Finite Element Analysis of Geogrid Encased Stone Columns

Abstract

Stone columns in soft soil improve bearing capacity because they are stiffer than the material which they replace, and compacted stone columns produce shearing resistances which provide vertical support for overlying structures or embankments. Also stone columns accelerate the consolidation in the native surrounding soil and improve the load settlement characteristics of foundation. In this paper, the finite element method is utilized as a tool for carrying out analyses of stone column-soil systems under different conditions. A trial is made to improve the behaviour of stone column by encasing the stone column with geogrid as reinforcement material. The program CRISP-2D is used in the analysis of problems. The program allows prediction to be made of soil deformations considering Mohr-Coulomb failure criterion for elastic-plastic soil behaviour. A parametric study is carried out to investigate the behaviour of standard and encased floating stone columns in different conditions. Different parameters were studied to show their effect on the bearing improvement and settlement reduction of the stone column. These include the length to diameter ratio (L/d), shear strength of the surrounding soil and, the area replacement ratio (a s ) and others. It was found that the maximum effective length to diameter (L/d) ratio is between (7-8) for Cu, between (20-40) kPa and between (10-11) for Cu = 10 kPa for ordinary floating stone columns while the effective (L/d) ratio is between (7-8) for encased floating stone columns. The increase in the area replacement ratio increases the bearing improvement ratio for encased floating stone columns especially when the area replacement ratio is greater than (0.25). The geogrid encasement of stone column greatly decreases the lateral displacement compared with ordinary stone column.

Treatment of Iraqi collapsible soil using encased stone columns

“…However, little research focused on treatmentfor collapsible soil in which water inclusion was not ideally represented.On other hand, there are several local publications focused on encased stone columns to improve soft soils. Recent example on that by (Fattah &Majeed 2012) in which finite element analysis had been employed to study a geogrid encased stone columns that are assumed to be supported by a soft clay layer. (Buringh 1960) outlined the main features of soil conditions in Iraq according to the geomorphological regions: the Mountains and foothill region, the Mesopotamian plain, and the Deserts (see Fig.…”

Numerical Simulation Of The Treatment Of Soil Swelling Using Grid Geocell Columns

“…A trial was conducted by Fattah and Majeed (2012) to improve the behavior of a stone column by encasing the stone column with a geogrid as reinforcement material. A parametric study was carried out to investigate the behavior of standard and encased floating stone columns in different conditions.…”

Performance of Encased Silica-Manganese Slag Stone Columns in Soft Marine Clay

“…When the load was applied to the tank wall, the load/settlement behavior was linear and the failure did not take place. Fattah & Majeed (2012b) studied the geogrid-encased floating stone columns and found that the maximum lateral displacement occurred at an effective encasement length ratio (length of geogrid encasement along the stone column/total stone column length) of 0.6. Gniel & Bouazza (2009) carried out experiments on geogrid-encased stone columns and found that maximum bulging occurred at a depth of 2D.…”

“…Damoerin et al (2015) carried out a series of tests to increase the shear strength of the soil by improving the cement column and found that this increased the shear strength of the soil. Fattah and Majeed (2009) studied the behavior of encased floating stone columns and found that the bearing improvement ratio increased by increasing the area replacement ratio for both ordinary and encased stone columns. Fattah et al (2010) carried out tests on stone columns by varying the SCR and found that the stiffness was increased with an increase in stiffness of the treated soil.…”