Consolidation analysis of composite foundation with partially penetrated cement fly-ash gravel(CFG) piles under changing permeable boundary conditions

Based on the double-layered foundation theory, the composite ground with partially penetrated cement fly-ash gravel(CFG) piles was regarded as a double-layered foundation including the surface reinforced area and the underlying untreated stratum. Due to the changing permeability property of CFG piles, the whole consolidation process of the composite ground with CFG piles was divided into two stages, i.e., the early stage(permeable CFG pile bodies) and the later stage(impermeable pile bodies). Then, the consolidation equation of the composite foundation with CFG piles was established by using the Terzaghi one-dimensional consolidation theory. Consequently, the unified formula to calculate the excess pore water pressure was derived with the specific solutions for the consolidation degree of composite ground, reinforced area and underlying stratum under instant load obtained respectively. Finally, combined with a numerical example, influencing rules by main factors(including the replacement rate m, the treatment depth h1, the permeability coefficient Ks1, Kv2 and compression modulus Es1, Es2 of reinforced area and underlying stratum) on the consolidation property of composite ground with CFG piles were discussed in detail. The result shows that the consolidation velocity of underlying stratum is slower than that of the reinforced area. However, the consolidation velocity of underlying stratum is slow at first then fast as a result of the transferring of effective stress to the underlying stratum during the dissipating process of excess pore water pressure.

Experimental Study of Dynamic Characteristics on Composite Foundation with CFG Long Pile and Rammed Cement-Soil Short Pile

Based on the idea of optimization design of pile type, the two kinds of the typical pile type are selected, which containing flexibility pile (e.g. rammed cement-soil pile is for short RCSP), and rigid pile (e.g. cement-flyash-gravel pile is for short CFGP). The three kinds of the composite foundation are designed, which are CFGP, CFG long pile and CFG short pile (for short CFGLP-CFGSP), CFG long-short pile and rammed cement-soil short pile (for short CFGLP-RCSSP). Natural earthquake is simulated by using the engineering blasting;the dynamic characteristics and dynamic response of the composite foundation are studied through field test. CFGLP-RCSSP is closed to linear relation. The bearing capacity of the four composite foundation of the CFGP, CFGLP-CFGSP, and CFGLP-RCSSP in the site are 225 kPa, 179 kPa, and 197 kPa, separately increases 150%, 98.8% and 119% compared to the natural foundation. The vibration main frequency is mainly depended on properties of foundation soil and piles between vibration source and measuring point, pilling load value. Horizontal vibration main frequency greater than the vertical vibration main frequency and the vertical vibration main frequency close to the first-order natural frequency of composite foundation. With the pilling load increasing, the CFGLP-RCSSP pile composite foundation combined frequency decreased. Under the same blast energy, the acceleration peak on the CFG pile composite foundation is less than CFGLP-CFGSP the corresponding values, as the load increases, the peak acceleration gently. CFG pile composite foundation is favorable on seismic. The distribution of peak acceleration is consistent within 4 m from pile top in the CFGLP_RCSSP composite foundation. The maximum of the horizontal acceleration peak along the pile body occurs at a distance of pile top 4 m or the pile top, and that of vertical acceleration peak occurred at a pile top.

Bearing capacity and mechanical behavior of CFG pile composite foundation

CFG pile (i.e., pile constructed by granular materials of cement, fly-ash and gravel) composite foundation is applied in subsoil treatment widely and successfully. In order to have a further study of this kind of subsoil treatment technology, the influencing factors and calculation methods of the vertical bearing capacity of single CFG pile and the CFG pile composite foundation were discussed respectively. And based on the obtained solutions, effects by the cushion and measurements to reduce negative friction area were analyzed. Moreover, the developing law of settlement and bearing capacity eigenvalue controlled by the material strength with the increase of load were given for the CFG composite foundation. The in-situ static load test was tested for CFG pile. The results of test show that the maximum test load or half of the ultimate load is used from all the points of test, the average bearing capacity eigenvalue of single pile is 390 kN, and slightly greater than the design value of bearing capacity. The bearing capacity eigenvalues of composite foundation for 3 piles are greater than 300 kPa, and the mechanical properties of CFG pile composite foundation are almost identical in the case of the same load and cushion thickness. The pile-soil stress ratio and the load-sharing ratio can be adjusted through setting up cushion thickness.

