摘要
顶管与定向钻、盾构并列为当今三大非开挖技术,顶管施工因其环境破坏小、综合成本低、施工周期短等优点被广泛应用于油气管道穿越工程中。目前,对于顶管施工设计中最关键的参数——顶力的计算多依赖于经验计算公式,这样可能出现由于设计值不足而使顶进中断或设计值过高而使工程成本大增的情形；对在顶进过程中管道的力学特性亦缺乏了解,施工过程中可能出现严重的管道破坏现象而造成工程损失。
本文对顶管施工的关键内容——顶力计算进行了细致的理论分析,提出完整的顶管施工顶力计算方法和步骤,建立顶力计算模型并推导出顶力计算公式。在此基础上,采用C++语言编制顶管施工顶力计算软件以便于工程应用。采用有限元软件ANSYS分别对直线顶进状态下和纠偏过程中钢筋混凝土管的力学特性进行了数值模拟研究。主要研究内容和成果如下：
1、将模糊层次分析法(FAHP)引入到顶管掘进机型优选中。首先建立递阶层次模型并据此建立优选关系矩阵,然后进行指标权重计算并通过比较大小确定最佳方案。该法实现了决策由定性向定量的转化,提高了决策结果可信度,是一种科学、有效的方法。
2、对顶管施工顶力计算进行了细致的理论分析,提出完整的顶力计算过程可分为以下三大步骤：土压力计算理论选择→管土摩擦系数确定→顶力计算模型建立。通过卸荷拱效应判断进行土压力计算理论的选择,并对土柱法、普氏卸荷拱法、太沙基法及马斯顿法等四种常见的土压力计算方法进行对比分析。依据是否采用注浆工艺,进行管土摩擦系数的确定。建立顶力计算模型依次计算总顶力的两个组成部分：顶进正面阻力和管周摩擦阻力,对于管周摩擦阻力的计算引入管土相对刚度判断,进而分别建立刚性管道和柔性管道土压力模型,并最终推导出适用条件明确、计算结果可靠的顶力计算公式。
3、顶管施工顶力计算软件编制。在本文相应内容研究成果的基础上,在Visual C++环境中使用微软基础类库(MFC)编制计算程序,并最终形成包含掘进机型优选、顶力计算和中继间布置等功能的顶管施工顶力计算软件。并对内摩擦角和覆土深度等计算参数进行敏感性分析。本计算软件主要有如下特色：建立土体参数Access数据库并采用ADO技术与计算软件连接起来；添加国家规范和部分经验公式计算功能与本文计算结果进行对比；软件界面简洁,模块层次清晰,并配合编译的HTML帮助文档易于使用。
4、采用ANSYS软件分别对直线顶进状态下和纠偏过程中钢筋混凝土管的力学特性进行数值模拟研究。直线顶进工况包括在不同顶进长度、不同顶进深度、不同管径、不同混凝土等级以及不同土层等；纠偏过程工况包括不同纠偏阶段和不同偏差角度,并对采用衬垫环和不采用衬垫环的情况进行比较。在建立三维有限元模型过程中,充分考虑到管周注浆层的作用,采用线弹性本构模型将其模拟为弹性层,并在管道—注浆层—土体间接触面上建立接触对,更合理地模拟管土间相互作用。通过对计算结果进行后处理和分析,得到管道在不同工况下的应力分布规律和强度校核情况,以及各工况因素对其影响规律。
Pipe jacking, along with directional drilling and tunnel boring, is rated among the first three trenchless technology, and pipe jacking technology is widely applied in the oil and gas pipeline crossing projects for the advantage of less damage to the environment, lower comprehensive costs and shorter construction period. At present, the calculation of jacking force which is the most critical parameter for the pipe jacking construction design, is mostly dependent on the empirical calculation formula, which may lead to the interruption of jacking for the insufficient designed value or the sharply increase of the project costs for the higher designed value. There is also a lack of knowledge for the pipeline mechanical properties during the jacking process, and there may be the occurrence of serious failures of pipes which may bing about the loss of project.
This paper makes engrained and detailed theoretical analysis on jacking force calculation which is a pivotal content for the pipe jacking construction, presents integrated method and process for jacking force calculation, builds the model of jacking force calculation and derives the jacking force calculation formulas. On the basis of above contents, this paper establishes the jacking force calculation software of pipe jacking construction utilizing C++ language for project application. And makes numerical simulation studies on the mechanical properties of pipeline under the state of straightline advance and disalignment using the finite element analysis software ANSYS. The main contents and achievements are present as follows:
1. Using fuzzy analytic hierarchy process (FAHP) for the optimization of excavating machine type. Firstly the hierarchical model and priority relation matrix are set up, then the index power is calculated and compared so the optimum selection is made. This method achieves the conversion of decision from qualitative to quantitative, improves the credibility and is a sort of scientific and effective measure.
2. Makeing full and detailed theoretical analysis on jacking force calculation, the integrate method for jacking force calculation is present as follow:first the selection of earth pressure theory, second the friction coefficient is defined and lastly the model of jacking force calculation is built. The selection of earth pressure theory is performed through the unloading arc effect. Soil column theory, Promojiyfakonkv arch theory, Terzaghi theory and Marston theory are contrasted. The friction coefficient is defined in the light of whether lubrication process is adopted. The model is built for the ordinal calculation of two parts of jacking force:front resistance and friction round the pipeline. Adopting the pipe-soil relative rigid judgement, the rigid and flexible pipe models are built separately for the circumferential friction calculation. And lastly the jacking force calculation formulas are derived with definite appliance condition and reliable results.
3. Establishment of the jacking force calculation software. On the basis of relevant theoretical analysis and using MFC in VC++ environment, the software is finally formed containing the function of excavating machine type optimization, jacking force calculation and relay bay settings. The sensitivity of the calculating parameters includes angle of internal friction and depth of overburden. The features of the software are listed as below:firstly the database of soil parameters is set up and connected with the software through ADO technique; secondly the calculation of national criteria and some experience formulas are added in the software for a contrast with this paper; lastly with terse interface, clear module hierarchy and HTML help tutorial, the software is convenient for appliance.
4. Numerical simulation on the mechanical properties of reinforced concrete pipeline under the state of straightline advance and disalignment using ANSYS. The straightline advance working conditions contain variant jacking distance, jacking depth, pipe diameter, concret grade and soil type. The disalignment working conditions contain variant rectification period and deviation angle, and also the comparison between situations with and without package ring. During the process of modeling, the injecting slurry is simulated as an elastic layer adopting linear elastic constitutive model considering its effect, and the contact pair is set up on the interface between pipeline, injecting slurry and soil, which can imitate the interaction between pipeline and soil more reasonably. Through analysis of ANSYS post process of results, the stress distribution regularity and strength check consequent of pipeline in variant working conditions are obtained, and the influence of the working condition factor is also present.
引文
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