Study On The Strength Weakening Of Soft Subsoils Of Guiding Dike In Changjiang Estuary Under Wave-induced Loading

In the design of offshore structures which are experiencing wind, wave or micro-quakes, the residual deformation control of the structure after being completed is of primary importance. To simulate the characteristics of the subsoil's beneath such structures, it is necessary to understand the residual deformation law of the subsoils under repeated or cyclic loading.During constructing a dike in Yangtze Estuary, some of the caissons were sinking into the soil for 1-5m or sliding away about 20m from the original place when a strong storm was attacking this area. Dynamic triaxial test were carried out to simulate the behavior of foundation soil under wave loading. Based on a great number of undrained triaxial tests of the chosen silty clay under repeated loads, mathematical models are formulated to predict the residual deformations under single- and multi-level repeated stresses.The test results show that the excessive settlement and lateral movement of the caissons are due to the strength weakening of the soft clay during the strong storm. Meanwhile it is found that the residual deformation under undrained repeated loads is composed of two parts: one resulting from unloading to zero of the first repeated stress cycle; the other due to the residual deformation accumulated during the cyclic stress process under applied repeated stress level. The verification of the established models by the measured values has shown that the predicted value agree well with the measured ones.Based on the test results, an improvement method associating vertical drains with surcharge loading is proposed to strengthen the foundation soil. With the improved soil foundation, the dike has been reconstructed and undergone several strong storms without any damage.