【作者】 罗大生；

【导师】 彭振斌；

【作者基本信息】 中南大学 ， 地质工程， 2012， 博士

【摘要】 珠三角地区和长三角地区一样：软土处理一直是基础工程建设中一个棘手的问题；软土地基处理技术和设计理论也得到了很大的发展。但是,由于种种原因,道路出现的不均匀沉降、桥头跳车、工后沉降较大和后期质量缺陷处治等问题依然不同程度存在。对此,作者根据钉形搅拌桩的特点,选择在珠三角地区有代表性的广州市番禺区黄榄快速干线市政道路标第二标段,采用此工法处理软土路基,并充分结合工程施工和原位测试,对软土路基加固中桩、土的实际应力、沉降进行测试,对钉形搅拌桩的受力特性和复合地基沉降进行分析研究。通过广泛收集珠三角地区典型地段的工程勘察资料,总结出了珠三角地区软土的工程地质特征：在低压时呈现出的是软化现象,而在高压下表现出来的则是硬化型,属于典型的结构性软土；珠三角地区软土属于深厚软土,具有天然含水量高、天然孔隙比大、压缩性高、渗透固结性低、抗剪切强度低和承载力低、固结时间长等特点。通过在钉形搅拌桩桩体内埋设应变片和单桩载荷试验,对钉形搅拌桩桩身应力、轴力和侧摩阻力与深度的变化规律进行了研究；通过在桩间土中埋设孔压计和沉降计,对路堤堆载作用下钉形搅拌桩复合地基的沉降特性进行了研究分析。结论：桩身应力在扩大头变截面处出现应力集中导致应力骤增,而扩大头以下桩身应力迅速减小。桩身轴力沿深度逐渐衰减：在扩大头变截面以上桩体衰减速率较下部快；在变截面以下1m-6m桩身轴力逐渐减小,由于在本试验中桩身9m以下地层条件较好,因此该段桩身轴力有少量增长。在同一深度,桩身应力(桩身轴力)随着荷载的增大而增大：在上部扩大头,应力的增加幅度较大,在下部桩身,应力基本不变。基于钉形搅拌桩桩身质量检测结果和桩身荷载传递规律,判定钉形搅拌桩的单桩破坏模式为桩身质量破坏,提出了钉形搅拌桩单桩极限承载力计算方法(Qu=ηfcuπD2/4,建议η的取值为0.5～0.7)。在本试验中,钉形搅拌桩桩间土的沉降-深度曲线大致可以分为两段：第一段沉降较大,位于桩身9.0m以上,沉降值随桩体深度的增加逐渐减小,说明钉形搅拌桩复合地基的沉降主要发生在桩身9.0m以上。第二段位于桩身9.0m以下,沉降较小。将钉形搅拌桩复合地基加固区的沉降分三部分进行考虑：分别为钉形搅拌桩变截面以上加固区域沉降量S1,变截面以下加固区沉降量S2和下卧层沉降量S3。计算得出本试验段最终总沉降量S的理论值为376.738mm。珠三角软土地区黄榄快速干线采用钉形搅拌桩加固道路路基取得了实际的工程意义和效果。更多还原

【Abstract】 Soft soil treatment has been a prominent issue on the construction of infrastructural facilities in the Pearl River Delta Region and the Yangtze River Delta region. The soft soil treatment technology and design theory have been developed greatly in recent year. But for various reasons differential settlement、bridge-head and post-construction settlement still exist to some extent in the operation of road. So according to the characteristics of T-shaped mixing pile, Panyu District, Guangzhou City, Huanglan fast road is selected and acted as representative of the soft soil of Pearl River Delta area. The fast road is treated by T-shaped mixing pile. Through combination of construction and Situ test, T-shaped mixing pile force characteristics and the composite foundation settlement are analyzed.Through soft soil engineering survey datas are extensive collected in the typical area of Nansha, the engineering geological characteristics of soft soil are summarized. The nansha compression lines of soft soil is shown:softening phenomenon is occurred under lower pressure, and hardening curve appear under higher pressure; Nansha’soft soil have some typical features such as high water content, high porosity, High permeability of compressibility, consolidation, low shear strength low bearing capacity and so on, which impact the reinforcement of city road seriously.Though strain gauges are equiped in the body of T-shape cement-soil mixing pile and single pile load tests are did, the law between axial force transmission, stress transmission and distribution of skin friction with depth are analyzed. The study is shown:due to the stress concentration the cross-section of pile body stress increased, and the pile body below the cross-section stress diminishes quickly. Along the depth of pile shaft force gradually attenuation, and in expanding heads above the pile attenuation rate is lower fast, expand the head the following3m-9m of pile shaft force reduce gradually, because the following9m formation conditions are good, so when the pile body with a small amount of the axial force growth; The same depths pile body stress (pile body axial force) with the load increases, expand the head of a larger extent increase of stress, under the stress of pile of basic unchanged. Based on the nail form stirring pile body quality testing results and pile body load transfer law, judge nail form mixing pile of single pile failure mode for pile quality damage, puts forward the nail form of mixing pile bearing capacity of single pile limit calculation method (Qu=ηfcuπD2/4, suggest the value of η is0.5～0.7). The curve of depth-soil settlement located in roadbed can be roughly divided into two sections:the first section above9.0m depth of pile that occur main settlement of all have lager settlement, and settlement value is gradul decreasing with increasing depth. The second section below9.0depth of pile have small settlement, only a few mm. The settlements of composite foundation of T-shape cement-soil mixing pile are considered from three aspects:strengthening regional settlements S1above cross-section of pile, strengthening regional settlements S2below cross-section of pile and subjacent bed of composite foundation S3respectively. All the theoretical settlement of composite foundation is to376.738mm. Though the foundation of city roads are reinforced by T-shape cement-soil mixing piles in Nansha’area, the actual engineering meaning and effect are obtained.更多还原