杨劲屾¹，张良翰²，黄锐^3,4

(1.玉溪市大戛高速公路投资建设开发有限公司，云南玉溪 653100； 2.云南建设基础设施投资股份有限公司，云南昆明 650501； 3.桥梁结构健康与安全国家重点实验室，湖北武汉 430034； 4.中铁大桥科学研究院有限公司，湖北 武汉 430034）

摘 要： 为了解深厚嵌岩超长单桩的承载性能，以戛洒江特大桥4号墩桩基（采用超长群桩基础，基桩嵌岩段超过50 m）为背景，采用FLAC3D仿真计算软件建立有限差分模型，计算桩顶竖向荷载作用下，不同桩长（71，81，91 m）和桩径（1.5，1.8，2.0，2.2 m）组合单桩的沉降、荷载~沉降变化规律以及竖向荷载分担比例。结果表明：该桥桩身弹性压缩所占桩顶沉降的比例均超过60%，深厚嵌岩超长桩的桩顶沉降大部分由桩身弹性压缩引起；增大桩径对提高深厚嵌岩单桩承载力的效果明显；增加桩长不能明显提高单桩承载力，且增加桩长会增加桩顶沉降；深厚嵌岩超长单桩的桩顶荷载主要由嵌岩段侧阻承担，其荷载分担比例均超过60%；类似地质情况桩基设计时，可适当选择较大的桩径、较短的桩长。

关键词： 桩基础；深厚嵌岩；承载力；竖向荷载；沉降；荷载分担比例；有限差分法

中图分类号： U443.15；U441

文献标志码：A

文章编号：1671-7767(2021)01-0071-05

Study of Load Bearing Performance of a Very Long Single Pile Inserted Deep into Rocks

YANG Jin-shen¹, ZHANG Liang-han², HUANG Rui^3,4

(1. Yuxi Dajia Highway Investment and Construction Development Co., Ltd., Yuxi 653100, China; 2. Yunnan Infrastructure Investment Co., Ltd., Wuhan 430034, China; 3. State Key Laboratory for Health and Safety of Bridge Structures, Wuhan 430034, China; 4. China Railway Bridge Science Research Institute, Ltd., Wuhan 430034, China)

Abstract: To examine the load bearing performance of the very long single pile inserted deep into rocks, the pile foundation of pier No.4 of Jiasajiang River Bridge was taken as the background project for study. The foundation consists of very long group piles, with the length of piles inserted in the rocks exceeding 50 m. The FLAC3D model of the foundation was built, to calculate the settlement, load-settlement variation law as well as the sharing ratio of vertical loads of the piles with different lengths (71, 81, and 91 m)and different diameters (1.5, 1.8, 2.0 and 2.2 m)in the foundation under the action of vertical loads. The results indicate that the pier-shaft elastic compression accounts for over 60% of the pile-top settlement, suggesting that a large portion of pile-top settlement of the very long pile deeply inserted into the rocks is induced by pier--shaft elastic compression. To enlarge the pile diameter can significantly improve the load bearing capacity of the pile of such type. Nonetheless, increasing the pile length could not evidently improve the load bearing capacity of a single pile, which would, on the contrary, increase the pile-top settlement. The loads on the top of the very long single pile inserted deep into the rocks were mainly taken by the lateral resistance of the section buried in the rocks, which shared over 60% of the loads. In the design of pile foundation in similar geological condition, it is proper to choose piles with large diameter and short shaft.

Key words: pile foundation; inserted deep into rocks; load bearing capacity; vertical load; settlement; load sharing ratio; finite difference method