Field experiment and research of improved subsoil against softening for regulation works of deep water channels in Yangtze River estuary

Soil in Stratum ②2-0 close to the surface layer under a levee is extremely prone to softening under the action of wave loads,hence impeding grievously the progress of the works.After the construction scheme against softening of subsoil with installation of prefabricated drains and riprapping as the pre-loads to resist subsoil softening was proposed,field experiments were made to verify the construction scheme.To execute offshore monitoring and measurements,and those in typhoon periods,it was the first time that a method using multiple stationary inclinometers fixed on hinged continuous settlement plates was adopted and the accuracy of the measurements was 0.001 mm.It was also the first time that all the automatic monitoring and measuring instruments were installed on the seabed over a long period of time.It can be seen from the settlement curves and the curves of pore water pressure measured for more than a year that the curves showed good regularity with no abnormal points and were also quantitatively accurate and stable.During the field measurements,though the site where the experiments were conducted was several times attacked by typhoons,no sudden and rapid subsidence occurred.The experiments proved that the scheme for anti-softening was very successful.