Keywords : Sand
Engineering and Technology Journal,
2017, Volume 35, Issue 4, Pages 421-430
The stability of tunnels and other underground structures under the influence of dynamic load is one of the important issues that should be studied carefully. The objective of the present paper is to study the effect of the geogrid reinforcement in transfer of the dynamic load to the underground structure. The underground structure was simulated as a plastic pipe within the soil. The investigation focuses on the influence of parameters such as load amplitude, depth of geogrid layer and width of geogrid layer using the finite element method by QUAKE/W computer program for the analysis. It was concluded that when the geogrid reinforcement width equals (1B), the total stress on the crown of pipe decreases by about (17%) compared with unreinforced soil, but this percentage decreases to (10%) when the geogrid width equals to (2B). The percent vertical settlement on the pipe crown decreases by about (35%) when using reinforcement of width equals (2B) compared with test results unreinforced soil, while when the width equals (1B), the percent vertical settlement decreases to about (15%), this indicates that when the width of reinforced soil increases, the vertical settlement decreases.
Experimental and Numerical Analysis of Piled Raft Foundation Embedded within Partially Saturated Soil
Engineering and Technology Journal,
2017, Volume 35, Issue 2, Pages 97-105
This paper presents an experimental and numerical study to investigate the load carrying capacity of piled raft foundation embedded within partially saturated sandy soil. The effect of matric suction on the bearing capacity of the foundation system was investigated. The experimental work consists of two models of foundation, circular raft foundation and circular piled raft foundation. The circular raft foundation has dimensions of 10cm in diameter, and 2.5cm thickness, while the piled raft foundation has the same dimensions of the circular raft model but with a single pile of 2.0cm in diameter and 40.0cm in length fixed at the center of the raft. Both models are loaded and tested under both fully saturated condition and unsaturated conditions, which are achieved by, predetermined lowering of water table. The lowering of water table below the soil surface was achieved in to two different depths to get different values of matric suction and the relationship between matric suction and depth of ground water table was measured in suction profile set by using three Tensiometers (IRROMETER). The soil water characteristic curve (SWCC) estimated by applying fitting methods through the software (SoilVision). A validation process then was carried out for the case of circular piled raft foundation with lowering the water table 45cm bellow soil surface in the aid of a sufficient finite element computer program ABAQUS 6.12. An eight-node axisymmetric quadrilateral element CAX8RP and CAX8R were used to simulate the soil continuum and piled raft respectively. The interaction method used to simulate the intersect surfaces of the system (pile-raft-soil) is a surface-to-surface discretization method under the concept of master and slave theory. The behavior of piled raft material is simulated by using a linear elastic model while the behavior of soil is simulated by an elasto-plastic model by the use of the Mohr-Coulomb failure criterion. The results of the experimental work demonstrate that the matric suction has a significant role on the bearing capacity of all tested models. It shows that the ultimate bearing capacity of circular raft foundation under a partially saturated condition is increases by about (7.0-8.0) times than the ultimate bearing capacity of fully saturated condition when lowering the water table 45 cm below the soil surface. While the ultimate bearing of circular piled raft foundation under partially saturated condition increases by about (8.0-9.0) times than the ultimate bearing capacity of fully saturated condition when lowering the water table 45 cm below the soil surface. The results of the ultimate bearing capacity of piled raft foundation that obtained from the experimental model and from the numerical modelling for the same soil condition and same matric suction indicate that a successful validation is achieved for the simulation process.