الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
The ever increasing demand of competent land for urbanization has been a challenge for geotechnical engineers to develop an optimized methodology for transforming comparatively weak soil into an acceptable condition. In most of the cases, the inadequacy arises in terms of unsatisfactory bearing capacity of the soil, and/or, excessive settlement. Footings require a special attention due to different types of acting loads. Nowadays more ambitious structures transmit not only large compressive forces but also considerable amount of tensile forces or inclined and eccentric loads to foundations. Replacement of weak soil by some strong soil or improvement of engineering properties of weak soil by different ground improvement techniques are used in such situation. If such soil cannot be removed or uneconomical to remove then we can use ground improvement techniques. Soil reinforcement is one of the most popular ground improvement technique, ease of construction, overall economy and less time consuming are major advantages of soil reinforcement. For many years ago, the beneficial effects of using reinforcement to improve the property of soil have been demonstrated. Nowadays the use of reinforcement technique using geosynthetics is widely used instead of traditional techniques to solve many problems in geotechnical engineering practice. The importance of this technique arises as geosynthetics provide tensile reinforcement through frictional interaction with infill materials. As the planar reinforcements, geocells are also used in foundations, pavements, railways, embankments, slopes etc., to improve the load-bearing capacity and stability of structures. Geocell is one of the geosynthetic products used primarily for soil reinforcement, it was originally developed by the US Army Corps of Engineers in 1970s for quick reinforcement of cohesionless soil in the military field. Geocell developed in the USACE study was originally named the “sandgrid”. Commercial geocell products made from polymeric materials became available in late 1980s. Geocell is the latest development in the field of geosynthetics and its benefits have been highlighted by several researchers. Geocell is three dimensional, polymeric honeycomb like cell structure created by welding high intensity thermoplastic sheet. Geocells are easier to work with, as they can be folded for transportation purposes and stretch themselves when filled with sand, concrete or stone. They also provide a lateral confinement to the fill thus
providing strengt. Due to the above mentioned ease of workability and serviceability, geocells are widely used in geotechnical engineering for various applications by reinforcing soft soil strata and stabilizing slopes and embankments. Also geocell confines the soil particles within its pockets which prevents the lateral spreading of soil which allows the soil layer to behave as a stiff mattress and hence the load is distributed over a larger area. This study present a review of some of the recent experimental works on geocell-reinforced soil below foundations. Geocell reinforcement used as a method to improve the bearing capacity of strip footings resting on soft clay Foundation soil, this type of cells with different heights, widths and thickness easily manufactured and placed underneath the individual footings leading to significant improvement in their response. The used material in experimental work is known commercially as presto HDPE geocells and manufactured by Presto Products company (presto geosystems) Wisconsin, USA. The type used in this research is GW20V-75 mm (3 in) Depth. Study of bearing capacity of footing under eccentric or eccentric – inclined load has been carried out by many researchers in the past but without reinforcement (Meyerhof 1963, Meyerhof 1965, and Prakash and Saran 1971). This laboratory-testing program attempts to provide a better understanding of the behavior of strip footing resting on reinforced soft clay with geocell under vertical, eccentric, inclined and eccentric- inclined loads. The laboratory model tests consist of a rigid rectangular tank- 2000 mm in length, 500 mm in width, 1100 mm in depth and a handle gear box loading machine applied static load on a rectangular model rigid plate of 250 mm in width, 500 mm in length and 25 mm in depth. It was conducted to quantify and evaluate the effect of geocell as reinforcement material on the behavior of strip model footings resting on soft clay under vertical, eccentric, inclined and eccentric-inclined loads. The studied parameters include the performance of clay without any reinforcement or replacement, sand replacement performance above clay subgrade, optimum length of geocell layer, optimum number of geocell layers and performance of optimum geocell section reinforcement. The ultimate bearing capacity improvement due to the soil reinforcement is represented using a non-dimensional factor, called the bearing capacity ratio (BCR). The results indicate that the ultimate bearing capacity of footings can be appreciably increased by soil reinforcement under vertical load as well under eccentric-inclined load. The Bearing capacity ratio obtained from experimental work is 2.54. Also it has been observed that such
reinforcement resists the lateral displacement of soil underneath the footing leading to a significant decrease in the vertical settlement and hence improving the ultimate bearing capacity. The recommended cells width and height that give the maximum ultimate bearing capacity improvement are presented and discussed. Finally, Based on the laboratory model tests results, it was observed that the effect of geocell appeared in decreasing the surface deformation, settlement and increase the bearing capacity as it provide a lateral confinement. The reinforced composite formed by the geocell and the infill soil has a higher stiffness and shear strength than the unreinforced soil.