Stiffness-Based Quality Control Evaluation of Modified Subgrade Soil Using Lightweight Deflectometer

Despite the availability of reliable stiffness-based quality control evaluation techniques, developing countries still adopt traditional density-based quality control assessment on unbound pavement layers. The objective of this study is to evaluate the effectiveness of lightweight deflectometers (LWD) as a quality control device for modified subgrade under varying drop weights. Experimental investigations were performed on a 240-m long and 9-m wide experimental stretch constructed in Gujarat, India. Mean target stiffness value on the modified subgrade using LWD with 10, 15, and 20-kg drop weights were 40, 51, and 64 MPa, respectively. Percentage variations between target and evaluated stiffness values on the modified subgrade were 2.60, 3.10, and 0.28%, for 10, 15, and 20-kg drop weights, respectively. Subsequently, the influence of in situ moisture content and density on stiffness values of modified subgrade for various drop weights was assessed by correlation analysis, and the results depict a good R2 value from 0.74 to 0.82. The LWD backcalculated moduli (10 kg) and dynamic cone penetrometer estimated resilient moduli values of modified subgrade were compared, and the mean percentage variation was 3.78–4.95%. Thus, there is a substantiate relationship between in situ density and stiffness values that follow similar trends under varying LWD drop weights. Therefore, LWD stiffness-based evaluation on modified subgrade soil contributes to enhancing the effectiveness of quality control measures during construction of low volume roads.