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GEOLOGY ENGINEERING. MOHD FAIZ BIN MOHAMMAD ZAKI (INTRODUCTION TO ENGINEERING GEOLOGY). INTRODUCTION. Objectives of the subject are: To provide knowledge and ability to identify the types and classification of related geological materials and structures. To provide ability to under-
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GEOLOGY ENGINEERING MOHD FAIZ BIN MOHAMMAD ZAKI (INTRODUCTION TO ENGINEERING GEOLOGY)
INTRODUCTION Objectives of the subject are: To provide knowledge and ability to identify the types and classification of related geological materials and structures. To provide ability to under- stand the principles of geology in civil engineering constructions.
ENGINEERING GEOLOGIST An engineering geologist is an individual who applies geologic data, principles, and interpretation so that geologic factors affecting the planning, design, construction, and maintenance of civil engineering works are properly recognized and utilized (Geologist and Geophysicist Act 1986).
GEOLOGICAL ENVIRONMENT • The geological environment is where civil engineering structures are constructed. • Effect of geologic elements (rock, soils, landslides, earthquakes, groundwater) must be understood to ensure safety & sustainable development.
CONT… • Civil engineering works are all carried out on or in the ground. Ground properties & processes are therefore significant – both the strengths of rocks & soils, & the erosional & geological processes which subject them to continual change.
ROCK MECHANICS To provide knowledge on related rock mechanics principles To develop ability to apply, to analyse and to evaluate the relevant rock engineering and rock mechanics principles in designing safe and economical civil engineering structures for sustainable developments.
WHY STUDY GEOLOGY? • Unstable ground does exist. Some ground is no ‘terra firma’ & may lead to unstable foundations. • Site investigation is where civil engineers encounter geology. This involves the interpretation of ground conditions (often from minimal evidence), some 3-D thinking, & the recognition of areas of difficult ground or potential geohazards. .
CONT… Unforeseen ground conditions can still occur, as ground geology can be almost infinitely variables, but they are often unforeseen due to inadequate site investigation. Civil engineering design can accommodate almost any ground conditions which are correctly assessed & understood.
CONT… Most rocks encountered by engineers are 10 – 500 M years old. They have displaced & deformed over time, & some are then exposed at the surface, by erosional removal of rock that once lay above them.
CONT… • Natural ground materials, rocks & soils, cover a great range of strengths; granite is 4000 times stronger than peat soil. • Assessment of ground conditions must distinguish between intact rock & rock mass (discuss in Rock Mechanics).
CONT… • Note that a strong rock may contain so many fractures in a hill side that the rock mass is weak & unstable. • Ground conditions also vary greatly due to purely local fractures such as underground cavities, inclined shear surfaces & artificial disturbances.
CONT… • Earth consists of 3 mainlayers – crust, mantle&core. • Crust (10 – 70km): outer most layer wheresediments/soils, rocks, water, petroleum & minerals arefound. Intrusive igneous rocks form the major composition of crust.
CONT… • Mantle (2880 – 3200km) comprise layers of very dense rocks (olivine & basalt). Temperature within mantle is 20000C.
CONT… • Core is about 50000C & 3500km thick, consists of molten formed by nickel & iron, divided into inner & outer core.
CONT… • Core & mantle consist of melting & partially melting material, this creates dynamic motion to earth crust (floating & continuously moving by convection current from underneath).
CONT… …
CONT… The theory that has come to be known as continental drift was not proposed until the early twentieth century (Taylor, 1910; Wegener, 1915). Wegener, for example, believed that the earth had only One large continent called Pangaea 200 million years ago. He believed that Pangaea broke into pieces that slowly drifted
CONT… Plate tectonics is fundamental to understanding geology and how the Earth’s surface works. According to the plate tectonic theory, the earth’s surface contains tectonic plates, also known as lithosphere plates, with each plate consisting of the crust and the more rigid part of the upper mantle
CONT… The basic hypothesis of plate tectonics is that the earth's surface consists of a number of large, intact blocks called plates, and that these plates move with respect to each other There are three types of plate boundaries: divergent boundary, convergent boundary, and transform boundary.
CONT… The earth's crust is divided into six continental-sized plates (African, American, Antarctic, Australia-Indian, Eurasian, and Pacific) and about 14 of subcontinental size (e.g., Caribbean, Cocos, Nazca, Philippine, etc.).
CONT… The interaction between plates at the boundaries is responsible for the following phenomena and features: -earthquakes - volcanoes -mountain chains -igneous rocks -folding -faulting -metamorphic rocks.
CONT… The most widely accepted explanation of the source of plate movement relies on the requirement of thermomechanical equilibrium of the earth's materials. The upper portion of the mantle is in contact with the relatively cool crust while the lower portion is in contact with the hot outer core. Obviously, a temperature gradient must exist within the mantle
CONT… The variation of mantle density with temperature produces the unstable situation of denser (cooler) material resting on top of less dense (warmer) material.
CONT… Eventually, the cooler, denser material begins to sink under the action of gravity and the warmer, less dense material begins to rise.
CONT… The sinking material gradually warms and becomes less dense; eventually, it will move laterally and begin to rise again as subsequently cooled material begins to sink. This process is the familiar one of convection.
CONT… The motion of the plates over geological time (i.e. 10s and 100s of millions of years) has resulted in rocks that were once buried deep in the crust to be exposed at the ground surface.
CONT… Plate tectonics causes the creation of new rocks through magma rising from the mantle together with partial melting in subduction zones. It also causes the creation of mountain chains which brings rocks that were once buried to be exposed at the ground surface.
CONT… Once at the surface they are attacked both physically and chemically, resulting in them being broken down into sediments which are readily carried away by water, wind and ice to be deposited elsewhere.
CONT… These sediments are transformed eventually into rocks through burial, cementation and recrystallisation.
CONT… In subduction zones high temperatures and high pressures are generated deep in the crust and this causes the rock to undergo changes in texture as well as mineralogy.
CONT… These processes form a complex cycle that gives rise to three distinct families of rock materials: (i) igneous rocks (ii) sedimentary rocks (iii) metamorphic rocks.
CONT… This cycle is called the ‘rock cycle’
CONT… …
Geologic Fault A fault is a crack in the Earth's crust. Typically, faults are associated with, or form, the boundaries between Earth's tectonic plates. In an active fault, the pieces of the Earth's crust along a fault move over time. The moving rocks can cause earthquakes.
CONT… Faults are often not just one orderly break in the rock, but are instead a number of fractures caused by similar motions of the Earth's crust. These clusters of faults are called fault zones.
CONT… Inactive faults had movement along them at one time, but no longer move. The type of motion along a fault depends on the type of fault. The main types of faults are described below. • Normal dip-slip fault • Reverse dip-slip fault • Transform (strike-slip) faults
EARTHQUAKE Earthquakes are a major problem for mankind, killing thousands each year Faults are fractures in the Earth’s surface along which displacement has occurred If movement could take place continuously along faults then major earthquakes would not occur.
CONT… However, most faults become locked such that forces (movement of plate tectonics) causing the displacement continue to increase until the shear strength of the obstruction is exceeded, resulting in the sudden release of a significant amount of strain energy, causing the earthquake.
