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.

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.

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.

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。

CFG桩在公路软土地基处理中的应用研究

为提高软土地基承载力和稳定性,论文依托实际工程,将水泥、粉煤灰、赤泥和再生砖骨料作为原材料制作CFG桩,将其应用于软土地基中,形成复合地基,并通过室内试验检测新拌混凝土立方体的抗压强度,评价CFG桩的力学性能。研究结果为,当赤泥掺量为10%,粉煤灰掺量为10%,再生砖骨料掺量为40%时,3 d、7 d和28 d抗压强度分别为22.63 MPa、16.98 MPa和33.96 MPa,不仅满足强度性能要求,还提高了建筑固体废弃物的再生利用率。最后,总结了CFG桩在软土地基处理中的施工技术要点。

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。

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。

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。

回填土地基上独立基础的CFG桩复合地基设计

CFG桩复合地基主要用于多层及高层建筑物,以往的研究和应用主要是针对基础埋深相对较深的情况。对于回填土地基的独立基础,采用桩基础相对较多,采用CFG桩复合地基较少。文章从受力机理、变形特性和工程造价等角度对桩基础和CFG桩复合地基进行对比分析,探讨了CFG桩复合地基的优势。同时,依托具体工程实例,依据不同规范,对回填土地基上独立基础的CFG桩复合地基沉降计算进行对比分析。结论如下:对于承载力要求不高的独立基础,相比桩基础,CFG桩复合地基在满足承载力和变形控制的前提下,能够大幅度节约工程造价;位于回填土地基上的独立基础CFG桩复合地基设计以沉降控制为主,承载力计算和沉降计算均需考虑填土的不利影响,沉降计算需按照整体进行协同计算。

软弱公路路基CFG桩处理后路基稳定性模糊评价分析

评价CFG桩处理软弱公路路基强度效果常用桩体完整性、复合地基承载力、低应变及静载实验四个参量进行综合评价。本研究将CFG桩四个评价参量进行量化,并基于模糊综合评价理论,将评价参量进行系统化,并选用专家评分、最佳隶属程度的方法界定CFG桩成桩的综合稳定性。该方法在CFG实例工程中具有较好的适用性,其评价成果较好地反映了路基处理后的实际效果,同时验证了该方法的正确、可靠性,对软弱路基的CFG路基处理方法具有较好的指导意义。

CFG桩在城市临铁软弱土层地基处理中的优势探讨

结合具体工程实例,通过施工方案比选,讨论了CFG桩在处理城市临铁软弱土层地基中的优势,就CFG桩施工技术要点展开了详细的研究,并提出了施工质量控制措施。考虑到城市临铁软弱土层地基的复杂性,研究进行了复合地基静荷载试验。结果表明,CFG桩可以有效提高地基承载力,在软弱土层地基处理中具有重要应用价值。

软土厚度不均匀地段CFG桩褥垫层厚度设计

褥垫层作为CFG桩软土加固技术的组成部分之一,其厚度的设计可以有效保证CFG桩技术的加固效果,在实际应用CFG桩技术时,常受到工程所在地的软土分布情况影响,通过分析桩体的应力扩散厚度以及桩体刺入褥垫层的厚度,计算褥垫层的设计厚度,通过实际软土厚度不均匀的桥梁工程案例进行验证,利用监测和模拟的方法,根据沉降量的变化情况反映最佳的CFG桩褥垫层厚度,经对比可知,最佳的CFG桩褥垫层厚度约为0.5 m,计算的褥垫层设计厚度为0.48 m,两者相较误差较小,通过计算得到褥垫层厚度可满足使用要求。

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桩在大藤峡灌区南木补水干管人饮控制阀房地基中的应用

文章结合大藤峡灌区南木补水干管人饮控制阀房地基工程的地质条件,通过方案比较和实际需求,提出了利用水泥粉煤灰碎石桩(CFG)的地基处理方案,并对该方案进行了理论计算和经济分析。研究表明,CFG桩在改善地基稳定性和承载力方面具有显著优势,同时在经济性上也具备竞争力。此外,还介绍了CFG桩基础的设计、施工过程及其在工程中的应用效果,以期为类似地质条件下的地基处理提供有效参考。

铁路高填方CFG桩复合地基沉降分析

目的研究高填方CFG桩复合地基的沉降变形规律,为同类型工程项目的施工提供参考。方法以新建长株潭城际铁路与长石铁路联络线CSLLXZQ-1标高填方CFG桩复合地基工程为背景,采用ABAQUS软件建立高填方CFG桩复合地基三维模型,针对该工程路堤填筑高度相对较高的情况,采用“生死单元”方法模拟高填方路堤的分层填筑过程,并将模拟计算结果与沉降实测结果进行对比研究。结果随着高填方CFG桩复合地基桩长、桩径、垫层厚度分别增大100%、33.3%、66.6%,桩间距减少40%时,复合地基沉降量分别减少63.2%、46.9%、7.9%、61.3%。结论在数值模拟中采用“生死单元”方法分级加载来模拟高填方路堤荷载,与实测结果更加吻合。

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桩与管桩处理深厚淤泥层的适用性研究

某高铁车站分布有深厚淤泥及淤泥质砂,具有含水量高、孔隙比大及强度低的特点,处理规模巨大,不仅要控制路基工后沉降,而且要消除砂土液化。采用CFG桩联合预应力管桩的加固方案,但试桩表明,CFG桩在深厚淤泥中的成桩质量不佳,遂将CFG桩变更为预应力管桩。预应力管桩现场试桩及沉降监测表明,成桩质量良好,处理后地基承载力和沉降均满足设计要求。

成本管控下高层建筑CFG桩复合地基优化设计

为降低工程成本,对漯河市某在建高层建筑地基进行方案优化。以项目中的15号楼为例,考虑桩长和桩间距两个因素,设计3种CFG桩复合地基比选方案,满足承载力要求的前提下以经济性作为评价指标,计算3种比选方案的工程造价并与原设计方案进行对比分析,研究结果表明:当桩长为16 m、桩直径为0.4 m、桩间距为1.35 m时为最优方案,仅单栋建筑比原设计方案节约造价20.142万元。为进行不同地基基础方案对比,设计桩间距亦为1.35 m的预应力高强混凝土管桩地基方案,并根据桩端持力层深度确定桩长为22 m。管桩内径为0.21 m,外径为0.4 m,桩周长为1.26 m,承载力满足要求。计算该方案工程造价,与CFG桩复合地基方案中的最优方案进行经济性对比,结果表明:仅单栋建筑采用CFG桩复合地基优化方案较管桩方案可节省工程造价57.806万元,对于需要进行地基处理的11栋楼仅复合地基就可节省约635.866万元,因此,最终确定该工程项目采用CFG桩复合地基优化方案。