Application Research Of Small Section Precast Square Piles In Soft Foundation Treatment Of Airport Expressway In Madagascar

Since the proposal of the “Belt and Road” initiative,China’s construction projects in Africa have been increasing dramatically.However,with the limits of local economic and technological condition,many mainstream domestic soft soil treatments cannot be applied in Africa.Therefore,it is necessary to find an effective,economical and easy-to-operate methods of soft foundation reinforcement according to local conditions.Madagascar Capital Airport’s expressway passes through a wide range of soft soil areas.The bridge-embankment transition section and the old road widening have strict settlement requirements.Based on the field data of the test section in Madagascar Capital Airport’s expressway,this paper analyzed the effect and design method of small section precast square piles reinforcing soft embankment.The main conclusions can be drawn as following:(1)The topographic and geomorphic conditions,hydrologic and engineering geological conditions,soft soil distribution and engineering characteristics along the project were identified based on the laboratory test and field exploration.The soft foundation treatment scheme was recommended considering the local economic and industrial conditions,engineering deformation and stability control requirements,and the small section precast square pile composite foundation is recommended for the bridge-embankment transition section.(2)The field experiment of treating soft embankment by small section precast square piles with pile cap has been implemented.Under the embankment load,the deformation characteristics of the small cross-section precast square piles composite foundation were analyzed.The load-sharing ratio of pile soil in test section is 71.4%.The pore water pressure of embankment was greatly affected by rainfall.Using geogrid gravel cushion can make full use of the bearing capacity of small section precast square pile.(3)Preloading method has been applicated in comparison test section.The reinforcement effect of two soft embankment treatment method was discussed.The post-construction settlement of the preloading section is about 4.7 times that of the small section precast square pile composite foundation.The preloading method is suitable for projects which the postconstruction settlement and time requirements are not strict.(4)The buckling of small section precast square pile was analyzed by method of specifying general requirements and energy theory.The method of matching the diameter and length of small section precast square pile in soil has been suggested.The stability coefficient in the design is suggested to be 0.95.(5)According to statistics,the actual bearing capacity of small section precast square pile is 40%～90% larger than the bearing capacity calculated by standard method.Therefore,it is suggested that the bearing capacity of small section precast square pile should be determined by actual measurement.When calculating the bearing capacity of small section precast square pile in cohesive soil by standard method,the lateral friction resistance of pile in cohesive soil can be multiplied by the correction coefficient of 1.2.(6)The cost of small section precast square pile can be saved by optimizing the steel reinforcement pair of small section precast square piles.It is significance for the promotion and application of small section precast square pile in Africa.