砂层压密特性及其对劈裂-压密注浆扩散过程的影响

Compaction behavior of sand layer and its effect on diffusion process of fracture-compaction grouting mode

劈裂-压密注浆模式是砂层注浆工程中的重要模式,砂层自身的压密特性对劈裂-压密注浆扩散过程具有显著影响,基于此,以山东青岛地区含黏性土砂层为典型砂层介质,通过侧限压缩试验测试了不同条件下的砂层压缩变形曲线,测试压力范围0~2 MPa,砂层黏性土含量10%~50%,砂层初始含水量12%~28%,分析了黏性土含量及初始含水率对砂层压密过程的影响,从是否形成砂骨架的角度揭示了砂层压密变形机理。采用二次抛物线模型来拟合砂层侧限压缩过程应力-应变数据,建立了可描述砂层非线性压密过程的数学模型,模型参数可通过初始压缩模量及2 MPa下的特征应变量确定。在此基础上,认为劈裂-压密注浆过程中劈裂通道两侧砂层的压密过程近似符合侧限条件,分析了黏性土含量对砂层劈裂-压密注浆扩散过程的影响。研究结果表明:黏性土含量是影响砂层压密特性的主控因素,当黏性土含量低于25%左右时,砂层压缩过程中会形成砂骨架,砂层整体可压缩性较差,反之,不会形成砂骨架,砂层整体可压缩性较好;存在最优初始含水率(20%左右),当砂层初始含水率由最优初始含水率增加或者减少时,相同压力条件下砂层压缩量均会减小;砂层压密过程数学模型曲线与试验数据较为一致,所创建的数学模型可较好地描述砂层压密过程;相同注浆时间条件下,黏性土含量与注浆扩散过程中的劈裂通道开度正相关,而与浆液扩散半径及注浆压力负相关;在相同注浆终压条件下,黏性土含量与浆液扩散半径正相关。在砂层劈裂-压密注浆设计中应充分考虑砂层压密特性对注浆扩散过程的影响。

Fracture-compaction grouting mode is a kind of important mode in sand grouting projects.Com-pressibility of sand has a strong effect on fracture-compaction grouting process.As the clayey sand layer in Qingdao district is a typical medium,a series of confined compression tests were conducted to clarify the characteristics of compressibility of sand.In compression tests,the grouting pressure was set at scope of 0~2 MPa,with the clay content at 10% to 50% and the initial water content at 12% to 28%.The effect of clay content and initial water content on the compression process of sand was analyzed,and the compression mechanism of sand layer was revealed in view of sand skeleton formation.The quadratic parabola model was used to fit the stress-strain data in the compression process.A mathematical model was developed to describe the nonlinear compression process of sand.Characteristic parameters in the model can be determined by initial compression modulus and strain value at 2 MPa.Finally,the compression process of sand layer on both sides of fracture channel was considered according to the confined compression condition approximately.Influence of clay content on fracture-compaction grouting process was studied.Results show that that the main control factor for the compressibility of sand is clay content.When clay content is lower than 25%,sand skeleton will form and the compressibility of sand will be poor.In a converse condition,sand skeleton will not form and compressibility will be good.There exists an optimum initial water content(about 20%) in the compression process of sand.When the initial water content of sand becomes lower or higher than the optimum value,the compressed volume of sand layer at constant pressure will be smaller.Fitting curves of mathematical model of sand compression process have good consistency with test data.In the same condition of grouting time,the width of fracture is positively correlated with clay content,and grouting radius and grouting pressure is negatively correlated with clay content.In the same condition of grouting end pressure,grouting radius is positively correlated with clay content.In fracture-compaction grouting design engineering projects of sand layer,the effect of compressibility of sand on grouting diffusion process should be fully considered.