【作者】 邹健；

【导师】 张忠苗；

【作者基本信息】 浙江大学 ， 岩土工程， 2010， 博士

【摘要】 通过室内模型试验、现场试验、电子显微镜扫描及理论分析相结合的方法,针对桩端后注浆过程中,浆液的扩散机理和桩侧桩端的残余应力开展了一系列有益的研究,主要的工作和成果如下：(1)利用自行设计开发的注浆模拟装置对粘土中浆液的扩散方式进行研究。结果表明：在粘土中注浆,随着浆液水灰比的增大,浆泡的直径减小,浆脉的数量及长度增加,浆脉的宽度减小,浆液的扩散方式逐渐由以压密为主向以劈裂为主过渡。粘土中劈裂注浆可分为三个阶段：鼓泡压密阶段、第一劈裂面阶段、后续劈裂面阶段。(2)在粘土中水泥浆压滤效应理论模型的基础上,推导出压滤效应的理论公式,并通过室内模拟试验对其进行验证。室内模拟试验表明：水泥浆无法通过渗透作用穿过粘土；滤出水的流量与压滤压力正相关,与粘土厚度负相关；最终水灰比不受初始水灰比、水泥浆高度、粘土厚度及压滤压力的影响,在试验中基本为一常量；最终压滤量与水泥浆高度及初始水灰比呈线性正相关；压滤结束时间与水泥浆高度、粘土厚度及初始水灰比呈线性正相关,与压滤压力呈反比。原子吸收试验表明,在压滤作用下,Ca2+离子随着滤出水扩散到粘土中,与吸附在土颗粒上的Na+和K+离子交换,从而降低了土颗粒表面双电层的厚度,进而使土体颗粒更加紧密。(3)利用扫描式电子显微镜,对注浆前后粘土、压滤效应前后粘土及注浆前后泥皮土进行对比分析,结果表明：原状粘土的断面形态为松散的絮状结构；经过清水压密固结,粘土颗粒间的孔隙明显减小,呈密实絮状结构；压滤作用使粘土颗粒团聚成粘土团,使土体强度提高；而压力注浆,使粘土团进一步粘聚成一个整体,土体强度大幅提高。原状泥皮土为絮状结构,经过压力注浆,桩侧泥皮转变为紧密团粒结构,泥皮土强度得到提高。(4)在水泥浆流变特性的研究基础上,推导出不同流型浆液渗透注浆扩散半径的表达式。并通过利用水泥浆流变特性对其进行简化,给出了不同水灰比水泥浆渗透注浆球面及柱状扩散半径的显式计算公式。(5)引入有效应力比的概念,建立了考虑压滤效应的粘土中压密注浆球(柱)孔扩张的控制方程,给出了径向应力和径向位移的表达式,并与传统孔扩张理论进行对比。结果表明,浆液越稀,传统的孔扩张理论的误差越大。(6)以幂律流体的平板窄缝流动为假定,得到了桩端后注浆劈裂注浆过程中,浆液在桩底的扩散半径和沿桩侧的上返高度的计算公式。结果表明,劈裂注浆时,浆液在桩底的扩散半径与浆液在桩侧的上返高度随着水灰比、裂隙高度(桩侧泥皮厚度)、注浆压力的增大而增大。(7)通过工程实例,对桩侧冒浆的处理措施及处理效果进行研究。桩侧冒浆的主要原因为桩侧泥皮厚、成桩龄期短、持力层可注性差、桩底沉渣厚等。桩侧冒浆可以通过提高持力层可注性,降低浆液水灰比,减小桩侧泥皮和桩底沉渣厚度并提高泥皮强度,间歇注浆四方面加以预防及处理。发生冒浆并通过复注达到设计注浆量的桩,其极限承载力略高于普通注浆桩。(8)分析了桩端后注浆残余应力的产生和消散,及其对后注浆桩极限承载力、侧摩阻力和端阻力的影响。注浆结束后,注浆压力的消散,使持力层进入超固结状态,使相同桩端位移下可发挥的端阻力提高。桩端后注浆桩的残余应力,通过对桩端土的预加载作用,提高端阻的发挥比例。若不考虑桩端后注浆对桩残余应力的影响,会造成对桩侧摩阻力的高估和桩端阻力的低估。更多还原

