Semester

Fall

Date of Graduation

2020

Document Type

Dissertation

Degree Type

PhD

College

Statler College of Engineering and Mineral Resources

Department

Mining Engineering

Committee Chair

Yi Luo

Committee Member

Ihsan B Tulu

Committee Member

Qingqing Huang

Committee Member

Ming Gu

Committee Member

Lihong Zhou

Abstract

The objective of this work is to address three challenging topics, (1) effects of overburden key strata on subsurface subsidence; (2) effects of longwall subsidence on interstate highways and highway bridges; and (3) effects of dewatering mine water on surface subsidence over inactive room-and-pillar mines, in mine subsidence and to continue improvement of mine safety and health by reducing mine-subsidence related hazards.

Surface and subsurface subsidence events induced by underground mining activities are often capable of causing significant disturbances not only to surface structures, but also to subsurface structures. In this work, models and techniques to study three challenging topics in mine subsidence will be developed and detailed as follows.

An accurate subsurface subsidence prediction model is necessary in order to assess the disturbances to various subsurface structures. Decades of research have demonstrated that variations of lithology in the overburden have significant influence on the subsurface strata movements and deformations during ground subsidence process. The key strata theory states that the thick and hard key strata serve as the backbone of the overburden and controls the movements of the overlying thin and soft weak rock strata. A new version of subsurface subsidence prediction model considering the key strata effects on subsurface strata movements and deformations is developed. The influence function method, proven to be accurate and versatile for surface subsidence prediction, is employed to predict the subsidence on each of the overburden strata from mining horizon progressively upward to ground surface with the assumption that the predicted subsidence on a given stratum serves as the subsidence source for the stratum immediately above. The new subsurface subsidence prediction model is demonstrated with an actual case to show its applicability and improvement.

Surface subsidence events induced by underground longwall mining operations can cause various problems to interstate highways and their bridges, ranging from structural integrity and stability to functionality. Accurate subsidence predictions, correct influence assessments and effective mitigation measures are the keys to ensure the continuous service of interstate highways, safety of travelers and smooth mining operations. Highway bridges, as a kind of special road construction that can only tolerate smaller movements and deformations than road pavements, are particularly susceptible to severe influence caused by subsidence-induced ground movements and deformations. The techniques to use the predicted final and dynamic surface subsidence to assess their influences on the integrity, stability and functionality of highway structures (e.g., road surface pavements, concrete slabs, transverse joints, etc.), bridge structures, vehicle dynamics, comfort and drivability are presented. Mitigation measures to protect the highway and bridge structures and to ensure traffic safety are also proposed along with an application case.

Investigating inactive mine subsidence is often a very difficult task because many factors, both mining- or non-mining-related, can affect the possibility and the formation process of surface subsidence events over inactive room-and-pillar mines. Among them, mine water frequently plays an important role in causing such subsidence events. However, mine water could also serve the purpose of preventing subsidence. The dewatering of inactive room-and-pillar mines has been identified as the main cause for a number of serious mine subsidence events in the past. In this work, the mechanism of mine water to prevent surface subsidence over inactive room-and-pillar coal mines is studied. Two mathematical models are proposed to quantify the potential effects of mine water on the structural stability of mine pillars and roof, as well as the potential for causing surface subsidence. The models are validated with a documented subsidence case.

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