Keywords : Piled raft foundation
Behavior of Piled Raft Foundation Model Embedded within a Gypseous Soil Before and after Soaking
Engineering and Technology Journal,
2017, Volume 35, Issue 5, Pages 445-455
The paper explain an experimental study to show piled raft system behavior when embedded within gypseous soil in three different stats (dry, socking for 1 day and placing a bearing layer of dense sand below the gypseous soil when socking for 1 day). A small-scale “prototype” model of steel box with dimension of (60cm length x 60cm width x 75cm heights) was used for carried out the model tests. Two different lengths of reinforced concrete pile models (40cm and 45cm) of 2.0cm dia. were used to keep the same imbedded length ratio during testing piled raft and piles only. Three different configurations of pile groups (single, three and six piles) were tested in the laboratory in two ways, first; the raft does not contact with the soil and the second; the raft is in contact with the soil. In dry state, the gypseous soil showed a very high carrying capacity with reduction in settlement. Piled raft foundations show an efficient in dry state, where the load carrying capacity increased and the settlement decreased. The improvement ratios in the load carrying capacity were about 16% for single piled raft and 39% for group of three-piled raft, while settlement reduction ratios were about 18% for single piled raft and 45% for group of six-piled raft. When the gypseous soil socked with water for 1 day, the ultimate bearing capacity of foundations is generally reduced by about (69%-83%) compared with dry state for all model configurations. The improvement ratios in ultimate bearing capacity due to using piled raft in soaking state was about (11% -50%) whilst the reduction settlement ratios was about (16% -44%).
Experimental and Numerical Analysis of Piled Raft Foundation Embedded within Partially Saturated Soil
Engineering and Technology Journal,
2017, Volume 35, Issue 2A, 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.