Differential settlement is a key issue when designing cap systems over soft soils. Regulations often require that the minimum post-settlement grade of a final cap system be at least two percent. Often, this constraint requires analysis of many cross-sections along the cap system to verify that settlement does not cause a grade reversal. This paper presents a simplified approach to estimating settlement over soft soils. The approach is based on the conventional method of estimating differential settlement as it considers settlement due to primary consolidation and secondary consolidation. Depending upon the extent of the cap and the variation of the thickness of compressible soil, estimates of settlement using the conventional approach may be cumbersome as many cross-sections may be required to represent likely scenarios. The proposed simplified approach does not depend on the selection of specific cross-sections. Rather, a closed form solution that incorporates changes in surface slope, variations in thickness of the underlying soil layers, and of vertical loads along a horizontal direction is presented. By selecting a representative range of soil parameters, the proposed simplified method can be used to estimate a change in slope that is not related to a specific cross-section. The simplified method was used to evaluate the expected change in slopes for sulfate sludge basins. Settlements in these basins are due to the load imposed by the proposed cap system. Using a cross-section containing 14 points, the conventional approach was used to validate the new approach.
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