Investigating pile anchor support system for deep foundation pit in a congested area of Changchun

Foundation pit engineering has been developing rapidly with the challenges associated with modern urbanization. As a result, deep excavations can now be performed at the heart of coastal metropolises with dense existing structures and adverse soil and hydraulic conditions. On the other hand, foundation engineering is challenged with sustainability and economic viability such that cost-effectiveness is a key factor provided that the robustness and safety requirements are fully satisfied. This paper presents the design of the retaining system for a deep foundation excavation that is located in a second-tier inland city with less crowed existing structures and good soil and hydraulic conditions. This is representative of the current trend of the suburban development of major cities and the development of below first-tier cities, as a response to the saturating of the major cities. Different designs are reviewed for this case in order to strike the balance between structural capability and cost-effectiveness. The analysis indicates that a hybrid solution is particularly suitable for such type of construction. Specifically, results show that the maximum displacement, bending moment, and shear force in the pit can be reduced by over 50%, 40%, and 30%, respectively, by the combination of soil nailing wall and pile anchor compared with a single support solution. And for the combination of non-prestressed anchor bolts and prestressed anchor cables can effectively save the cost while improving the safety factor of foundation pit during excavation. The findings are instructive to similar projects with cost-effectiveness as a major factor.