CFG桩广泛应用于地基处理，以煤矸石作为粗骨料配置桩体混凝土，既能有效利用煤矸石，又能减轻其堆积占地及环境污染。而CFG桩体埋置在土体中，存在多种侵蚀介质影响其性能，故考虑在桩体外侧包裹波纹塑料套管形成统一整体，能较好改善桩侧摩阻力和耐久性能。基于混凝土试验、模型试验与数值计算，研究分析波纹塑料套管煤矸石CFG桩复合地基的可行性及其承载特性。主要研究内容与结论如下：

（1）以粉煤灰替代水泥率、煤矸石取代碎石率、养护龄期三类试验变量，分析各参数对煤矸石混凝土抗压强度与坍落度的影响。以C20抗压强度等级为基准，结合CFG桩体工作性能需求，通过混凝土试验选取编号F40M40（水：水泥：粉煤灰：砂：普通碎石：煤矸石：减水剂=1：1：0.67：2.98：3.32：2.22：0.01）作为煤矸石混凝土最优配合比，同时测定其弹性模量，为后续模型试验与数值计算提供依据。

（2）按照相似理论设计并完成天然地基、煤矸石混凝土桩复合地基、波纹塑料套管+煤矸石混凝土桩复合地基、土工格栅+波纹塑料套管+煤矸石混凝土桩复合地基4组模型对照试验。研究表明，波纹塑料套管桩表现为明显的摩擦桩特性，能够充分调动桩周土体承担上部荷载，桩顶荷载越高，桩侧摩阻力发挥越充分，复合地基沉降变形控制效果显著；土工格栅在高荷载作用下能充分发挥其张拉膜效应，在提高桩土应力比、桩体荷载分担比的同时降低桩端阻力比，进一步改善复合地基的承载性能与沉降变形。

（3）在模型试验工况的基础上建立数值计算模型，与模型试验结果比较，二者在变化规律上基本一致。设置光滑套管桩复合地基对照组，以此为基础提出一种新型桩体优化方法，即部分光滑波纹套管桩。研究表明，桩体轴向应力在套管型式分界处存在突变点，该突变点在不高于0.4倍桩长的光滑区间内随其增长逐渐趋近于中性点；相较于波纹套管桩复合地基，光滑区间在0.1、0.2倍桩长时沉降变形相差不大，桩体控制应力均有所降低，可有效降低负摩阻力对桩体的不利影响。比较不同桩长、桩间距和桩体模量对照组的数值计算结果，分析各因素变化对桩体轴向应力、桩土顶部差异沉降等的影响，对比各指标变化规律并揭示其工作机理，为桩体优化设计提供思路。

CFG pile is widely used in foundation treatment. Using coal gangue as coarse aggregate to mix pile concrete can not only make effective use of coal gangue, but also reduce its accumulation area and environmental pollution. CFG pile is buried in the soil, there are a variety of erosion media, which affects the performance. Therefore, it is considered to be wrapped by corrugated plastic casing on the outside of the pile to form a unified whole, which can better improve the lateral friction resistance and durability of the pile. Based on concrete test, model test and numerical simulation, the feasibility and bearing characteristics of corrugated plastic casing coal gangue CFG pile composite foundation were studied and analyzed. The main research contents and conclusions are as follows:

(1) The influence of the parameters on the compressive strength and slump of coal gangue concrete was analyzed by using three test variables: the ratio of fly ash replacing cement, the ratio of coal gangue replacing gravel and curing age. Based on the C20 compressive strength grade and combined with the working performance requirements of CFG pile, the number F40M40 (water: cement: fly ash: sand: ordinary gravel: coal gangue: water reducing agent = 1:1:0.67:2.98:3.32:2.22:0.01) was determined as the optimal mix ratio of coal gangue concrete, and the elastic modulus was measured at the same time. It provided a basis for subsequent model test and numerical calculation.

(2) According to the similarity theory, four groups of model control tests were designed and completed: natural foundation, gangue concrete pile composite foundation, corrugated plastic casing + gangue concrete pile composite foundation, geogrids + corrugated plastic casing + gangue concrete pile composite foundation. The results show that the corrugated plastic casing pile has obvious characteristics of friction pile, which can fully mobilize the soil around the pile to bear the upper load. The higher the pile top load value is, the more fully the pile side friction resistance can play, and the settlement deformation control effect of composite foundation is remarkable. Geogrid can give full play to its tension film effect when the load is higher. And it can increase the pile-soil stress ratio and pile load-sharing ratio, and reduce the ratio of pile tip stress to pile top stress. Thus, the bearing capacity and settlement deformation of composite foundation can be further improved.

(3) The numerical calculation model was established based on the model test condition. Compared with the model test results, it is confirmed that the variation law of the two was basically consistent. The control group of the composite foundation of smooth casing pile was set up, and a new pile optimization method was proposed based on this, that is, partially smooth corrugated casing pile. The results show that there is a mutation point of pile axial stress at the boundary of casing type, and the mutation point gradually tends to the neutral point with the increase in a smooth interval no higher than 0.4 times the pile length. Compared with the composite foundation of corrugated casing pile, there is little difference in settlement deformation between the smooth zone of 0.1 and 0.2 times the pile length, and the control stress of pile decreases, which can effectively reduce the adverse effect of negative friction on pile. The numerical calculation results of the control group with different pile lengths, pile spacing and pile modulus were compared, and the influence of various factors on the axial stress of pile, differential settlement on the top of pile and soil, and pile-soil stress ratio were analyzed. On this basis, the variation law of each index was compared and its working mechanism was revealed, which provided ideas for the optimal design of piles.

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