Fatigue behaviour of geomaterials under cyclic environmental loading

循环载荷在工程应用中经常遇到。风对高层建筑物施加动态荷载。北极沃茨的波浪和冰荷载对海洋结构物和交通基础设施构成威胁。降水和地下水位的季节性变化对土方工程施加了重复荷载。地面冻融循环与交通荷载共同作用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循环的、动态的。矿物开采和石油和天然气开采也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，以量化在该领域遇到的循环荷载下不同地质材料的疲劳行为和预期寿命，以便可以开发新技术来预防危害，保护环境，优化材料寿命和自然资源回收。 在这项拟议的研究中研究的第一类地质材料是蒙特尼地层，这是加拿大主要的天然油气资源之一。由于其致密的孔隙结构，水力压裂（HF）已被用于开发这一资源。它涉及将化学处理过的流体高压注入地层，以形成裂缝网络，从而提高石油和天然气产量。水力压裂造成的压裂液和碳氢化合物污染对天然水源的潜在风险已经引起了公众的关注。水力压裂还引发地震事件，可能对地面设施造成有害影响。 迫切需要改进目前的HF处理，以增强这种致密材料中的水力流动，并减少处理释放的地震能量。我们建议通过以可控的“疲劳”方式使其失效来解锁紧密的材料。众所周知，材料在比单调模式低的循环施加应力下以循环疲劳模式失效。我们假设，一个较低的破裂压力，需要在周期性（脉动）加载下分解的致密材料。在受控脉动过程中，破裂带可能更均匀，而不是局部的。研究计划的第一阶段涉及实验室规模的实验。在第二阶段，测试数据将用于小规模现场实验的可行性研究。第三个阶段是开发新技术开发Montney地层。 这项研究计划显然具有科学和社会环境经济影响。这项研究计划的结果很容易转移到上述研究领域。技术转让和与工业伙伴和监管机构的合作解决公众关注的问题，促进环境保护，并促进我们的经济和就业。

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.