MODULUS LOAD TEST RESULT ANALYSIS OF RAMMED AGGREGATE PIERS IN COHESIVE SOILS

This article analyzes the results of load tests on 30 real size rammed aggregate piers (RAPs) used in the construction projects of various states in America, between 2001 and 2007. These piers were mostly tested in cohesive soils, including CL and ML. The Navg-values of the Standard Penetration Test of these soils were between 3 and 30. In this research, the parameters of pier diameter, pier length, pier slenderness ratio, soil elasticity modulus, pier elasticity modulus, design limit pier top settlement and stress and pier stiness modulus were considered. The pier diameters were 0.60, 0.75 and 0.90 m, and their length was between 1.8 and 5.1 m. The piers slenderness ratio (length to diameter) was between 2.4 and 31.7 MPa. Test results reveal that when the pier length or slenderness ratio is increased, the average top settlement changes little and shows a constant trend. More precisely, the minimum and maximum settlement values were 6.5 mm and 16.1 mm, respectively, and the average settlement was 11.35 mm. The results of in situ load tests on 12 RAPs in ML soil on smallscale piers, in Iran, in 2011, similarly showed that the minimum and maximum settlements were 7.2 mm and 13.1 mm, respectively, and the average settlement was 10.35 mm. The small-scale pier diameters were 0.185- 0.105 m, and the pier lengths were 0.35-1.5 m. Based on these results, it seems that the average pier top settlement value could provide a suitable basis for estimating the piers stiness modulus and preliminary designing of single RAPs. Based on the parameters aecting the estimation of pier top settlement and regression of results, an equation was achieved in this research which showed good agreement between calculated and measured results. This equation is based on pier slenderness ratio (Lt=DP ) between 2.3 and 6.7, and the ratio of pier elastic modulus to matrix soil modulus (EP =ES) between 5 and 88.