Estimation of Modular Ratio and Modulus of Deformation of Granular Piles from In Situ Compression Tests-Paper

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The paper presents a method for estimating the deformation modulus of in-situ soil and the modular ratio of granular piles from compression load-test results. The modular ratio is the ratio of the granular pile’s deformation modulus to that of the surrounding soil.<br /><br />The method uses the measured load–settlement response and the settlement influence factors developed by Mattes and Poulos. Because the influence factor depends on pile geometry and modular ratio, the authors estimate soil modulus for a range of assumed modular ratios. They account for the proportion of test load transferred to the pile, which can be less than the total applied load when the test plate or granular bed is wider than the pile. The resulting modulus estimates are compared with expected values for the soil types present; this comparison identifies a plausible modular-ratio range and, in turn, the pile’s deformation modulus.<br /><br />The approach is applied to three published field tests involving granular piles in soft clay, sandy silt and fine sand, and marine and silty clays. For a load proportion of 25%, the estimated pile deformation-modulus ranges are 26.5–115.2 MPa, 91.8–760 MPa, and 11.5–140 MPa, respectively. The corresponding modular-ratio ranges are 5–32, 6–100, and 5–100.<br /><br />The authors conclude that their back-analysis method can derive representative deformation parameters from in-situ compression tests and support settlement prediction and granular-pile design. The estimates depend on assumed soil-modulus ranges and load-transfer proportions, so appropriate site-specific soil characterization remains important.

Keywords

deformation modulus

granular piles

modular ratio

compression load-test

load-settlement response

settlement influence factors

in-situ soil

back-analysis

soil characterization

settlement prediction