土工格栅加筋路基土的松弛特性

Relaxation Characteristics of Geogrid Reinforced Subgrade Soil

为了研究土工格栅加筋路基土在长期车辆荷载条件下的流变特性,采用格栅材料的黏弹特性与土体的非线性弹性本构模型,分析了路基加筋土复合材料的应力松弛方程,通过三轴流变加载试验与理论对比分析,验证了所建立的松弛方程能够很好地描述加筋土的松弛特性及各因素的影响规律。结果表明:在初始剪应力相同的情况下,加筋土试件的松弛速率与松弛幅度均随围压增大而减小,松弛稳定时间也随之缩短;在相同围压下,随着格栅铺设角度的降低,试件达到相同轴向应变时的初始剪应力降低,松弛幅度也随之降低;在相同围压下,保持格栅铺设角度不变,随着加筋土含筋率的增大,试件达到相同轴向应变时的初始剪应力增大,松弛幅度也随之增大。在路基加宽实际工程中,应根据路基受力特点,靠近路基中央,水平铺设土工格栅可充分发挥加筋土的抗剪性能,而靠近路基边缘,可适当调整土工格栅的铺设方向来增大加筋土的抗剪承载能力;适当增加路基土中的土工格栅含量,可有效提高加筋土的抗剪性能,但较高的含筋率会造成后期松弛幅度较大,导致路基后期承载能力大幅下降,路基变形严重,因此,不能单纯依靠增加土工格栅含量来增强路基承载力,需要根据路基实际荷载情况确定出合适的加筋土含筋率。

In order to study the rheological characteristics of geogrid reinforced subgrade soil under long-term vehicle loads,the stress relaxation equation of reinforced soil composite material of subgrade is analyzed by using the viscoelastic properties of grid material and the nonlinear elastic constitutive model of the soil.Through triaxial rheological loading test and theoretical comparative analysis,it is verified that the established relaxation equation can well describe the relaxation characteristics of reinforced soil and the influence rules of different factors.The result shows that(1)Under the same initial shear stress,the relaxation rate and relaxation amplitude of the reinforced soil specimens decrease with the increase of confining pressure,and the relaxation stability time also shortens.(2)Under the same confining pressure,with the decrease of grid laying angle,the initial shear stress when the specimen reaches the same axial strain decreases,and the relaxation amplitude also decreases.(3)Under the same confining pressure and keeping the grid laying angle unchanged,with the increase of the reinforcement ratio of the reinforced soil,the initial shear stress when the specimen reaches the same axial strain increases,and the relaxation amplitude also increases.(4)In the practical project of subgrade widening,according to the stress characteristics of the subgrade,horizontally laying geogrids near the center of the subgrade can give full play to the shear resistance of the reinforced soil,while the laying direction of the geogrid can be appropriately adjusted near the edge of the subgrade to increase the shear resistance of the reinforced soil.(5)Appropriately increasing the geogrid content in subgrade soil can effectively improve the shear resistance of the reinforced soil,but higher reinforcement ratio will cause larger relaxation range at later stage,resulting in substantial decrease in the bearing capacity of the subgrade and serious subgrade deformation at later stage.Therefore,it is not only necessary to increase the geogrid content to enhance the bearing capacity of the subgrade,but also to determine the appropriate reinforcement ratio of the reinforced soil according to the actual load of the subgrade.