Ground Improvement Using Compaction Techniques on Calcareous Sands and Verification Tests Procedures-Paper

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The paper describes ground improvement for a 500,000 m² mixed-use development in Dubai, where reclaimed and natural calcareous sands contain abundant carbonate and shell material. Soil conditions varied considerably, with loose to dense sands over competent strata at depths of roughly 4–10 m. Improvement was needed to meet stiffness, settlement, shear-strength and seismic-liquefaction requirements.<br /><br />Three compaction methods were selected according to local soil conditions and treatment depth: vibrocompaction to about 8 m, dynamic compaction to about 8 m, and rapid impact compaction to about 4 m. Site-wide cone penetration tests (CPTs) guided method selection and served as the principal means of verifying performance. A target CPT resistance profile was developed by combining requirements for a minimum Young’s modulus of 15 MPa, a friction angle of at least 35°, limits on differential settlement, and a liquefaction factor of safety greater than 1.1.<br /><br />Standard CPT correlations largely assume silica sands and can underestimate the resistance of calcareous soils because fragile carbonate grains and shells crush during testing. The authors therefore describe applying a shell correction factor of 1.7 and, for the overconsolidated Zone 2A East soils, a stiffness correlation factor (α) of 4.5 to estimate modulus from CPT resistance. Compaction-induced increases in lateral stress and overconsolidation were also considered.<br /><br />Post-treatment CPTs were assessed using paired tests and a 1 m rolling average against the target profile. The study concludes that reliable acceptance of ground improvement in calcareous sands requires CPT correlations and correction factors that reflect both particle crushability and compaction-induced stress changes. Appropriate interpretation can help achieve technically sound, cost- and time-efficient treatment, with associated environmental benefits.

Keywords

ground improvement

calcareous sands

vibrocompaction

dynamic compaction

rapid impact compaction

cone penetration test

liquefaction resistance

Young’s modulus

carbonate grains

Dubai development