DEM Simulation of the Load Transfer Mechanism of a GRPS Embankment with a Fixed Geogrid Technique

As a new technique, a fixed geogrid in a geogrid-reinforced and pile-supported (GRPS) embankments has been used to reduce the total and differential settlement. To investigate the load transfer mechanism of the fixed geogrid technique of a GRPS embankment, three discrete element method (DEM) models of pile-supported embankments were established, including an unreinforced embankment, a geogrid reinforced embankment, and a fixed geogrid reinforced embankment. The efficacy of the pile, the evolution law of the contact force chain and the axial force of the reinforcement, and the microscopic load-bearing structure of the soil were investigated. Numerical simulation results showed that the embankment self-weight and surcharge load were transferred to the pile through the soil arching and tensile membrane effect. The settlement could be effectively reduced via the addition of the reinforcement, and the fixed geogrid technique was more conducive to improving the load-bearing ratio of the pile than the traditional reinforcement technique. Compared with the traditional technique of a GRPS embankment, the fixed geogrid technique had a better effect on reducing the total and differential settlement. With the increase in the surcharge load and the settlement of the soft subsoil, the reinforcement transferred a greater load to the pile. The results also showed that the stress of the embankment fill was concentrated at the pile top in all three models. The GRPS embankment with a fixed geogrid technique had a lower soil stress concentration than the other two cases. The contact force chain and stress in the embankment also showed that the reformation of the microscopic load-bearing system of the embankment fill was the internal mechanism that caused the development of the soil arching and the redistribution of stress. Furthermore, the evolution of the fabric parameters in the arching area could reflect the evolution of the soil arching structure. In the fixed geogrid case, the proportion of the load transferred to the pile from the soil arching effect was reduced, and the vertical load transferred to the pile top by the tensile membrane effect accounted for 22–28% in this study. Under the combined effect of the tensile membrane and the soil arching, the efficacy of the pile could increase by 10%.

Study on Long-Term Performance of Geogrid-Reinforced and Pile-Supported Embankment at Bridge Approach

Bridges have been widely used in highway and railway engineering, especially in mountain areas. The differential settlement between bridge abutment and approach embankment is one of the most challenging problems, and it will result in “bumps” to affect the driving safety and comfortableness at the end of a bridge. The geogrid-reinforced and pile-supported embankment (GRPS embankment) is proposed to mitigate the differential settlement at the bridge approach. In this paper, the model tests and numerical studies are carried out to study the long-term performance of the GRPS embankment considering the consolidation of subsoil. Firstly, a series of model tests are conducted to evaluate the long-term performance of the GRPS embankment using a specially designed model box. Then, the numerical model is constructed using the finite element software MIDAS, and the numerical model is verified from the model test results. Finally, a parametric study is conducted to investigate the influences of pile net spacing, pile modulus, and filling modulus.

Long-Term Stability of High-Speed Railway Geosynthetic Reinforced Pile-Supported Embankment Subjected to Traffic Loading Considering Arching Effect

Geosynthetic reinforced pile-supported (GRPS) embankment is widely used in the construction of high-speed railways on soft foundations. Arching effect, which is a common phenomenon in the system involving soil-structure interaction, is considered a key factor in the design of GRPS embankment. Its performance has been found inevitably to affect the post-construction settlement and bearing capacity of the embankment. However, the existing design methods are mainly based on static loading condition; soil arching effect under high-cycle loading has not been fully understood. In this study, a series of numerical simulations were conducted to study the long-term behavior of GRPS embankment under traffic loading, with the consideration of arching effect in soil. An implicit–explicit transition calculation algorithm was implemented to predict the permanent deformation under high-cycle traffic loading through the data transfer and conversion between implicit and explicit numerical stages, in which the mixed “implicit” and “explicit” calculation strategy were carried out based on the high-cycle accumulation (HCA) model. By using the proposed algorithm, a cross-section of high-speed railway GRPS embankment was selected as a case for discussion. Results indicate that the affected areas of stress concentration over piles in the embankment are reduced under traffic loading. With different levels of stability, the variation of stress concentration ratio of the arching effect can be mainly classified into three groups: stable, gradually weakened, and destroyed. Through parameter study, the effect of subsoil stiffness is discussed and a reasonable modulus ratio between pile and subsoil is suggested for the design reference.

Evaluation of an Improved Technique for Geosynthetic-Reinforced and Pile-Supported Embankment

With a large number of applications of conventional technique for geosynthetic-reinforced and pile-supported (GRPS) embankment (called CT embankment), many deficiencies have been exposed. In view of the deficiencies, an improved technique, fixed-geosynthetic-reinforced and pile-supported embankment (called FGT embankment), is developed. To investigate the performance of the FGT embankment, the comparison analyses and parametric studies are conducted by Finite Element Method (FEM). The influencing factors investigated include elastic modulus of soil, tensile stiffness of geosynthetics, pile length, pile spacing, and pile elastic modulus. In addition, the cost evaluation for the FGT embankment and CT embankment is also made. The results show that the FGT embankment can significantly reduce the settlement and differential settlement, enhance the stability, and provide an economical and effective measure for the construction of high embankment at the bridge approach.

Load Distribution Form of Soil between Piles in Geosynthetic Reinforced Pile-Supported Embankment

The strict control standards for post-construction settlement of high-speed railway require high accuracy of settlement calculation. Harmonizing the contradiction that settlement calculation theory lags far behind the engineering practice, the computational method of additional stress of foundation urgently needs improvement. For Geosynthetic Reinforced Pile-Supported (GRPS) embankment, as the stress caused by the load acting on soil between piles is an essential part of the whole, the computed results of additional stress of foundation largely depend on the load magnitude and load distribution form of soil between piles. Starting with the mechanical behavior of GRPS embankment, this paper analyzes the classic assumptions of soil arch form and their computation theory of load acting on soil between piles, and then deduces the distribution function of parabolic load, which can provide basis for further research on calculating the additional stress.

Study on Behavior of Geosynthetic Reinforcement in GRPS Embankment

Geosynthetic-reinforced and pile-supported (GRPS) embankment systems have been emerged as an effective alternative successfully adopted worldwide to solve many geotechical problems. In the GRPS embankment system, a reinforced earth platform was lying above the piles and includes one or more layers of geosynthetics at the base of the embankment. The geosynsthetic reinforcement carries the lateral thrust from the embankment, creates a stiffened fill platform to enhance the load transfer from the soil to the piles, and reduce the differential settlement between pile caps. A numerical study was conducted to investigate the tension distribution of the geosynethic reinforcement in the GRPS embankment. Four influence factors were investigated, which included the elastic modulus of piles, the elastic modulus of soft soil, the tensile stiffness of geosynthetic reinforcement, and the number of geosynthetic layers. Numerical results suggested these four factors have different influence on the tension distribution and the maximum tension in the geosynthetic reinforcement.