Rock Slope Engineering

Civil Applications, Fifth Edition

Duncan C. Wyllie

• Publisher: CRC Press
• Year: 2017
• ISBN:
  9781498786287
• Edition: 5
• Topic: Technology & Engineering
• Subtopic: Civil Engineering
• Index: Technology & Engineering

Rock Slope Engineering covers the investigation, design, excavation and remediation of man-made rock cuts and natural slopes, primarily for civil engineering applications. It presents design information on structural geology, shear strength of rock and ground water, including weathered rock. Slope design methods are discussed for planar, wedge, circular and toppling failures, including seismic design and numerical analysis. Information is also provided on blasting, slope stabilization, movement monitoring and civil engineering applications.

This fifth edition has been extensively up-dated, with new chapters on weathered rock, including shear strength in relation to weathering grades, and seismic design of rock slopes for pseudo-static stability and Newmark displacement. It now includes the use of remote sensing techniques such as LiDAR to monitor slope movement and collect structural geology data. The chapter on numerical analysis has been revised with emphasis on civil applications.

The book is written for practitioners working in the fields of transportation, energy and industrial development, and undergraduate and graduate level courses in geological engineering.

Chapter 1

Principles of rock slope design

1.1Introduction

A variety of engineering activities requires excavation of rock cuts. In civil engineering, projects include transportation systems such as highways and railways, dams for power production and water supply, and industrial and urban development. The design of rock cuts, and their excavation and stability are closely related to site geological conditions that may vary from strong, blocky rock containing well-defined discontinuities, to weak, highly weathered rock in which the remnant discontinuities, if any, have little influence on stability. Between these two extremes, a wide spectrum of conditions exists that must be quantified and incorporated appropriately into the design.

Figures 1.1 and 1.2 show contrasting examples of rock slopes with respect to rock strength and structural geology.

Figure 1.1Rock slope in very strong granite in which upper blocks of rock can slide from right to left on planar joints dipping at about 30° (near Agassiz, British Columbia, Canada). (a) Concrete buttress and tie-back anchors; (b) slope geometry showing dimensions of sliding blocks, bolt lengths and buttress configuration (Gygax Engineering).

Figure 1.2Excavated slope at 56° in highly weathered rock for highway construction: (a) image showing reinforcement of slope with soil nails and shotcrete (Sao Paulo, Brazil); (b) layout of soil nails in slope face.

In Figure 1.1, the rock is a very strong, blocky granite containing a set of high-persistence, planar joints dipping from right to left at about 30°. Movement of blocks of rock on these smooth, planar joints had opened tension cracks on a steeply dipping orthogonal joint set. Previous instability in this area had occurred with no warning because only a few millimetres of movement was required for the shear strength on the smooth joints to be reduced from peak to residual. Stabilization of the slope involved the construction of a reinforced concrete buttress with the lower part secured with tensioned rock anchors to stable rock below the sliding plane, and the upper part acting as a cantilever to support the sliding blocks.

Figure 1.2 shows an excavated face at an angle of 56° in highly weathered schist with a portion of the face reinforced with soil nails (steel dowels fully embedded in cement grout) on a 2-m square pattern and covered with a 100-mm (4 in.)-thick layer of reinforced shotcrete. The bolt lengths alternate between 5 and 6 m (16–20 ft) to avoid creating a potential plane of weakness at the end of the bolts that would occur if they were all the same length.

Other stabilization measures at this site include erosion control of this low-strength rock by installing lined ditches on each bench, and growing grass on the exposed rock faces.

In addition to man-made excavations, the stability of natural rock slopes in mountainous terrain may also be of concern. One of the factors that may influence the stability of natural rock slopes is the regional tectonic setting. For example, factors of safety of natural slopes may be only slightly greater than unity where rapid uplift of the land mass, and corresponding down cutting of the water courses, is occurring. Also, earthquake ground motions may loosen surficial rock and cause slope displacement. Such conditions exist in seismically active areas such as the Pacific Rim, the Himalayas and Central Asia.

The required stability conditions of rock slopes will vary depending on the type of project and the consequence of failure. For example, for cuts above a highway carrying high-traffic volumes, it will be important that both the overall slope be stable, and that few, if any, rock falls reach the traffic lanes. This will often require careful blasting during construction, and the installation of stabilization measures such as rock anchors. Because the useful life of such stabilization measures may be only 10–30 years, depending on the climate and...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Dedication
• Contents
• List of tables
• List of figures
• Introduction to the fifth edition
• Foreword to fifth edition
• Foreword to fourth edition
• Authors
• Nomenclature
• Authors
• 1. Principles of rock slope design
• 2. Structural geology and data interpretation
• 3. Weathered rock and slope stability
• 4. Site investigation and geological data collection
• 5. Rock strength properties and their measurement
• 6. Groundwater
• 7. Plane failure
• 8. Wedge failure
• 9. Circular failure
• 10. Toppling failure
• 11. Seismic stability analysis of rock slopes
• 12. Numerical analysis
• 13. Blasting
• 14. Stabilisation of rock slopes
• 15. Movement monitoring
• 16. Civil engineering applications
• Appendix I: Stereonets for hand plotting of structural geology data
• Appendix II: Quantitative description of discontinuities in rock masses
• Appendix III: Comprehensive solution wedge stability
• Appendix IV: Conversion factors
• References
• Index