Three (3) Main Types of Rocks:
1. Igneous Rocks (L. ingis, fire) – are rocks formed from once hot molten mass known as magma or lava which cooled and crystallized into rock
made up of aggregates of interlocking silicate minerals.
2. Sedimentary Rocks, (L, sedimentum, settling) – are formed from accumulation of sediments of the weathered fragments of older rocks
deposited in layers near the earth’s surface by water, wind and ice. This weathered fragments caused by mechanical and chemical weathering
of igneous rocks.
3.Metamorphic Rocks (Gr. Meta + morphe, change of form) – are composed of igneous & sedimentary rocks that have been changed by high
temperature & pressure within the crust. This process is called metamorphism where tremendous heat & pressure with activity of water &
gases promote recrystallization of rock masses.
IGNEOUS ROCKS:
are normally crystalline in nature, having been formed beneath the surface and at the surface of the earth from the solidification of molten
silicates called “Magma”.
Types of Igneous Rocks Based on Deposition:
1. Extrusive/Volcanic – crystallized at the earth’s surface as a result of volcanic activity and exhibited fine-grained to glassy.
2. Intrusive/Plutonic – originated at depth and cool more slowly and exhibited medium to coarse-grained, largely depending on the
size of the intrusion.
COMMON EXAMPLES of IGNEOUS ROCKS:
1. granite
2. granodiorite
3. quartz diorite
4. andesite
5. basalt
6. gabbro
7. peridotite
8. rhyolite
9. dacite
10. rhyodacite
11. obsidian
12. pumice
13. diorite
14. amygdaloidal basalt
15. dunite
16. volcanic breccia
EXTRUSIVE/PYROCLASTIC IGNEOUS ROCKS
1. Lava Flows – consists of mobile rock material reaching the surface through vents and fissures and pouring sub – axially or submarine. The
flows to the sub aerial surface depend for their extent on the fluidity of the magma.
Lahar - hot or cold mixture of water and rock fragments flowing down the slopes of a volcano and (or) river valleys
Lava flows - streams of molten rock that pour or ooze from an erupting vent.
2. Volcanic Breccia – larger fragments fall around
volcanic vent and build a cone including:
3. Blocks – larger angular fragments
4. Bombs – rounded fragments size of an apple
5. Cinders – sizes of nuts
6. Tuff – finer material carried by air currents deposited at some distance from the vent.
7. Ash – size of peas
8. Dust – finest particle
SEDIMENTARY ROCKS
Are formed in layers from materials deposited by water, wind ice or other agents.
* Sedimentary rocks are distinguishes by:
a. Stratification, which is produced during and after deposition.
b. Presence of fossils
c. Texture and structure. These facets often indicate the transport and sedimentation history, the nature of the source material cement etc. The
sum of this is the “facies” which defines the nature of the environment of deposition.
Sedimentary Rocks are formed in one of three (3) Ways:
1. By decomposition, disintegration of former rocks followed by accumulation to form clastic deposits. These are products of weathered eroded
and transported surface materials, usually conveyed in a fluid medium. They are characterized by their high silica / quartz content, or by a
significant clay mineral content.
2. By organic means, where animal or vegetable remains accumulate, whether as shell beds, rocks, oozes, etc. They produce carbonate rocks if
shelly materials accumulate, pure siliceous deposits with diatoms.
3. By chemical means. These mainly include evaporates which are sulphates, silicates, silicates, phosphates, chlorates, chlorides etc. These form
mainly by evaporation or precipitation from bodies of surface water.
Sedimentation :
- It is essentially a sorting of disaggregated material according to density and solubility. It is the act or process of accumulating
sediment in layers or the process of deposition of sediment.
Induration:
It is the hardening of a rock material by the application of heat/pressure or introduction of cementing material.
Lithification:
It is the conversion of newly deposited sediments into an indurated rocks.
