Study On The Construction At The Shallow Bias Section Of He Jia Wan Tunnel

With the expansion of railway construction and improvement of technology standard, tunnel length takes higher portion in the railway line, due to the characteristic and complexity of the geological structure, construction difficulty thus is increased. The following article is based on bid section 2 of He Jia Wan tunnel construction, posts few treatment measures by researching the issues caused at the shallow bias tunnel. This tunnel is located SanGuan town, TaoJiang country, Yiyang, HuNan province, the tunnel portal is surrounded by whole of weathering rock-with the features as strong weathering slate, color as brown yellow, extremely fractured, crashed rock, loose, poor stability, and the bias voltage, thin covering layer, high pressure in safety issue of the project construction. The single line tunnel is 339 meters long, three out of three, consists of three segments of open cuts tunnel, three segments of hidden hole and two peak slanting cut portal, are designed to enter from the hole, somehow during the construction, the entering part is listed as the excavation section, belongs to the rock blasting, and it is only 35 meters away from an existing operation line, the railway operators require the blasting construction is processed in the blocked point, so the daily construction period is only two hours, which can not be satisfied the project requirements, and it is 39 meters away from the Tuo Mu Chong tunnel, such tunnel has already completed the construction, while it can make use of the related equipment and field. With the overall consideration, in line with the view of convenient construction management, cost savings, Shorten the duration of the requirement, the final construction scheme after discussing with the design institute, is taken as to excavate from the outlet to the inlet section. This article focus on introducing the construction technique and project management at the third hidden hole (DK154+240-DK154+311). The roof drainage ditches by the outlet section and the slope protection construction have been constructed in accordance with the design, meanwhile excavating 8 meters to the hidden hole, a 0.5-1.5 cm crack is appeared from the left guide wall’s arch foot vertical to the roof surface, and along the roof surface extends to the tunnel trunk; the first and second section’s secondary lining at DK154+311-293, has appeared transverse cracks, and the hidden hole positioning at DK154+244 (only 4 meters to the tunnel exit) appears an initial support deformation invading limit from the excavation. With the discussion of the causes and designing, treatment scheme is drafted up, efficiently solved the issues, eliminate the potential safety hazard, for the future construction of similar projects to provide some reference.