Engineering Geology science, Thesis of Engineering Geology

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Engineering Geology

AMSTERDAM • BOSTON • HEIDELBERG • LONDON • NEW YORK • OXFORD PARIS • SAN DIEGO • SAN FRANCISCO • SINGAPORE • SYDNEY • TOKYO Butterworth-Heinemann is an imprint of Elsevier

Engineering Geology

Second Edition

F. G. Bell

Butterworth-Heinemann is an imprint of Elsevier Linacre House, Jordan Hill, Oxford OX2 8DP, UK 30 Corporate Drive, Suite 400, Burlington, MA 01803, USA

First edition 1993 Second edition 2007

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ISBN-13: 978-0-7506-8077- ISBN-10: 0-7506-8077-

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Contents

• Igneous Rocks 1. Rock Types and Stratigraphy
• Metamorphism and Metamorphic Rocks
• Sedimentary Rocks
• Stratigraphy and Stratification
• Folds 2. Geological Structures
• Faults
• Discontinuities
• Weathering 3. Surface Processes
• Movement of Slopes
• Fluvial Processes
• Karst Topography and Underground Drainage
• Glaciation
• Wind Action and Desert Landscapes
• Coasts and Shorelines
• Storm Surges and Tsunamis
• The Origin and Occurrence of Groundwater 4. Groundwater Conditions and Supply
• The Water Table or Phreatic Surface
• Aquifers, Aquicludes and Aquitards
• Capillary Movement in Soil
• Porosity and Permeability
• Flow through Soils and Rocks
• Pore Pressures, Total Pressures and Effective Pressures
  • Hydraulic Uplift Phenomena Critical Hydraulic Gradient, Quick Conditions and
• Groundwater Exploration viii
• Assessment of Field Permeability
• Assessment of Flow in the Field
• Groundwater Quality
• Wells
• Safe Yield
• Artificial Recharge
• Groundwater Pollution
• Soil Classification 5. Description, Properties and Behaviour of Soils and Rocks
• Coarse Soils
• Silts and Loess
• Clay Deposits
• Tropical Soils
• Dispersive Soils
• Soils of Arid Regions
• Tills and Other Glacially Associated Deposits
• Frost Action in Soil
• Organic Soils: Peat
• Description of Rocks and Rock Masses
• Engineering Aspects of Igneous and Metamorphic Rocks
• Engineering Behaviour of Sedimentary Rocks
• Building or Dimension Stone 6. Geological Materials Used in Construction
• Roofing and Facing Materials
• Armourstone
• Crushed Rock: Concrete Aggregate
• Road Aggregate
• Gravels and Sands
• Lime, Cement and Plaster
• Clays and Clay Products
• Desk Study and Preliminary Reconnaissance 7. Site Investigation
• Site Exploration – Direct Methods
• In Situ Testing
  • Field Instrumentation ix
  • Geophysical Methods: Indirect Site Exploration
  • Maps for Engineering Purposes
  • Geographical Information Systems
  • Introduction 8. Geology, Planning and Development
  • Geological Hazards, Risk Assessment and Planning
  • Hazard Maps
  • Natural Geological Hazards and Planning
  • Geological-Related Hazards Induced by Man
  • Derelict and Contaminated Land
  • Open Excavation 9. Geology and Construction
  • Tunnels and Tunnelling
  • Underground Caverns
  • Shafts and Raises
  • Reservoirs
  • Dams and Dam Sites
  • Highways
  • Railroads
  • Bridges
  • Foundations for Buildings
• Suggestions for Further Reading
• References
• Index

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E n g i n e e r i n g G e o l o g y

Figure 1.

Approximate mineral compositions of the more common types of igneous rocks, e.g. granite approximately 40% orthoclase, 33% quartz, 13% plagioclase, 9% mica and 5% hornblende (plutonic types without brackets, volcanic equivalents in brackets).

Figure 1.

