Abstract: The determination of lateral force capacity of piles is a problem to be solved in construction of soft soil area. Based on the Matlock p-y curve used in soft clay, a simplified double broken line model of Matlock p-y curve was proposed, and then the undrained shear strength index su and CPT cone tip resistance qc were used to represent the model parameter kini and pu . The dimensionless relative stiffness coefficient of pile and soil, noted as KR, was used as a classification standard to differentiate rigid pile and flexible pile. The relationships between the initial tangent modulus coefficient denoted KE and the horizontal soil resistance coefficient denoted KC were established. At last, the displacement standards for lateral capacity of rigid pile and flexible pile in soft soil foundation were developed. Results show that the displacement control standards can quickly determine the pile critical lateral capacity. it demonstrates a practical and reliable method of evaluating lateral capacity of pile foundation.

Key words: soft soil foundation, rigid pile, flexible pile, displacement standard, lateral capacity, p-y curve