Abstract: Aiming at the problem of foundation stability evaluation of a bridge in disease remediation, in order to study the shear strength characteristics and mechanical parameters of the undisturbed soil of silty clay which plays an important role in the stability of the bridge foundation, the large-scale in-situ direct shear tests on the undisturbed soil under different water contents are carried out. The results show that the deformation failure mode of the undisturbed soil is creep plastic failure. Its shear peak strength parameters in the saturateds state are as follows: \varphi = 17.1 °, c = 22.1 kPa, and those in the natural state are that \varphi = 20.6 °, c = 29.3 kPa. The strength parameters of the saturated soil are reduced by about 20% compared with those in the natural state. The test results may provide a basis for the stability analysis and calculation of the bank slope of the bridge foundation.