Settlement Characteristics of Cement Fly-Ash GravelPile-Plate Composite Foundation of High-Speed Railway

Field tests on settlement characteristics were carried out on the cement fly-ash gravel （CFG） pile-plate composite foundation on Beijing-Xuzhou section of Beijing-Shanghai high-speed railway. The settlements of the piles and the soil between pries were measured and analyzed. The results show that the settlement-time dependency experienced three phases： rapid development phase, stable development phase and stable phase. Therefore, surcharge preloading was necessary to reduce the settlement after construction. The finite element software Plaxis was used to calculate the deformations of the pile top and the soil between piles at the embankment center, as well as the settlements of CFG pile reinforcement area and the underlying stratum under surcharge preloading. The calculation results and the field test results were compared and analyzed. Both the results show that the settlement of the composite foundation mainly occured in underlying stratum. The settlement characteristics of pile-plate composite foundation under high embankment are also concluded.

CFG桩复合地基附加应力场研究

CFG桩复合地基具有提高承载力、减小变形和成本低等优势,在地基处理中得到广泛应用。然而,实际工程案例表明,现行规范中常用的沉降计算方法与实测值存在较大差距,其中一个主要原因是对附加应力场分布规律了解不足。结合北京海淀某住宅项目案例,现场进行单桩复合地基静载荷试验,进一步使用Midas GTS/NX有限元软件对CFG桩复合地基进行建模分析,得到了复合地基整体附加应力场的分布规律,并研究了桩径、褥垫层厚度与附加应力场的变化规律。这些结果对于理解CFG桩复合地基受力机理并指导设计具有重要意义。

重载码头堆场CFG桩网复合地基离心模型试验研究

CFG桩网复合地基广泛应用于处理软土地基。采用土工离心模型试验研究某码头堆场超大荷载下CFG桩网复合地基的变形和桩土应力特性,试验模拟了地基、CFG桩、树根桩、加筋垫层、防尘网和轨道梁基础、矿石堆载等,分析了超大荷载作用下复合地基表面变形、桩顶轴力、桩间土压力、桩土应力比的变化规律。试验结果表明,复合地基的沉降速率在稳定控制标准之内,沉降量满足堆场使用要求,防尘网基础和轨道梁基础水平位移和沉降均很小,桩土应力比为25.2~43.8,CFG桩网复合地基在350 kPa荷载作用下是稳定安全的,达到了预期加固效果。

基于现场试验的CFG桩复合地基桩帽与垫层效应分析

【目的】柔性垫层和桩帽对CFG桩复合地基的桩土应力比、荷载分担比和沉降均有较大影响,但目前柔性垫层与桩帽在现场试验中如何共同影响复合地基特性仍有待进一步的研究。【方法】以CFG桩复合地基软基处理的某路段作为工程背景,在土工格栅层数不变的情况下,对垫层厚度为100 mm、200 mm、300 mm,桩帽尺寸为0.8 m、1.0 m、1.2 m组合下的形式进行了现场原位试验,研究了CFG桩复合地基的桩土应力比、荷载分担比和沉降特性。【结果】现场试验表明:随着垫层厚度由100 mm增大到300 mm,桩土荷载比减小了51.5%,桩土应力比减小了52.5%,总沉降量增大了7.9%;随着桩帽直径由0.8 m增大到1.2 m,桩土荷载比增大了29.0%,桩土应力比减小了29.2%,总沉降量10.4%.本文区域地质条件,宜选用垫层厚度100 mm、桩帽直径为1.2 m的CFG桩复合地基形式。

CFG桩复合地基设计与施工工艺

以CFG桩复合地基为研究对象,介绍了CFG桩的概念和基本原理,并结合具体工程,从土层参数、桩径、桩间距、面积置换率等方面进行了CFG桩复合地基设计,对CFG桩复合地基施工技术要点展开了研究,开展CFG桩复合地基的现场载荷试验,并对试验结果进行分析。

