双向搅拌桩加固软土地基应用研究

针对在杭浦高速公路建设工程软土地基处理方案中,由常规水泥土搅拌桩被否决到双向水泥土搅拌桩被采用的变化过程,通过试桩施工,试桩桩身强度试验成果对比及理论分析和经济对比,介绍了双向水泥土搅拌桩及其施工工艺;同时论述了双向水泥土搅拌桩优越的工程特性及其良好的社会经济效益。     

变径双向水泥土搅拌桩技术及其应用研究

针对国内传统水泥土搅拌桩存在的缺陷,介绍了变径双向水泥土搅拌桩技术,并对其施工机械和施工工艺进行说明。为了验证变径双向水泥土搅拌桩的软土地基加固效果,通过现场试验和理论分析,分别就上部桩体扩径(钉形搅拌桩)和中部桩体扩径(中字形搅拌桩)这两种典型搅拌桩桩型的搅拌均匀性、桩身强度与承载力、路堤荷载下复合地基工作性状以及工程经济性等与试验段内的常规搅拌桩进行对比。试验结果表明,由于采用了变径和双向搅拌工艺,消除了溢浆现象,保证了桩身水泥掺入量,提高了桩身均匀性、强度及承载力;在路堤荷载作用下,采用变径搅拌桩可比常规搅拌桩节约近15%的水泥用量。     

水泥土搅拌桩变掺量施工工艺研究

基于对在上部荷载作用下复合地基中水泥土搅拌桩桩身应力分布特征的认识,对水泥土搅拌桩处理深厚软土地基,提出了沿桩身改变水泥掺量的施工工艺。通过在某软土地基进行试桩和对桩身质量的检测,研究了利用该工艺改善水泥土搅拌桩质量的施工方法。研究结果表明,采用变掺量施工工艺可提高水泥土搅拌桩的上部桩身强度,对于较长的水泥土搅拌桩,可改善搅拌桩的整体成桩质量,而且该施工工艺符合上部荷载作用下桩的受力特性。     

双向水泥土搅拌桩在地基处理中的应用

针对在高速公路建设工程软土地基处理方案中,由常规水泥土搅拌桩被否决到双向水泥土搅拌桩被采用的变化过程;通过试桩施工,试桩桩身强度试验成果对比及理论分析和经济对比,同时论述了双向水泥土搅拌桩优越的工程特性及其良好的社会经济效益。     

水泥土深层搅拌桩在河北某港口软基处理项目中的应用

以河北某港口软土地基处理项目为例,针对现场水泥土搅拌桩成桩质量检测结果,通过室内水泥土配合比试验,确定该港口软土地基处理质量问题成因,采用双向搅拌施工工艺和钻机钻头改良等措施,有效解决项目质量缺陷问题。     

国道112线高速公路软土地基处理新工艺应用研究

针对国道112线高速公路建设工程软土地基处理方案中,双向水泥土搅拌桩在天津地区的首次应用,通过常规水泥土搅拌桩与双向水泥土搅拌桩在施工过程桩身强度的对比分析,介绍了双向水泥土搅拌桩及其施工工艺;同时论述了双向水泥土搅拌桩优越的工程特性及其良好的社会经济效益。     

钉形水泥土双向搅拌桩在软基处理中的应用

钉形水泥土双向搅拌桩是进行软基处理的一种有效形式。本文首先对软土地基的深层加固方法进行比较,然后阐述钉形水泥土双向搅拌桩的概念及基本原理,分析其施工流程和施工工艺,并控制钉形水泥土双向搅拌桩在软基处理中的施工质量,最后就常见问题及处理方法进行探讨。     

超长钉形水泥土双向搅拌桩加固软土地基施工技术

结合滨江大道工程,介绍了钉形水泥土双向搅拌桩的工艺原理和进行软土地基加固的施工工艺;针对超长钉形搅拌桩的施工特点和难点,通过改进施工设备、优化施工工艺等措施,实现了25 m超长钉形水泥土双向搅拌桩的施工。经检测,超长水泥土搅拌桩的桩身强度及经超长钉形水泥土双向搅拌桩处理的复合地基承载力均满足设计要求,可供类似工程参考。     

