Fatigue behaviour of geomaterials under cyclic environmental loading

循环荷载是工程应用中经常遇到的问题。风对高层建筑施加动荷载。海浪和冰荷载对北极水域的近海结构和运输基础设施构成威胁。降水和地下水位的季节变化给土方工程带来了反复荷载。随着交通荷载的作用，地面的周期性冻融会影响路面和地下设施的长期使用性能。地震、滑坡等自然地质灾害在本质上是周期性和动态性的。矿产开采和石油和天然气开采还涉及对周围环境的循环负荷。这项拟议研究计划的长期目标是开发技术，以量化不同岩土材料在现场循环加载下的疲劳行为和预期寿命，以便开发新的技术，以防止灾害，保护环境，优化材料寿命和自然资源回收。 这项拟议研究中研究的第一类岩土材料是蒙特尼组，它是加拿大主要的石油和天然气资源之一。由于其致密的孔隙结构，水力压裂被用于开采这一资源。它包括将经过化学处理的流体高压注入地层，以创建裂缝网络，提高石油和天然气的产量。水力压裂引起的压裂液和碳氢化合物污染对天然水源的潜在风险引起了公众的关注。水力压裂还会诱发地震事件，可能对地面设施造成不利影响。 迫切需要对目前的高频处理进行改进，以增强这种致密材料中的水力流动，并减少处理所释放的地震能量。我们建议以一种可控的“疲劳”方式来解锁这种紧密的材料。众所周知，在循环应力低于单调模式下，材料以循环疲劳模式失效。我们假设，在循环(脉动)载荷下，需要较低的破裂压力来使致密材料解体。在受控脉动作用下，裂隙带可能更均匀，而不是局部化。研究计划的第一阶段包括实验室规模的实验。在第二阶段，试验数据将被用于小规模野外试验的可行性研究。第三阶段是开发开发蒙特尼油层的新技术。 这项研究计划显然同时具有科学和社会环境经济影响。这个研究项目的成果很容易被转移到上面列出的研究领域。技术转让和与行业伙伴和监管机构的合作解决了公众的关切，促进了环境保护，并促进了我们的经济和就业。

Cyclic loadings are commonly encountered in engineering applications. Wind exerts dynamic loads on tall buildings. Wave and ice load imposes threat to offshore structures and transportation infra-structures in arctic waters. Seasonal variation of precipitation and water table imposes repeated loads on earthworks. Cyclic freezing-thawing of ground along with traffic loads affect the long-term performance of pavements and buried utilities. Natural geohazards such as earthquakes and landslides are cyclic and dynamic in essence. Mineral mining and oil and gas extraction also involve cyclic loading to the surrounding environment. The long-term objective of this proposed research program is to develop techniques to quantify fatigue behaviour and expected life span of different geomaterials under cyclic loading encountered in the field so that new technologies can be developed for prevention of hazards, protection of the Environment, and optimization of material life span and natural resource recovery. The first type of geomaterials studied in this proposed research is Montney Formation which is one of the major natural oil and gas resources in Canada. Due to its tight pore structure, hydraulic fracturing (HF) has been used for exploitation of this resource. It involves high-pressure injection of chemically treated fluid into the formation to create a fracture network enhancing oil and gas production. Potential risks to natural water sources by contamination of fracture fluid and hydrocarbons resulting from hydraulic fracturing have raised public concerns. Hydraulic fracturing also induces seismic events which may impose detrimental effects on surface facilities. There is an urgent need to modify the current HF treatment to enhance the hydraulic flow in this tight material and reduce the amount of seismic energy released from the treatment. We propose to unlock the tight material by failing it in a controllable “fatigue” manner. It is well known that materials fail in a cyclic fatigue mode under a cyclic applied stress lower than that in a monotonic mode. We postulate that a lower fracturing pressure is required to disintegrate the tight material under cyclic (pulsation) loading. Under controlled pulsation process, the fractured zone may be more homogeneous rather than localized. The first stage of the research program involves experimentation in laboratory scale. In the second stage the test data will be used and implemented to feasibility studies of small-scale field experiments. The third stage is the development of novel technologies for exploitation of Montney Formation. This research program clearly carries both scientific and socio-environmental-economic impacts. Findings from this research program are readily transferred to research fields as listed above. Technology transfer and collaboration with industrial partners and regulators address public concerns, promote protection of the Environment, and enhance our economy and employment.