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Geotechnical Engineering 

 
Authors: Andrew McG. Robertson and Jack Caldwell

Summary

This review looks at geotechnical engineering and the role of geotechnical engineers in mining. Topics covered include foundations, underground and open pit rock mechanics, soil mechanics, dams, and tailings impoundments. Several geotechnical engineering books are also discussed.

INTRODUCTION

The geotechnical engineer provides the roads, the foundations, the ponds, and a host of other infrastructure facilities for the mine. Then miner pulls the ore out of the ground. The process engineer gets the minerals out of the ore. The geotechnical engineer takes over again to deal with the wastes of ore removal and mineral extraction.

Accordingly in this review we take a detailed look at what the geotechnical engineer does on the mine. My intention is to tell you enough to understand the scope of work undertaken by the geotechnical engineer on a typical mine.

Your need for this information may arise because you are a geotechnical engineer contemplating a career on the mines, because you are a miner who has to employ and manage geotechnical engineers, or because you are a regulator charged with ensuring that the correct considerations have indeed gone into the mine plan your are being asked to permit.

WHAT IS GEOTECHNICAL ENGINEERING

Geotechnics is a catch-all phrase for al the earth science technologies. It includes the science traditionally described as geology, soil & rock mechanics, and geohydrology & hydrogeology. Geotechnical engineering is the application of these sciences in the design and construction of facilities for the benefit of mankind. Facilities which are largely dependent on geotechnical engineering for their successful construction include underground and open pit mines, tunnels, underground chambers, tailings and water dams, embankments and cuttings, road beds, and foundations for large structures. Typically, mine development requires all or most of these facilities.

Geotechnical engineering is a fundamental skill in the training of mining, civil, and geological engineers involved in the design and operation of mine and mill facilities. These engineers also specialize in or draw on the expertise of specialists in the related fields of geology, seismicity, geohydrology, hydrogeology, geochemistry, and geophysics. These technologies contribute to an understanding of the distribution and engineering properties of the rock, soil, and water components in any geotechnical structure or facility and of the forces to which they will be subjected.

WHAT DO GEOTECHNICAL ENGINEERS DO FOR MINES

ACCESS & HAUL ROADS
So obvious, it is trite to say, but to get to and around the mine you need access & haul roads. The geotechnical engineer locates, designs, and builds the roads.

FOUNDATIONS
All mine buildings have foundations. The geotechnical work involved in designing mine infrastructure foundations is generally done during the mine development phase. Best to get a foundation design engineer on your team at that time.

UNDERGROUND MINE ROCK MECHANICS
The increasing role of geotechnical engineers in underground mine rock mechanics has resulted from the need to achieve the following:

  • Improvement of underground rock support methods to improve worker safety.
  • Development of mining methods and mechanized support systems to improve worker productivity.
  • Development of alternative mining methods, such as block caving, to optimize resource recovery.

Geotechnical engineers are leading the way in the design and placement of mine backfill systems.

OPEN PIT MINE ROCK AND SOIL MECHANICS
The geotechnical engineer has always played major role in the design and operation of open pit mines. The economics of open pit mining resulted in a huge increase in this mining method in the late 1960s. At that time geotechnical engineering was well established as an essential part of large earth moving operations and slope stability determinations in the civil engineering industry. much of this technology and practice was transferred to the open pit mining industry. Thus we saw the development of mine management with geotechnical and civil engineering backgrounds rather than the more traditional mining backgrounds.

The 1970s was a period of expansion and development of the technology of open pit slope stability to cater for the rapid increase in the depth and size of very large open pits associated with the base metal mining industry.

In the early 1980s there was a substantial decline in the demand for this branch of mining Geotechnics as the number of open pits declined due to closure or reduced production. This changed with the mining resurgence of recent years. Increase in the demand for geotechnical engineers for open pit mining is partially the result of:

  • An increased need to address long-term stability and close-out requirements during the permitting and operational period.
  • Increased concerns and liability regarding worker and public safety.
  • New legislation and regulatory requirements at both the State and Federal levels.

DAMS AND SEDIMENT PONDS
Sediment pond The environmental scientist and surface water hydrologist are responsible for ensuring that the quality of the surface water leaving the mine site meets legal discharge criteria. The geotechnical engineer designs the sediment pond that controls the water before it leaves the mine. The biggest mine sediment pond I ever worked on was for a platinum mine where we designed and built a rock overflow dam to contain the remnants of the tailings that had escape a breach in the slimes dam.

TAILINGS IMPOUNDMENTS & WASTE ROCK DUMPS
Waste piles and tailings impoundments are geotechnical structures. Formal geotechnical design started in the 1950s. During the 1960s and 1970s the need for formal geotechnical engineering input to the design of such structures came from the need to construct larger facilities using more cost-effective methods. This was true particularly in the base metal industry. Substantial developments were seen in such topics as centerline cycloned tailings construction methods, earthquake resistant design, and seepage control.

