季冻区格栅加筋粉质粘土渠基融沉机理研究

Frost damage of concrete channel lining based on the silty clay channel base is serious in the seasonal frozen regions, adding geogrid into the clay channel base can effectively reduce the frost damage to the lining, however, the thawing settlement mechanism of the geogrid reinforced structure is not clear. This project takes the geogrid reinforced silty clay channel base in shenyang area as the research object, the largest values of the displacement and shearing strength in channel base will be measured and the geogrid-soil contact surface’s Goodman model parameters and the soil’s Duncan-chang model parameters will be determined by conducting the laboratory tests of freeze-thaw cycles, drawing and triaxial under the conditions of different moisture content, degree of compaction, reinforcement distance, number of freeze-thaw, freezing temperature and upper pressure, then the relationship between the parameters and the main influence factors will be established. Take the largest values of the displacement and shearing strength in channel base as the control objectives, the moisture content, degree of compaction and reinforcement distance will be determined when the values of the control objectives are optimal under the conditions of different number of freeze-thaw, freezing temperature and upper pressure by the means of MATLAB, and carry out the model tests and ABAQUS finite element calculation under the corresponding conditions. The accuracy and reasonableness of the moisture content, degree of compaction and reinforcement distance under different conditions of freeze-thaw will be evaluated based on the comparison of the optimal values of control objectives with the finite element calculations and test determinations, which can provide the theoretical support for thawing settlement optimum calculation and effective destruction control of reinforced clay structure in the seasonal frozen regions, and it can also improve the theoritical system of reinforced soil structure.

季冻区粉质粘土渠基上的混凝土渠道衬砌冻害严重，加入格栅可有效削减渠基冻胀，减轻衬砌冻害，但其融沉机理尚不明确。本项目以沈阳地区格栅加筋粉质粘土渠基为研究对象，通过不同含水率、压实度、加筋间距、冻融次数、冻结温度和基顶压力下室内冻融、拉拔和三轴试验，得出融化终了状态结构最大融沉位移、剪应力及格栅-土接触面古德曼模型和土体邓肯-张模型参数，确定各参数与主要影响因素间相关关系。以渠基最大融沉位移和剪应力为控制目标，用MATLAB得出不同冻融次数、冻结温度和基顶压力下的最优目标值及相应渠基含水率、压实度和加筋间距，并开展各条件下的模型试验及ABAQUS有限元分析。对比最优目标值与有限元计算值及试验观测值，判定所得各冻融条件下含水率、压实度和加筋间距的准确性与合理性，为季冻区格栅加筋粉质粘土渠基融沉优化计算和有效控制渠基融沉破坏提供理论依据，进一步完善加筋土结构理论体系。

本项目在深入分析含水率、压实度、加筋间距、冻融温度、冻融次数和上部压力等对加筋黏土结构冻融后力学性能影响的基础上，重点研究了多次冻融后加筋黏土渠基冻融变形、粘聚力和液态水的分布规律。通过各主要影响因素组合下的加筋黏土渠基冻融循环正交试验及对应条件下的渠基顶部冻融位移、土体含水率测定和三轴试验，得出了渠基顶部最大冻胀、融沉位移值，以及融化终了状态，渠基土体上、中、下三个高度处粘聚力和含水率等目标值。利用SPASS软件拟合由主要影响因素表示的渠基顶部最大冻胀、融沉位移，不同高度处粘聚力和含水率回归方程，探讨影响因素对各目标值的作用规律。采用Matlab软件得出基于渠基顶部最大冻胀、融沉位移值最小，土体各部位粘聚力值最大时各因素取值。结果表明：冻融次数为15次，冻结温度为-15℃时，土体上部各因素最优组合为含水率10%、压实度91%、加筋间距150mm、上部荷载10kPa；中、下部最优值组合为含水率10%、压实度84%、加筋间距150mm、上部荷载10kPa。对冻融变形而言，含水率和上部压力间的交互作用影响较为显著，含水率和加筋间距间的交互作用影响次之；在压实度和加筋间距共同作用时，加筋间距影响较显著，控制土体变形需根据加筋层数来选择最优的压实度。位移变化与土体上部含水率变化关系更为密切，位移变化量与含水率呈正相关趋势。实际施工中，可通过增加压实度，增大加筋层数，减小土体含水率来控制上层含水率的变化，从而减小冻融变形。对土体各部位含水率和粘聚力而言，冻融循环5次以上，加筋间距较小时，中部含水率较大；加筋间距较大时，下部含水率较大；冻融循环3次以下，上部含水率较大。初始含水率相同时，冻融后含水率随冻融次数的增加而增大。加入格栅有利于冻融后黏土结构中液态水的下渗，加筋间距150mm的土体粘聚力大于其他加筋间距的土体粘聚力，减小加筋间距可提高冻融后土体粘聚力值。本研究所得基于冻融后力学性能最优的加筋黏土渠基结构模式，为季节性冻土地区加筋土工程施工提供了理论参考。