The environmental impact and control of deep foundation pit formed by underground space development in deep soft soil area has always been the industry focus. In order to study the influencing factors and laws of soft soil subgrade deformation under the excavation and unloading of deep foundation pit supported by row piles, taking the deep foundation pit project adjacent to a soft soil subgrade in Hengqin New Area as an example, the soft soil parameters after vacuum combined surcharge preloading are determined by HS model, and a numerical model considering the undisturbed soft soil on the roadside is established, and then the results are verified with the field measured results. The following conclusions are obtained: (1) Affected by the lateral pressure of undisturbed soft soil on the roadside, in the stage of shallow excavation, the horizontal displacement of soft soil subgrade far from the foundation pit is greater than that near the foundation pit; (2)With the increase of excavation depth, the maximum horizontal displacement slowly develops to 40.5 mm near the excavation surface. Finally, the overall shape of horizontal displacement is inclined at the far side of the foundation pit, and "bulging" near the excavation surface. (3) The subgrade settlement is affected by pavement load and foundation pit excavation at the same time, among which the settlement caused by the pavement load accounts for 64.4% of the cumulative value. (4) The numerical calculation of the first stage and the second stage of foundation pit excavation are in good agreement with the measured results. Due to the influence of soft soil rheology, the horizontal displacement will continue to develop, and the measured value of the third stage of excavation is significantly greater than the numerical calculation. The research results can provide a scientific basis for the deformation prediction and control of the environmental impact of foundation pit in deep soft soil area.

In order to study the working performance of pre-stressed retaining wall, a 6 m high pre-stressed retaining wall numerical model was constructed based on the numerical modeling method verified by model test data. By comparing with the retaining wall without pre-pull force, the deformation, soil pressure distribution, principal stress direction, yield area development, stress path and overall stability of the characteristic element were investigated. The results show that: the pretension of pre-stressed reinforcement can effectively reduce the deformation of retaining wall, and its lateral displacement and vertical settlement are reduced by 42.1% and 32.5%, respectively. After pretension is applied, the magnitude of earth pressure and the direction of principal stress in the backfill change significantly, the integrity of the reinforced zone is enhanced, the range of yield zone behind the wall shrinks. The stress path variation law of the characteristic element and SRM stability calculation results indicate that the stability of retaining wall is improved after applying pretension.