Abstract
A stone column is one of the soil improvement methods that are mainly used for improving the geotechnical behavior of soft soils. For deep improvement of soft soil, the floating stone columns are considered the best and effective economically which provide lateral confinement and drainage and longitudinal skin friction. In this study, six tests were carried out on the natural soft soil of undrained shear strength of 5.5 kPa improved by single and two linear distributed floating stone columns. The stone column dimensions are 30 mm in diameter and 180 mm in length and the stone column material is sand of high internal friction angle of 48°. The natural and improved soil samples are tested under isolated raft foundation of dimensions 120×120 mm subjected to vertical static and cyclic loading of frequency 2Hz and continued for 50 seconds. The results showed a significant improvement in soil bearing capacity when reinforced with stone columns despite the small area replacement ratio, where the bearing capacity of improved soil increased by 120 to 145%. The compressibility of improved soil decreased by 57 to 86% in comparison with that of natural soft soil. Also, the floating stone columns reduced the porewater pressure, where the stone columns considered efficient in providing short drainage pathways. This can be one of the reasons why soil reinforced with floating stone columns hold higher cyclic and static stresses regardless the end bearing of stone columns.
Highlights
Most of the soils located in the middle and southern parts of Iraq are considered as soft to very soft cohesive soils especially in areas close to the marshes
Figure shows the effect of the area replacement ratio (Ar) on the improvement in the soil under the effect of cyclic and static loads, where the results indicated that the settlement under cyclic loads is greater than the static load in all tests especially in light loads and this difference decreased with increasing the applied loads to be roughly equal in high load
The applied cyclic stresses will help in generation high porewater pressure and when enough drainage paths are available will help in decreasing this pressure quickly, but when the capacity of available drainage, stone columns, are not enough to dissipate the porewater pressure, this will help in raising the Porewater pressure (PWP)
Summary
Most of the soils located in the middle and southern parts of Iraq are considered as soft to very soft cohesive soils especially in areas close to the marshes. Fahmi et al [5] investigated the behavior of the soft soil of 15 kPa shear strength and reinforced with ordinary and encased stone columns with geogrid under cyclic loading They used PLAXIS 3D software for verification of the enhanced method of utilizing stone columns and field load exams. Six tests are carried out on the natural soft soil of undrained shear strength (5.5 kPa) improved by single and linear two floating stone columns which have 30 mm diameter and 180 mm length to increase the bearing capacity of soil, reducing the expected settlement of soil, and increasing the time rate of porewater dissipation
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