Damages And Remedial Measures Due To Expansive Soil On The Buildings In Bishoftu Town

Abstract

Damage caused by expansive soil on buildings constructed in the Bishoftu town are investigated and remedial measures proposed. Forty-four buildings were randomly selected from different expansive soil locations. The investigation showed that out of those 44 buildings 36 or 82% of them are adversely affected. The extent of damage with respect to building type is very high on mud/cheka house (91%) and decreases when we proceed from G+0 HCB buildings (88%), G+1 buildings (67%) and G+2 buildings (50%) respectively. The damage has been analyzed and interpreted systematically with respect to type of foundation, wall, floor, pavement, door, window and fence. According to AASHTO classification system the study area expansive soil is grouped in A-7-5 and A-7-6 and with the USCS the soil is grouped in CH and MH. The test result showed that, w ranges from 26.73-49.03%, LL ranges from 61.6-94.4%, PI ranges from 23.8-54%, LS ranges from 10.84-22.36, FS ranges from 21.74-81.82%, Gs ranges from 2.67-2.72, % finer than 0.075mm ranges from 82.8-95.5% and OMC ranges from 28.6-37.83% and MDD ranges 1.22-1.42g/cm3. Cv ranges from 0.334-3.049m2/year, Cc ranges from 0.369-0.555 and eo ranges from 1.37-1.68. The study showed that the main causes of failures are improper foundation design, construction with low quality materials, moisture fluctuation, poor surface drainage, damaged utility lines, presence of trees and vegetation close to buildings. For the past nearly 8 months 6 instruments 2Dimensional crack monitors on 3 cracked buildings were installed, which is used as a precautionary measure. Additional crack opening on Building ID No.26 at vertical crack 1.29mm was observed. Inserting helical bar along and across the crack, regulate and reduces crack movement. Nowadays people are aware that building a new house on black cotton soil on the study area, for G+0 buildings with trench excavation at 1m depth replacing the expansive foundation soils by non-heaving materials and providing plinth beam foundation is recommended. For G+1 and G+2 buildings with 1.5m and 2m excavation depth respectively a cushion of freely draining granular soil is placed and compacted which acts as a barrier and the effect of swelling on the foundation is reduced.