Effect of Soil Replacement on Collapsibility of Footing Resting on Calcareous Sand- A Prototype Study

Abstract

Soil replacement technique is not a new method to improve a soil stratum possessing poor strength properties. Before, such a problem of facing a location with weak soil properties is simply solved by changing that spot of estate by another one. Nowadays, such a proposal is no longer valid as a solution since the finance of real estates is rising considerably so that altering a location to the favor of other is not a choice. Calcareous soils are soils rich of calcium carbonate which occur manly in the semiarid subtropics for both hemispheres. This soil is one of the famous collapsible soils similar to the well-known gypseous soils. It has very good strength properties when dry, but once wetted it undergoes large and almost instantaneous settlement, potential collapse of productivity, even if there is no additional load applied on it. This research is concerned in studying the effect of soil replacement technique in reducing collapse settlement. A laboratory prototype model is used in study using SW soil mixed with different percentages of calcium carbonates, and gradual replacement of calcareous soil with sand is carried out in terms of width of footing B. Each model is leached for continuous seven days, and time-settlement data are recorded. This is done again for different percentages of calcium carbonate ratios mixed with sand. Laboratory tests revealed that the degree of improvement in terms of settlement for replacing B/2 depth by sand is 0.36 (B is footing width), that for replacing B is 0.65, for replacing 2B is 0.88, and for replacing 3B is 0.92. The amount of CaCO3 in soil does not affect the degree of improvement observed. An empirical formula is derived using finite differences for relating degree of improvement with depth of soil to be replaced.