Diagenesis:
The process of conversion of soft sediment to rock. It is the chemical & physical changes occurring in sediments during & after their
deposition but before consolidation.
Sedimentary facies – stratigraphic facies differing from another part as parts of the some unit in both lithologic and paleontologic characters.
Example of Sedimentary rocks:
1. Sandstone
6. Shale
2. Limestone
7. Siltstone
3. Conglomerate
8. Claystone
4. Mudstone
9. chert
5. Graywacke
10. flint
Examples of Organic Sedimentary Minerals
1. Phosphate Rock
5. Rock Salt
2. Coal
6. Bentonite
3. Dolomite
7. Lime
4. Calcite
Sandstones - are clastic rocks in which the majority of the grains fall within the size range 0.06 mm to 2 mm. This covers all particles whether
they are formed of quartz, ferromagnesian minerals, sheltie materials or rock particles. The pore spaces are either wholly or partly filled with
groins of < 0.06 mm size, or cement or both.
Common Cementing Materials:
a. silica
b. calcite
c. iron oxide
d. clay minerals
METAMORPHIC ROCKS:
Are rocks formed from pre – existing solid rocks by mineralogical structural and chemical changes in responses to extreme changes in
temperature pressure and shearing are formed by alteration of parent rock through heat, pressure and chemical action of fluids and gases. The
parent rock may be either sedimentary igneous or some type of metamorphic rock itself.
Three (3) Types of Metamorphism
1. regional
2. Contact
3. dynamic / burial
REGIONAL : This involves the large scale action of heat and pressure producing a wide range of new minerals and a series of crystalline rocks
with a distinctive fabric resulting from mineral re – orientation. Examples: slates, schist, gneis.
CONTACT: It involve heat almost exclusively and is normally associated with igneous intrusions. It produces suites of “flinty” homogeneous
often characterless rock called HORNFELS, and often includes MARBLE. It is also referred to as thermal metamorphism.
DYNAMIC/BURIAL: This involves intense localized stresses tending to cause dislocation of minerals and break – up of rocks.
Examples of Metamorphic Rocks:
1. Marble – recrystallized carbonate rocks
2. Slate – are fine-grained to aphanitic metamorphic rock containing coarser fraction of quartz, feldspar, chlorite, etc.
3. Schist – are products of regional metamorphism and strongly schistose containing chlorite, hornblende, muscovite and talc.
4. Argillites – are firmly indurated and show some recrystallization and appear as low grade metamorphosed shale, mudstone and claystone.
5. Gneiss – are moderately coarse grained irregularly banded rock of diverse origin containing quartz and feldspar.
6. Quartzite
7. Amphibolites
Definition of Terms
Bedrock – a formation at some depth beneath a mantle of soil and is formed from the crust of the earth. It is dry, solid rock exposed to the
surface of the earth or overlain by unconsolidated materials
Homogeneous Rock- is one in w/c the physical proper-ties of all of its parts or elements are the same.
Heterogeneity – is a characteristic of a material which have unlike unlike qualities.
Competent Rock – is one w/c is sufficiently strong to transmit a compressive force under given conditions.
Competent Ground – is one that does not require support when a tunnel is excavated through it.
Friable – the tendency to crumble.
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Intact Rock- a rock material w/c can be sampled and tested in the laboratory & w/c is free of larger scale structural fractures such as
joints, bedding planes, partings, and shear zones.
Matte (regolith)- is a loose fragments of rock and soil that act as a cover for bedrock. Soil above bedrock are called “Overburden”.
Rock Mass – is the in-situ rocks made up of the rock substance plus structural discontinuities.
Isotropic- is one that has the same physical, viz elastic properties in every direction at any point.
Anisotropic – is one w/ certain of its properties varies with direction at any point
Consolidation – is the process by which loose, soft or liquid earth become coherent and firm. It is an adjustment of a saturated soil in
response to increased load, involves squeezing of water from the pores & a decrease in void ratio.
