The characteristics of high compressibility, low bearing capacity, heterogeneity and complex components of waste soil are the difficult problems in the treatment of deep landfill. In view of the situation that the subgrade of an expressway passes through a deep landfill, the treatment depth is large, the post construction settlement is small Prestressed concrete pipe pile with fast construction speed (PHC pile) technology is used to treat the foundation of landfill site; the subgrade monitoring system with sensors such as earth pressure, displacement, settlement and pore pressure is used to monitor the mechanical behavior of PHC pile and subgrade during and after construction. It is found that the thickness reaches 38.3m, the organic matter content is 5 ~ 22%, the natural unit weight is 13-17kn / m3, the compression modulus is 0.3-5mpa, and the cohesion The bearing capacity of soil between piles is close to 0, the bearing capacity of soil between piles is 90-110kpa, and after the corrosive landfill is treated with PHC piles, most of the load is borne by PHC piles, the pore water pressure dissipates in about 100 days, and the maximum settlement of subgrade is about 80mm. After 127 days of filling, the settlement of subgrade tends to be stable. This shows that PHC pile technology can significantly improve the foundation bearing capacity of deep landfill. The technology and the comprehensive treatment scheme of the whole process monitoring system can provide a reference for the treatment of deep landfill in the highway industry.