Abstract: Voids may be natural or manmade .The calcareous sediment rocks contain voids as they are susceptible to water dissolution. The voids could also be the result of activities like mining, tunnelling etc .These voids either continuous or discrete, impose a hitch in the smooth designing of foundations. The problem is further aggravated as the foundation is to be designed to withstand seismic forces. The systematic scientific study of the effect of underground voids on the stability of foundation began by mid eighties of the last Century as some laboratory level investigations were initiated in conjunction with numerical studies using Finite Element Method. A series of investigations led to the conclusion that the depth and eccentricity of voids play a vital role in the analysis of stability of foundation. There exists a critical depth and a critical eccentricity beyond which the effect of a void becomes insignificant. Efforts were on to reduce the magnitude of the critical depth and eccentricity. A certain depth of top weak soil can be replaced by a layer of granular fill and the footing made to rest on this prepared layer. The performance can be further improved by reinforcing the granular fill with geo-synthetics .The geo-synthetic reinforcement possess the inherent drawback of excessive settlement during the initial stages of loading which adversely affects the performance of footing over voids. Recent developments in laboratory investigations reveal that this issue can be overcome by using pre-stressed reinforced granular beds, which reduces the initial settlement considerably. The challenge in the present scenario is the economical application of laboratory findings in in-situ activities giving due share to the durability aspects of the Pre-stressed Reinforced Granular Bed.
Keywords: Underground Void , Critical depth , Critical Eccentricity , Multiple Voids , Granular Bed , Prestressed Reinforced Granular Bed.