后植筋技术在CFG桩复合地基静载试验中的应用

为了克服传统堆载法静载试验的局限性,提出在试验桩周围工程桩上后植钢筋的方式组成反力系统的新型静载试验。以某高层建筑CFG桩复合地基为例,详细介绍了后植筋锚桩反力系统的设计。该新型反力系统成功应用于最大加载量为4498.2kN的CFG桩复合地基静载试验,相比传统堆载法可减小使用配重91.7%,节约费用78.8%。该新型反力系统中各后植筋轴力表现为靠近主梁的较大,远离主梁的较小,最远端后植筋轴力发挥不充分。后植筋锚桩反力法对于静载试验具有较重要的工程实用价值。

CFG桩复合地基设计要点

结合已有研究成果及工程实践,从CFG桩复合地基设计角度出发,对设计过程中的附加压力、变形计算深度、压缩模量、压缩模量提高系数、地下水等设计要点进行了分析,并探讨了桩长、桩径、桩间距等参数的选取原则,得出桩径越小,经济性越好,但同时相邻桩相互影响问题更加突出等结论。

提高CFG桩Ⅰ类桩成桩率应用研究

文中结合实际工程实践及相关规范,分析了CFG桩复合地基中影响CFG桩Ⅰ类桩成桩率的因素,通过控制钻机垂直度、混凝土坍落度、充盈系数等指标,CFG桩Ⅰ类桩比例由87.3%提升至97.8%,提高了12.1%,效果显著。研究成果可为类似工程提供参考。

水泥土搅拌桩+CFG桩在公路工程软基处理中的应用

文中以绵阳某公路项目为例,对水泥土搅拌桩+CFG桩复合地基在公路工程软基处理中的应用进行研究,采用静载试验对复合地基的承载力特征值进行验证。结果表明,水泥土搅拌桩+CFG桩复合地基展现出良好的承载力和稳定性,具有较高的经济效益和社会效益。

CFG桩复合地基在高填方路基加固中的应用——以一汽大众生活区配套道路工程为例

针对佛山市南海区一汽大众生活区配套道路工程特定的场地特点,经分析比较,选用CFG桩复合地基对软土地基条件下的高填方路基进行加固处理,论文介绍了CFG桩复合地基计算方法,分析了CFG桩的桩长、桩径、桩间距对路基沉降的影响,综合考虑设计合理与经济性,最终确定CFG桩的桩径为0.5 m,桩长为8 m,桩间距为1.8 m。

CFG桩复合地基在高层建筑中的应用与分析

以广东一高层建筑使用的CFG桩复合地基为例,分析CFG桩的设计以及处理效果,探究在本地区的适用性,进行复合地基增强体静载试验以及复合地基静载试验。试验表明:CFG桩可以大幅度提高复合地基承载力,有效降低建筑沉降,同时荷载在加载到最大设计值时,Q-S曲线仍未出现陡降段,承载力仍有很大的储备空间,可以对设计进行更深的优化。

高层建筑CFG桩复合地基施工技术及质量管理措施

研究了高层建筑CFG桩复合地基施工技术及质量管理措施,在掌握工程概况的基础上,从施工工艺、施工准备、振动沉管、混合料灌注、桩头切割打磨、桩帽及褥垫层施工等方面出发,分析了振动沉管灌注成桩施工工艺,提出了施工方案优化、可视化技术交底、材料质量控制、施工过程监控等质量管理措施,不仅缩短了工期,节约了成本,还有利于提高CFG桩复合地基施工质量和效率。

CFG桩+土工织物联合冲碾压技术在公路软土地基的应用

为探究软土地基施工技术,文章结合川中多雨潮湿地区的软土地况特点,以四川某高速公路为例,对单CFG桩软土地基处理和CFG桩+土工织物联合冲碾压两种软土地基施工技术进行研究,并对两种技术成果进行沉降测试。结果表明:1)在CFG桩处理软基路段工程初期阶段,软土地基的沉降速率较快,但随着时间的推移,土体逐步固结,沉降速度开始减缓直至稳定;2)工程完成后产生的整体沉降量小于25 cm,最大不均匀沉降量小于4 cm;3)施工后路基整体表现较为稳定,未发生开裂变形现象,满足设计施工要求标准;4)在软土地基处理上,CFG桩+土工织物结合冲碾压技术不仅在沉降量控制上优于单CFG桩处理法,且在均衡荷载分布、提升路基稳定性方面展现出优良的性能。

