不同荷载水平及速率下超软土水相核磁共振试验研究

大规模建设中面临越来越多的淤泥等超软土地基处理,其目的是尽可能排出超软土体中的水而使土体固结,以改善其物理力学性能.静动力排水固结法试图利用高能量冲击而将超软土中部分结合水转换为自由水,进而实现更多水的排出而有效固结.然而,目前还不十分清楚能造成这种水相变化的冲击荷载究竟要达到何种水平及速率.为此,在模拟条件的、淤泥土的不同类型荷载水平及速率试验基础上,进行核磁共振水相测试,探索了典型荷载水平及速率下这种超软土中结合水可转化为自由水的条件及规律,主要为:1)对应于通常工程荷载的较低能量真三轴试验荷载速率与水平(1.6 MPa/s与100 kPa及以下),淤泥类超软土中非自由水不能转化为自由水.2)对应于静动力排水固结法条件的高速冲击荷载下(每击荷载水平3787 kPa,速率631.2 MPa/s),非自由水可转化为自由水;且冲击总能量越大(遍数及击数越多),就越易析出自由水.3)约束样品的侧限刚度对非自由水转化为自由水的影响可忽略.

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.