双向水泥土搅拌桩技术及常见施工问题处理

介绍双向水泥土搅拌桩施工机械、施工工艺、技术要求等,提出双向水泥土搅拌桩工艺试桩的工作内容、施工质量控制要点和常见施工问题的处理措施。     

变径水泥土搅拌桩处理软土地基的应用研究

本文介绍了变径水泥土搅拌桩作为一种新型的地基处理方式在高速公路软基处理中的应用情况,并对其施工机械和施工工艺进行说明。通过现场试验和理论分析,分别从桩身强度、承栽力及工程经济等方面与同标段的常规水泥土搅拌桩进行了比较。结果表明,通过对常规水泥土搅拌桩机械设备的改造,采用了双向搅拌的施工工艺,从而保证了桩身的水泥掺入量,提高了桩身强度;变截面的设计使得扩大头部分的面积置换率得到提高,有利于提高单桩和复合地基的承载力;同时,相对节约了工程成本,经济效益较明显。     

钉形双向水泥土搅拌桩单桩承载特性研究

作为一种新型的软土地基处理方法,钉形双向水泥土搅拌桩的单桩承载特性异于常规双向搅拌桩。在现场载荷试验的基础上,通过数值模拟分析了钉形搅拌桩单桩承载特性。结果表明:钉形搅拌桩单桩承载性能受扩大头高度和上、下桩径比等设计参数影响,单桩极限承载力随着扩大头高度和上、下桩径比的增加而增大,但增长速度逐渐变缓,存在着最佳扩大头高度和最佳桩径比。并引用单桩极限承载力提高系数和单桩水泥用量增加系数两个指标从经济角度验证了最佳值的存在,得到最佳扩大头高度为1 m,最佳桩径比为2。最后,通过理论分析,基于单桩三种破坏模式给出了钉形双向水泥土搅拌桩单桩极限承载力计算方法,试算结果与实测值偏差在10%左右,较为可靠。     

Bearing capacity optimization of T-shaped soil-cement column-improved soft ground under soft fill

During dredging activities, a large amount of dredged clay slurry or lump is produced. A dumping site composed of soft clay near the water body is often used to deposit dredged soft fill. Soil-cement columns are commonly employed to treat the soft ground for this application. Under soft fill, failure of soft clay dominates the behaviour of composite ground. Hence, a soil-cement slab is needed to form a load transfer platform above the columns, which is costly. As an alternative, the use of T-shaped column with an enlarged column cap is proposed. In this study, the responses of composite ground with T-shaped column are measured experimentally, which are used to calibrate a numerical model. The results of numerical parametric analyses show that the implementation of T-shaped column under soft fill can change the governing failure mode into column failure, once the diameter of column cap exceeds a certain value, after which the improvement efficiency is the same between T-shaped column and column-slab system. The height of column cap results in negligible difference in bearing capacity, and a minimum value of 0.3 m is suggested for use in design to avoid punching failure.     

管桩水泥土复合桩承载性能影响因素分析

管桩水泥土复合桩是适用于软土地基的一种新型复合桩,可由PHC管桩在水泥土初凝前压入水泥搅拌桩中,通过两者特定匹配关系复合而成。结合静载荷试验的相关资料,以ABAQUS为工具建立有限元模型,研究了管桩桩长、截面含芯率、水泥土外径及弹性模量对管桩水泥土复合桩竖向承载性能的影响。得到管桩和水泥土桩的最佳匹配关系,最终实现其优化设计。研究表明：管桩桩长、截面含芯率是影响管桩水泥土复合桩承载特性的主要因素,水泥土弹性模量对其影响较小。管桩与水泥土长度比宜取3／5～4／5;截面含芯率宜取0．19～0．25;水泥土桩外径应比管桩外径大300mm以上,以满足构造要求。     

水泥搅拌桩施工引起深层土体水平位移分析

针对水泥搅拌桩施工时水泥浆的注入对周围地层造成扰动,从而引起土体发生水平位移的问题,介绍了以柱形圆孔扩张理论为基础的Chai方法及其计算步骤,应用Chai方法分析了试桩C1,C2的现场试验数据。结果表明:当C1完工时,实测水平位移随深度的改变而变化,水平位移最大值达到34 mm,桩底以下土体也会产生一定的水平位移;当C2完工时,实测水平位移随深度的变化趋势与单桩（C1）施工情况的变化趋势基本一致,水平位移最大值达到72 mm;Chai方法可以用于计算单根水泥搅拌桩施工的情况,而对于多桩施工情况,无法考虑施工顺序和桩身强度的影响,产生较大的计算误差;以土体水平位移不超过10 mm作为施工的安全控制值时,单根水泥搅拌桩施工对周围环境的影响范围大约为9 m。     

