Study On The Influence Of High-speed Railway Tunnel Construction With Small Clear Distance And Small Angle Crossing

In recent years,the construction of high-speed railway network in China has accelerated,and the mileage of railway tunnels has also increased rapidly.The distribution of high-speed railway network is limited by underground and above-ground buildings(structures),complex terrain and geological conditions.The increasingly dense road network means that the tunnel line selection is restricted,and the small net distance between tunnels is gradually emerging.When the small spacing tunnel crosses at a small angle,the construction difficulty is also much higher than that of other small spacing tunnels due to the overlap of the two tunnels and the relatively long proximity distance.Therefore,when the two high-speed railway tunnels with small spacing and small angle cross section are constructed at the same time,it is of great engineering significance to explore the mutual influence law between the two tunnels,determine the mutual influence area,and seek the control method to weaken the influence of the tunnel.Based on the small clearance and small angle cross section of Yanshantou Tunnel and Zhulinxia Tunnel as the research objects,through data collection and investigation,field measurement and numerical simulation,this paper studies the mechanical behavior and influence law of small clearance and small angle cross section,the safety of single tunnel excavation in cross section,and the interaction zoning between two tunnels in cross section.The main research results and conclusions are as follows :(1)Through the field test of the cross section with small clearance and small angle,it is found that in the field construction process of the cross section,the two tunnels have certain mutual influence,but are safer.It indicates that according to the key and difficult points of the cross section,the proposed countermeasures and the main construction process are reasonable and feasible,that is,in the cross section,the Yanshantou tunnel passes through the intersection before the bamboo forest tunnel,and at the same time,the two tunnels reserve sufficient safety distance in the construction process to ensure that only a single tunnel is constructed within the range of safety distance.(2)Through three-dimensional simulation calculation,the displacement,stress and internal force of the initial support under two conditions of single tunnel construction and two tunnels close construction are compared.It is concluded that the displacement of the key points of the initial support is related to the depth of the tunnel,the parameters of the surrounding rock and the support conditions during the construction of the cross section tunnel.When the tunnel is constructed alone,the distribution of displacement,stress and internal force on the left and right sides of the initial support is relatively uniform,and there is no obvious bias.The adjacent construction of the two tunnels has a certain degree of mutual influence in the cross section,and its influence is related to the depth of the tunnel,the surrounding rock parameters,the relative position of the tunnel section,the net distance of the two tunnels and the supporting conditions.’ Unloading ’ may change the stress state of the initial support of the tunnel after excavation.(3)By calculating the safety factor of the key section,the safety of the adjacent construction of the two tunnels and the bias direction of the initial support are related to the relative position of the section.The safety factor of the initial support of the single-line and double-line tunnels is greater than the strength safety factor of the initial support structure1.8,which also verifies that the construction process of the two tunnels is safe.The safety of the adjacent construction of the two tunnels is related to the relative position of the cross section.In the construction process of single-line tunnel crossing the cross section of double-line tunnel,the construction of single-line tunnel has a great adverse effect on the double-line tunnel,and the construction of double-line tunnel has little adverse effect on the safety of single-line tunnel.The vertical displacement of the inverted arch of the single-line tunnel and the vault of the double-line tunnel is the most vulnerable.In similar projects,the vertical displacement of the inverted arch of the single-line tunnel and the vault of the double-line tunnel can be used as key monitoring items in the construction process.(4)Based on the strength reduction method,the safety of two tunnels in cross section is studied.It is found that the safety factor of single tunnel decreases gradually with the increase of buried depth in the range of 10-100 m.The lower the surrounding rock grade,the greater the safety factor of a single tunnel,the stronger the self-stability of the tunnel;under different surrounding rock parameters,with the increase of buried depth,the change rate of safety factor is smaller,and the influence of the increase of stratum load on the decrease of safety factor is smaller.Under the same buried depth and surrounding rock parameters,the safety of single-line tunnel is stronger and the safety reserve is larger than that of double-line tunnel.When the surrounding rock parameters are V,the safety factors of single-line and double-line tunnels are less than 1,which cannot be self-stabilized under the condition of bare tunnels.The safety reserve of surrounding rock is insufficient,and strong support or other auxiliary construction measures are needed.The greater the buried depth,the smaller the influence of tunnel size(diameter D,height h)on tunnel safety.(5)The safety of two tunnels in the cross section is studied.Under the condition of determining the surrounding rock parameters of the cross section,the safety net distance of the two tunnels increases gradually with the increase of the buried depth,and the range of mutual influence is also gradually increased.Under the condition of a certain buried depth,the safety net distance of the two tunnels increases gradually with the increase of surrounding rock grade,and the range of mutual influence increases gradually.When the relative position of the two tunnel sections is staggered,the safety net distance is greater than that of overlap or parallel;according to the safety net distance point(K = 1)obtained under different working conditions of the double-track tunnel down close to the single-track tunnel and the single-track tunnel up close to the double-track tunnel,and combined with the upper and lower limit influence range of the surrounding rock level,the strong influence area,weak influence area and no influence area of the two tunnels under the conditions of different buried depths and surrounding rock levels of the cross section can be obtained.Different measures should be taken to ensure the safety of the adjacent construction in the cross section for different risk levels.