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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 • • • • Age Climate Weathering Erosion Physical site factors • These factors are identified from aerial photographs • • • • • 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 » » » » 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: • • • • • 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 • • • • • 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 • • • • 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 • • • • 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 • • • • • 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 • • • • Rock jointing Climate Topography permeability Mechanical weathering )disintegration) • • • • 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 2KAlSi2O3 H2CO3 H2O kaolinite Al2Si2O5 OH4 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 • 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 • • • • 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