Field Evaluation of the Vertical Bearing Capacity of a Screw Pretensioned Spun High-Strength Concrete Pile

This study has evaluated the vertical bearing capacity by conducting static load tests for noise-free and vibration-free screw pretensioned spun high-strength concrete (PHC) piles installed using two different methods (end-squirting shoe and pre-boring methods). Vertical bearing capacity differences seem to occur due to the displacement of soils near the external circumference of a pile, depending on the installation method. A method by which to evaluate the bearing capacity of screw concrete piles is suggested by considering the equations that already have been used to calculate the bearing capacity of piles. Based on static load tests and analysis, the pile installed using the end-squirting shoe method was assumed to be a bored pile and it was reasonable to use the equation proposed by the Japanese Geotechnical Society. At the same time, the pile installed using the pre-boring method was deemed a low soil displacement pile and so it was reasonable to apply the equations proposed for calculating the bearing capacity of the driven pile suggested by the Architectural Institute of Japan.     

Development of Prebored Screw Pile Method and Evaluation of Its Bearing Characteristics

The pile-driving method produces considerable noise and vibrations. Hence, an auger-drilled pile method was developed as a low-noise and -vibration substitute. However, this method does not guarantee the bearing capacity of the pile unless some amount of pile-driving is performed. Therefore, the noise and vibration problems cannot be completely solved. In this study, a prebored screw pile method is proposed to solve these problems. In this method, piles are constructed by the rotary penetration of a screw pile into a prebored hole filled with some cement milk and whose diameter is smaller than that of the screw pile. To determine the shape of the screw pile, laboratory tests with model screw piles were conducted. Also, field load tests were conducted on an actual screw pile fabricated based on the laboratory test result and on a smooth-surfaced pile. In addition, the behavior of the screw pile was estimated by using three-dimensional finite element analysis. The results of the field load test and the numerical simulation showed that the ultimate bearing capacity and the unit skin friction of the screw pile are very superior to those of the smooth-surfaced pile and the cement milk is an important factor in the prebored screw pile method.     

软土区旋喷式插筋微型桩工艺试验研究

软土地质条件下建筑物的沉降变形和承载力要求越来越高,对基础施工工艺提出了较高要求。在高压旋喷施工工艺的基础上,提出旋喷式插筋微型桩施工工艺,开展了微型桩工艺试验研究,结果表明该工艺大幅提高了单桩桩基承载性能,为实际工程应用提供了技术数据支持。     

上海市东方医院青岛分院钻孔桩施工技术

上海市东方医院（同济大学附属东方医院）青岛分院桩基工程,工程量大,工期紧,因上部存在填土、淤泥质土,地层条件较复杂。根据工程实际情况采用了旋挖钻机、冲击钻机、回转钻机成孔工艺,采取加长钢护筒、泥浆护壁等技术措施,有效解决了缩径、孔壁坍塌问题,保质保量按期完成了施工任务,取得了很好的经济和社会效益。     

泥浆护壁成孔灌注桩后注浆技术正确应用研究

为保证泥浆护壁成孔灌注桩后注浆技术正确应用,首先分析了后注浆技术对泥浆护壁灌注桩的作用机理以及天津地区的应用现状,然后通过对影响其应用效果的多种因素,如从业人员资格、成孔成桩质量、注浆阀、注浆泵、注浆相关参数等分析研究,提出相应的措施或建议。     

阜阳华纺新天地超长空桩成孔施工控制措施

阜阳华纺新天地桩基工程,原计划基坑底面施工调整为地面施工,增加了近14 m的空桩。为此,工程桩施工质量存在桩位、孔底沉渣厚度、钢筋笼位置、砼质量、砼桩顶标高等方面控制的相关问题。本文介绍了其施工情况,其经验可供类似工程借鉴。     

改进的无网格法及其在冻土区桩基温度场中的应用

采用带权正交基函数对传统的无网格法中的基函数进行了改进,避免了计算过程中可能出现的矩阵不可逆情况,而且编程容易实现且计算效率高。并将其应用到冻土区桩基包括了热传导和相变潜热的温度场中,同时考虑了混凝土水化热释放对桩周冻土的影响,将计算结果和有限元计算结果及现场实测数据进行了比较分析,从趋势和最大数值看都反映了实测曲线的趋势,又把不同深度处桩侧和不同桩径处温度随时间的变化规律计算结果和有限元计算结果做了对比,都验证了该方法的可行性和优越性。     

粗砂砾石地层中高压旋喷桩隔水帷幕施工技术

太原万达广场A2区商住楼基坑工程部分区域为粗砂砾石地层,基坑隔水帷幕中深层搅拌桩无法有效使用。提出了在粗砂砾石地层采用高压旋喷桩隔水帷幕的施工技术方案,采用双套管锚杆钻机引孔、单管高压喷射工艺进行施工,成功实施了这一工程。经检查,喷射注浆体相互咬合良好,有效桩径内水泥含量均匀无夹块现象,隔水帷幕止水效果良好。     

随钻测斜技术现状与发展趋势

在桩基领域,随着基础设施建筑对桩基础承载能力和桩孔垂直度的质量控制要求越来越高,现有常规桩基成孔监测技术已不能满足要求;在钻探领域,随着深井、超深井、科学钻探井及水平井的成井要求越来越高,由于地层因素、工艺技术等导致的实际钻孔轨迹偏离设计轨迹的井斜问题愈发突出,井斜的监控变得越来越严格,现有仪器已不能很好地满足钻孔轨迹测量的高精度要求。针对上述问题,本文梳理了随钻测斜技术发展现状,并结合地质岩心钻探、旋挖桩孔施工工艺特点,提出实现绳索取心钻探钻孔轨迹和大直径长钻孔灌注桩孔垂直度高精度实时监测的方案,这一思路的推广将对指导施工操作、保证钻孔/桩孔的整体质量产生积极影响。     

成层软土地基预固结处理后桩基水平承载力估算方法

目前通过对软土地基预加固处理来提高桩基水平承载力已被工程界认可,但如何在工程前期设计过程中估算软土地基预处理后桩基水平承载力提高值仍是技术难点。基于此,参考Bowles[1]的地基土水平抗力计算式,同时考虑成层软土地基预排水固结处理影响,通过数学推导,推求出根据原状软土室内土工试验抗剪强度指标及预加固处理时间,估算软土地基预处理后桩基水平承载力提高值的实用计算方法。考虑桩侧土弹塑性屈服影响,推导出成层软土中水平受荷桩弹塑性解析解及塑性区深度的计算式,给出了桩顶水平位移、桩身最大弯矩的无量纲计算式及相关计算源代码。依托于浙江省某水闸桩基工程案例,根据提出的计算方法对桩基水平承载力、桩顶水平位移及桩身最大弯矩等性状进行预估计算,并与地基预处理前、后现场试桩检测值进行验证对比,认为桩基水平承载力、桩顶水平位移及桩身最大弯矩等预估计算成果与工程现场试桩的检测值较接近,对类似工程设计具有较好的参考价值。