【作者】 张汉舟；

【导师】 谢永利；

【作者基本信息】 长安大学 ， 道路与铁道工程， 2008， 博士

【摘要】 针对高填路堤下软黄土地基处理问题,通过现场调研及资料统计分析了甘肃软黄土地基特征及其病害,通过原位测试、静载荷试验、静力触探、有限元仿真与理论推导,系统研究了强夯法、振动沉管挤密砂石桩、土工格室垫层、水泥粉喷桩与桩-筏式复合地基等软黄土地基处理技术特点及适用性。研究成果为黄土区高速公路的设计与施工提供了重要的理论与技术支持。甘肃软黄土主要分布于地势低洼、地下水位高、排泄条件差的区域,厚度一般在4.5~22m之间;呈现出软土、黄土、盐渍土等复杂特性。2000kN·m夯击能时,软黄土地基最佳夯击数为7~9击;水平影响范围为8m,有效处理深度为5.0m左右;仅适用于厚度较小的软黄土地基。龄期对振动沉管挤密砂石桩复合地基承载力的影响明显,而桩长的影响不明显;桩间距对复合地基的承载力影响较小,而对沉降量和桩间土强度影响较大;桩土应力比集中在1.5~2.5之间;振动沉管挤密砂石桩处理软黄土地基效果较好。土工格室垫层加固软黄土地基的影响范围为其层厚的50%左右;可使地基表面所受竖向应力减小40%左右;适于处理厚度小于4m的浅层软黄土地基;垫层合理厚度为20cm;最后基于Winkler弹性地基梁假定,给出了加固后地基承载力计算公式。水泥粉喷桩处理软黄土地基有限元分析及试验表明:铺设垫层可使桩土协调变形,使不同基底面积作用下土中应力衰减趋于相同,并给出了垫层厚度与模量值的范围;桩长对沉降影响显著,且存在有效桩长;桩土应力比与载荷板形状有关,集中在3~8之间;柔性基础下复合地基的破坏模式为桩间土先破坏进而导致复合地基整体破坏;桩、土准模量随着填土荷载呈现出先硬化后软化最后趋于稳定的特性;推导出了基于弹性理论的承载力与桩土沉降差公式。最后提出了桩-筏式复合地基处理软黄土地基方法及其设计与施工方法。更多还原

【Abstract】 Questioning the treatment technique of soft loess foundation under high embankment, the characteristics and diseases of soft loess foundation are analyzed through on-site survey and data statistics. Through in situ tests, static loading tests, static sounding, finite element and theoretical analysis, treatment technologies of soft loess such as heavy tamping, sand column of vibration diving casting and crowd dense, geocell cushion, cement DJM pile and pile-raft composite foundation are studied systematic.On-site survey and data statistics show that soft loess of Gansu province is mainly distributed in the area with low terrain, high level of ground water and poor drainage conditions. The thickness of soft loess is 4.5~22m. The soft loess shows complex properties of soft soil, loess and saline soil.Field tests of dynamic consolidation on soft loess foundation indicate that the best tamper number under the condition of 2000kN·m dynamic consolidation energy is 7~9. Horizontal influence range is 8m and effective treatment depth is 5m. As a result dynamic consolidation method is only suitable for foundation with thin soft loess.Field tests of foundation treatment with sand column of vibration diving casting and crowd dense state that the age of column has distinct impact on composite foundation bearing capacity and the length of pile and pile distance have less impact on bearing capacity. Pile distance has distinct impact on displacement and strength of soil among piles. Stress ratio of pile to soil is 1.5~2.5. As a result the treatment effect of soft loess foundation with sand column of vibration diving casting and crowd dense is better.The FEA and on-site tests of foundation treatment with geocell cushion indicate flexible geocell cushion restrains the lateral deformation of ground within the limits of 50 percentage of its thickness and reduces stress at the surface of roadbed by 40 percentage of original stress. Reinforcement effectiveness using geocell raft is better for superficial soft loess foundation with the thickness less than 4 meters. Economical thickness of geocell is 20 centimeters. At last according to the theory of Winkler the formula calculating bearing capacity of ground reinforced with flexible geocell cushion is derived.The FEA and on-site tests of foundation treatment with cement DJM pile show that cushion can harmonize deformation of pile and soil and reduce the stress in the soil under it, and equate damping rate of stress in soil under load plates with different area. The rational thickness and modulus of cushion is put forward. The length of pile within effective length has remarkable influence on settlement. Stress ratio of pile to soil is 3~8, which significantly related to the shape of loading plate. Under flexible foundation the soil among piles destroys firstly and leads into the destruction of composite ground. Quasi modulus of pile and soil among piles hardens at first, then softens and stabilizes at last. The formula of bearing capacity and differential settlement between pile and soil is proposed on the base of elastic theory. At last, design method as well as construction craft and quality control specification of the technology of reinforcing soft loess foundation under high embankment with pile-raft system is proposed.更多还原