The Study On Treatment Measures For Basement Deformation Of Collapsible Loess Tunnel

China is one of the countries with the widest loess distribution in the world because of its vast territory and complicated geology.During the construction of tunnels in collapsible loess area,the bearing capacity of the basement is usually difficult to meet the mechanical requirements of the structure because of the particularity of the mechanical properties of collapsible loess.After the completion of the tunnel,it is often accompanied by large deformation of the basement.In addition to compression deformation,the deformation of the base is more collapsible deformation.If the basement is not strengthened during the service life of the tunnel,under the action of surrounding water,the basement of the tunnel will undergo large collapsible deformation.Eventually leading to serious diseases such as ring and longitudinal cracking of the tunnel primary lining structure.It directly threatens the safe use of tunnels in operation period.Therefore,in order to ensure the stability of tunnel structure,this paper actively explores a tunnel basement reinforcement technology for aeolian sand and loess geological conditions.From the point of view of ensuring long-term stability and safety of the tunnel in loess collapsible area,the exploration in this paper has very important practical significance.In this paper,based on Lanzhou South Ring Expressway,the reinforcement measures of collapsible loess tunnel basement are studied.The main results are as follows:(1)Based on the collapsibility characteristics of loess,this paper studies the reinforcement scheme and control parameters of tunnel basement,proposing reinforcement scheme of collapsible loess tunnel basement,then giving the control parameters respectively for the reinforcement design of rotary jet grouting pile and compaction pile of collapsible loess tunnel.Through simulation analysis,it is concluded that the deformation characteristics of tunnel primary lining structure and surrounding rock can be improved by using jet grouting pile to reinforce tunnel basement,so as to improve the stability of primary lining structure.Finally,the destruction mechanism and optimization scheme of deformation of Rotary Shotcrete Support Structure are summarized.It is proposed that the collapsibility of loess surrounding rock in this area is effectively reduced after rotary jet grouting pile reinforcement in arch foot areas on both sides.Thus to a certain extent,it improves the uneven settlement phenomenon of tunnel caused by the collapsibility of the surrounding rock.The bearing capacity of surrounding rock in arch foot area on both sides is increased,the mechanical properties of surrounding rock are improved,and it is beneficial to improve the long-term stability of tunnel primary lining structure.(2)On the basis of investigating a large number of Loess Tunnel Diseases,according to different types of subsidence diseases of basement,combining with the practice of dealing with settlement diseases of Loess Tunnels in Gansu Province in the past few years,and it proposes five settlement treatment and control measures,including the schme of lock foot support and transverse support beam,the scheme of concrete cast-in-place pile and transverse support beam and lock foot support,the scheme of steel pipe pile and transverse reinforced concrete support plate and lock foot support,the scheme of steel pipe pile and inverted arch deepening,the scheme of steel pipe pile and foundation grouting.(3)From the point of view of reliable operation and easy maintenance,this paper puts forward optimum layout scheme of central ditch and inspection well of collapsible loess tunnel and the optimum waterproof and drainage structure of construction joints and settlement joints.In this paper,the central ditch is set at the bottom of the inverted arch in the middle line of the tunnel overpass lane,which avoids encroaching on the inverted arch filling,improve the integrity of the tunnel structure and ensure that the central ditch is located below the inverted arch of the tunnel.In order to prevent the leakage of water at the longitudinal construction joints of arch foot,to use optimized waterproofing treatment of structural structure of medium-buried steel-edged rubber water-stop beltin the water-rich loess section of an area.At the same time,in view of the existing problems of waterproofing construction technology and waterproofing materials,this paper optimizes the waterproofing design of construction joints and deformation joints,cancels the expansion water stop strip between construction joints and deformation joints,and replaces it with trapezoidal back-mounted drainable rubber water stop strip,and adds butterfly-shaped buried water stop strip at deformation joints,so as to improve the waterproofing effect of construction joints and deformation joints and reduce the leakage disease.