花岗岩残积土是中国东南部沿海地区工程建设中常见的土体，采用加筋土技术对高填方边坡能很好地提高其整体稳定性与土体的抗剪强度。首先通过直剪切摩擦试验研究了筋-土界面的摩擦特性；然后在不同加筋层数及不同干密度情况下，对花岗岩残积饱和土和加筋饱和土分别进行了三轴固结排水剪切试验，探究不同干密度、不同加筋层数情况下的加筋效果。试验与机理分析表明：不同加筋层数的试样对应的规格化强度系数都大于1，这说明在土体中加入筋体能有效地提高抗剪强度，减少土体的变形。随着加筋层数的增加，规格化强度系数增加，说明加筋层数的增加能提高加筋效果，但两层加筋的规格化强度系数与一层加筋相比并不是线性增加，第二层加筋效果有减弱的趋势；随着干密度的下降，规格化强度系数上升；随着围压的增加，加筋土的规格化强度系数降低。土工格栅主要通过提高土体黏聚力来提高土体抗剪强度，导致土体的黏聚力显著地提高，而对内摩擦角的影响却不大；通过理论计算结果与测试结果对比，验证了准黏聚力增量公式的合理性，且第二层加筋对准黏聚力增量的贡献相对较小。

Granite residual soil, distributed widespreadly in China Southeast coastal region, is a commonly soil mass used for the urban construction projects. Using readily available the local soils as filling materials for high-fill embankments and slopes is an most costing economic strategy. For high-fill slopes, using geogrid reinforced soil technology can improve soil shear strength and enhance the slope stability. Firstly, direct shear friction tests were done to investigate the frictional characteristics of the reinforcement-soil interface. Furthermore, in order to study the impacts of dry densities and number of reinforcement layers on the shear strengths of reinforced granite residual soil, triaxial consolidation and drainage shear tests were used to investigate shear strength and deformation of both saturated granite residual soil and saturated reinforced granite residual soil separately. The testing results show as follows. The specimen normalized strength coefficients corresponded to different reinforcement-layer number are overall greater than unity, this shows that embedded reinforcing geogrid into the soil body can both enhance soil shear strength and decrease soil body deformation effectively. The normalized strength coefficient does not have a linear relation with reinforcing-layer number increasing, and effect of the second reinforcement layer tends to be weaken on soil shear strength increasing. The normalized strength coefficient increases as dry density deceasing and reduces as confining pressure increasing. The geogrid primarily enhances soil shear strength through increasing the apparent cohesion of reinforced soil obviously, the quasi-cohesion increment calculating formula is proven to be reasonable for the saturated reinforced granite soil through comparing theoretical calculating results against test results, and the second reinforcement layer only contributes slightly increasing to the quasi-cohesion increment.