HEAP LEACH PADS
Working together the mining engineer, the process manager, the metallurgist, and the civil engineer design and operate the heap leach pad. And when the mine is worked out the geotechnical engineer is let to close the pad and get it ready for its long geomorphic history. If the geotech is wise he will team up with a geologist and together they will understand how the landscape come into being, and will try to replicate those processes that promote stability in the area.

ANALYSIS AND DESIGN
The geotechnical engineer is also generally a civil engineer. So go to the site http://www.icivilengineer.com/ for information about software, tools, new, and other information that is of interest to the civil and geotechnical engineer and can be used in a mining context.


BEST PRACTICE BOOKS

GENERAL
In this section we make bold as to designate our choice of the best books on geotechnical engineering as is relevant to mining. These are personal choices based on use, familiarity, and even a love of the books we write about. These are the classics. Some may even be out of date. But they are all fundamental to good and best engineering practice.

The power of the internet supports and expands on this great geotechnical book approach. As an experiment, with Google, I did a search using as keywords the headings of the chapters and sections and subsections of the books. For each and every section, there is a plethora of interesting, relevant, and new information. Thus my theory: with this book and a link to the internet, you can read and learn as much about geotechnical engineering as you need and as your interests take you. And with that I need so more about geotechnical engineering in mining. Other than look at all the links associated with this posting.

SATURATED SOIL MECHANICS
There are literally thousands of books on geotechnical engineering. And hundreds of them address aspects of geotechnical engineering relevant to mining. A few minutes searching through the standard channels is sure to bring up one that focuses on the things that interest or concern you.

If you elect to read only one book on geotechnical engineering in order to get to the basics, we can do no better than recommend Soil Mechanics in Engineering Practice (Third Edition) by Karl Terzaghi, Ralph B Peck and Gholamreza Mesri. I confess the original by Terzaghi & Peck was my university text book and thus I am partial & prejudice. Mesri Gholamreza has done a masterful job of updating the original, so it is as fresh and relevant today as it was way back then.

This book has character and insight-unlike so many bland repetitions in so many modern textbooks stuffed with simple problems designed to train students to answer multiple-choice exams. Rather, this book gives you insight into the nature of geotechnical engineering and the philosophy that is so essential a part of its successful practice. In my opinion, you cannot call yourself a geotechnical engineer if you have not read and absorbed this book.

PARTIALLY SATURATED SOIL MECHANICS
A great companion to Terzaghi and Peck is Soil Mechanics fort Unsaturated Soils by D. G. Fredlund and H. Rahardjo. This book is published by Wiley as is Terzaghi and Peck and is in the same binding. It is worthy of being the companion volume.

In this volume you will find everything you want about the characterization, analyses, and use of unsaturated soils. Keep in mind that in many of the drier parts of the world where there are mines, the soil is not saturated, i.e., the pore spaces of the soil are not filled with water as tends to happen in the wetter parts of the world.

Most often this partial saturation can be made to work in your favor. I recall working in South Africa on slimes dams that stood stable to great heights at slope inclinations not possible for saturated soils. I have designed and built covers for mine waste that harness the benefits of partial saturation to limit seepage to the waste.

EARTH MANUAL
Available in full free for electronic download is the U.S. Department of the Interior, Bureau of Reclamation's Earth Manual. This book has the practical bent that is needed to design and build earthworks at mines. Here are the beginner's guide to the identification and classification of soils, quantifying the index properties of soils and their engineering properties. Here are the principles of investigation, exploratory methods. Sampling and testing procedures, and how best to record data about soils. In an extended section on the control of earth construction are chapters of earthworks, foundations, embankments, dams, canals, and soil stabilization. I have used this book in the field, so have most U.S. geotechnical engineers. It is readily available to you and should be a key part of your mining-related geotechnical library.v

ROCK MECHANICS
The greater part of Rock Slope Engineering by E. Hoek & J.W. Bray is available free on Google books. In this book are the fundamental principles of rock mechanics and their application to rock slopes. To the extent the pages are block or you cannot purchase a copy see the website for RocScience where most of the important information is readily downloadable. Reading this will not make you a rock mechanics expert, but it will make you knowledgeable enough to solve (or at least manage the solution of) most mining-related rock mechanics problems.

TAILINGS
Tailings impoundments are the great mining geotechnical structures. Still relevant and profound is Planning, Design, and Analysis of Tailings Dams by Steven G. Vick. As this book is getting a bit out of date, we recommend a Google search of any topic that is critical to the safe and cost-effective operation of your mine.

NAVFAC
For a superb collection of design manuals related to geotechnical engineering go to the NAVFAC site. Do a search for geotechnical or do a search for soil mechanics. These searches will bring up eminently usable and proven manuals that detail the design and construction of geotechnical structure. While originally written for naval facilities (hence NAVFAC) these volumes have gained a well deserved reputation amongst practicing civil engineers working in all areas of geotechnical engineering. I am certain you will find here what you need.

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