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‫تحليل التضاريس‬
Terrain analysis
Reference
• Terrain analysis
– by
Douglas S. Way
Definition
• Processes of interpreting a
geomorphological area
• To determine the effect of natural and man
made features on engineering application
• Set of activities which leads to the
classification compilation of terrain
characteristics
Landforms
• Land units have resulted from
• Constructional geological processes
• Destructional geological processes
• Have range of physical characteristics
Factors on landform formations
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Age
Climate
Weathering
Erosion
Physical site factors
• These factors are identified from aerial
photographs
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Topographic relief
Drainage pattern
Photographic color and tone
Erosin gully analysis
Land use and vegetation cover
Objective of terrain analysis
• By using physical site factors to obtain the
following
• Geology
» Rock type
» structures (fracture, fault )
• Soil
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Type
Moisture
Depth to bed rock
Depth to water table
Suitability of terrain analysis
• To draw boundaries between different
rocks and soil units
• To identify the types of landform
• To evaluate the engineering properties of
landforms and its suitability as:
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Constructional material
Foundations
Ground water supply
Excavation
Building stones
Terrain analysis ability
• Cover large area
• Help to identify and locate weak areas
Type of landform
Major features
- plains
- Depressions - Plateaus
Minor features
Hills
Mesas
Slopes
Butte
Alluvial fans
Canyon
Valleys
Piedmont
Ridge
- Mountains
Technical terms
- Physiography : genesis and evolution
- Geomorphology : form of earth, configuration of
surface and change in evolution of landforms
- Topography : landform in cross-section
Climate
• Characteristics
– Temperature
– Humidity
– Rainfall
– Frequency of climate change
Arctic climate
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Rain is < 10” / year
Cold and dry
No plants ( little moisture )
Summer temperature is 4 C°
Winter temperature is -28 to -34 C°
Type of weathering : frost wedging
Humid climate
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Rain < 40” to 80” / yr
Summer temp. is 10 to 27 C°
Winter temp. is 6 to 16 C°
Evaporation is less than rainfall
Type of weathering : mechanical and chemical in addition to
frost wedging
Soil develop deep profiles
Silica rich with high organic content soil
Tropical climate
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Rain < 60” to 80” / yr
Warm and cold
Temperature is 21 – 32 C°
No big difference between winter and
summer
Type of weathering : chemical is more dominant than
mechanical
( high rain )
Soil with high concentration of aluminum and iron oxides
Arid climate
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Rain < 20 “ / yr
Warm and cold
Summer temperature is 16 to 42 C
Winter temp. is 6 to 32 C
Evaporation exceeds rainfall
Type of weathering : mechanical and chemical but present at slow rate
(low rainfall )
poly mineral rocks( granite ) weather more rapidly than mono mineral
rocks (limestone)
limestone and sandstone form upland cliffs and cap rocks while granite
and metamorphic rocks occupy the more weathered lowlands
Soil free from organic and more susceptible to wind erosion
Weathering
• Act at the surface
• Decomposition and disintegration of rocks
• Two form of weathering : mechanical and
chemical
Factors influenced weathering
• Rock hardness
– Mineral type
– Cement ( iron oxide )
• Chemical composition
– Differential expansion of colored minerals
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Rock jointing
Climate
Topography
permeability
Mechanical weathering
)disintegration)
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By physical compression or splitting forces
Broken rock of smaller pieces
No mineral alteration
Coarse and angular in general
Pressure release
• Overburden material is removed
• Rock is exposed to surface by erosion or
uplifting
• Develop fractures and cracks allow water ,
acids, ice, and roots to penetrate the rock
and further disintegrate rock
Crystal growth
• Growth of ice or salt crystals in cracks and
pores of rock
• Water freezes, volume expands, exert a
pressure ( 2100 tones/ft² )
• This force when repeated is shatter the
rocks
• Water evaporate and salt crystal form in
fractures
Thermal expansion contraction
• By rapid heating and cooling in arid region
• exfoliation
Root action
• Vegetation growth cause splitting forces in
rocks
• Penetrate smallest cracks and cause
water to enter
Chemical weathering
( decomposition )
Rocks and minerals are broken down into very smaller units,
alteration . Chemical compounds tend to break down into
simpler and more stable one
 Greatest effect in warm and high humidity area
 New minerals, more stable and suited to the lower
temperature and pressures in the earth surface are found
 Agents are water, oxygen carbon dioxides and organic
acids
Chemical activities
1- Oxidation
Reaction with O2 to form greater volume and lower density. Red
or brown stains is formed. This can take place in rocks
which contain iron with the presence of water. The resulting
ferric compounds contain more oxygen than original
compounds . Slight oxidation produce the mineral hematite
(Fe2O3)
2- Carbonation
It is formed by the reaction between carbonic acid and calcite to
form calcium and bicarbonate ions in solution.
