室内承载板法土工试筒约束的综合修正

室内承载板法是测定土样回弹模量的标准试验方法,其基本原理是根据实测的各级承载板压力和回弹变形的关系,运用圆形垂直刚性分布荷载作用下的弹性半空间体竖向位移理论公式来计算土样回弹模量.但是,由于击实成型的测试土样受到土工试筒的筒底和筒壁的约束作用,土样的有限尺寸和受力条件与半无限的弹性半空间体理论存在较大的差别,造成土样回弹模量测试结果偏大,导致测试结果难以应用于路面结构设计,所以有必要对室内承载板法的土样回弹模量测试结果进行约束修正.为此,首先推导了具有刚性下卧层的弹性层轴对称课题的应力和位移理论解,并通过轴对称有限元法,验证了理论解的正确性,从而考虑土工试筒筒底的约束作用,以竖向位移理论公式提出了室内承载板法测定土样回弹模量的高度修正系数K1.其次,在高度修正的基础上,通过轴对称有限元法考虑土工试筒筒壁的约束作用,提出了室内承载板法测定土样回弹模量的直径修正系数K2.综合高度修正和直径修正,提出了不同直径D的承载板测定土样回弹模量的综合修正系数K,以及K和D的回归公式.最后,通过不同直径承载板进行了室内测试验证.验证结果表明,所提出的综合修正系数可用于室内承载板法测定土样回弹模量的土工试筒约束的综合修正,并保证了测试结果的合理性和可靠性.

Comprehensive correction for restraint action of soil tube with laboratory bearing plate method

The laboratory bearing plate method is a standard testing method for the determination of the soil resilient modulus.The basic principle is that the resilient modulus of soil specimen is computed with the theoretical formula of vertical displacement in elastic semi-space under the circular vertical load of rigid distribution in accordance with the relationship between each level of plate pressure and resilient displacement.However,the compacted soil specimen is restrained by the bottom and wall of testing tube,so the finite size and loading condition of specimen are quite different from the theory of semi-infinite elastic semi-space to make a larger testing result of soil resilient modulus.It is difficult to use the testing results in pavement designs.Therefore,it is necessary to consider the restraint action of tube to correct the testing results of soil resilient modulus with the laboratory bearing plate.Firstly,the theoretical solutions of stress and displacement for the elastic layer with rigid underlayer in line with the axisymmetric solid problem are developed in this paper.The correctness of theoretical solution is verified with the axisymmetric finite element method.The height correction coefficient K_1 in the laboratory bearing plate method is put forward with the theoretical formula of vertical displacement to consider the restraint action of the bottom of testing tube.Secondly,on the basis of the height correction,the diameter correction coefficient K_2 is proposed with the axisymmetric finite element method to consider the restraint action of the wall of testing tube.Thirdly,the comprehensive correction coefficient K in the different diameter D of bearing plate is put forward according to the height correction and the diameter correction and the regression formula of K-D obtained.At last,the soil resilient moduli of the bearing plates of different diameter are tested and verified,the results show that the comprehensive coefficients can be used to correct the restraint action of tube in testing soil resilient modulus with the laboratory bearing plate,and ensure the rationality and reliability of the testing results.