武广客运专线桩—网复合地基内力及变形监测与有限元分析

【作者】 石洋海；

【导师】 魏丽敏；

【作者基本信息】 中南大学 ， 岩土工程， 2008， 硕士

【摘要】 桩-网复合地基是一种处理和加固软弱地基的有效方法,通过桩、网、褥垫层三者之间的相互作用共同承担荷载,能有效解决软弱地基上修建高速铁路所面临的工后沉降控制和路基稳定性两大技术难题。本文在前人工作的基础上,通过室内试验、现场试验、理论分析和数值模拟相结合的方法,对铁路客运专线路基中桩-网复合地基的工作性状和加固效果进行理论探索和工程实践分析,主要工作和结论如下:(1)根据现场地质条件和设计方案,合理选择监测断面,制定了科学的监测方案,全面监测桩-网复合地基中地基沉降、剖面沉降、水平位移、土压力及桩-土应力比、桩顶应力、土工格栅应变等的发展规律。(2)对现场3个监测断面填筑期和预压期(共计216天)的监测结果进行整理分析,其填筑高度为H=6.2m。结果表明:①地基沉降随填筑高度的增加而增加,预压152天后沉降基本稳定。实测地基最大沉降值为12.92mm～13.79mm。②坡脚水平位移随深度增加而减小,实测水平位移值的变化范围为29mm～74.8mm,最大水平位移出现在地表以下1.5m～2m,且地表以下10 m及以下深度处,基本没有水平位移发生。③填筑期间桩-土应力比随填土高度增加而变大,变化范围为1.6～5.4;填土结束以后桩-土应力比逐渐趋于稳定,变化范围为4.4～6.2。上述结果验证了采用桩-网复合地基控制地基沉降的有效性。(3)根据等效面积置换率原则进行平面应变处理,将桩体转化为沿线路纵向无限长的墙体,通过设置无厚度界面单元模拟桩和土工格栅与土体之间的接触作用,采用岩土工程有限元分析软件对桩-网复合地基进行有限元模拟。(4)将现场监测结果与有限元模拟结果进行对比,结果表明地基沉降、水平位移、桩-土应力比、桩顶轴力、土工格栅拉力等的实测结果与数值模拟结果变化规律一致,验证了模型的合理性。(5)采用上述有限元模型,分别改变褥垫层厚度、褥垫层弹性模量、桩间土弹性模量、桩间距等参数,研究上述因素对桩-网复合地基沉降、桩-土应力比、桩身轴力以及土工格栅拉力的影响规律和影响程度。更多还原

【Abstract】 The pile-net composite foundation is an effective method to improve and strengthen weak foundation of soft soil, which bear the loads through the interaction among the piles, the geo-grid, the cushion layer. When high-speed railway is built on soft soil foundation, the pile-net composite foundation can solve the two technology difficulties effectively, which is the residual settlement control and Stability of embankment.On the basis of somebody else have worked, methods such as testing in laboratory and in the field, theory analysis, numerical simulation, etc. were used to study the working performance and strengthened effects of the pile-net composite foundation by theory discussion and practice analysis, which was applied in the special railway line for passenger transport. The main achievement and conclusion are as follows:(1) according to the on-the-spot geological condition and the design scheme, the monitor section was choosed rationally and the scientific monitoring scheme was made to monitor in an all-round way the development laws of the foundation settlement, section settlement, horizontal displacement, soil pressure and pile-soil stress ratio, stress on the pile, geo-grid strain, etc. in the pile-net composite foundation.(2) After analyzing the 3 monitor sections on-the-spot, which the periods of building and press in advance last for 216 days and the whole building height was 6.2 meters, the results were as follows:①The settlement of the foundation increased as the height of the building at the same time. It basically kept steady after been pressed in advance for 152 days. And the measured biggest settlement of the foundation varied between 12.92 millimeters and 13.79 millimeters.②The horizontal displacement decreased as the depth increased, and the measured horizontal displacement varied between 29 millimeters and 74.8 millimeters. The biggest horizontal displacement appeared at the depth between 1.5 meters and 2 meters. It was showed that there was no horizontal displacement at the depth of 10 meters and the deeper place was the same. ③The pile-soil stress ratio increased as the height of the building at the same time, which varied from 1.6 to 5.4. After the embankment were finished, the pile-soil stress ratio tends towards stability gradually, which varied from 4.4 to 6.2.The results above have proved that the pile-net composite foundation is effective in controlling the settlement.(3) Based on the principle of replacement rate of equivalent area, the treatment of plane strain was applied to turn the piles into the limitless long wall along the longitudinal line.The interaction of contact between piles, geo-grid and soils was simulated by interface unit without thickness. And the finite element software for rock and soil engineering was applied to simulate the pile-net composite foundation.(4) After compared the monitor results on-the-spot with the results of finite element calculation, it showed that the vary law of numerical simulation was the same as the measurement results, which were the foundation settlement, horizontal displacement, pile-soil stress ratio, stress on the pile, geo-grid force, etc. So the rationality of the model was verified.(5) Take the finite element model above, and change the parameter for thickness and the elastic modulus of the cushion layer, elastic modulus of the soils between piles, interval among piles. The influence law and influence degrees to the settlement in the pile-net composite foundation, the pile-soil stress ratio, axle stress on piles and geo-grid force was analyzed with the factors above.更多还原