Dyke on the south side of the Isle of Skye, Scotland.

several tens of metres but their average width is on the order of a few metres. The length of their surface outcrop also varies; for example, the Cleveland Dyke in the north of England can be traced over some 200 km. Dykelets may extend from and run parallel to large dykes, and irregular offshoots may branch away from large dykes. Dykes do not usually have an upward termination, although they may have acted as feeders for lava flows and sills. They often occur along faults, which provide a natural path of escape for the injected magma. Most dykes are of basaltic composition. However, dykes may be multiple or composite. Multiple dykes are formed by two or more injections of the same material that occur at different times. A composite dyke involves two or more injections of magma of different composition.

Sills, like dykes, are parallel-sided igneous intrusions that can occur over relatively extensive areas. Their thickness, however, can vary. Unlike dykes, they are injected in an approxi- mately horizontal direction, although their attitude may be subsequently altered by folding. When sills form in a series of sedimentary rocks, the magma is injected along bedding planes (Fig. 1.3). Nevertheless, an individual sill may transgress upwards from one horizon to another. Because sills are intruded along bedding planes, they are said to be concordant, and their outcrop is similar to that of the host rocks. Sills may be fed from dykes, and small dykes

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Figure 1.

The Whin Sill, Northumberland, England.

viscous than andesitic or rhyolitic magma. Hence, there is relatively little explosive activity and the associated lava flows are more mobile. However, certain volcanoes, for example, those of the Hawaiian Islands, are located in the centres of plates. Obviously, these volca- noes are unrelated to plate boundaries. They owe their origins to hot spots in the Earth’s crust located above rising mantle plumes. Most volcanic material is of basaltic composition.

Volcanic activity is a surface manifestation of a disordered state within the Earth’s interior that has led to the melting of material and the consequent formation of magma. This magma trav- els to the surface, where it is extravasated either from a fissure or a central vent. In some cases, instead of flowing from the volcano as lava, the magma is exploded into the air by the rapid escape of the gases from within it. The fragments produced by explosive activity are known collectively as pyroclasts.

Eruptions from volcanoes are spasmodic rather than continuous. Between eruptions, activity may still be witnessed in the form of steam and vapours issuing from small vents named fumaroles or solfataras. But, in some volcanoes, even this form of surface manifestation ceases, and such a dormant state may continue for centuries. To all intents and purposes, these volcanoes appear extinct. In old age, the activity of a volcano becomes limited to emis- sions of gases from fumaroles and hot water from geysers and hot springs.

Steam may account for over 90% of the gases emitted during a volcanic eruption. Other gases present include carbon dioxide, carbon monoxide, sulphur dioxide, sulphur trioxide,

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Figure 1.

Distribution of the active volcanoes in the world. S, submarine eruptions.

hydrogen sulphide, hydrogen chloride and hydrogen fluoride. Small quantities of methane, ammonia, nitrogen, hydrogen thiocyanate, carbonyl sulphide, silicon tetrafluoride, ferric chlo- ride, aluminium chloride, ammonium chloride and argon have also been noted in volcanic gases. It has often been found that hydrogen chloride is, next to steam, the major gas pro- duced during an eruption but that the sulphurous gases take over this role in the later stages.

At high pressures, gas is held in solution, but as the pressure falls, gas is released by the magma. The rate at which it escapes determines the explosivity of the eruption. An explosive eruption occurs when, because of its high viscosity (to a large extent, the viscosity is gov- erned by the silica content), the magma cannot readily allow the escape of gas until the pres- sure that it is under is lowered sufficiently to allow this to occur. This occurs at or near the surface. The degree of explosivity is only secondarily related to the amount of gas the magma holds. On the other hand, volatiles escape quietly from very fluid magmas.

Pyroclasts may consist of fragments of lava that were exploded on eruption, of fragments of pre-existing solidified lava or pyroclasts, or of fragments of country rock that, in both latter instances, have been blown from the neck of a volcano.

