Evaluating Subgrade Compaction for Different Soils Using Nondestructive Lightweight Deflectometer

Insufficient compaction of the subgrade can result in nonuniform deformation, leading to severe subgrade distress. To address this issue and find a new method for rapid detection and evaluation of subgrade compaction, we used the lightweight deflectometer (LWD) to analyze the dynamic deformation modulus ($E_{vd}$) of subgrades filled with four types of soils—silt (ML), well-graded gravel (GW), lean clay (CL), and poorly graded sand (SP)—in different regions of Gansu province, China. Concurrently, we measured the degree of compaction ($D_{oc}$) using the sand replacement method (SRM) to establish its correlation with dynamic deformation modulus ($E_{vd}$). A strong correlation between the degree of compaction and dynamic deformation modulus was established for soils ML, GW, CL, and SP, and suitable formulas were selected based on curve variations. The developed formulas enabled back-calculation of the dynamic deformation modulus requirements corresponding to different degrees of compaction ranging from 90 to 100, facilitating direct queries and quick field checks. Results demonstrated that the LWD, as a reliable rapid detection method, effectively controlled subgrade compaction quality in field construction. Moreover, it extended the testing area and increased measurement frequency, thus providing a practical means for quickly evaluating the qualification rate and uniformity of subgrade compaction.

When we build roads, most subgrade underneath the roads needs to be filled with soil. If we don’t pack the soil properly in the filling process, the subgrade can crack and become uneven over time. It’s hard to fix this problem once the road is open, so it’s important to make sure the soil is packed tightly enough before the road is finished. There are two ways to check if the soil is packed properly: one is a traditional method called the sand replacement method, and the other is a machine called the lightweight deflectometer. These methods help identify insufficient compaction of the subgrade and prevent uneven deformation problems during the filling process. What’s more, the lightweight deflectometer is a fast, convenient, and reliable tool that can assist or serve as an alternative to the traditional sand replacement method for controlling subgrade construction quality. This study is important because it helps us understand how to evaluate compaction of the filled subgrade in a different way.