تحليل التضاريس Terrain analysis

1. تحليل التضاريسTerrain analysis

2. Reference • Terrain analysis • by Douglas S. Way

4. 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

5. Landforms • Land units have resulted from • Constructional geological processes • Destructional geological processes • Have range of physical characteristics

6. Factors on landform formations • Age • Climate • Weathering • Erosion

7. 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

8. 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

9. 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

10. Terrain analysis ability • Cover large area • Help to identify and locate weak areas

11. Type of landform Major features - plains - Depressions - Plateaus - Mountains Minor features

12. Technical terms - Physiography : genesis and evolution - Geomorphology : form of earth, configuration of surface and change in evolution of landforms - Topography : landform in cross-section

21. Climate • Characteristics • Temperature • Humidity • Rainfall • Frequency of climate change

22. 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

23. 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

24. 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

25. 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

26. Weathering • Act at the surface • Decomposition and disintegration of rocks • Two form of weathering : mechanical and chemical

27. Factors influenced weathering • Rock hardness • Mineral type • Cement ( iron oxide ) • Chemical composition • Differential expansion of colored minerals • Rock jointing • Climate • Topography • permeability

28. Mechanical weatheringdisintegration) ) • By physical compression or splitting forces • Broken rock of smaller pieces • No mineral alteration • Coarse and angular in general

29. 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

30. 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

31. Thermal expansion contraction • By rapid heating and cooling in arid region • exfoliation

32. Root action • Vegetation growth cause splitting forces in rocks • Penetrate smallest cracks and cause water to enter

37. 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

38. 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)

39. 2- Carbonation It is formed by the reaction between carbonic acid and calcite to form calcium and bicarbonate ions in solution. * calcium bicarbonate is about 30 times more soluble than calcium carbonate

40. 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

41. 4- Hydration The combination of rock minerals and water molecules which cause volume expansion (about twice the original volume) * Anhydrite + water Gypsum

42. 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

43. sedimentary • Consist of fragment previously weathered • Relative weathering resistance depend on cementing agent • Rocks are cemented by silica dominate their surrounding material

44. Metamorphic rock • Degree of resistance depend on • Degree of metamorphism • Original rock type • structure

45. Erosion • Transportation of weathered material • Down slope by mass wasting • By fluvial • By eolian processes

48. 1:60000 image scale *The entire drainage pattern the gullies (channelized flow), the tributaries, and the major channels. *high altitude photographs *the different patterns can indicate: - Rock types - soil - rock attitude - structure