| Due to the rapid development of economy, there is an increasing tendency for the demands of transportation infrastructure, and thus the highways and railways, as the most convenient transportation, have been developed on a large scale. Geogrid-reinforced and pile-supported (referred to as GRPS) embankment, an economic and effective technique, has been used extensively in the construction of highways and railways. Soil arching effect, which has been proved to be a key factor for the load-transfer in GRPS embankment, is attracting wide attention of the researchers. However, the insufficient investigations on the formation-evolution mechanism of "soil arching", as well as its bearing characteristics, cause the fact that the theoretical development still lags behind in the engineering application of GRPS embankment. Hence, a series of laboratory model experiments and Discrete Element Method (DEM) numerical models were conducted to systematically investigate the formation-evolution mechanism and the bearing characteristics of "soil arching". The main contents are presented as follows.(1) The features and evolution mechanism of "soil arching" were investigated based on a series of 2D laboratory model tests. Photographic technology was adopted to obtain the displacement field of embankment fill during the tests, and thus the features of "soil arching" could be visualized. Meanwhile, the evolution of "soil arching" was preliminarily investigated based on the variations of the displacement field and soil pressure. Then, parametric study was performed to identify the effects of the embankment height, H, and the geosynthetic reinforcement, on "soil arching". Test results indicate that the development of "soil arching" is highly dependent on the pile-soil relative displacement As, and significant soil arching effect can be achieved when ?s is larger. For the embankment height, H, it mainly has an effect on the features of "soil arching". To be specific, when H is smaller than 0.7(s-a) ((s-a) referring to the pile clear spacing herein), only "shear plane" can be formed; when H is larger than 0.7(s-a), but smaller than 1.4(s-a), a "partial arching" can be formed; and when H is larger than 1.4(s-a), a "full arching" can be formed. It should be noted that, geosynthetic reinforcement has an effect on the development of "soil arching", but the effect on the final features and bearing capacity of "soil arching" can be barely observed. However, it is difficult to reveal the formation-evolution mechanism of "soil arching" thoroughly owing to the friction resistance between the embankment fill and testing apparatus.(2) On the basis of laboratory model test in the published studies, a series of DEM models was established to investigate the formation-evolution mechanism of "soil arching" in macro- and microscopic view. First, an Improved Multi-layer Compaction Method (referred to as IMCM) is proposed to establish the DEM model, and thus the initial stress state of the embankment can be more reasonable. Validation is then conducted by comparing the DEM results with experimental data. Second, detailed macro-behavior (e.g., soil pressure, displacement of embankment fill) and micro-behavior (e.g., contact force chain, direction of major principal stress and principal direction of fabric anisotropy) analyses are performed. Numerical results indicate that "soil arching" in embankment is formed by the Strong Force Chain (referred to as SFC hereafter), while the Weak Force Chain (termed as WFC hereon) acts as a support system. Pile-subsoil relative displacement As has a significant influence on the development of "full arching" (for an embankment with H larger than 1.4(.s-a)). At smaller As, only "inclined shear planes" could be formed in embankment. Then, with an increase in As, the "inclined shear plane" would be transformed into a "catenary-shaped arching" with an arching height of 0.5(s-a). With a further increase in ?s, the arching height of "catenary-shaped arching" increases gradually and approaches to the maximum value of 0.8(s-a) finally, and then, maintains a relatively stable state within the ?s range of interest in this study.(3) Based on the laboratory model test in the publications, a series of DEM models was conducted to investigate the evolution of "soil arching" under the quasi-static load. In a DEM model, the quasi-static load was applied on the embankment surface via the servo mechanism step by step. Then, detailed macro-behavior (e.g., load-transfer efficacy) and micro-behavior (e.g., contact force chains, major direction of stress and fabric anisotropy) analyses were performed. Numerical results indicate that the "full arching" is fully mobilized under the quasi-static load and experiences a "development-failure-reforming" process with the increase of quasi-static load. The "disintegration" of the particles, which are used to carry the SFC, is the essential reason for the failure of "soil arching", causing the decrease of the fabric anisotropy of SFC and load-transfer efficacy.(4) A DEM model was established on the basis of the previous laboratory model test to investigate the dynamic response of a piled embankment. Sinusoidal cyclic loading was applied on the surface of the embankment to model the traffic loading. Then, detailed macro-behavior (e.g., load-transfer efficacy and embankment fill displacement) and micro-behavior (e.g., contact force chains and fabric anisotropy) analyses were performed to investigate the dynamic response of "soil arching" under cyclic loading in macro- and microscopic. Numerical results indicate that, the bearing capacity of "full arching" weakens gradually under the cyclic loading and maintains a relative stable state finally. The "soil arching" always exists in embankment under the cyclic loading. However, the mobilization of "soil arching" is dependent on the demands of the load-transfer of embankment. To be specific, the bearing capacity of "soil arching" would be mobilized gradually within the loading stage, while a "dormant" state of "soil arching" would be gradually formed during the unloading.The findings obtained in this investigation can provide significant reference for revealing the load-transfer mechanism of GRPS embankment. More importantly, it can also give valuable guidance to the practical engineering of GRPS embankment. |
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