Evaluation of Differential Settlement of Subgrade for Highway-Widening Projects

Abstract

Highway widening is an important way to improve the existing expressway capacity and promote the development of transportation systems. The differential settlement between the old and new subgrade is the key factor to evaluate whether it is necessary to carry out ground improvement for the new foundation, which will cause longitudinal pavement cracking and even subgrade instability. Therefore, the most critical task in the highway expansion project is controlling differential settlement, particularly post-construction differential settlement. In this study, a fluid-structure coupling settlement analysis model was developed based on FLAC3D, and a modified Cam-clay (MCC) model was used to describe the difference between new and old foundation parameters. The working conditions of different subgrade heights and groundwater levels were simulated to analyze their influence on the differential settlement during and after construction. With the increment value of the transverse slope (∆i) and maximum slope (k) of new and old subgrade settlement curves as evaluation indexes, the differential settlement size of widened subgrade under different working conditions is evaluated, which provides a basis for the design of widened foundation engineering and provides suggestions on whether reinforcement measures should be taken. The results show that the post-construction differential settlement increases with the increase in groundwater level and subgrade height. Under the requirement of ∆i ≤ 0.5%, it is not necessary to take reinforcement measures under the condition of local water levels under a 2 m subgrade height and −9 m and −11 m groundwater levels under a 4 m subgrade height. However, when the water level rises further, or the height of the subgrade increases further, it is necessary to take foundation reinforcement measures. Meanwhile, for the requirement of k ≤ 0.5%, foundation reinforcement measures should be taken for all working conditions regardless of the water level or subgrade height. The research results can provide theoretical value and reference for foundation treatment in roadbed-widening engineering.

Numerical Analysis of Differential Settlement in Road Due to Widening Considering Different Reinforcement Techniques

“…The findings of the centrifugal model tests and the numerical simulations coincide well, and the research can be used as a solid scientific basis for designing and optimizing highway widening projects [38,52]. Under the widening process in road projects, it is crucial to investigate post-construction differential settlement [27] and the mechanism of pavement deformations [32]. This study has the potential to draw the attention of a wider audience from academic and road construction project teams in terms of understanding the approach to the determination of software parameters in the field and laboratory and their use in numerical analysis applications.…”

“…Differential settlement ultimately develops due to expansion of the road [25], which increases and decreases later [26]. The differential settlement increases with increasing groundwater level and subgrade height [27]. The differential settlement creates a soil arching effect in the embankments [28], which is higher at the edge of the slope than at the centerline [29].…”

“…centrifuge tests [11,31], numerical modeling [12,14,17,27,[32][33][34][35][36][37], and field tests [20]. As differential settlement develops in the middle of the embankment, transverse cracks simultaneously appear at the surface [38].…”

Review of Sensor-Based Subgrade Distress Identifications

“…Nowadays, common subgrade settlement detection instruments include ground-penetrating radar, total station, interferometric synthetic aperture radar, distributed optical fiber, and other equipment and software. These instruments can judge whether the subgrade has settled by measuring the road surface elevation, pressure, vibration, and deformation [17].…”

Numerical Analysis and Experimental Study of the Mechanical Response of Pavement Slab Supported on an Inhomogeneous Settlement

“…Research indicates that the force deformation characteristics of highway construction and expansion are different, and these differences are mainly manifested in the different consolidation degrees of the foundation under the new and old subgrade of highway reconstruction and expansion projects. This has caused the differential settlement of foundations, which is reflected in the top surface of the subgrade, and eventually causes the longitudinal cracking of the road surface [1][2][3][4]. Xiao used a centrifuge model test combined with a finite element method (FEM) to investigate the development law of transverse differential settlement between the modern tram pile-plank-supported subgrade and the surrounding pavement subgrade and suggested a critical transverse differential settlement rate according to the requirements of allowable tensile stress [5].…”