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During the construction of deep foundation pits with rich water straight grooves, instability of deep foundation pits due to groundwater frequently occurs, posing a huge challenge to construction safety and economy. Based on the deep foundation pit of the intercity connecting line of Beijing New Airport, the technical method of combining theoretical analysis and on-site monitoring is adopted to analyze the influencing factors of groundwater on the retaining structure of deep foundation pit, and control and analyze the influencing factors. The deformation control technology for deep foundation pit is proposed. The following conclusions are obtained: (1) Based on the on-site geological conditions and the mechanism of groundwater level change, the deformation and failure forms and precipitation forms of deep foundation pits are obtained through theoretical analysis. (2) Based on the Deformation monitoring technology of deep foundation pit, the change of groundwater level and Deformation monitoring of retaining structure are carried out. (3) Combining on-site monitoring with theoretical calculation, conducting comparative analysis of data, summarizing the influencing factors of deep foundation pit damage, obtaining targeted deformation control technology for deep foundation pit, guiding the construction of practical projects, and providing reference for similar projects.

Using corn straw as raw material, the effects of three different ways of returning corn straw to the field, namely direct returning corn straw to the field, decomposed corn straw returning to the field and maize straw biochar returning to the field, on saline-alkali soil were studied by indoor culture. The results showed that maize straw directly returned to the field was the best way to improve the stability of saline-alkali soil aggregates; maize straw biochar returned to the field was the best way to reduce the alkalinity of saline-alkali soil; maize straw directly returned to the field and decomposed maize straw returned to the field enhanced the activity of soil urease and alkaline phosphatase, while reducing the activity of soil catalase. Maize straw biochar returned to field reduced soil urease activity and increased soil catalase activity, but had no significant effect on soil alkaline phosphatase activity.