支墩立柱法密贴下穿既有隧道暗挖施工变形及力学响应研究OA

Mined construction at zero distance beneath an existing tunnel poses substantial risks and challenges,and ensuring the operational safety of the tunnel is the primary consideration in both design and construction.Taking Chigang Station of Guangzhou Metro Line 12 as the engineering background,this study proposes a zero-distance close-contact undercrossing mined construction method using a strut-pier column method.A numerical model was established to simulate the entire construction process of the proposed method.The stress and deformation response patterns of the existing tunnel and key structures under this method were investigated and verified through field monitoring,and the implementation performance of the strut-pier column method under different influencing factors was further examined.The results showed that:(1)under the proposed method,the bottom slab of the existing tunnel exhibited a"U"-shaped deformation in both the transverse and longitudinal directions,with a maximum settlement of about 2.5 mm.The sidewalls on both sides of the mined passage underwent symmetric deformation,with a maximum value of about 3.3 mm.(2)The tunnel bottom slab along the short diagonal of the mined excavation area sustained relatively high compressive stress,and the strut-pier columns located at the middle of the mined undercrossing passage and along the short diagonal of the mined excavation area carried relatively large loads.Therefore,the column cross-section and the area of the column top slab could be appropriately increased.(3)As the surrounding-rock grade became poorer and the cover depth increased,the vertical displacement of the existing tunnel tended to increase.The axial force of the columns varied only slightly with the surrounding-rock grade but increased with the cover depth.Excavating the central pilot drift at the final stage improved tunnel deformation control and reduced the column axial force.Reducing the concrete strength of the columns had little influence on tunnel deformation control but rapidly reduced the safety margin of the columns.