非饱和土在冲击载荷下力学响应试验研究.doc

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摘   要

地基的强夯法作为一种对非饱和土夯实有利的冲击荷载，是当今应用于工程上的主流地基压实方法，具有方便、快捷、经济等特点，但是由于非饱和土的结构不规律、应力复杂等特性，至今没有一套完善、有效的理论及规范来指导施工，依然以经验为主，故强夯机理以及技术的发展与改进仍需进一步的完善。本实验通过强夯法模型试验，研究非饱和土在冲击荷载下的力学响应和参数变化，为强夯法理论的进步与完善提供一定的参考。

本实验利用落锤、动态测试仪和土压力盒等工具，对非饱和土进行冲击加载并对动应力测量，得到土体应力随深度的分布曲线，以分析动应力在竖直方向和水平方向的分布和传播规律；同时也测量夯坑深度和宽度以及冲击前后土体参数的变化，来研究冲击载荷下非饱和土的受力特征。

研究发现：（1）在冲击荷载作用下，土体应力随土体深度增加而减小，且应力波的波峰持续时间很短，但应力值在衰减结束时不为零；（2）在冲击载荷作用下，含水率降低、孔隙比变小、饱和度提高，而密度在近夯击点附近增加较多，远离夯击点增加较少；（3）土体的水平和竖直方向的变形随着夯击次数的增加趋于稳定，最终会达到一个临界值；（4）随着深度的增加，冲击的影响在逐渐减弱；竖直方向动应力主要作用在浅层区域，且越靠近冲击点衰减越快；随着冲击次数的增多，动应力先是持续增强，当达到一定冲击次数时动应力增长逐渐减慢，最后基本一致。

关键词：非饱和土，冲击荷载，土体应力，土体参数 

Abstract

Foundation of dynamic compaction method as a of unsaturated compacted soil beneficial impact load, is today's application in engineering of mainstream foundation compaction method, with convenient, fast, economic and other characteristics, but due to the unsaturated soil structure is irregular, complex features force. So far, there is no a set of perfect and effective method and standard to guide the construction, still to experience based, so strong tamping mechanism and technology development and improvement still need further improvement. In this experiment, the mechanical response and parameters of unsaturated soil under impact load were studied by means of dynamic compaction test, which provided reference for the improvement and improvement of dynamic compaction method.

This experiment use hammer, dynamic testing instrument and soil pressure box tool, for unsaturated soil impact loading and the dynamic force measurement, got the soil stress distribution curve with depth, in order to analyze the dynamic stress in the vertical direction and the horizontal direction distribution and propagation rules; also measured tamping pit depth and width as well as the impact of changes in soil parameters and to study the stress characteristics of saturated soil non under impact load.

The study found that: (1) under the impact load, the soil stress decreases with the increase of soil depth, and the stress wave of very short duration, but the stress value is not zero in attenuation at the end; (2) under impact load, reducing the moisture content, void ratio, saturation decreases the degree of increase, while the density near the tamping point near the more far away from the tamping point increased less; (3) the horizontal and vertical direction of soil deformation with increasing compaction number tends to be stable, will eventually reach a critical value; (4) with the increase of depth, the impact of the effect is gradually weakened; the vertical dynamic stress of the main role in the shallow area, which is closer to the point of impact attenuation increases; with the increase of impact times, the dynamic stress is strengthened continuously, when reaching a certain number of impact when the dynamic stress growth gradually slowed down, finally consistent.

Key Words ：Unsaturated soil, Impact load, Soil stress, Soil parameters.