Research Of Rainfall Effect On The High Fill Foundation Of A Yunnan Airport

As China is embarking on One Belt,One Road Initiative,Yunnan province is committed to be “An Air Corridor ” for the cross border cooperation between China and its neighboring countries,thereby securing it as a new growth engine of the region.Yunnan is almost a mountainous province with more than 90% of its territory being mountain.The geomorphic units are diverse.The terrain is complicated,relief.Based on above facts,together with the large area of excavation and filling,high fill and many hydrodynamic,geological conditions are hence very complex.The high fill foundation in the airport faces difficulties caused by the construction and original instable area.Rainfall and ground water are likely to affect the stability of the foundation and the side slope when the area is largely filled.In this paper,the author took a Yunnan airport as a study case.The rainfall infiltration theory and percolation theory were considered as theoretical guidance.Its geological conditions were studied.Factors deforming and destroying high filled foundation due to rainfall were analyzed on the basis of the characteristics of filling materials,of structures and filling deformation.Experiment of the earth-rock aggregate permeability was carried out,based on the observation.Features of permeability at varied rainfall periods from high filled foundation were obtained through numerical simulation.Features of deformation of the coupling flow and stress field of high fill foundation were also obtained.The evolution of the coefficient of the slope for the high foundation under the effect of rainfall was obtained as well.The main results are as follows:(1)Rocks in the research area are soluble according to its geological conditions.Growing below the influence depth from the foundation’s additional pressure,Karst can not affect stability of the airport foundation.High filled project met with the problems of uneven sedimentation of the foundation and unstable side slopes,due to complex geography and growth of karst.(2)Rainfall has a great effect on the deformation of the fill foundation,as the field survey and observation indicate.Fill foundation features prominently uneven sedimentation,partial bulging of side slopes due to raining.Sedimentation is mainly caused by humidification.Failure of side slopes is mainly caused by infiltration deformation.(3)The experiment found that the content of rocks greatly affected the permeability of earth and rock mixtures,its coefficient having an exponential growth as the content of rocks rise.When the percentage of content of rocks is under 30%,the coefficient of permeability is relative small.When the speed of permeability increases,the sample is bulging and deformed.Its surface is damaged.When the content of rocks is between 30%-50%,the coefficient of permeability rises by one level.Due to permeability,very grained red earth can be carried away,leaving the water turbid.When the content of rock is more than 50%,the coefficient of permeability continues to increase,with the sample bubbling and surging.This shows that a permeable passage is formed under the force of permeability.This phenomena is named as piping.(4)The permeability values of unsaturated soil were analyzed to obtain the characteristics of seepage field of filling foundation.They are as follows:(1)the rainfall permeability range in unsaturated earth and soil mixture is mainly in superficial layers of slopes.As rainfall permeates,slopes and slopes shoulders are transiently saturated.Seepage is accumulated at the foot of slopes along superficial slopes.Transient saturated area is lastly dissipated,since it follows its unique principles.(2)As rainfall increased,time for earth’s saturation needs fewer time.When the wetting front goes deeper,water pressure of pore accordingly goes up.(3)The period and intensity of rainfall have the similar effect.(4)As the coefficient of earth and rock mixture becomes small,permeability becomes difficult.Dissipation also becomes difficult.Thus the pore water pressure will increase.(6)Drainage facility installed at the foot of slopes is more conducive to releasing the pore water pressure;(7)The initial landforms in filling foundation have a great effect on pore water pressure.When the initial landforms are moderate,the depth of filling foundation is proportional to them.When pore water is gathering at certain places or moves downward,it can dissipate around,with the increase of pore water at the foot of the slope.(5)Stress of rock soil strained by coupling pore water pressure was analyzed to obtain the following: rainfall is a factor of high fill foundation stress field and displacement field.The vertical displacement occurred at the top of the slopes,and the horizontal displacement took place happened at the side slope.(6)Under the effect of rainfall,the plastic zone of high fill foundation and transient saturation tend to develop in a uniform manner.Given to its geological conditions in this paper,the filled foundation is stable,and the shoulder and foot of the slope is unstable.The co-efficiency of the slope tend to decrease as rainfall continues.