings settlement is put forward, that is the design must meet neither the project safety and construction conditions requires nor the surroundings minimal settlement need. This concept will change the traditional ideal that focuses on the safety and construction conditions to also concern the surroundings capability. In the end of this paper, the calculated results are compared with the observed value in one example foundation pit, and are in good agreement with the observed results in which settlement reduced by bracing displacement is already knocked off.更多还原