Foundation pit post-installation beam string structure construction method

The invention relates to a construction method for installing a beam string structure after a foundation pit. The construction method comprises the following steps that S1, a site is excavated to the elevation of a steel support installation plane; s2, beam string structures and steel supports except for the unearthed position are installed; s3, soil is excavated in the site and concentrated in the area right opposite to the beam string structure, and in the soil excavation process, a soil slope with a certain gradient is reserved at the soil excavation position of the beam string structure and used for allowing an earthwork vehicle to go in and out and balancing the soil pressure outside the pit; s4, after the other parts except the unearthed position are excavated, a part of soil is collected from the slope bottom to the slope body of the soil slope, a soil table used for installing and balancing soil pressure is reserved, and a beam string structure at the unearthed position is installed; s5, prestress is applied to the beam string structure at the unearthed position; and S6, the reserved soil platform is excavated out of the site through a long-arm excavator. The soil outlet is reserved in the position of the beam string structure, the influence of soil outlet on the steel support is avoided through the method that the beam string structure is installed at the specific position, and the foundation pit earthwork excavation convenience is improved.