典型荷载条件下淤泥孔径分布特征核磁共振试验研究

Nuclear magnetic resonance experimental study on the characteristics of pore-size distribution in muck under several typical loading cases

模拟了淤泥地基加固工况对应的几种典型荷载效应,并利用核磁共振测试寻求典型荷载水平和速率下,淤泥孔隙及其孔径分布的变化规律,以探讨淤泥地基典型加固条件下微细观结构的三维响应.结果表明:在一定压力作用下,淤泥中最大孔隙数将会减少,应力水平越高,减少量越大,而当冲击荷载达到更高的某一水平时,淤泥中最大孔隙和最小孔隙所占比例均会减小,孔隙更趋于均匀;约束样品的侧限刚度将会增加淤泥土的总受力水平,进而更易减小大孔隙所占比例;当荷载水平680 kPa时,加载速率是决定相对最大孔隙占总孔隙数比例的关键因素,速率较小会使得该比例增大,速率较大则使得该比例减小,其界限值在>0.8 MPa/s与1.6 MPa/s之间;一定的冲击荷载和速率水平下,随着作用次数即总能量的提高,淤泥中的相对大孔隙和最大孔隙部分会明显减少,而当间隔时间较短的作用次数再提高时,上述效应会降低;对于有效减少较大孔隙而言,淤泥受冲击的次数存在某个合适的量值.上述规律有助于从内部本质上寻求和掌握各种静动力排水固结法处理淤泥类软基的微观机理,为其科学设计及施工优化提供了进一步的依据.

Several typical loads are applied to muck specimens to simulate muck ground treatment conditions. Then tests of pore structural distribution of the soil are performed by the method of nuclear magnetic resonance（NMR）, for seeking variation of their internal structure under the typical load level and rate, and thus to further determine the muck ground reinforcement mechanism and responses in micro-structure aspect. The results suggest that：（1） the max-pore decreases under a certain load, and the reduction increases with load level; nevertheless, when the impact load reaches a considerable level, both the max-pore and small-pore decrease;（2） the confining stifiness efiect of constraint samples induces a decrease in the proportion of large-pore;（3） at a certain load level（680 kPa or less）, the loading rate is the key factor determining the relative proportion of maximum void ratio： smaller lading rate will make the void ratio increase,larger lading rate will make the void ratio reduced, and its boundary value is between 0.8 MPa/s and 1.6 MPa/s;（4） with a certain load level and rate, an the number of impact times increses, namely as the total energy is enhanced,the large-pore as well as the max-pore considerably decreases; however, this efiect will be reduced when the interval time is short and as the number of impact times increases further. i.e. the large-pore efiectively decreases. There exists a suitable value of the number of impact times for the muck specimens. These results refiect the rule of difierent loading efiects in the micro of micro fine structue and provide a basis for the design and construction optimization for muck ground improvement.