石灰桩加固高含水率旧路基的挤密效应研究

发布时间：2018-06-23 20:32

本文选题：石灰桩 + 高含水率路基土　；参考：《福州大学》2014年硕士论文

【摘要】：福建省地处湿热地区,受降雨与地下水等影响,路基湿度持续上升,道路运营几年后,其含水率已经大大超过原有最佳含水率,导致路基强度与刚度下降,从而诱发路面病害。因而,如何有效恢复既有旧路基性能始终困扰着工程技术人员。相比地基处理,高含水率旧路基加固存在着以下特殊性：地基处理的质量控制标准主要是承载力,而路基主要是压实度；高含水率旧路基土压实难度大,通过一般排水手段或动力加固难以排除土周围的非自由水。鉴于此,本文利用生石灰吸水膨胀的性能,采用理论推导、室内模型试验、数值模拟等技术手段,探索石灰桩加固高含水率旧路基的挤密机理。主要工作与结论如下：(1)通过室内模型试验,测定了不同旧路基土与不同石灰砂桩桩径下桩身不同深度处的桩径膨胀量；桩周土不同深度与不同径向半径处的径向应力大小的变化。结果表明：石灰砂桩桩径最终膨胀率随初始桩径与桩身深度增大而减小；按灰砂比1：1配制的石灰砂桩5小时内大概完成了其80%的膨胀,桩径膨胀率在2天左右达到峰值,且路基土内成桩膨胀的软芯临界初始桩径为20cm。(2)将石灰桩桩周正常固结土与超固结土的应力-应变模型分别简化为弹塑性模型与三折线性软化模型,基于广义SMP准则、塑性非相关联剪胀、拉压模量不等、平面应变轴对称假设,分别推导出适用于正常固结土与超固结土的单桩与群桩扩孔挤密桩周土的塑性半径、应力场、应变场与位移场的解析解。(3)石灰单桩计算中,数值解比实测值大7.6%,弹塑性模型解析解比实测值小5.3%,基本满足工程计算精度。桩周土强度越大,其塑性半径与径向应力也越大；塑性半径随初始桩径增大而增大,增大初始桩径能增强挤密效果。桩顶与桩底处有不同程度轴向膨胀刺入,使径向应力沿径向有所减小,一定程度削弱了桩周土的径向固结效果,工程中,应采取桩端用较少量配比的生石灰来降低其竖向膨胀量。(4)石灰群桩中,弹塑性模型与线性软化模型解析解分别比数值解小6.7%与14.56%,弹塑性模型计算较合理,线性软化模型不适合用于计算正常固结土。相同条件下的石灰群桩比单桩具有范围更大的塑性加固半径,采用群桩加固更符合实际。采用方形布桩、增大初始桩径、路基土强度较大时桩周土的塑性应变与塑性贯通长度越大。当桩距与桩径比例一致时,初始桩径越小,挤土效果越好；方形布桩比梅花形效果好。
[Abstract]:Fujian Province is located in the humid and hot area, affected by rainfall and groundwater, the subgrade humidity continues to rise. After a few years of road operation, its moisture content has greatly exceeded the original optimal moisture content, resulting in the subgrade strength and stiffness decreased, thus inducing pavement disease. Therefore, how to effectively restore the performance of the existing old roadbed has always troubled engineers and technicians. Compared with the foundation treatment, the consolidation of the old roadbed with high moisture content has the following particularities: the quality control standard of the foundation treatment is mainly bearing capacity, while the roadbed is mainly compacted, the compaction of the old roadbed with high moisture content is difficult, It is difficult to eliminate the non-free water around the soil by general drainage or dynamic reinforcement. In view of this, this paper, by means of theoretical derivation, laboratory model test and numerical simulation, is used to explore the compaction mechanism of lime pile in strengthening old roadbed with high moisture content by using the property of water absorption and expansion of quicklime. The main work and conclusions are as follows: (1) through indoor model tests, the dilatation of pile diameter at different depth of pile body under different roadbed soil and different lime sand pile diameter is measured; The variation of radial stress at different depth and radial radius of soil around pile. The results show that the final expansion ratio of lime sand pile diameter decreases with the increase of initial pile diameter and pile body depth, and the lime sand pile prepared at 1:1 of lime sand ratio has approximately completed 80% expansion within 5 hours, and the pile diameter expansion ratio reaches its peak value in about 2 days. And the critical initial diameter of soft core is 20cm. (2) the stress-strain model of normal consolidation soil and overconsolidated soil around lime pile is simplified into elastic-plastic model and three-fold linear softening model, respectively, based on the generalized SMP criterion. Under the assumption of plane strain axisymmetric assumption, the plastic radius and stress field of single pile and pile group pile around compacted piles, which are suitable for normal consolidated soil and overconsolidated soil, are derived respectively. The analytical solution of strain field and displacement field. (3) in the calculation of single lime pile, the numerical solution is 7. 6 larger than the measured value, and the analytical solution of the elastoplastic model is 5. 3 less than the measured value, which basically satisfies the engineering calculation accuracy. The larger the strength of soil around the pile, the larger the plastic radius and radial stress, and the more the plastic radius increases with the increase of the initial diameter of the pile, the more the compaction effect can be enhanced by increasing the initial diameter of the pile. At the top of pile and the bottom of pile, there is different degree of axial expansion, which reduces the radial stress along the radial direction and weakens the effect of radial consolidation of soil around the pile to some extent. The vertical expansion of lime should be reduced by using a small proportion of quicklime at the end of the pile. (4) in lime pile group, the analytical solutions of elastic-plastic model and linear softening model are 6.7% and 14.56 less than those of numerical solution, respectively. The calculation of elastic-plastic model is more reasonable. The linear softening model is not suitable for the calculation of normal consolidated soils. Under the same conditions, the lime pile group has a larger plastic reinforcement radius than a single pile, and it is more practical to use the pile group reinforcement. The plastic strain and the plastic through length of the soil around the pile increase with the increase of the initial diameter of the pile and the strength of the subgrade soil. When the ratio of pile spacing to pile diameter is the same, the smaller the initial diameter of pile, the better the effect of soil squeezing, and the better the effect of square pile is compared with that of plum blossom.
【学位授予单位】：福州大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：U416.1

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