硫酸盐渍土中灌注桩腐蚀劣化机理与承载性能演变

Bored piles are more and more widely applied in the engineering constructions in saline soil areas. However, the erosion deterioration greatly affects the service life of bored piles. Hence, the erosion deterioration has become one of the most important issues for the applications of bored piles in saline soil areas. It is necessary and urgent to take a systematical study on the erosion deterioration of bored piles in saline soil areas. The sulphate saline soil, widely distributed in the northwest of China, is one of the most common saline soils. The abundant sulfate ions in the saline soil cause serious erosion deterioration of bored piles. From construction to service process, the bored piles suffer from sulphate attack in the whole life. The bored pile exhibits different erosion mechanisms and effects in different parts. The sulphate attack deteriorates the microstructure, and degrades the strength and rigidity of bored piles. Simultaneously, it inflicts severe damages on the pile-soil interface, which will significantly change the bearing performance of bored piles. Therefore, the erosion deterioration has a significant effect on the bearing performance of a bored pile in saline soil areas. This project aims at conducting a thorough study on the mechanisms of erosion deterioration of bored piles suffered from sulphate attack in the whole service life. For this, the strength of the pile, the shaft resistance and the evolution rule of the bearing performance will be carefully studied by taking the service environment and the properties of bored piles into consideration. Some novel theories and testing skills, such as the corrosion tests, the microscopic detection, the pile loading tests, as well as the chemical analysis combining damage mechanics theory, will be systematically employed in the research work. The ultimate desire of this program is to develop a theoretical model for evaluating the erosion deterioration and the service life of a bored pile. The expected results of this research will serve as a valuable benchmark for anti-corrosion design and maintenance, as well as safe management of bored piles in sulphate saline soil areas.

灌注桩在盐渍土地区工程建设中的应用需求日益增大，其腐蚀劣化问题已成为亟待解决的重要课题。硫酸盐渍土是我国西北等地内陆盐渍土的主要类型之一，其土体及地下水中含有大量引起灌注桩腐蚀劣化的硫酸根离子。灌注桩从施工养护到服役的全过程均受到硫酸根等腐蚀介质的侵蚀作用，且不同部位的腐蚀方式和腐蚀效应存在明显差异。腐蚀作用将使桩身结构劣化，强度、刚度降低，同时产生桩-土界面损伤导致桩的承载变形特性改变。本项目针对硫酸盐渍土中灌注桩的腐蚀特点和服役条件，采用室内模拟腐蚀试验、微观观测、模型桩腐蚀承载试验和化学-损伤力学理论分析等方法，深入研究灌注桩成桩服役全过程腐蚀劣化机理，探讨腐蚀进程中桩身强度、桩侧摩阻力及桩的承载变形性能演变规律，提出灌注桩硫酸盐腐蚀损伤劣化评价和服役寿命评价的理论模型。本项目研究可为我国盐渍土地区灌注桩的设计与维护、防腐措施制定以及安全管理提供合理有效的理论支撑和科学依据。

随着我国西部大开发战略的实施，位于盐渍土地区的灌注桩应用需求日益增大。然而，盐渍土地区灌注桩受硫酸盐腐蚀劣化，普遍存在结构强度和承载性能迅速减低，服役寿命严重不足的问题。本项目针对灌注桩的成桩特点和腐蚀环境条件，采用化学分析、微观观测、力学测试和理论解析等多种研究方法，深入研究其侵蚀的发生、发展过程及劣化机理，揭示桩基承载变形性能的演变规律，提出硫酸盐腐蚀环境下灌注桩的服役安全性与寿命评价理论，取得了有重要意义的成果。通过室内养护成桩腐蚀试验，分析试件尺寸、质量和抗压强度变化，明确了腐蚀产物生成、膨胀裂缝形成及混凝土劣化的演变进程。探讨了桩径、水灰比、硫酸盐溶液浓度等对灌注桩长期性能的影响，研究了复合腐蚀下混凝土劣化过程及腐蚀机理。通过观测试样微观结构及物相变化，研究了干湿循环、全浸泡和部分浸泡等腐蚀方式对灌注桩腐蚀效应的影响规律。考虑水分输运、化学反应、对流和损伤作用影响，建立硫酸根离子输运模型和硫酸盐在混凝土桩中的非稳态扩散反应方程，形成了灌注桩硫酸盐腐蚀损伤劣化过程评价模型。研究灌注桩内部水分迁移，结晶形成和累积，混凝土膨胀开裂与强度劣化进程，建立了水压力作用下的硫酸盐扩散侵蚀模型。通过硫酸盐腐蚀界面剪切试验，研究了桩-土界面损伤劣化机理及其参数的变化规律。基于Weibull分布损伤理论，提出了硫酸盐腐蚀界面剪切损伤模型及其参数，研讨了损伤参数对界面剪切性能的影响。考虑化学反应引起的桩身膨胀，建立双曲线非线性桩侧土有效应力模型，研究了硫酸盐侵蚀与荷载作用下桩-土界面摩阻力与桩承载力退化规律，建立了硫酸盐侵蚀下混凝土灌注桩桩侧摩阻力、桩基承载力和沉降量等承载性能评价计算模型。根据多孔介质中的蒸发和毛细作用计算理论，结合化学结晶理论提出混凝土在硫酸盐结晶作用下的破坏模型，据此分析了桩基等地下混凝土结构的破坏机制，探讨了硫酸盐浓度、太阳辐射以及地下水位等对灌注桩服役寿命的影响，提出了综合考虑环境因素和桩身特性的混凝土桩使用寿命预测理论模型。