Sediments – the products of the breakdown of rocks & loose materials. They may be transported by an agent of erosion such as running
water in stream.
- as a mass of organic and inorganic and solid fragmented material, or the solid fragment itself that comes from weathering of rock
and is carried by, suspended in, or dropped by air, water, or ice, or a mass that is accumulated by any other natural agent and that
forms in layers on the earth’s surface such as sand, gravel, silt, mud, fill or loess.
- a solid material that is not in solution and either is distributed through the liquid or has settled out of the liquid.
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Mountain – are part of the earth’s crust higher than a hill, sufficiently elevated above the surrounding land surface with more than 300
m (1,000ft) elevation.
Hill – are land surface rising rather predominantly above the surrounding area, generally considered less than 300 m (1,000 ft) from
the base to the summit.
Plateau – areas elevated or high standing rocks that are essentially horizontal, can be steeply dissected by erosional forces into rugged
mountain like landscape.
Valley – low-lying land bounded by higher ground, usually traversed by a stream or river which receives the drainage of the
surrounding heights.
PROPERTIES OF ROCKS
Rock is a natural substance. It has structural features which are not encountered in most engineering material. Its performance under action of
load, water, temperature and tectonics of earths crust depends upon the following properties:
1) physical
5) elastic
2) mechanical
6) plastic
3) electrical
7) strength
4) thermal
A. PHYSICAL PROPERTIES OF ROCKS
1. Mineralogical Composition, Structure & Texture
2. Specific Gravity
3. Unit Weight
4. Porosity
5. Void Ratio
6. Natural Moisture Content
7. Saturation Moisture Content
8. Degree of Saturation
9. Permeability to Water
10. Chemical Effects
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Mineral Composition – a property controlling the strength of rock comprising the element present mostly rock forming-minerals such
as quartz, feldspar, micas, hornblende, augite, olivine, calcite, kaolinite, dolomite. Rocks containing quartz as binder are the strongest
followed by calcite & ferrous minerals as the cementing agent “Glue”. Rock with clayey binder are the weakest.
Structure – applies to well-pronounced macroscopic features of the rock such as position, arrangement, attitude of a system of joints,
fractures, folds, faults, etc.
Texture – refers to arrangement of its grains or particles on a freshly exposed rock surface easily seen by the naked eye.
Specific Gravity, G – ratio of the weight of material to the weight of an equal volume of water. In other words, G is a number
expressing how many times a material is heavier or lighter than an equal amount of volume of water as expressed in
G=
Wd
.
W sat in air – Ww –W sat in water
weight of rock (soil) particles in g
G=
(volume of soil particles (1.00)
Unit Weight
The unit weight, Y of soil and rock above the groundwater table is expressed as the ratio of the total weight of the rock (soil) in air,
W to the total volume V of the rock, all voids included:
Y = W/V
Rocks containing heavy mineral have higher unit weight than rocks with lighter minerals. Usually, igneous and metamorphic rocks
have greater unit weight than sedimentary rocks. The more porous the rock is, the less is its unit weight.
Porosity of Rock
Voids, (pores and fractures) in rock are very important forms of non-uniformity of structures and texture in rocks. Pores are
interconnected voids having connection to the air. Voids or pores in rocks affects negatively its mechanical – viz., strength – properties. A small
amount of porosity in the form of cracks has a large effect upon the deformation of rocks. Porosity, N is the amount of voids based on the total
volume V in rock:
%Porosity=Vv/Vt *100
N = Vs/V = e/1+e = V –(Ws/Gyw
V
where :
Vv = volume of voids
e = n/1-n = void ratio
Ws= dry weight of rock solids
G = specific gravity of soil or rock
Yw = unit weight in water, and
V = Vs + Vv = Vs +Va + Vw
Vs = volume of solids in the rock specimen
Va = volume of air or gas in the rock specimen
Vw = volume of water in the rock specimen
Void Ratio
Is the ratio of the volume of voids, Vv to the volume of solids, Vs of the rock expressed in decimal fractions. It is a dimensionless number which
simply shows how many times there are more voids than solids in the rock:
e = Vv = n
Vs
1-n
The volume of solids, Vs can be calculated as:
Vs = Ws
G.Yw
Water in Rock
Fractures and other rock defects are the easiest passages of ingress for groundwater in the rock.
