Theory Analysis And Experiment Research Of Geocell Reinforced Low Embankment And Rigid Pavement System

Recently, the low embankment has been receiving more and more attention for the design of road structures attributed to its advantages, such as economic space occupa-tion and saving construction cost, compared with the high embankment. However, for some special land especially the soft soil area, the low embankment cannot exploit its advangages if effective soft ground treatment measures were not taken. The reason is that the limited filling height of the low embankment cannot diffuse the upper load ef-fectively which easily leads to excessive differential settlement problems. In order to solve the issue of load proliferation for the design of low embankment in soft soil area, this thesis presented a new type of geocell reinforced low embankment-rigid pavement system (GRLERPS) by putting the geocell and its internal gravel packing placed on the top of the embankment. As a new road structure type, the GRLERPS has a good poten-tial for applications, because it combines the high flexural and shearing strength of geocell and land resource-saving of the low embankment, as well as advantages of the concrete rigid pavement, such as readily available raw materials, capability of carring heavy traffic and long design life. But the new system is still in the exploratory re-search stage. In this thesis, an in-depth systematic research on GRLERPS is carried out from two aspects:load bearing mechanism analysis and the settlement analysis, by means of theoretical analysis, model test and finite element analysis. The main work can be clarified as follows:(1) Through the relevant existing literature at home and abroad, the knowledge has been summarized and analyzed as the references for the investigations on the pro-posed new system, which includes low embankment structure, the response of the em-bankment under the traffic load, as well as the application and its reinforcement me-chanism of geocell structural layer.(2) The research of the applicability of the geocell structural layer as the lower layer is conducted dividing into two parts:the flexural capacity of the geocell structure layer and its anti-erosion ability. On the basis of the finite element analysis of the flexural capacity of geocell structure layer, a flexural modulus and mid-span deflection relations is established quantitatively. This can be used as a reference for the same type of experiment data processing. Subsequently,6trials based on superposed beam theory are designed to study the of geocell structure layer bending modulus determination and its influencing factors. The trial results show that the expanded width of the geocell has great influence on the bending modulus, geocell should be expanded as far as possible to nearly diamond shape. Analysis of the rigid pavement base erosion me-chanism indicates that, the internal reason of flushing phenomenon can be attributed to the soak softening effect of the free water accumulated in the bottom of the board, the external one due to repeated flushing of the hydrodynamic pressure caused by traffic. The utilization of the geocell gravel structure layer can not only form a good drainage channel under the rigid pavement to make the infiltrated water drain in time, but also be softened slightly by the water because of its unique strength and stiffness formation mechanism. Learning from the successful experience of the geomembrane bag against erosion, a layer of permeable geotextile is adopted to put on the geocell structure layer, to reduce the direct scouring action of the hydrodynamic pressure, thus to ensure its anti-erosion ability.(3) A comprehensive introduction on the main parts and their function of the GRLERPS in soft soil area is presented in this thesis, and its load bearing characteris-tics are further analyzed. Subsequently, the ADNIA is used to establish its plane strain model to calculate the proliferation problem of the stress and deformation in the em-bankment caused by traffic load. This model proves that the presence of the geocell structure layer will improve the stress state of the concrete pavement significantly and make the stress inside the roadbed decayed faster. In the engineering design of prac-tical calculation, the results reveal that the elastic foundation layer board model available in the existing norms can be utilized to analyze the load stress at the critical load position for the road panel of the new system.(4) By the finite element simulations, the deformation characteristics of the structure layer of the road with geocell are compared qualitatively with that without geocell. Results indicate that the geocell structure layer can effectively reduce the dif-ferential settlement of the foundation surface. Furthermore, it is found that the total settlement value reduced significantly by adopting geocell structure layer, in case of a comparative study of setting the same thickness of the same parameters geocell cu-shion on the ground surface. However, the performance of controlling differential set-tlement between the two methods is nearly the same. What is more, the orthogonal tests of three levels and seven factors that might affect the differential settlement be-tween the boards are designed. Variance and range analysis show various influence factors in this order from high to low:geocell structure layer thickness, the height of low embankment, the modulus of the soft soil, the modulus of low embankment, the modulus of the geocell layer, the thickness of road panel, the modulus of road panel. Thus, the most effective way, to control the differential settlement between plates, is to increase the height of geocell structure layer and the fill height of the low embank-ment.(5) Based on the similarity theory, two sets of the comparable model tests are de-signed and completed. To study the load bearing and deformation characteristics of the GRLERPS, six small items in the model test are divided into three stages to compare the difference of the performance between the two systems possessing the geocell structure layer or not. The simulation of periodic traffic load is carried out by a model car running back and forth on the roadway slabs. The car is drived by a novel link mechanical system which transforms the circular motions of concrete mixer into reci-procating linear motions. The model test results show that the proposed GRLERPS is feasible.