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Experimental study on the strength behavior of EHP
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摘要: 针对实际工程应用中水泥土搅拌桩出现的桩身强度分布不均匀、成桩质量差等问题，对传统的边钻进边搅拌施工工艺进行改进。改进的水泥土桩采用钻孔外预先搅拌均匀水泥土浆液，再边钻孔边浇筑的施工工艺，从而形成一种性质可调控的新型环保均质塑性桩体（Environmental Homogeneous Plastic Pile），即EHP工法桩。通过对现场取芯样和室内方法制备水泥土试样开展一系列的无侧限抗压试验，并结合桩体芯样剖面物质组成分析，对EHP工法桩的强度特性进行了研究。建立了不同形状水泥土试样强度间的定量关系，通过引入强度折减系数对改进施工工艺现场制备桩体强度的折减幅度进行分析。结果表明：改进施工工艺制备的水泥土桩桩身均匀性和桩体强度均优于传统施工工艺制备的水泥土桩，且有效地基加固深度明显增大；和室内标准养护试样相比，不同施工工艺制备的水泥土桩，均出现一定程度的强度折减；对于EHP工法桩，桩体强度折减系数随水泥掺量的增加而减小，在0.55~0.75范围内变化；和传统施工工艺制备的水泥土桩相比，EHP工法桩的强度降低幅度相对较小，具有更优良的承载能力。Abstract: An improved soil-cement mixing pile construction method was developed to solve the issues such as uneven distribution of pile strength and poor pile quality obtained by using the traditional mixing-while-drilling method. Based on the new method, an Environmental-Friendly and Homogeneous Plastic (EHP) pile was formed following the procedure that cement-soil slurry mixture was blended outside the drilling hole before being mixing while drilling, which enables the operation to be controllable and adjustable. In this study, a series of unconfined compression tests were conducted on cement-soil samples prepared in the laboratory and field to evaluate the strength characteristics of EHP piles with various cement contents. The quantitative relationships between the unconfined compressive strength and different shapes were established. The strength reduction coefficient was employed to analyze the reduction in the unconfined compressive strength for in-situ EHP piles. Results indicate that the uniformity and strength of EHP plies are better than those constructed using the traditional construction technology. The improved construction technology can reinforce soft ground within greater depth. Compared with the samples made in laboratory and cured under standard conditions, a reduction in unconfined compressive strength of cement-soil mixing pile was found. The reduction coefficient RP of strength was introduced to evaluate the reduction in the strength of EHP piles. Results show that the value of RP decreases with the increasing cement content and RP is in the range of (0.55, 0.75). Compared with the pile constructed using the traditional method, the reduction in unconfined compressive strength for EHP pile is relatively small, indicating a better bearing capacity.
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图 1 流动度随含水率变化曲线
Figure 1. Changing law between the fluidity andwater content for soil and cement soil
图 3 EHP工法桩和MIP桩芯样无侧限抗压强度随桩身深度变化规律
Figure 3. Changing law between qu and drilling depths of samples from MIP and EHP
图 6 标准条件下养护圆柱体与立方体试样qu的比较
Figure 6. Comparisons of qu between cylindrical and cube-shaped specimens cured under standard conditions
图 7 标准条件下养护圆柱体与立方体试样qu关系
Figure 7. Relationships between qu of cylindrical and cube-shaped specimens cured under standard conditions
图 8 现场制备试样和室内制备试样无侧限抗压强度的比较
Figure 8. Comparisons of the unconfined compressive strengths of specimens prepared in the laboratory and field
表 1 原土的基本物理力学指标
Table 1. Basic physico-mechanical properties of soil
土颗粒重度/
(kN·m−3)液限/% 塑限/% 塑性指数 砂粒质量
分数/%粉粒质量
分数/%黏粒质量
分数/%黏聚力/kPa 内摩擦角/° 26.7 27.0 14.8 12.2 16.2 63.8 20.0 20 7 
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表 2 芯样无侧限抗压强度的平均值、方差和变异系数
Table 2. Average, variance and coefficient of variation of unconfined compressive strength for core samples
桩体
类型水泥
掺量/ %芯样无侧限抗压强度 平均值/ kPa 方差 /(kPa)2 变异系数 EHP工法桩 8 355.4 523.31 0.06 10 641.6 2 538.3 0.08 13 958.8 5 925.1 0.08 MIP桩 13 869.6 22 466.2 0.17
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