Moisture Content, w
Is the weight of water Ww present in a rock expressed in percentage by oven-dry weight of the rock:
w = Ww x 100 =
W-Ws x 100
Ws
Ws
Degree of Saturation, S
S = Vw = w
Vv
wsat
Permeability
is the property of porous material that permits the passage or seepages of fluids, such as water and/or gas, through its
interconnecting voids.
Chemical Action
The chemical action of rainwater which enters the rock from the surface is referred to as the chemical weathering.
B. Chemical Properties
Mineral are composed of different chemical element that combined together solidification and deposition beneath the earth’s crust.
C. Electrical Properties
Most rocks are dielectric, hence, subject to dielectric constant measurement. This and other electrical properties depend upon the
type of rocks, its structure and texture, porosity, and moisture content. The resistivity of rocks varies from 10-2 to 1016 ohm-cm.
D. Thermal Properties
Thermal properties of rocks has its purpose in engineering design:
- heat & temperature are of special interest in engineering in the design and construction of tunnels & other kinds of U/G openings
(vertical shafts, power plants, shelters, storage spaces, and mines);
- an increase in temperature lowers rock strength & increases ductility;
- knowledge on the thermal conditions in rock & geothermal
gradient has technical and economic importance such as:
1. observing health condition & heat endurance limits to workmen;
2. design efficient U/G ventilation & air-conditioning system;
3. choosing an ideal method of construction;
4. design the soil/rock artificial freezing and thawing facilities.
E. Mechanical Properties
Mechanical properties of rocks depends on:
- nature of the rock substance;
- stratigraphy of the rocks in situ;
- rock defects;
- testing methodology.
Different Mechanical Properties of Rocks:
1. Hardness
2. Durability
3. Permeability to water
4. Elasticity
5. Plasticity
6. Deformability
7. Strength
1. Hardness - is the resistance to abrasion.
2. Durability – depends upon the nature of the rock environment- such as the climate and atmosphere for example- and the amount
of exposure of rock or building stone in the structure. Also, the rate of solution action on limestone, dolomite, and cement grout;
resistance of rock to frost action; rate of weathering; and porosity of rocks maybe correlated with durability.
3. Elasticity – Every solid material deforms under the action of a load, viz., stress. To every kind of stress there is a corresponding
strain. If the stress is not too large, the strained ideal material will recover its unique, natural state, the original shape and size to
which the material returns when the external loads are removed. If the material recovers completely is called perfectly elastic.
4. Plasticity – the character of a rock that changes shape in any direction without rupture under a stress. It is characterized by the
existence of a yield point beyond which permanent strains appear. In other words, the plastic deformation of a material is the
permanent deformation after complete unloading of materials.
5. Deformation - is the character of rock that changes from its original form or volume or rock specimen; or change by externally
applied loads or in-situ rocks or by tectonic forces (compressive and/or shear stress).
6. Strength Properties of Rocks
- ability of a material to resist externally applied loads;
as applied to rock “strength” can be defined when all the strength governing factors such as rock environment; size of rock
specimen; kind of intensity and duration of load; all-around lateral confining pressure; temperature, pore water pressure; and the
failure criteria are known;
- Rock strength is governed by the following factors:
1. fabric and texture
2. mineralogy
3. water content
4. depth of original
it is also governed by the qualitative and quantitative mineral composition of the rock.
7. Permeability to Water
STRESS AND STRAIN
Stress – the force applied to a plane divided by the area of the plane and it causes rocks to deform.
