توصيفگر ها :
ريزشمع ها , روانگراشونده , نشست , ظرفيت باربري , شتاب نگاشت زلزله
چكيده انگليسي :
Today, one of the solutions proposed for stabilizing and increasing the bearing capacity of soil is the use of micropiles. Micropiles are essentially small-diameter piles (usually less than 30 centimeters) that are often reinforced with lightweight steel and injected with cement grout. One of the challenges in seismology is Iran's location in a highly seismic zone, which, considering the increasing population and the subsequent rise in the need for construction and various civil engineering projects, along with the limited suitable land for constructing the required structures, has led to the emergence of numerous methods for strengthening and improving the natural conditions of the soil. Additionally, considering the soil layering, the presence of a saturated sand profile is likely, which can be prone to liquefaction when subjected to dynamic loading.
The study of the interaction and seismic behavior of micropiles in liquefiable soil is significant, given that micropiles act as bearing and settlement elements and, due to the injection of cement grout, improve the mechanical properties (strength and behavior) of the surrounding soil. In this research, after introducing and describing the mechanical and practical characteristics of micropiles, the background of the subject and previous studies conducted in this regard are reviewed, along with a brief presentation of their results and shortcomings. The next chapter addresses the problem statement and the modeling approach, introducing the appropriate software for finite element analysis.
In the following chapter, various factors influencing the seismic behavior of micropiles in liquefiable soils are analyzed and discussed. These factors include inclination angle, length, diameter, and spacing between micropiles, with specific modeling addressing the effect of each parameter on settlement and the load-bearing capacity of the soil. These models and analyses were conducted using the Plaxis 3D V.20 finite element software, where fixed assumptions regarding the volume of materials used in the micropile group, the number of soil layers, mechanical properties of the soil, earthquake acceleration records, and static loading were considered. Subsequently, by varying the parameters of the micropiles, such as length, diameter, angle, and number, the effect of these variables on settlement and soil bearing- capacity was examined, and the optimal condition among the constructed models was identified.
Using the specifications of the optimized micropile group, three models with varying thicknesses of the liquefiable layer were constructed to determine the effect of this parameter on the load-bearing capacity and settlement of the soil. Analyzing the results presented in the fourth chapter reveals that, with fixed materials and thickness of the liquefiable layer, as the number of micropiles increases and their length increases, compared to when the number decreases and the diameter of the micropiles increases, the micropiles demonstrate better performance, resulting in reduced soil settlement and increased bearing capacity. Additionally, increasing the angle of inclination of the micropiles has also improved the physical characteristics of the soil, meaning that soil settlement has decreased and its bearing capacity has increased. When the parameters of the micropiles are kept constant and the thickness of the liquefiable soil layer is increased, it is observed that the amount of soil settlement increases, and consequently, the bearing capacity of the soil decreases.