H2O  CO2  H2CO3
H2CO3  CaCO3  Ca    2HCO-3
* calcium bicarbonate is about 30 times more soluble than
calcium carbonate
3- Desilication
The reaction of carbonic acid with silicate compounds, the
reaction of this acid with feldspar mineral release clay
minerals, silica in solution
* So feldspar weathers by this activities
2KAlSi2O3  H2CO3  H2O  kaolinite Al2Si2O5 OH4  K2CO3  4SiO2
4- Hydration
The combination of rock minerals and water molecules which
cause volume expansion (about twice the original volume)
* Anhydrite + water
Gypsum
Susceptibility of rock to weathering
• Different type of rocks show various mode
of weathering
• Igneous susceptible to chemical
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originate deep in the earth, not in
harmony with surface
sedimentary
• Consist of fragment previously weathered
• Relative weathering resistance depend on
cementing agent
• Rocks are cemented by silica dominate
their surrounding material
Metamorphic rock
• Degree of resistance depend on
– Degree of metamorphism
– Original rock type
– structure
Erosion
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Transportation of weathered material
Down slope by mass wasting
By fluvial
By eolian processes
*The entire drainage pattern the gullies (channelized flow), the
tributaries, and the major channels.
*high altitude photographs
image scale
1:60000
*the different patterns can indicate:
- Rock types
- soil
- rock attitude
- structure
Drainage Pattern Types
- Dendritic (most common)
- treelike branching
- tributaries join the gently curving main stream at acute
angles
- homogeneous soil and rock and uniform material
- landforms of soft sedimentary rocks, volcanic tuff,
dissected glacial till and dissected coastal plains
Angular:
is a variation of dendritic or trellis systems
The faults, fractures or jointing systems have modified the
classic form. Sharp, angular bends in the mainstream
* Tributaries control by rock features.
* The direction of angulations indicate the rock type
- sandstone develops
jointing patterns
- limestone cleavage
joints that intercept at acute angles
Rectangular:
patterns are variation of a dendritic system
- tributaries join the main stream at right angle and form
rectangular shapes
- controlled by bed rock jointing, foliations or fracturing
- stronger pattern, the thinner the soil cover
- forms in slate, schist
- form in gneiss, in resistive sandstone in arid climates
Parallel
Systems develop on homogeneous, gentle, uniformly sloping
surface and main stream may indicate a fault or fracture
- Tributaries join stream at right angle
- Landform of young coastal plains
- Large basalt flows
Karst
With surface and subsurface drainage network
- Result from solution weathering of limestone
- Few streams ends in sinkholes
- Scattered sinkholes depressions
- Some gullies lead into sinkholes
Trellis
Is modified dendritic forms with parallel tributaries and short
parallel gullies occurring at right angles.
