【作者】 陈波；

【导师】 丁坚平； 袁志英；

【作者基本信息】 贵州大学 ， 矿业工程， 2009， 硕士

【摘要】 随着我国西部大开发的快速发展,基本建设规模不断扩大,中心城市的高层和超高层建筑进入一个迅速发展阶段,深基坑支护工程也随之增加。基坑工程的稳定问题也越来越引起工程技术人员的高度重视。但目前对红粘土基坑边坡的失稳机理、支护设计方法及施工新工艺的研究甚少,因此本文以贵阳市开阳磷矿办公大楼深基坑为研究对象,采用理论计算和数值模拟结合规范规定的计算等方法对上述问题开展研究,初步取得如下成果:（1）通过对贵州红粘土形成过程、地质特征、物质成分与结构特征、物理力学性质以及红粘土深基坑存在的工程地质问题进行研究分析,得出贵州红粘土具有高含水量、高塑性、大孔隙比,低渗透性,中高压缩性,抗剪性能差别大,较高承载力,低膨胀量,高收缩性的工程特性。因此贵州红粘土不同于其它类型的红土的显著特征是物理性质指标离散性大,在不受外力扰动的情况下,具备一定的工程力学性能,是一种特殊性土。地质剖面具有“反剖面”特征,即上硬下软。（2）以工程实例-开磷深基坑为支撑,结合红粘土基坑工程的特点,对红粘土基坑边坡的变形、失稳机理及施工新工艺进行了研究,采用了先数值仿真模拟,找出薄弱部位,重点照顾,优化设计的工作方法。论文首先介绍了常规基坑工程中常用的一些支护型式及其适用条件,再着重介绍了红粘土基坑“上硬下软”存在“软基座”的特点,得出以下结论:①存在“软基座”的红粘土基坑边坡,一般基岩面起伏较大,多为岩溶强发育场地,岩体完整程度一般较差。②地下水水位标高大致与软基顶面保持一致,基坑边坡会承受一定的动水压力荷载。③基坑边坡所处的工程地质条件复杂,常规、单一的支护型式通常满足不了治理此类基坑边坡的要求。④支护设计时应重点对基坑底“软基座”部分采取有效的治理手段,如含超前支撑的肋锚、桩锚和咬合桩等复合型的支护型式。⑤由于此类基坑的复杂性和特殊性,治理费用昂贵,研究新的施工工艺,节约成本,意义重大。该工程以锚索基本试验数据为支撑,在红粘土深基坑的较破碎岩体中成功应用了压力分散型锚索,与普通的拉力型锚索比较,工程造价节约30%以上。⑥通过工程实例施工结果的验证,证明数值模拟分析软件FLAC^3D对红粘土基坑边坡的设计与预测施工工况具有一定的指导与预测作用。⑦红粘土基坑边坡由于上硬下软及基底有“软基座”存在,竖向位移值一般均大于水平向位移值。（3）开阳磷矿办公大楼基坑为红粘土深基坑,根据基坑边坡的工程地质条件,采用理论上的极限平衡法,《建筑基坑支护技术规程》（JGJ 120-99）规定的圆弧条分法、结合手算和数值仿真模拟,对基坑边坡的稳定性进行了计算分析评价,得出稳定性系数K=0.34～0.60均小于1.0,基坑不稳定,必须加固处理。进而设计基坑支护型式为锚杆（索）墙、顶部冠梁、横向连梁,超前纵向肋柱组成的复合型支护体系,对支护后稳定性计算结果均为整体稳定,效果良好。（4）为进一步评价预测红粘土基坑边坡的安全性,采用数值模拟方法对红粘土基坑变形破坏特征进行了各工况的模拟分析,并与实际施工各工况进行了对比,结果表明使用FLAC^3D软件对深基坑边坡进行稳定性分析是可行的,因此可以应用数值模拟方法对基坑施工过程进行仿真模拟,预测变形的发展变化,发现工程中薄弱部位,以指导施工采取进一步有效措施。（5）开磷深基坑工程的创新点就是成功应用了压力分散型锚索,它与传统的岩土锚固方法（拉力型锚索）相比,压力分散型锚固系统的优点是将集中荷载分散为几个较小的荷载作用于固定段的不同部位,使粘结应力峰值大大降低,因单元锚索的固定长度很小,不会发生粘结效应逐步弱化,使粘结应力均匀地分布在整个固定长度上,最大限度地调用整个锚索固定长度范围内的地层强度,锚索承载力可随固定长度的增长而成比例提高。通过对开磷深基坑的FLAC^3D的模拟分析得到:采用压力分散型锚索在红粘土深基坑支护上的作用要优于传统的支护方式,所采用的锚索长度要小于传统的拉力型锚索长度,从而节约材料,降低了工程造价。更多还原

【Abstract】 With the rapid development of the western region in China, the scale of capital construction is expanding promptly and the construction of high and ultra-high-rise building enter rapid development stage. For the increase of foundation pit excavation and support, the excavation stability has been more and more concerned by scientist and engineer. Therefore this paper applies the method of theoretical calculation and numerical simulation to analyze the stability of excavation which is Guizhou kaiyang Phosphate office. Achievements are made in the following five aspects:1. Based on the research of formation、material composition、structural characteristics、physical and mechanical properties of guizhou red clay and the engineering problem of red clay foundation , find out that the guizhou red clay has the engineering characters such as high moisture content、high plasticity large void ratio low permeability high load high-shrinkage and large difference between shear performance. Therefore the different between other types of clay is that guizhou red clay has poor indicators of the physical properties and good mechanical properties.2. Based on the characteristics of foundation pit excavation, this paper researches the deformation and failure mechanism and emphasis on the commonly used applications of excavation support and their condition.3. For instance of the excavation of kayang phosphate office, this paper applies the theoretical analysis to stability of excavation and then designs the form of support, such as anchor (cable) wall. The calculation result is that the excavation is entire stable after the support.4. By the use of numerical simulation to analyze deformation and failure characteristic of the excavation and compared to the actual work, the result shows that the method which analyzed the stability of deep foundation by FLAC3D software is feasible. So the method of numerical simulation could be used in the construction process simulation to predict the development of deformation change and identify the weak areas to guide the construction to take further effective measure.5. Compared with other traditional anchor methods, the pressure of anchoring decentralized system will be concentrated load for a few scattered smaller loads in different parts of the fixed section. So that the peak bond stress greatly reduced due to the fixed cable unit and the length is very small. The bounding effect would not be gradual weakening. According to the experiment in kayang, the result is that the dispersion in the pressure-type anchorage system in the red clay of deep excavation on the role of the superior to the traditional way of support.更多还原