Method for constructing large-span station with two-wing open type half-cover excavation and half-reverse construction

A method for constructing a large-span station by two-wing open type semi-covered excavation and semi-reverse construction, comprising the following steps:

• step 1:
• leveling a site and constructing retaining piles for enclosing an inner small foundation pit;
• step 2:
• constructing middle upright post piles of the station, which is divided into two parts:
• constructing pile foundations and constructing steel pipe posts;
• step 3:
• excavating an earthwork of a first-stage inner small foundation pit downward in sequence to a designed elevation, hanging a mesh, spray a layer of concrete to seal a surrounding rock, erecting steel purlins as waist beams, and installing prestressed anchor cables for enclosing the foundation pit;
• step 4:
• when the construction reaching to the designed elevation below top plates, constructing the top plates within the range of the middle first-stage inner small foundation pit, cutting and excavating, and constructing top longitudinal beams;
• step 5:
• constructing primary retaining piles for a second-stage annular foundation pit;
• step 6:
• removing the retaining piles of the first-stage inner small foundation pit and excavating the second-stage annular foundation pit;
• step 7:
• constructing local concrete waist beams on the primary retaining piles of the second-stage annular foundation pit, and constructing local concrete supports between the local concrete waist beams and the middle top plates;
• step 8:
• installing cantilever retaining walls on the upper parts of the top plates, backfilling the middle of retaining walls with soil, restoring temporary road traffic, thus completing the construction of semi-covered excavation cover plates with two-wing open;
• step 9:
• excavating an earthwork of a third-stage semi-covered excavation foundation pit from top to bottom from two wings, excavating along with supporting;
• the support measures above the elevation range of the soil rock interface being the primary retaining piles, installing prestressed anchor cables, hanging a steel mesh, and then constructing shotcrete panels;
• step 10:
• carrying out a foundation pit acceptance when excavating reaches 300 mm above a cushion layer of the foundation pit, and draining the accumulated water in the pit, and constructing a waterproof layer of a bottom plate, a cushion layer, and a bottom plate;
• step 11:
• laying a waterproof layer on a side wall, and constructing a second lining of the side wall and a middle plate from bottom to top;
• step 12:
• removing the temporary concrete supports and completing the construction of the top plates on both sides;
• step 13:
• removing the cantilever retaining walls above the top plates, laying a waterproof layer on the top plates, backfilling with soil, and restoring the pavement.