Ground Improvement Of Soil-rock Composite Ground And Reasonable Layout Of Buildings In Yan’an City

With the land levelling projects are gradually increasing,the construction of the project has been vigorously developed.Many geotechnical problems have been caused by the special topography of Yan’an City.The problem of the uneven settlement of soil-rock composite ground is more prominent,causing damage to a lot of buildings.Therefore,it is imperative to conduct special researches on the ground treatment of soil-rock composite ground and the reasonable layout of buildings in Yan’an.This dissertation will focus on the classification of soil-rock composite grounds in Yan’an City,the selection of ground treatments,the calculation method of composite ground settlement with rigid lower layer and the reasonable layout of buildings on soil-rock composite grounds.The main research contents and results are as follows:(1)This paper briefly states the types of foundations and failure modes of buildings on soil-rock composite ground in Yan’an City.The soil,the rock and the special geotechnical soil are classified in Yan’an City.And then,they are classified in detail by the engineering geological characteristics.According to the interface of soil and rock,soil-rock composite ground is divided into one-way inclined rock of underlying bedrock,two-way inclined type of underlying bedrock and half-soil type of half-rock.The corresponding fracture modes of three kinds of soil-rock composite ground is divided into a one-way oblique crack,a figure-shaped crack and a penetrating crack.(2)By Combining with the common foundation treatment method in Yan’an City,this paper studies the suitability of replacement layer of compacted fill,composite foundation with compacted soil-lime columns,composite foundation with cement-fly ash-gravel pils,and composite foundation with multiple reinforcement of different materials or lengths.For the replacement layer of compacted fill,the critical value of the replacement thickness of the low-rise and multi-storey buildings under the condition of differential settlement is calculated by numerical simulation to meet the requirements of differential settlement;Composite foundation with compacted soil-lime columns and composite foundation with cement-fly ash-gravel pils are studied to determine the suitability by tht surface settlement,differential settlement and pile-soil stress ratio.Composite foundation with multiple reinforcement of different materials or lengths are studied to determine the suitability of the semi-rock foundation by changing the soil modulus,pile distance and length.(3)For the one-way sloping soil-rock composite ground,the influence law of the dip angle of soil-rock interface on the foundation deformation is analyzed,and the horizontal safety distance of the shallow foundation of the soil-base side from the soil-rock interface is given.Reasonable arrangement on soil-rock composite ground is provided by relevant theoretical reference.(4)The calculation formula of the sliding stability safety factor of the unidirectional inclined soil-rock composite ground along the underlying rock face is established.The relationship between the building arrangement distance and the stability safety factor under different bedrock inclination angles is studied.The least stability and the building arrangement distance corresponding to the maximum stability safety factor at different inclination angles are calculated.