【Abstract】 Model test, field test, scanning electron microscopy, and theoretical analysis were carried out to study the spreading mechanism of grout and the bearing behavior of post grouted drilled shaft. The study has provided some key findings summarized as below.(1) Compaction grouting and fracture grouting were researched using a grouting simulation test device which was developed by the author. The results show that the diameter of grout ball and the width of grout fracture decrease with increasing grout water cement ratio, whereas the quantity and length of grout fractures increase with increasing grout water cement ratio. Under certain grouting pressure, the diffusion of grout will gradually turn from compaction grouting to fracture grouting as the water cement ratio increases. Fracture grouting in clay can be divided into three stages:(i) grout ball stage, (ii) first fracture surface stage, and (iii) following fracture surface stage.(2) Basd on the theoretical model of pressure filtration of cement grout in clay, the theoretical formulaof pressurefiltration was deduced, and then it was verified by 20 model tests. The test results show that cement grout can not penetrate into the clay without fractures. The flow of squeezed water has positive correlations with clay thickness and filtration pressure. The final water cement ratio is nearly a constant in these tests, it do not have correlations with initial water cement ratio, grout thickness, clay thickness and filtration pressure. The final squeezed water is linearly correlated with the grout thickness and the initial water cement ratio. The finish time is linearly correlated with grout thickness, clay thickness, and initial water cement ratio, and is in inverse proportion to filtration pressure. Atomic Absorption Spectrometry test shows that the Ca2+ ions from cement grout spread with the squeezed water into the clay, then the Ca2+ ions exchange with Na+ and K+ adsorbed in clay particles. This process reduces the thickness of the electri c I ayer so soi I particles become ti ghter.(3) Scanning electron microscope was used to analyze the effect of grouting and pressure filtration on clay and mudcake. The results show that the natural Xiaoshan clay is of flocculent structure. After consolidation, the porosity between the clay particles is significantly reduced. After pressure filtration, the separated clay particles become more close to each other and form clay agglomerates of diameter about 30μm. Pressure grouting will further improve the soil strength by making the clay agglomerates into a unit. The original mudcake is of flocculent structure, and after grouting, the porosity of the mudcake is significantly reduced. (4) The expression of permeation radius was derived from the spherical/cylindrical diffusion model theory and the rheological property of cement grout, and then it was simplified by utilizing the rheological property of cement grout.(5) The control equation of cavity expansion theory of compaction grouting in saturated clay was derived by introducing an effective stress ratio. In this control equation, the pressure filtration can be taken into account. Furthermore, equations of radial stress and radial deformation were derived. The comparisons between this present theory and the traditional cavity expansion theory show that traditional cavity expansion theory can not consider the impact of effective stress ratio and pressure filtration, so lower effective stress ratio will lead to larger error.(6) Basd on the assumption of exponential fluid and narrow plate model, formulas for calculating the penetration radius and the climb height in fracture grouting were deduced. It shows that the penetration radius and the climb height increase with increasing water cement ratio of grout, grouting pressure, and gap width (mudcake thickness).(7) Theoretical study and case study both indicate that thicker mudcake, shorter curing age, lower groutability of bearing layer, and thicker debris will lead to larger climb height and higher risk of overflow. The overflow of grout can be prevented by increasing the groutability of bearing layer, and reducing the water cement ratio of grout, the mudcake thickness, and the debris thickness. The overflow of grout can also be prevented by intermission grouting. In the same grouting quantity, the overflow shaft has higher bearing capacity than the ordinary shaft.(8) Theoretical analysis and field tests were carried out to study the generation and dissipation of residual stress on base grouted drilled shaft and their effects on ultimate bearing capacity. After grouting, the dissipation of shaft tip additional stress makes the bearing layer over consolidated, resulting in an increase in tip resistance at a given tip displacement. At the same time, by preloading the shaft tip soil, the residual stress improves the end bearing capacity, and thereby enhances the single shaft bearing capacity as well. If the residual stress is neglected, the skin friction will be underrated and the end bearing resistance will be overrated.更多还原