Evaluation of stiffness-based approaches for assessing soil compaction in laboratory and field

Abstract

Sometimes referred to as the “dark art” of civil engineering, earthworks remain an essential yet costly and often uncertain component of modern infrastructure projects. Increasingly, pavement design emphasizes mechanistic-empirical, modulus-based performance for compliance. However, fill placement and compaction specifications currently rely on dry density, and the relationship between dry density and stiffness is poorly understood in field practice. At the same time, contractors and clients are demanding greater traceability and faster turnaround times for earthworks conformance which traditional “spot-test” quality assurance methods cannot provide. Intelligent Compaction (IC) technologies offer a potential solution by delivering site-wide, real-time stiffness modulus measurements with each pass of a roller, utilizing accurate GPS and integrated sensors. While IC has gained some acceptance for quality assurance through pass coverage tracking, its implementation for quality control—linking soil response under the roller drum to fundamental soil properties, particularly dry density—remains a challenge.

This research aims to address this gap and presents the following:

• Laboratory experiments involving Bender Elements and drained, unsaturated 1D compaction established a strong correlation between compaction, degree of saturation, and stiffness index small strain shear modulus (G0).

• A construction-phase field trial was conducted to compare the stiffness index parameter Compaction Meter Value (CMV) across various compaction conditions.

From this, a simple compaction framework incorporating method-based specifications with stiffness indices is proposed. This framework is applied to a historical light weight deflectometer and plate load test modulus dataset (ELWD and EPLT), and the challenges associated with implementing a stiffness-controlled approach are explored.