桩端后注浆过程中浆土相互作用及其对桩基性状影响研究

发布时间：2018-08-08 17:27

【摘要】：桩端后注浆技术已经成为提高桩基承载力,控制桩基沉降的重要措施,已在工程实践中得到了广泛的应用。本文在分析土体可注入性的基础上,对不同的浆土相互作用方式进行了分析,分别分析了浆液从可注入到部分可注入再到不可注入等过程中渗透、滤过、压密和水泥浆压滤等一系列问题,在此基础上分析了后注浆对桩基性状的影响。本文主要的工作和成果如下： (1)分析了土体的可注入性对浆液扩散及浆土相互作用的影响,研究了滤过效应对浆液渗透扩散的影响,在质量守恒的基础上引入线性滤过定律,建立了考虑滤过效应的浆液球形渗透扩散模型,得到了浆液浓度、土体孔隙率、浆液注入的水力梯度等随注浆过程的变化情况。分析结果表明：由于滤过效应的影响,浆液在注入过程中,水泥颗粒逐渐滤出,土体的孔隙率逐渐减小,注浆水力梯度逐渐增加,离注浆孔越近,土体孔隙率降低越大,水泥颗粒的滤出量随时间、滤过系数、注入速率、初始半径的增加而增加,随水灰比的增加而降低。注浆后通过桩端土层不同位置处动力触探试验发现,离桩基越近,动力触探击数越大,土体的加固效果越好。 (2)考虑渗透注浆过程中注浆压力逐渐转化为渗透力的作用,分别分析了浆液球孔、柱孔扩散条件下渗透作用对土体的影响,得到了浆液渗透力作用下土体中的应力和变形情况,结果表明：球孔、柱孔条件下渗透产生的径向应力随水灰比和土体渗透系数的减小而增大,径向变形随土体模量增大而降低。分别给出了考虑渗流作用的球状、柱状压密注浆模型,将注浆压力分为直接作用在土体上转换为有效应力的面力αp0和作为体力的渗流力(1-α)p0,分别考虑了两部分对土体的作用,结果表明在离孔较近的主要加固区土体中的径向应力和径向位移随着α值的减小而减小。利用传统孔扩张压密注浆理论得到结果偏不安全。 (3)在分析水泥浆液特性的基础上,采用浆液泌水分界水灰比将浆液压滤过程分为自由排水阶段和非自由排水阶段,在自由排水阶段根据体积守恒得到浆液自由排水模型,在非自由排水阶段借鉴固结排水理论,考虑浆土界面排水连续性,推导了浆液压滤固结模型,通过对影响浆液非自由排水阶段参数的分析表明,在非自由阶段,浆体内的超孔隙水压力随着时间不断的消散,浆体脱水能力也逐渐降低,压滤系数越大,浆土界面排水能力越好,浆体内的超孔压消散越迅速。进行了室内单向压滤试验,对试验结果进行反分析得到了不同注浆压力和不同水灰比时压滤系数的取值范围。 (4)分析了桩端注浆预压作用对桩基端阻力、侧阻力的重要影响,考虑浆液上返对桩侧阻力的加固作用,分析了浆液上返的条件,给出了考虑成层地层中浆液上返的计算方法,并通过工程实例说明了该方法的可行性；在分析不同注浆方式加固机理的基础上,结合现有的桩侧阻力、桩端阻力经验公式,分别给出了后注浆桩侧阻力和端阻力的分析方法。并通过现场试验对后注浆的加固作用进行了分析,结果表明浆液对砂性土的挤密效果较好；距离桩基越近,对土体的加密效果越好。 (5)给出了两种计算后注浆桩沉降的方法,在荷载传递法的基础上,采用双曲线的荷载传递函数,推导了后注浆桩桩身荷载沉降关系曲线；通过对后注浆桩承载力提高量的统计分析得出了在不同桩顶位移条件下承载力提高系数的分布情况,并通过正态分布函数进行了拟合,给出了一种基于沉降控制标准的后注浆承载力预测方法。最后通过工程实例证明了本文给出的两种方法的合理性。
[Abstract]:Post grouting technology has become an important measure to improve the bearing capacity of pile foundation and control the settlement of pile foundation. It has been widely used in engineering practice. Based on the analysis of the injectivity of soil, this paper analyses the different methods of interaction between slurry and soil, and analyzes the inpouring of the slurry from injection to inpouring to non injection. A series of problems such as infiltration, filtration, compaction and cement slurry pressure filtration are used in the process of entry. On this basis, the effects of post grouting on the properties of pile foundation are analyzed. The main work and results of this paper are as follows:
(1) the influence of the injectivity of soil on the diffusion of slurry and the interaction of slurry and soil was analyzed. The effect of filtration effect on the infiltration and diffusion of the slurry was studied. The linear filtration law was introduced on the basis of the conservation of mass, and a spheric permeation diffusion model was established, which considered the filtration effect, and the slurry concentration, the porosity of soil and the injection of slurry were obtained. The analysis results show that the cement particles gradually filter out during the injection process, the porosity of the soil gradually decreases and the grouting hydraulic gradient increases gradually because of the influence of filtration effect. The hydraulic gradient of grouting gradually increases, the porosity of the soil decreases as the grouting Kong Yue is near, the filtration amount of the cement particle is with the time and filtration system. The number, injection rate and initial radius increase and decrease with the increase of water cement ratio. Through the dynamic penetration test at different positions of the pile end, the closer the pile foundation is, the greater the number of dynamic penetration is, the better the soil reinforcement effect is.
