DISCUSSION ON DESIGN AND CALCULATION METHOD OF PILE-PLANK SUBGRADE FOR UNBALLASTED TRACK

摘要

Pile-plank subgrade is a new type of structures for unballasted track on soil subgrade,which design and calculation theories are not mature.Based on related test research results, a simplified analytical design and calculation method of pile-plank subgrade was proposed.The spatial statically indeterminate pile-plank structure is simplified into profile and cross-section.The two calculation models are analyzed separately, and have merits like definite stressing, simple parameters and easy to calculate.In profile calculation model, bearing plate and pile foundation are simplified to"multi-braced continuous elastic foundation beam".Reaction force of subgrade is neglected for most unfavorable condition.Meanwhile, only support of pile foundation is considered.Pile foundation's reaction and bearing plate's internal force and deflection are calculated by elastic theory under most unfavorable load combination.In cross-section calculation model, bearing plate and pile foundation are simplified to "high pile cap beam".Subgrade slope stability should be no less than prescribed value to ensure effective level constraint for pile foundation.And subgrade settlement should be checked strictly to avoid separation from bearing plate.Thus, bearing plate should be constructed after subgrade settlement stability.