The Experimental Study On The Geogrid Reinforced Cohesion Backfill Structures And Its Stability Analysis

Reinforced structures formed by bringing the tension material into the soil can improve the stability,anti-seepage,drainage,anti-freezing and insulate the contamination effectively. Although the application of reinforced structures has been tremendous both on the quantity and scope currently,the deformation behaviour and working mechanism of reinforced earth structures have not been well understood and rational analysis theory and design methods for these structures are not available.Sliding damage is the main failure mode of the slopes, researches and practices indicated that the reinforced slopes can improve the stability evidently. However,there are many influence factors so that it is necessary to do the sensitivity analysis to determine which ones are the principal factors and which ones are the secondary factors.It will contribute to focus on the most important factors to achieve the optimum arrangement.In this paper,the upper bound limit analysis method is used to probe into the sensitivity of influence factors that affect the limit height of reinforced slopes.Coarse-grained soil is always recommended for the reinforced structures both by standards and other manuals.Whereas China is vast and complicated in territory,geological conditions are various among different district,it will be not reasonable and economic to only use the coarse-grained soil in the area which be lack of this kind of fills.Therefore,the research on the application of reinforced structures using fines especially for clay must be significantly.This paper presents the research of pullout behavior of geogrid embedded in red clay.An experimental investigation is conducted using geogrid tests of eight different moisture content of the soil.Effective predication of the ultimate pullout resistance is a necessary condition for the design of reinforced structures.Based on the results of experiment and analysis method proposed by Koerner in 1989,a new method to predict the pullout resistance applicable to clay fills.Wall facing is an indispensable part in the retaining walls,but it is never considered in the design. The researches indicates that the wall facing can induce the design inclined to be conservative. According to the real wall facing used in practice,three model facing were made in the laboratory.The influence on the behavior of model retaining walls including displacement of facing,deformation of the geogrid and the ultimate bearing capacity from wall facing were tested in this paper.The main investigations and achievements are composed of following portions.(1)Studies of sensibilities of influence factors on critical height ofreinforced steep slope Based on the fundamental theory of upper-bound limit analysis of plasticity,the limit heights and stability coefficients of the reinforced steep slopes with different slope angles,top slope angles,internal friction angles,cohesive,reinforcement tension strengths,reinforced spacing,reinforcement arrangement,unit weights,seismic intensities and additional loads are calculated based on a code written by the authors.The sequence of sensibilities is listed;and the results show that the internal friction angle and earthquake are the key factors that influencing the critical heights of the reinforced steep slope.Whereas,the sensibility of cohesive is descend contrast to the gentle slope.Therefore,the emphasis should be placed on the selection of the internal friction angle for steep slope and the effect of earthquake as well.(2)Field experimental research of geogrid reinforced embankment.This paper reports the results of field experiment on geogrid reinforced embankments constructed on a part of first-order highway from Heihe to Dalian.In the test,The structural responses including earth pressures,geogrids strain,and settlements on pavement are investigated for the reinforced embankments with two geogrid types,three different reinforcement spacing and one district without reinforcement.Based on the contrast analysis, the distribution of earth pressure behind the flexilbe facing and the geogrid strains with height or reinforrnent layer,and their dependence on the time are discussed.Also the influence of the reinforcement on the settlement and its restriction to the frost heaving of the soil are given.In general,this experiment reveals the embankment's real work condition,and the results showed here gives a good reference for the succeeding research and the similar engineering.(3) Pullout behavior of geogrid in red clay and the PredictionThis paper presents a research of pullout behavior of geogrid embeded in red clay.An experimental investigation is conducted under eight different moisture content of the soil.Tests results indicate that the geogrid mainly represents pullout failure embedded in clay,and the ultimate resistance is water-sensitive.It decreased with the rise of the moisture content firstly, and then tended to a constant around the plastic limit where the ultimate pullout force is independent of the normal pressure.The display of strain demonstrates that the decrease of the ultimate pullout force is due to the reduction of the friction capability between the soil and geogrid.Besides this,the moisture content influenced the process of the pullout behavior as well.The load-displacement curve can be separated into three parts:linear ascending segment, nonlinear ascending segment and ultimate segment,the increase of moisture content shortened the second segment,which means that the ultimate pullout force will be reached soon after the end of the first segment.The prediction of the ultimate resistance in current standard is depend on the internal friction angle times a ratio to simulate the interaction between reinforcement and soil.While the more accurate prediction needs more consideration.This paper based on the ultimate pullout resistance comes from three parts those are friction resistance from longitudinal and transverse ribs and the bearing resistance from transverse ribs.According to the results of experiment,each part was calculated individually and the prediction equation changed with moisture content was obtained.(4) The influence of facing stiffness on the performance of three geogrid reinforced soil retaining model wallsConsideration of the influence of the facing type on reinforcement loads is lacking in current limit equilibrium-based design methods for the internal stability design of geosynthetic reinforced soil walls.Also the displacement of walls and the strain of geosynthetics are also related to the facing type.This paper reports the results of the three instrumented model walls. The walls were nominally identical except one wall was constructed with a rigid concrete block face,the other with a hinge joint wood face,and another with a flexible wrapped face.The displacement of wall face decreased with the increase of the stiffness of wall facing under the same surcharge.And the reinforcement strain in the flexible wall will be greater than the stiff one.Besides this,the stiffness of wall face also effects the strain distribution of each level.The results demonstrate quantitatively that a stiff facing wall can bear more surcharging but it expressed as brittle failure.