Suitability Assessment of Stone Columns to Improve Soil Foundation in Kathmandu Valley, Nepal

Kathmandu Valley consists of a dynamic subsoil profile, so utilizing an effective method like stone columns to mitigate any forthcoming geotechnical problems is of utmost importance. Stone columns enhance the soil properties by increasing bearing capacity, reducing settlement, and improving the liquefaction reduction potential, especially in soft clay. The purpose of this study is to evaluate the suitability of the stone column in Kathmandu Valley considering its real soil profile. In the analytical computation of bearing capacity, Hansen’s method and the Indian Standard codes were used for unimproved whereas, in the case of improved soil analysis Priebe’s method and the Indian standard codes were used. Analyzing 62 locations of the valley, stone columns of diameter 0.5 m was found to be very effective with allowable bearing capacity increased by 98% on average for isolated footing. For mat foundation, approximate increment of 10 and 176% was observed for stone columns of 0.5 m at spacing of 3.33  and 1.25 m respectively. The comparison of settlement reduction maps before and after installment of stone column showed that the settlement significantly reduced with the inclusion of stone columns. However, three site-specific analyses showed that presence of weaker layer below the depth of stone column decreases their effectiveness, indicating the importance of stone column to encapsulate those weak layers. Thus, the study demonstrates high feasibility of improving soil properties on installing the suitable stone column in Kathmandu Valley.