The size of pyroclasts varies enormously. It is dependent on the viscosity of the magma, the violence of the explosive activity, the amount of gas coming out of solution during the flight of the pyroclast, and the height to which it is thrown. The largest blocks thrown into the air may weigh over 100 tonnes, whereas the smallest consist of very fine ash that may take years to fall back to the Earth’s surface. The largest pyroclasts are referred to as volcanic bombs. These consist of clots of lava or of fragments of wall rock.

The term lapilli is applied to pyroclastic material that has a diameter varying from approxi- mately 10 to 50 mm (Fig. 1.5). Cinder or scoria is irregular-shaped material of lapilli size. It usually is glassy and fairly to highly vesicular.

The finest pyroclastic material is called ash. Much more ash is produced on eruption of acidic than basic magmas. Acidic igneous rocks contain over 65% silica, whereas basic igneous rocks contain between 45 and 55%. Those rocks that have a silica content between acid and basic are referred to as intermediate, and those with less than 45% silica are termed ultrabasic. As mentioned, the reason for the difference in explosivity is because acidic material is more viscous than basic or basaltic lava.

Beds of ash commonly show lateral variation as well as vertical. In other words, with increas- ing distance from the parent vent, the ash becomes finer and, in the second case, because the heavier material falls first, ashes frequently exhibit graded bedding, with coarser material occurring at the base of a bed, and becoming finer towards the top. Reverse grading may

E n g i n e e r i n g G e o l o g y

parts of the deposit. The term ignimbrite is used to describe these rocks. If ignimbrites are deposited on a steep slope, they begin to flow, and they resemble lava flows. Ignimbrites are associated with nuées ardentes (Fig. 1.6).

Lavas are emitted from volcanoes at temperatures only slightly above their freezing points. During the course of their flow, the temperature falls until solidification takes place some- where between 600 and 900∞C, depending on their chemical composition and gas content. Basic lavas solidify at higher temperatures than do acidic ones.

Generally, flow within a lava stream is laminar. The rate of flow of lava is determined by the gradient of the slope down which it moves and by its viscosity that, in turn, is governed by its composition, temperature and volatile content. Because of their lower viscosity, basic lavas flow much faster and further than do acid lavas. Indeed, the former type has been known to travel at speeds of up to 80 km h-^1.

The upper surface of a recently solidified lava flow develops a hummocky, ropy (termed pahoe- hoe); rough, fragmental, clinkery, spiny (termed aa); or blocky structure (Fig. 1.7a and b). The pahoehoe is the most fundamental type, however, some way downslope from the vent,

E n g i n e e r i n g G e o l o g y

Figure 1.

Nuee ardente erupting from Mt. St. Helens in May 1980, Washington State.

it may give way to aa or block lava. In other cases, aa or block lava, may be traceable into the vent. The surface of lava solidifies before the main body of the flow beneath. Pipes, vesicle trains or spiracles may be developed in the lava, depending on the amount of gas given off, the resistance offered by the lava and the speed at which it flows. Pipes are tubes that project upwards from the base and are usually several centimetres in length and a centimetre or less in diameter. Vesicles are small spherical openings formed by gas. Vesicle trains form when gas action has not been strong enough to produce pipes. Spiracles are openings formed by explosive disruption of the still-fluid lava by gas gener- ated beneath it. Large flows are fed by a complex of streams beneath the surface crust so that when the supply of lava is exhausted, the stream of liquid may drain away leaving a tunnel behind.

Thin lava flows are broken by joints that may run either at right angles or parallel to the direc- tion of flow. Joints do occur with other orientations but are much less common. Those joints that are normal to the lava surface usually display a polygonal arrangement, but only rarely do they give rise to columnar jointing. These joints develop as the lava cools. First, primary joints form, from which secondary joints arise, and so it continues.

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Figure 1.

(a) Ropy or pahoehoe lava, Craters of the Moon, Idaho.