CFG桩复合地基施工技术在高层建筑中的应用

CFG桩复合地基施工技术在应用时需要严格控制桩的纵平和间距,以确保地基处理效果的稳定性和可靠性。文章从CFG桩复合地基的理论基础出发,对高层建筑CFG桩复合地基施工技术的实际应用进行了分析,并结合现场实测数据,验证了CFG桩复合地基施工技术对地基承载能力和抗侧移能力的显著提升效果,为高层建筑的安全施工提供了可靠的技术支持和保障。

CFG桩复合地基质量问题的检测与分析

某工程场区地层以粉土、黏性土及砂性土为主,地下水位较高,设计采用CFG桩复合地基。CFG桩复合地基检测结果显示,单桩及复合地基承载力均达不到设计要求,针对出现的质量问题采用低应变法和钻芯法检测对比查找并分析出现质量问题的原因。采用高压旋喷桩对地基进行补强加固处理,并对补强加固后的复合地基进行检测,检测结果显示复合地基承载力满足设计要求,建筑物沉降观测结果表明,建筑最大沉降量与整体倾斜值均满足设计与相关规范要求。可为解决同类工程质量问题提供参考。

CFG桩复合地基新型嵌入式褥垫层桩-土应力比改善特性

CFG桩复合地基具有较好的环保效益,近年来在软基处理中推广迅速。鉴于天然地基自身较差的工程特性,加之CFG桩施工扰动易引发表层土持力性能进一步弱化,受荷状态下刚性的CFG桩与桩间土易形成过大的桩-土应力比,褥垫层结构破坏风险增大,不利于复合地基协同受力。研究提出对截桩面下约50 cm厚剧烈影响区土层采用压实碎石换填,再铺设水泥土垫层而形成新型嵌入式褥垫层结构,以改善CFG桩复合地基持力性能,得到以下结论:①基于单桩复合地基现场载荷试验对比分析,采用嵌入式褥垫层测得的桩-土应力比显著低于常规平铺褥垫层,极限载荷下桩-土应力比较常规褥垫层的22.9降至13.8,降幅约40%,且全过程桩-土应力比曲线波动相对平缓,尤其是达到极限承载力后无陡降,有利于地基安全受荷;②采用数值试验手段模拟CFG群桩复合地基竖向受荷特性,嵌入式褥垫层对桩间土压缩层起到了显著的综合强化作用,既有效减小了桩向褥垫层的相对刺入,也使得褥垫层的变形形态更均匀平整,局部刺入和翘起得到有效缓解,避免了桩-土应力比过大对褥垫层结构的破坏;③嵌入式褥垫层条件下不同部位CFG桩的水平变形状态更优,顶部较强的约束将CFG桩受力模式由接近“悬臂式”变为接近“简支式”,对复合地基边桩和角桩的变形受力状态改善显著。

CFG桩加碎石桩两种桩型复合地基工程应用

场地存在可液化土的高层建筑,地基处理除了考虑地震影响需消除地基液化外,还需要提高地基承载力、控制变形,单一桩型碎石桩复合地基无法满足要求时,可采用多桩型复合地基方案。北京通州某高层住宅楼的岩土工程勘察结果显示,场地内存在可液化土层,同时天然地基承载力和变形也不满足上部结构要求,单一桩型复合地基难以满足全部地基处理需求。经综合比较分析,采用CFG桩加碎石桩两种桩型复合地基处理方案,进行了方案设计和确定了施工工艺;在施工完成后对复合地基进行了检测,并对建筑物进行了长期沉降观测,表明已消除地基液化的影响,同时满足承载力及变形要求,建筑物沉降收敛稳定。本工程应用结果表明,对场地存在可液化土的高层建筑,采用CFG桩加碎石桩两种桩型复合地基,具有良好的处理效果。