Strain – the result of stress applied to a body, causing deformation of its shape and/or a change of volume.
Types of Stresses
1. Compressive Stress (which results in shortening or flattening) – it is the stress generated by forces directed toward one
another on opposite sides of a real or imaginary plane.
2. Tensile Stress (which results in stretching and elongation) – it is the stress generated by forces directed away from one
another or opposite sides of a real or imaginary plane.
3. Shear Stress (which results in a sort of smearing) – it is the stress (force per unit area) that acts parallel to a (fault)
plane and tends to cause the rocks on either side of the plane to slide by one another.
Tensile Strength in Rocks
- is considered to be the maximum stress developed by a given specimen of a material in a tension test performed to rupture under
specified condition;
- in rock mechanics, knowledge on tensile strength of rocks is important in analyzing rock strength and stability of roofs and domes
of U/G openings in the tensile zones of rocks, in mining of minerals, in preparing rock drilling and blasting programs and other
endeavors in rock engineering.
Shear Strength in Rocks
Is the maximum resistance, S to deformation by continuous shear displacement upon the action of shear (tangential stress).
Shear strength in rocks is needed due to:
- stability problem in U/G opening;
- assessment of the degree of stabilization in rock slopes;
- evaluation of stability of a structure against sliding on its base laid on rocks.
Compressive Strength
Is a function of the following:
- specimen size
- confining pressure
- shape
- rate of loading
- porosity in rocks
- moisture content
- surface quality of bearing platens rock specimen end surfaces;
As the confining pressure, is increased , the strength of the rock increases; also, the amount of the permanent set, or
irreversible deformation before fractures increases. Compressive strength of rock also decreases with increase in rock
porosity, viz., volume of voids. This is so because at the location of voids there is a lack of bond contact between rock
particles.
Rock Laboratory Strength Tests
1. Unconfined Compressive Test
- Universal Testing Machine
- Portable Point Load Tester
2. Shear Strength
- Portable Shear Box
3. Tension Strength Test
- Brazilian Test
ROCK AS A CONSTRUCTION MATERIALS
Rocks are not only used as foundation materials, sources of jewelries/luxuries, raw materials for manufacturing, etc. but also in construction
industry.
Rocks are used in construction industry particularly for the following:
a. aggregates for concrete mix
b. facing for building
c. protective blanketing of earth dams
e. filling/backfilling for reclamation
These rocks are taken from quarries where rock is separated from its natural beds and processed for construction. Their products are
Dimension Stone, Crushed Stone and Broken Stone.
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Dimension Stone – are blocks with more or less even surfaces of specified shape and size. But today this stone are rapidly being
replaces in building construction by reinforced concrete and baked-clay products and therefore are generally use only for facing of
expensive building (granite, limestone).
•
Crushed Stone – are broken stone that undergone crushing stage into a specified sizes and coming from limestone, granite, basalt,
sandstone and quartzite.
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Broken Stone or Boulders – used as riprap serving as protective layer on the upstream face of the earth embarkment to protect it
from wave action and general erosion by water.
Factors to Consider for Selection of Rock as an Ideal Construction Materials:
1. Quality – rocks for dimension stone must be free from cracks, uniform texture and posses attractive colors. Rocks for crushed stone
and riprap must have satisfactory strength, soundness, and low water absorption, roughly squared, flat faced, has specific gravity of
2.6 and higher as the rock and must be heavy enough to resist displacement by wave action, ice pressure and thrust of drifting
objects. Also to be considered are geological character such as : origin/source, composition, weathering grades, degree of fracturing
and durability
2. Supply – it must be sufficient for about 20 years of initial expenses and amortization costs are to be justified. It must also consider
type of rock, volume and degree of fragmentation (quarry rock).
3.
Economic – it must consider the location of the quarry to the delivery point, availability of labor and wage status, drainage
condition, and stripping costs (removal of clay, sand, gravel and unsuitable rock from the surface), price and competitor suppliers.