Research On Engineering Characteristicof Fully-heavily Sandstoneof Red-bed Areafillerin Bazhong Airport

With the acceleration of the westerndevelopment process, theconstruction and engineering of the red beds area in southwest China is undergoing vigorously. This thesis focuses mainly on the selection of materials used for fill in airports which feature large capacity;considerable height and width. Due to those particular characteristics, this kind of projects have caused suchengineeringaccidents as large numbers of building inclinations, slope instability and collapse of filled foundation.First of all, modified compaction test on the fully-heavily weathered sandstone has been conducted to find out themaximumdrydensity and optimummoisturecontent according to the size of the sand, coarse or fine.On that basis, shear experiment has been made to analyze the influence of rate of water content and compactness on the intensityparameter;penetrationtest has also been practiced underdifferentcompactiondegree according to different sizes of gravels. the influence and relevant mechanism of various indicators on the intensity of the red layer and seepage deformation have also been analyzed in detail. Parameters are recommended afterwards for the filler, in this case, fully-heavily weathered sandstone. Besides, based on the experimentparameter, analytical calculation has been conducted on the stability of high-fillslope through numerical method. Finally,thefeasibility and reliability of using fully-heavily weathered sandstone as the filler of high embankment in Pakistan-china airport.Through the analysis of the test data, main conclusions are summed up as follows:In the process of compaction, coarse-grained materials of the fully-heavily weathered sandstone are broken into smaller pieces and are reduced in number,whereas those fine-grained materials are increased and the general gradations are improved. By analyzing the data, the optimal density appears when the pro portion of these two kinds of materials is 4:6.Through the middle-sizedshear experimentconducted indoor, the maximum s hear strength comes with the optimal moisture content. The position of its pea k moves backwards with the increase of moisture content, which appears mainl y within 2-5mm. Besides, the peak shear stress builds up withthe increases of the normal stress. Generally, the relationship of the shearing strength and shear displacement is presented as linearity before the shear displacement reaches th epeak shear stress. After that, when the normal stress is low, shearing strength would not be reduced evidently with the increase of the displacement. Instead, It will stay at the same level as the residual strength. With high normal stress,theshearing strength would be reduced evidently with the increase of the displa cement, after which it would approach the residual strength of corresponding n ormal stress gradually and stay close to it.Through shearing tests conducted on fully-heavily weathered sandstone wit h different compactnesses, the conclusion can be that, the difference value betw een the peak strength and residual strength becomes larger with the decrease o f compactness. What’s more, when the compactness is lower than K=92, the c hange of the parameters of shear strength is relatively obvious, which tends to drop dramatically.The permeability test shows that the permeability coefficient of samples in the form of fully-heavily weathered sandstone for compaction is very low wit h its order of magnitudes ranging within 10-4~10-7cm/s, which classifies it as permeability rock-soil. However, under adverse conditions, for instance, when t he compactness is lower than K=87% and the porosity is over n=42%, the per meability coefficient will increase significantly. Besides in the process of perme ation, samples would be permeated and deformed.Under reasonable design and construction conditions, the shear strength an d permeability characteristics of fully-heavily weathered sandstone as the filler could meet the requirements of the airport construction. However, considering t hat the fully-heavily weathered sandstone would be softened to a large extent by water as well as the high sensibility of fill slope to internal friction angle, whenfilling in the complicated gully area, moisture content of fully-heavily wea thered sandstone should be kept at around 10%. In addition, waterproof measur es should be taken and the compactness should also be increased so as to stre ngthen the internal friction angle of the fill body and insure that the fill slopei s stable.