- Indicate structure not rock type
- tilted, interbedded, sedimentary rocks in which the main
parallel channels follow the strike of the beds
Radial:
Is a circular network of almost parallel channel flowing a way
from a central high
- A major stream is found in point the bottom of
topographic features
- volcanoes
- isolated hills
- domelike landforms
Annular:
Develops on topography forms similar to those associated with
radial patters, but joints control the parallel tributary
- Sedimentary domes
- Granite domes
Braided
is found in alluvial plains in arid regions
- coarse soil
Centripetal
is variation of radial
- drainage directed downward toward a central point
- In basin or sinkhole
- eroded anticline or syncline
Pinnate
Is modified dendritic patterns
- indicate a high silt content soil
- found in loess
- fine tex. Flood plains
Subdendritic
Is complex combination of rectangular and parallel dendritic
- Indicated different condition, rock type
Internal
Is not have of an integrated drainage
* granular material, high permeability
* porous rock materials
* in alluvium areas
* beach ridges
* sand dunes
Deranged
In nonintegrated drainage
* flat or undulating surface
* high water table
* swamps depressions, or lakes
* in flood plains, till plains
Intrusive rocks
Landforms
- Batholith
* 40mi2(60km2)area
* dome shaped
* Irregular massave domed roof
* enlarges downward
- Stocks
* loss then 40mi2
* similar to batholiths
- Laccolith
* leans shaped
* concordant with surrounding rock structure & cause uplift
- Sills
* similar to the laccolith except no uplift
* Dikes enter a crack between rock
Intrusive rocks
Tone: light gray in acidic rocks dark gray in basic rocks
Drainage: Dendritic patterns
Soil: thin layer of residual soil (2feet thick) SM with ML
Trenching: Excavation of material for pipelines is expensive to
dig 6 feet deep trench
Intrusive rock
Construction material:
sand is mixed with silt and clay “not suitable”
Aggregate is not recommended for use in concrete
Building stone is suitable, “excellent building stone”
Land slides:
may occur due to fracturing and water
Ground water supply:
not sufficient as water supply
Dam construction:
Good areas for dam
Foundation: high load bearing capacities
Sedimentary rock
The sediments originates from
* Remnants of decomposes or disintegrated igneous
metamorphic or sedimentary rocks (clastic rocks such as
conglomerate, sandstone, shale)
* Derived from chemical reactions (Limestone and gypsum)
* Derived from organic sources like coral
Characteristics of Sed. Rocks
* Diversity of their physical and engineering properties
(strength, porosity, permeability)
* Numerous type of structures
- Bedding
- interbeding of different rocks flat, tilted
- Solution cavities
- Anticline / syncline
- Uplifting: cause drying and further jointing perpendicular
to the bedding
Sandstone
Sandstone consolidated sand grains (silica or orthoclase)
* form: flat table rock of equal elevation due to its bedding
: Rugged topography due to its relative resistance to
weathering
Interpretation of pattern elements
Tone: light, banded
Drainage: angular or rectangular
Soil: GM (silty gravel)
GC (clayey gravel)
SM (silty sand)
SC (clayey sand)
Sandstone
Trenching: may require blasting seepage may occur
Construction material:
Sand good source from sand dunes
Agg. From fair to excellent
Building stone strong sandstone is good and important
source of stone
Ground water: very good aquifer
Dam: seepage problem
Foundation: Mostly high load bearing capacities
Limestone
Limestone is formed by processes as:
1- organic deposition (diatoms, coral)
2- chemical precipitation ‫ ترسيب‬contains impurities such as sand,
silt or clay
3- chemical reactions (Dolomite, replacement of Ca++ by Mg++)
Weathering properties
1- weather by chemical process as carbonation
2- water dissolves limestone through joints and forms channels
and solution cavities
3- form depression
4-form table rocks with vertical faces ‫نجد سهل واسع مرتفع‬
5-coral form jagged cliff ‫حرف ما وخشن ومسنن‬
Limestone
Tone: light gray uniform banded
Drainage: Angler
sail: GM , ml
GC , CL
Trenching: may require blasting coral
power equipment
Construction:
Material: sand not suitable
Agg. Good (limestone)
poor (coral)
Building good
