Reliability-Based Geotechnical Design

最新版本的《加拿大公路桥设计规范》(CHBDC 2014)包括了岩土设计理念的重大变化。该规范现在包括取决于现场理解程度的阻力系数，以及取决于故障后果严重性的新后果系数。 根据多年来进行的研究，申请人校准了2014年CHBDC中出现的阻力和后果因素，以达到目标可靠性水平。然而，仍需要大量的研究来提炼这些因素，并将其扩展到涵盖其他极限状态。为此，本研究提案将处理以下两项主要任务： 1)CHBDC下一版已确定的主要目标之一是制定岩土抗震设计规范条款，将其纳入岩土设计章节。为了实现这一目标，需要确定设计荷载和抗力系数，以适当地针对岩土系统中极端事件地震极限状态的期望可靠性指标。这项研究将从研究地震荷载下的斜坡稳定性开始，其中斜坡由空间可变的随机场表示。在不同水平的地面运动激励下，将根据地面参数统计和斜坡几何形状的函数来估计破坏概率。然后使用全概率定理将结果组合在一起，以评估各种边坡设计的可靠性，给出地基强度统计的样本估计。设计程序和因素将被建议用于CHBDC和加拿大国家建筑规范(NBCC)。然后，研究将扩展到各种其他岩土工程问题，如浅基础、深基础和围护结构。 2)当一个结构由多个基础支撑时，结构的失效往往需要多个基础单元的失效--如果是这样的话，基础系统被认为具有一定的冗余性。当存在基础冗余时产生的一个重要问题是，为了实现期望的目标系统可靠性，各个基础构件的目标可靠性应该是什么？这项研究任务的目标是调查岩土冗余度与系统可靠性之间的关系，以便对单个基础构件做出知情的设计决策。 上述两项研究任务都是培训高素质人员的绝佳机会，特别是这些人员将直接看到他们的研究成果在加拿大主要设计实践准则中的需求、应用和实施。

The most recent edition of the Canadian Highway Bridge Design Code (CHBDC 2014) includes substantial changes in geotechnical design philosophy. The code now includes resistance factors that depend on the level of site understanding, as well as a new consequence factor that depends on failure consequence severity. Drawing from research performed over many years, the applicant calibrated the resistance and consequence factors appearing in the 2014 CHBDC to achieve target reliability levels. However, much research is still required to refine these factors and to extend them to cover other limit states. To this end, this research proposal will address the following two main tasks: 1) One of the major identified goals for the next edition of the CHBDC is to develop geotechnical seismic design code provisions to include in the geotechnical design chapter. To accomplish this goal, design load and resistance factors need to be determined that properly target the desired reliability index for extreme event seismic limit states in geotechnical systems. The research will start by looking at slope stability under seismic loading, where the slope is represented by a spatially variable random field. Failure probabilities as functions of ground parameter statistics and slope geometry will be estimated, conditioned on various levels of ground motion excitation. The results will then be combined using the total probability theorem to assess the reliability of various slope designs, given sample estimates of ground strength statistics. Design procedures and factors will be proposed for use in the CHBDC and the National Building Code of Canada (NBCC). The research will then be extended to a variety of other geotechnical problems, such as shallow foundations, deep foundations, and retaining structures. 2) When a structure is supported by multiple foundations, failure of the structure often requires the failure of more than a single foundation element - if so, the foundation system is said to have some redundancy. An important question that arises when foundation redundancy exists is what should the target reliability of individual foundation elements be in order to achieve a desired target system reliability? The goal of this research task is to investigate the relationship between geotechnical redundancy and system reliability so that informed design decisions can be made about individual foundation elements. Both of the above research tasks are excellent opportunities for the training of highly qualified personnel, especially since these personnel will directly see the need, application, and implementation of their research results in major Canadian design codes of practice.