【作者】 姚凯；

【导师】 姚占勇；

【作者基本信息】 山东大学 ， 道路与铁道工程， 2013， 硕士

【摘要】 黄河冲(淤)积平原的高速公路,沿线地区土质多为粉土、粉质粘土及粘土互层。相关研究表明,若不进行合理的地基加固,桥涵构造物台背将发生较大的不均匀沉降,影响行车安全。强夯法是一种经济高效的地基加固技术,但其设计参数、施工工艺和工程控制指标因地基土质、地下水位以及上部结构等因素的差异而不同。因此,研究黄河冲(淤)积平原区强夯加固地基技术,可为该区域及其他类似地区高速公路的设计、施工及养护管理提供指导,具有显著的工程应用价值和社会经济效益。本研究选择济乐高速公路典型地基,通过现场试验确定强夯加固地基的合理工艺参数,完善相关地基加固设计并指导施工。运用FORTRAN语言编制程序计算试验段地基沉降量,采用FLAC3D软件进行天然地基沉降的数值模拟,将计算结果与现场实测沉降值进行比较以分析强夯减小地基沉降的效果。通过现场检测(静力触探、动力触探)数据,进一步评价强夯的加固效果。运用FLAC3D分析地下水位对粉土地基强夯的影响并提出夯击能与临界水位高度的关系式,同时也研究了含水量对粘土地基强夯的影响,并归纳总结了相应的处置措置。通过上述研究主要得出如下结论：四标、九标试验段在1500kN·m夯击能作用下地基有效加固深度分别在6m、6.5m左右,强夯有效加固深度系数α分别为0.155、0.168。两试验段1500kN·m夯击能作用下的径向影响距离可达6m,径向有效加固距离在2～4m之间。试验地基条件下,单点夯对相邻夯点处的孔隙水压力影响很小,故相邻夯点可以连续夯击,而不必间隔跳夯。连续进行单点夯击时,表层土发生液化的可能性要大于深层土,地下水位越高,液化可能性越大。为了避免强夯引起地基土液化,保证加固效果,强夯施工前应按照设计要求检测地下水位情况。一般来说,在地下水范围内,埋深越小,超孔隙水压力增长量越大,消散越慢；埋深越大,超孔隙水压力增长量越小,消散越快。两个试验段第1遍以及第2遍点夯后24小时超孔隙水压力基本完全消散,夯后48小时超孔隙水压力完全消散,建议类似条件的地基强夯间歇时间调整为48小时。沉降分析表明,试验段地基经强夯加固后,地表总体沉降量占地基总沉降的40%以上,剩余沉降量显著降低。对比数值计算结果与现场沉降观测数据可知,强夯地基沉降量明显小于天然地基，说明通过强夯加固能够显著减小工后沉降，缩短路基放置时间。现场静力触探和标贯试验表明，在有效加固深度范围内地基承载力明显增强，强夯加固效果明显。对于粉土地基，地下水位越高，强夯时液化可能性越大，发生液化的范围也越大。随着夯击能的增大，临界水位高度也会增大，幂函数y=0.449×0.280能准确反映出两者的相关关系。粘土地基含水量过高,强夯时会形成橡皮土。为保证强夯加固效果，可通过井点降水、强夯置换、灰土处置等方式进行处理；同时需要及时回填夯坑避免坑积水。更多还原

【Abstract】 In the Yellow River alluvial plain, silt and silty clay are widespread. Severe differential settlement of freeway foundation would happen without reinforcement. Recently dynamic compaction has been widely used in ground reinforcement because of its economical efficiency. But the design parameters and construction methods of dynamic compaction should be based on quite many factors, such as the soil type and underground water level. So it is of great importance to study the reasonable dynamic compaction methods for the Yellow River alluvial plain, which will be useful for the design and construction of freeway in this area.Based on the Jile freeway construction engineering, two sections were chosen to do in-situ test to determine the reasonable parameters for a better design. Foundation settlement calculation was done by FORTRAN and FLAC3D. Then the calculation results were compared with the test data to analyze the effect of dynamic compaction on reducing settlement. Some field tests (static penetration, dynamic penetration) were also done after the reinforcement to evaluate the soil improvement. FLAC3D was used to analyze the effect of water table on dynamic compaction in the silt groud. We also studied the influence of water content on clay foundation during dynamic compaction. Then the treatment measures for dealing with water were summarized.The following results were found in the research:With the effect of1500kN-m dynamic compaction, the effective reinforcement depths of the two sites were6m and6.5m respectively and the effective reinforcement depth ratio were0.155and0.168respectively. In terms of the reinforcement width,1500kN-m dynamic compaction could affect more than6m, but the effective reinforcement width was between2-4m. When hammering one point, it had very little effect on the adjacent one. If one single point was hammered continuously, the liquefication possibility of surface soil is larger than that of deep soil. In order to avoid liquefication caused by dynamic compaction, detection of underground water level should be conducted. In general, the smaller the depth, the more the excess pore water pressure increased and the slower the excess pore water pressure dissipated. In the two sites, excess pore water pressure dissipated completely48hours after hammering. Settlement analysis showed that dynamic compaction could reduce more than40%of the total settlement. Comparing numerical results with the field settlement observation data, the settlement of reinforced ground is much less than that of natural foundation. Static penetration and dynamic penetration test showed that foundation bearing capacity was significantly enhanced after reinforcement within the the effective reinforcement depth. For silt foundation, the higher the underground water level, the severer liquefaction would happen. The equation y=0.449x0.280could reflect the relationship of critical water table depth and tamping energy. In order to ensure the good effect of dynamic compaction, well-points dewatering, dynamic compaction replacement and lime soil disposal method will be helpful if there is much unfavourable water. The ram pits should also be pluged-back immediately after hammering to avoid water filling.更多还原