An enormous number of structures and roads are put on expansive subgrade soils and may be exposed to the swelling and shrinkage risk. To prevent the expanding weight of the subgrade layer under loaded pavement, one of the following strategies may be utilized are geogrid layer. Reinforced pavement layers have been propagated in the field of civil engineering because of their profoundly adaptable and diversified use. In this study, axisymmetric models of pavement layers have been created by 2-D Plaxis software and all of these models included geogrid layers at various positions concentrated to research the impact of geogrid on the critical pavement responses. Geogrid was placed at the bottom of asphalt layer, bottom of base layer, tope and middle of the subgrade layer. All models are loaded with incremental contact pressure between 50 and 600 kPa. Analysis processes have been made for all models and the obtained investigation results show a significant effect on pavement behavior when the a geogrid layer was used under various tire pressures. Also, there is an increase in the bearing capacity of a model that includes geogrid at the top and middle of the subgrade layer by about 35% and the resistance of the asphalt layer to deformation and cracking failure was improved.

In this article, the issue of mining impact on road pavements and subgrade is presented, taking into account the interaction between geosynthetic reinforcement and unbound aggregate layers. Underground mining extraction causes continuous and discontinuous deformations of the pavement subgrade. Structural deformations in the form of ruts are associated with the compaction of granular layers under cyclic loading induced by heavy vehicles. Horizontal tensile strains cause the loosening of the subgrade and base layers. The granular layers under cyclic loading are additionally compacted and the depth of ruts increases. Moreover, tensile strains can cause discontinuous deformations that affect the pavement in the form of cracks and crevices. Discontinuous deformations also affect the pavement in the fault zones during the impact of mining extraction. The use of geosynthetic reinforcement enables the mitigation of the adverse effects of horizontal tensile strains. Horizontal compressive strains can cause surface wrinkling and bumps. Subsidence causes significant changes in the longitudinal and transverse inclination of road surface. Both examples of the laboratory test results of the impact of subgrade horizontal strains on reinforced aggregate layers and the selected example of the impact of mining deformation on road subgrade are presented in this article. The examples show the beneficial impact of the use of geosynthetic reinforcement to stabilize unbound aggregate layers in mining areas.

The stress superposition effect in the midline area of the multi-wheeled vehicles produced by moving vehicles load is generally ignored, which leads to smaller results in research of subgrade service depth. Based on the elastic mechanics theory, the analytical solution of subgrade dynamic response under moving vehicles load is derived with compound elastic layers. The characteristics of subgrade dynamic stress distribution under the action of moving vehicles are analyzed by using Midas Gts Nx numerical simulation software, and the influence of static and dynamic axle load on the subgrade service depth is compared. The results demonstrate that the subgrade dynamic stress in the under-wheel area attenuates rapidly along the depth direction, while the subgrade dynamic stress in the midline area increases at first and subsequently decreases along the same direction. With the increase of subgrade dynamic stress, the shape of dynamic stress isosurface changes from bimodal to unimodal. Whether in the form of static or dynamic axle load, the subgrade service depth in the middle line area is larger than that in under-wheel area, and the influence of dynamic axle load on the subgrade service depth is greater than that of static axle load. The wheel distance and vehicle velocity have a significant influence on the subgrade service depth.With the increase of vehicle velocity, the subgrade service depth decreases. With the increase of wheel distance, the subgrade service depth decreases.

The performance evaluation of new and old subgrades is critical for the quality and safety of reconstruction and extension projects. It is necessary to achieve rapid and easy performance testing. In this study, a Portable FallingWeight Deflectometer (PFWD) is chosen to rapid evaluate the performance of subgrade. First, a testing area, the reconstruction and expansion project of the Hefei to Dagudian section of the Shanghai-Shaanxi Expressway, is selected. Then, the PFWD modulus E_p of resilient tested by PFWD and the corresponding water content w and compacting degree K tested by the cutting ring method for old subgrade are obtained. And the correlation relationship between E_p and w and K is established. The performance of old subgrade can be rapid obtained by PFWD. Meanwhile, for the new subgrade, the correlation relationship between E_p and bending value L, w and K is established, and the performance can also be rapid tested by PFWD. Finally, a rapid evaluation method for the reconstruction and expansion of subgrade performance was proposed, which aims to provide technical support for ensuring construction quality and safety and provides a technical reference and a theoretical basis for the prediction of similar subgrade performance.

Prediction of soft soil sub-grades settlement has been a big challenge for geotechnical engineers that are responsible for the design of roadbed embankment. The characteristics of low strength, poor permeability, high water contents, and high compressibility are dominant in soft soils, which result in a huge settlement in the case of long-term loading. The settlement prediction in soft soil subgrades of Jiehui Expressway A1, Guangdong, China, is the focus of this study. For this purpose, the necessary data of settlement is collected throughout the project execution. The numerical analysis is conducted by using the Richards model based on Linear Least Squares Iteration (LLS-I) method to calculate and predict the expected settlement. The traditional settlement prediction methods, including the hyperbolic method, exponential curve method, and pearl curve method, are applied on field settlement data of soft soil subgrades of Jiehui Expressway A1. The results show that the Richards model based on Linear Least Squares Iteration (LLS-I) method has high precision, and it has proven to be a better option for settlement prediction of soft soil sub-grades. The model analysis indicates that the mean absolute percentage error (MAPE) can be minimized as compared to other soft soil sub-grades settlement prediction methods. Hence, Richards's model-based LLS-I method has a capability for simulation and settlement prediction of soft soil subgrades.