stone
facing stone very good-excellent
Ground Water: cam be found but very hard
Dam: seepage
due to channel-cavities
channel-cavities
Slate: foliated meta. rock formed by heat and pressure on shale
* has parallel foliation planes (slaty cleavage)
* low grade of met am orphism
* weathers very quickly by mechanical means
* develops rugged topography with sharp ridges
Slate
Tone: uniform light gray
Drainage: Rectangular
Soil: CM , silty clays
Trenching: Easy with equipment
Sand: not suitable
Aggregate: not suitable
Facing stone: not suitable
Ground water: maybe available
Dam construction: not suitable
Foundation: shallow fourdatim
Schist
Tone: light faint parallel banding
Drainage: rectangular – angular
Soil: ML,CL
Trenching: easy with power equipment
Sand: not suitable
Aggregate: not suitable
Building stone: not suitable
Facing stone: good
Ground water: suitable in weathered and fractured
Dam seepage along fracture
Foundation: should take care due to clay and schistosity
Gneiss
Tone: Uniform light gray
Drainage: rectangular – angular
Soil: SM silty sand
clayey sand (SC),ML
MH,CL and CH
Trenching: heavy equipment and blasting
Sand: not suitable
Aggregate: good to fair
Facing stone: good to poor
Ground water: may occur in fractured
Dam: suitable
Foundation: excellent foundation material
- Terrain evaluation is study of large area and used in
- planning
- site investigation
- Objective
- classification of the area into terrain class
- Engineering terrain class can be studied
- similar eng. Properties can be assumed for similar class
- Type of classification
PUCE Pattern Unit Component Evaluation
Basis of the PUCE
- topography
- underlying rock and structure
- soil and vegetation cover
PUCE operates of 4 levels as:
1- Provinces
2- Terrain Pattern
3- Terrain unit
4- Terrain component
Terrain pattern
Terrain unit (1:25000 or larger)
Terrain component (1:2500 or larger)
Terrain provinces
1:250000
Terrain pattern
Patterns and units are described using,
* Aerial photography Interpretation
* Field validation
Process of terrain analysis
1- To classify terrain on the basis of similarity or homogeneity of
certais properties, attributes
2- To assess (qualitative) or evaluate (qualitative) like area for
the properties of the terrain that are significant for the
desired purpose
PUCE class is composed repetitive association ‫ إتحاد تكراري‬of
members of the next class in the hierarchy ‫تسلسل هرمي‬
a) aprovince consist of association of terrain pattern
b) a terrain pattern consist of association of terrain units
c) a terrain units consists of a repetitive association of terrain
component
The pattern and unites are describe using the following criteria:
a) Slope categories
Flat, gently undulating area
b) Soil categories
Shallow soil, sand, uniform soil, organic soil
c) Vegetation categories
Grassland, open wood land, forest area
d) Land use categories
Forestry, unused area, recreation, urban development
Terrain classes
A province
- rock with uniform age
- determined from geology map of scale 1:250000
- Association of terrain patterns
A terrain pattern
- uniform landscape
- Recurring ‫ متكرر‬topography soil associations, natural veg
amplitude
- characteristics drainage pattern
- uniform drainage density
A terrain unit (area)
- consist of a single land form
- characteristic soil and vegetation formation
A terrain component
- A part from a topography
- Uniform underlying litho logy and a uniform structure
- a consistent association of are class in the USC system
- a characteristic vegetation association
Class ification nomenclature ‫مصطلح رمز‬
The nomenclature used in PUCE system is numerical
a) Terrain components are allocated ‫ مقسمه‬eigh digits
b) Terrain units are allocated four digits
c) Terrain pattern are allocated three digits
d) Province are five digits
Province (35.003)
35 carboniferous system
.003 third recognized ‫ تعرف‬province of carb. age
Terrain pattern 25/2
2 relicf amplitude to 75 m
5 Drainage density
/2 second recogrize ‫ تعرف‬pattern in the province
Terrain unit 1.4.36
1.4 strongly undulating surface
.3 clay soil
6 forest
Terrain component 44203101
4 slope major axis cor
4 slope major axis to 10º
2 slope major axis to 2º
03 soil profile
1 land use – forestry
01 vegetation