Variable-diameter deep mixing column for multi-layered soft ground improvement: Laboratory modeling and field application

Deep mixing columns are commonly employed for soft ground improvement. However, the diameter of a single conventional column is a constant and the area replacement ratio does not vary with depth. Hence, the conventional column is not the ideal solution for multi-layered soft grounds, where different layers have remarkably different soil properties. Accordingly, this study proposes a better solution, which is the variable-diameter deep mixing column with a large diameter in the soil layer having high compressibility and a small diameter in the soil layer having relatively low compressibility. In this study, small-scale laboratory model tests were firstly employed to compare the performance of two-layered soft grounds improved by a variable-diameter column and a conventional column. The additional vertical stress in the soil and the column, the excess pore water pressure, and the ground settlement were analyzed. Then, a field application of variable-diameter columns for multi-layered soft ground improvement was presented; the design considerations, column installation, and monitored settlement were introduced and analyzed. The results indicated that the additional stress in the soil and the column in the highly compressible soil layer were much lower in the variable-diameter column-improved ground than in the conventional column-improved ground. Consequently, the variable-diameter column-improved ground yielded less total settlement and less post-construction settlement compared to the conventional column-improved ground.     

钉形搅拌桩复合地基承载力特性

为了研究钉形搅拌桩复合地基的承载特性,通过现场复合地基荷载试验对比分析了钉形搅拌桩和常规搅拌桩复合地基的承载力与桩土应力比,以三维数值模拟分析了设计参数对钉形搅拌桩复合地基承载力的影响,并探讨了钉形搅拌桩复合地基承载力计算方法。现场试验结果表明：钉形搅拌桩在节省水泥用量和施工时间的同时,取得了比常规搅拌桩更高的复合地基承载力,显示出很好的加固效果和经济效益。数值模拟结果表明：钉形搅拌桩复合地基承载力随着扩大头高度增加或桩间距减小而增大,随扩大头直径或桩长先增大后不变,即从复合地基承载力角度存在最优扩大头直径和桩长。钉形搅拌桩单桩承载力包括了扩大头下部土体的贡献,故可以将钉形搅拌桩等效为直径为扩大头直径的常规截面搅拌桩,按照桩、土复合的方法进行复合地基承载力计算,计算实例表明该方法计算的钉形搅拌桩复合地基承载力与现场荷载试验的结果比较接近。     

南京直立猿人化石博物馆钢管柱吊装技术研究

南京直立猿人化石博物馆是南京青奥会十大重点工程之一,其结构较为复杂,钢管柱直径1 050 mm,板厚50 mm,安装高度达到33 m,存在大量的高空安装和焊接难点。论文主要介绍了大直径钢管柱吊装前准备工作、吊装方法以及就位调整措施,以供同行参考。     

粉喷桩桩周土施工效应室内模型试验研究

粉喷桩在高速公路软土地基处理工程中得到广泛应用,但是目前对粉喷施工效应问题没有清晰的认识。针对粉喷桩施工效应问题,设计了粉喷桩室内模型试验机并采用大直径PVC管开挖取原状样进行粉喷桩施工试验。通过粉喷桩施工的模型试验,发现对于天然沉积的软土而言施工后桩周土的物理性质没有产生变化,但是桩周土的强度在距桩边一定的范围内强度降低,并且随着喷粉压力增大而增大,离桩边距离减小而增大。     

Large-scale load capacity tests on a geosynthetic encased column

Stone columns have been used to minimize the settlement of embankments on soft soils but their use in very soft soils can become challenging, partly because of the low confinement provided by the surrounding soil. Geosynthetic encased columns (GECs) have been successfully used to enhance to reduce settlements of embankments on soft soils. This paper describes an investigation on the performance of encased columns constructed on a very soft soil using different types of encasement (three woven geotextiles with different values of tensile stiffness) and different column fill materials (sand, gravel and recycled construction and demolition waste, RCDW). The results of load capacity tests conducted on large-scale models constructed to simulate the different types of GECs indicate that the displacement method adopted during column installation can lead to an enhanced shear strength in the smear zone that develops within the very soft soil. In addition, breakage of the column fill material was found to affect the load-settlement response of gravel and RCDW columns. Furthermore, the excess pore water pressure generated in the surrounding soil during installation, was found to remain limited to radial distances smaller than three times the GEC diameter.