With the widespread use of the waterproof and drainage technique of tunnel based on controlling drainage

some technical problems about tunnel lining design under external water pressure had been extruded more. According to construction examples of Longtan tunnel and Baiyun tunnel

optimization countermeasures about tunnel lining structure were studied against external water pressure by numerical simulation based on the mechanical response analysis of the lining under external water pressure. The study results showed there were increase stresses and internal forces on the side wall

the corner of the invert arch of the tunnel lining and the safety degree reduced more under external water pressure; a new concept of rise span ratio of the half below the tunnel lining was introduced from technical and economical aspects

whose addition was the chief countermeasure to optimize the structure of lining against external water pressure; the optimization countermeasures of the lining against external water pressure were put forward

which included in turn increasing the radius of the corner on the invert arch

decreasing the radius on the invert arch

thickening the arch on the invert arch and the arch of all lining

or these countermeasures could be used assembled sometimes.