潮间带咬合桩无泥浆护壁施工关键问题与对策——基于中东某取水井工程的顺序性分析

Key Issues and Solutions for Slurry-Free Construction of Intertidal Secant Pile Driving—A Case Study of an Intake Well Structure in a Middle East Project

摘要: 中东某项目取水井单体结构位于潮间带，采用“全钢护筒支护、无泥浆护壁”的特殊工艺施工钻孔咬合桩。本文按施工流程顺序，系统梳理了该工艺实施中暴露出的五个关键问题：(1) 护筒沉设阶段：长护筒在超软弱土层中难以保证绝对垂直与对中；(2) 钻进成孔阶段：石灰岩层硬度不均，且高强度素混凝土桩(C40/C50)的设计要求加剧了钻进困难与钻头损耗；(3) 钢筋笼安装阶段：护筒内狭小空间导致钢筋笼定位困难，保护层控制易失效；(4) 护筒起拔阶段：起拔护筒过程中混凝土易沿筒外缝隙流失造成方量损失；(5) 基坑开挖与后续结构阶段：已成桩体偏斜导致原设计“植筋挂网喷浆”永久衬砌工法无法实施，无法保证100 mm厚衬砌层的均匀成型。针对上述问题，本文详细阐述了相应的现场技术对策，包括护筒沉设的双向监控与微纠偏、钻头库动态适配、装配式高强定位垫块应用、基于起拔控制的混凝土流失防护与实时补偿，以及创新的“井底台阶法”。该法通过重构施工基准面，系统性恢复了衬砌结构的设计厚度与完整性，同时客观导致了约5%的井容量损失。工程实践表明，这套顺序性问题解决方案在保障结构安全与功能的前提下，有效应对了施工挑战，为类似极端地质条件下的桩基工程提供了系统的、包含技术经济权衡的实践经验。

Abstract: An intake well structure of a Middle East project, located in the intertidal zone, employed a special construction method of “full-length steel casing support without slurry wall protection” for secant piles. This paper systematically identifies five key problems encountered during the implementation of this method, following the construction sequence: (1) Casing Installation Phase: Difficulty in ensuring absolute verticality and centering of long casings in ultra-soft soil layers; (2) Drilling and Hole Formation Phase: Inefficient drilling and excessive tool wear due to uneven hardness of the limestone layer, compounded by the stringent requirements for high-strength plain concrete piles (C40/C50); (3) Reinforcement Cage Installation Phase: Difficulties in cage positioning and ineffective control of concrete cover within the confined casing space; (4) Casing Extraction Phase: Loss of concrete volume due to leakage along the outer wall of the casing during its extraction; (5) Excavation and Subsequent Structure Phase: The designed “shotcrete lining with planted rebar and mesh” method became inapplicable due to pile deviation, failing to guarantee a uniform 100 mm thick lining. Corresponding on-site technical countermeasures are elaborated, including bidirectional real-time monitoring and micro-correction during casing installation, dynamic adaptation from a tool library, application of prefabricated high-strength spacer blocks, anti-leakage control and real-time compensation during casing extraction, and the innovative “base footing bench method.” This method reconstructs the construction datum plane to systematically restore the design thickness and integrity of the lining structure, while objectively resulting in a loss of approximately 5% of the well’s capacity. Engineering practice shows that this sequential problem-solving approach effectively addressed the construction challenges while ensuring structural safety and functionality, providing systematic and pragmatic experience that includes technical-economic trade-offs for similar pile foundation projects in extreme geological conditions.