Nuclear magnetic resonance test and analysis on water phase of the ultra-soft soil under different load level and rate

In large-scale constructions, more and more ultra-soft soil foundation treatments are faced. The treatment purpose is to discharge as much as possible the pore water in the soft soil and make it consolidated, so as to improve its physical and mechanical performances. The static and dynamic drainage consolidation method is tried to use high-energy impact and convert part of the combined water in the ultra-soft soil into free water, and thus achieve more water discharge and effective consolidation. However, it is unclear what level and rate of the impact load could cause the water phase to change. For this, based on the tests with different load level and rate for the ultra-soft soil under simulated engineering condition, water phase test of the soil by nuclear magnetic resonance (NMR) was carried out, in order to explore the rules or conditions under which the combined water in this ultra-soft soil could be converted into free water at typical load level and rate. Our main conclusion is that: (1) corresponding to the engineering usual load, true tri-axial test at low load rate and level (1.6 MPa/s, the 100 kPa), the combined water in the ultra-soft soil cannot be converted into free water; (2) corresponding to the condition of high-speed impact load (a3787 kPa load level per blow and a rate of 631.2 MPa/s) used in the static and dynamic drainage consolidation method, the combined water in the ultra-soft soil could be converted into free water; and the greater the total impact energy, the easier the conversion into free water; (3) the effect of constraint sample confining stiffness on the conversion of combined water to free water can be ignored.