The Research Of The Saturated Fine Grained Soil Mechanism Under The Dynamic Load

With the rapid development of constructional engineering, specially the development of express highway and reservoir dam, which are beneficial to the people's livelihood, the diseases such as uneven sedimentation of structure, settlement, leakage and frost boiling have a harmful impact on the safety and service life of these major projects. The microshock liquation of saturated fine grained soil, caused by dynamic load in the large area, generates these diseases. At present, the liquation mechanics and evaluation of the saturated fine grained soil caused by the non-seismic force is a great concern of scholars and engineers. From the site test and indoor test, this article tries to study the characteristics of liquation damage and deformation of saturated fine grained soil under the cyclic load and the liquation mechanics, degree, vertical depth of influence by using the measured data.First, this article collected a lot of investigative data about saturated fine grained soil from our country and overseas, and found out shortages after analysis and comparison of the data.Secondly, the Yellow River Delta was determined as the test site and the test program was designed. Many kinds of advanced in-situ measurements and indoor tests were adopted to obtain test data for fitting and regression analysis, which is a beneficial attempt for liquefied differentiation. The site and indoor tests were performed as follows:(1) Through the site investigation and inspection, and with the aid of road foundation survey projects, a typical location was chosen for in-situ tests such as drilling, sampling, standard penetration test, cone penetration test, dynamic load test. From these tests, the stratal configuration, mechanics index and geophysics parameters of the saturated fine grained soil caused by sedimentation in the representative location of the Yellow River nowadays.(2) The indoor microstructure scanning electron microscope was used to observe the typical soil sample and the X-ray analysis was performed for the mineral composition. With a series of tests such as conventional indoor soil test, static triaxiality test and high pressure penetration test, the basic physical mechanics index and solidification and drainage status were obtained for the saturated fine grained soil in the Yellow River sedimentation.(3) The site cyclic load test was performed to analyze the deformation mechanism of the saturated fine grained soil of the Yellow River sedimentation under the load of the vehicle.As the site and indoor test results were analyzed, the following principle is obtained:1. According to the site drilling, sampling and indoor analysis, the characteristics of the Yellow River delta saturated fine grained soil was observed: sabulous clay with bit of clayey soil, including fine sand and powdery fine sand. The underground water is rather shallow, the water content in the soil mass rather high, and the intensity varies greatly. The microstructure characteristics of the soil mass are basically consistent in general. Fine particles adhere to the surface layers of most particles, most in the shape of ellipsoid; the contacts between particles are mostly direct extrusion, and only few particles are connected by chains. Most have framework structure.2. From the liquation process of the Yellow River delta foundation soil, the conclusions are reached as follows:(l)When cyclic vibration load is applied, the vibration energy absorption characteristic of the soil mass is influenced by the soil mass structure change caused by vibration. The attenuation of the normalization vibration energy within the research depth range conforms to the logarithm function relation. While the vibration energy is 140N/m2'time, the attenuation rate is the highest within the range of 0-30cm, and the soil mass is compact due to vibration, the soil mass of this layer absorbs about 40%-60% of the vibration energy. For the soil layer below 30cm deep, the energy attenuation rate slows down. The energy absorbed by the soil layer between 30-60cm is about 20%-30% of the total vibration energy, and the liquation mainly occurs on thislayer. The remaining energy on the soil layer of 90cm deep is about 10% of the total energy. With the increase of the energy, the influenced depth increases as well. The soil mass change within the influenced depth range is consistent with the above principle.(2) As the interlayer drainage is different, the soil mass pore pressure increase caused by the cyclic load presents different trends. If there is permeable layer, the pore pressure increases rather rapidly, and the accumulative increase presents a trend of gradual modification. As the pore pressure dissipates rather rapidly shortly after the vibration ends up, and finally the pore pressure approaches the self-weight stress of the upper covering soil layer. If there is membrane barrier interlayer, the pore pressure increases and exceeds the liquation critical value within a short time, which presents a trend of sudden change. After the vibration is over, the pore pressure dissipates rather quickly at the beginning, and slows down afterwards, and finally the pore pressure approaches the self-weight stress of the upper covering soil layer. If the load is applied from different directions, the soil layer liquation sequence is different. The liquation performance of the Yellow River saturated fine grained soil is different due to different drainage structure of the interlayer. If there is permeable layer, the antiliquation performance of the soil mass increases relatively. The impermeable layer can weaken the antiliquation ability of the soil mass.