Secondary consolidation characteristics and settlement calculation of soft soil treated by overload preloading
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摘要:
为了研究超载预压软土的次固结特征，分析超载预压处理软土地基的工后沉降，文章考虑应力历史对软土结构性的影响，模拟现场工况，对重塑洞庭湖软土试样进行超载预压后再压缩的一维固结蠕变试验。研究结果表明：经过超载预压的软土卸荷后再进行加载，压缩变形过程中主固结时间明显缩短，约为未经超载预压处理软土主固结时间的1/3，打设排水竖井对软土主固结时间几乎没影响；预压荷载越大，次固结系数越小，超载预压有利于消除软土的次固结沉降；随着建（构）筑物荷载的增加，次固结系数增大；打设排水竖井，未经预压处理软土的次固结系数略有增加，经过超载预压处理软土的次固结系数略有减小，但影响效果不是很明显。考虑应力历史，引入超载增量比，发现次固结系数与超载增量比呈线性递减关系，建立了相应的计算模型，提出了次固结沉降计算公式。试验及分析结果对预压处理地基的设计和施工具有一定的指导意义。
Abstract:In order to examine the secondary consolidation characteristics of the soft soil treated with overloading preloading and analyze the post-construction settlement of the soft soil foundation treated with overloading preloading, the soft soil of the Dongting Lake is remolded considering the influence of stress history on the structure of the soft soil. In the test, the field conditions are simulated, and the one-dimensional consolidation creep test of soft soil remolded samples is conducted after surcharge preloading and recompression. The results show that the main consolidation time of soft soil after unloading and loading after preloading is significantly shortened, which is about 1/3 that of soft soil without surcharge preloading, and the main consolidation time of soft soil is almost not affected by the construction of drainage shaft. Moreover, the higher the preloading, the smaller the secondary consolidation coefficient is, and the overloading preloading is helpful in eliminating the secondary consolidation settlement of soft soil. The secondary consolidation coefficient increases with the increasing building load. Furthermore, the secondary consolidation coefficient of soft soil without preloading increases slightly when the drainage shaft is set up, and that of soft soil after overload preloading decreases slightly, but the effect is not obvious. Considering the stress history and introducing the overload increment ratio, the relationship between the secondary consolidation coefficient and the overload increment ratio is found to be linearly decreasing. The corresponding calculation model is established, and the calculation formula of the secondary consolidation settlement is put forward. The results of the tests and analyses are of some guiding significance for the design and construction of precompression foundation.
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表 1 试验土样基本物理力学性质指标
Table 1. Basic physical and mechanical properties of the test soil samples
力学指标 密度/（g·m−3） 含水量/% 土粒比重 孔隙比 压缩系数/MPa−1 液限/% 塑限/% 塑性指数 液性指数 黏聚力/kPa 内摩擦角/（°） 取值 1.81 43.6 2.62 1.08 1.02 45.1 26.3 18.8 0.92 5.4 12.25 
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表 2 不同试验工况下的次固结系数
Table 2. Secondary consolidation coefficient under different test conditions
预压荷载
/kPa施加荷载
/kPa次固结系数 
/%
CαU/×10−2
（无竖井排水）CαD/×10−2
（有竖井排水）0 125 0.1916 0.2279 18.94 150 0.2641 0.2799 5.97 200 0.4269 0.4689 9.85 250 0.4887 0.5436 11.24 200 125 0.0790 0.0577 −27.01 150 0.1042 0.0844 −19.02 175 0.1316 0.1110 −15.66 300 125 0.0453 0.0397 −12.29 150 0.0746 0.0572 −23.36 175 0.1003 0.0739 −26.33 200 0.1177 0.0913 −22.45 250 0.1224 0.1061 −13.30 400 150 0.0407 0.0362 −11.16 200 0.0879 0.0769 −12.49 250 0.1008 0.0915 −9.22 300 0.1091 0.1018 −6.66
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表 3 拟合参数
Table 3. Fitting parameters
排水条件 a b R2 无竖井排水 0.1529 0.0254 0.9365 有竖井排水 0.1289 0.0217 0.8933
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