(2) considering the effect of grouting pressure gradually transformed into osmotic force in the process of infiltration grouting, the effect of infiltration on soil under the condition of slurry hole and column hole diffusion is analyzed, and the stress and deformation of soil under the effect of slurry permeability are obtained. The results show that the radial stress produced by the permeation under the condition of the hole and column hole is with the ratio of water to cement. With the decrease of soil permeability coefficient, the radial deformation decreases with the increase of soil modulus. The spherical and columnar compaction grouting model is given in consideration of the seepage effect, and the grouting pressure is divided into two parts, namely, the surface force alpha P0 converted to the effective stress in the soil and the physical force (1- alpha) P0, respectively. The results show that the radial stress and radial displacement of the soil in the main reinforcement area near the hole are reduced with the decrease of the value of the alpha.
(3) on the basis of the analysis of the characteristics of cement slurry, the slurry pressure filtration process is divided into free drainage stage and non free drainage stage by using the slurry flow boundary water cement ratio. In the free drainage stage, the free drainage model of the slurry is obtained according to the conservation of volume. The drainage continuity is considered by the consolidation and drainage theory in the non free drainage stage. The consolidation model of slurry pressure filtration is derived. Through the analysis of the parameters affecting the non free drainage phase of the slurry, it is shown that the excess pore water pressure in the slurry is gradually reduced with time in the non free stage, and the dehydration capacity of the slurry is gradually reduced. The greater the pressure filtration coefficient is, the better the water discharge capacity of the slurry interface is, the faster the excess pore pressure in the slurry is dissipated. The unidirectional pressure filtration test was carried out in laboratory, and the range of pressure filtration coefficient under different grouting pressure and water cement ratio was obtained by back analysis.
(4) the important effect of pile tip grouting on pile end resistance and side resistance is analyzed. The reinforcement effect of back resistance on the pile side is considered, the conditions of the return of the slurry are analyzed, the calculation method of the return of slurry in the stratified stratum is given, and the feasibility of the method is illustrated by an engineering example and the different grouting methods are analyzed. On the basis of the strengthening mechanism, combined with the existing pile side resistance and the empirical formula of pile end resistance, the analysis method of side resistance and end resistance of post grouting pile is given. The reinforcement effect of post grouting is analyzed by field test. The results show that the compaction effect of slurry to sand soil is better; the closer to the distance pile foundation, the encrypt to the soil The better the effect.
(5) two methods for calculating the settlement of post grouting piles are given. On the basis of load transfer method, the load transfer function of hyperbolic load is adopted to deduce the relationship curve of the load settlement of post grouting pile, and the distribution of the bearing capacity of the post grouting pile is obtained by the statistical analysis of the increase of the bearing capacity of the post grouting pile. By fitting the normal distribution function, a prediction method for the bearing capacity of the post grouting based on the settlement control standard is given. Finally, the rationality of the two methods presented in this paper is proved by an engineering example.
【学位授予单位】：浙江大学
【学位级别】：博士
【学位授予年份】：2013
【分类号】：TU473.1

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