FACULTY : CIVIL & ENVIRONMENTAL ENGINEERING DEPARTMENT : GEOTECHNICAL & TRANSPORTATION ENGINEERING LABORATORY : ENGINEERING GEOLOGY & GEOPHYSIC LABORATORY TOPIC : PLOTTING POLES AND CONTOURING OF STRUCTURAL GEOLOGY DATA ( LAB 4a )
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1/9 LAB 4a
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1.0 OBJECTIVE To plot poles and carry out contouring of the structural geology data.
2.0 LEARNING OUTCOMES a) b) c) d)
Students should able to use the geological compass. Students should able to measures the dip and dip direction of any planes. Students should able to plot poles of the structural geology data. Students should able to plot contour from the structural geology data.
3.0 THEORY Analysis of the orientation of structural geology data involves; • Plotting poles representing the dip and dip direction of each discontinuity. This plot will help to identify discontinuity sets, for which both the average orientation and the scatter (dispersion) can be calculated. • The second step in the analysis is to plot great circles representing the average orientation of each set, major discontinuities such as faults, and the dip and dip direction of the cut face.
4.0
EQUIPMENT AND MATERIALS
•Equal-area for plotting poles and great circles (Appendix C) •Equal-area polar net (Appendix D) •Kalsbeek counting net (Appendix E) • Tracing paper • Pencil 5.0
PROCEDURE
• Poles can be plotted on the polar stereonet on which the dip direction is indicated on the periphery of the circle, and the dip is measured along radial lines with zero degrees at the center. • The procedure for plotting poles is to lay a sheet of tracing paper on the printed polar net and mark the north direction and each quadrant position around the edge of the outer circle. A mark is then made to show the pole that represents the orientation of each discontinuity as defined by its dip and dip direction. Poles for shallow dipping discontinuities lie close to the center of the circle, and poles of steeply dipping discontinuities lie close to the periphery of the circle. • Concentrations of pole orientations can be identified using Kalsbeek counting net. The Kalsbeek net is made up of mutually overlapping hexagons, each with an area of 1/100 of the full area of the stereonet. • Contouring is performed by overlaying the counting net on the pole and counting the number of poles in each hexagon; this number is marked on the net. These numbers of poles are converted into percentages by dividing each by the total number of poles and multiplying by 100. Once a percentage is written in each hexagon, contours can be developed by interpolation.
FACULTY : CIVIL & ENVIRONMENTAL ENGINEERING DEPARTMENT : GEOTECHNICAL & TRANSPORTATION ENGINEERING
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TOPIC : PLOTTING POLES AND CONTOURING OF STRUCTURAL GEOLOGY DATA (LAB 4a)
AMENDMENT DATE:
2/9 LAB 4a
6.0 RESULT AND ANALYSIS • Discontinuities pattern. • Equal-area equatorial net for plotting poles and great circles.
7.0
QUESTION AND DISCUSSION
(1) Give two (2) methods to draw the structural geology data and discuss based on what situation we choose that method (each method).
a) Cross Section Techniques This kind of technique is generated from geological maps and can be seen as vertical slices through a map area showing a profile view of subsurface structure. Cross-sections are either trial sections, drawn to solve structural problems, or are drawn to supplement a fair copy map or illustrate a report. They are also drawn to site boreholes in the search for a lost aquifer or ore body. The geological cross sections drawing are not a small or trivial undertaking and methods for their generation have become sophisticated. This is because we are trying to make interpretations about the geometry of features (e.g. bedding, faults) at depth on the basis of surface geometries. Some aid in this regards may exist in the form of borehole or geophysical data. However, this is often the exception and skills should be tuned for cross section construction without such subsurface information.
30°
A cross section of the map
Dip and strike of a bedding plane
FACULTY : CIVIL & ENVIRONMENTAL ENGINEERING DEPARTMENT : GEOTECHNICAL & TRANSPORTATION ENGINEERING LABORATORY : ENGINEERING GEOLOGY & GEOPHYSIC LABORATORY TOPIC : PLOTTING POLES AND CONTOURING OF STRUCTURAL GEOLOGY DATA (LAB 4a)
b)
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3/9 LAB 4a
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Streonet Techniques In this technique, all circles on the sphere plot as circles on the plane, making it easier to construct the projection. The projection is conformal, meaning that angles and small shapes on the sphere project are true on the plane. Each projection represents the important data in the map so the contour can be made. Small regions on the sphere project true on the plane, making the stereographic a good map projection for small areas, but radial distortion increases away from the tangency point.
FACULTY : CIVIL & ENVIRONMENTAL ENGINEERING DEPARTMENT : GEOTECHNICAL & ENGINEERING FACULTY : CIVIL & ENVIRONMENTAL TRANSPORTATION DEPARTMENT : GEOTECHNICAL & ENGINEERING LABORATORY : TRANSPORTATION ENGINEERING GEOLOGY & ENGINEERING GEOPHYSIC LABORATORY LABORATORY : ENGINEERING GEOLOGY & TOPIC : PLOTTING POLES AND CONTOURING OF GEOPHYSIC LABORATORY STRUCTURAL GEOLOGY DATA (LAB 4a) TOPIC : PLOTTING POLES AND CONTOURING OF STRUCTURAL GEOLOGY DATA (LAB 4a)
(2) (3)
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5/9 LAB 4/9 4a LAB 4a
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Explain of geological structure the plotted in the stereonet with the aid of diagram. Explain the the type methodology to determine discontinuities survey data. According to the that has been plotted in thisorexperiment by thea stereonet, cancan determine Discontinuities cangeological be definedstructure as any form of mechanical breaks fractures within rock mass we which cause
the earth geographysuch asfracture the hill,planes mountain and manyzero other that representthe bydiscontinuities the contour. There are several tensile strength across the to approach orearth even surface lower. To determine survey data, we datas that required in data this experiment such as the dip directions andtodip angleshe in discontinuities. the geological map. It cansuch be plotted on need to collect some and assuming some parameters in order measure To collect data, the polar stereonet which dip direction dip degree is being used. In this experiment, have method 120 datas to be plotted. Using best tool is the geological compass.and Collecting datas by using geological compass is we a better because it can save a the tracing paper,using we have onmuch it which requires focustoon work orThere else the willkind be lot of time while other plotted method120 that dotes wasting timeison calculation findthe theplotting data needed. are result another slightly unaccurate base onthe thediscontinuities datas. After the datascalled were plotted, are groups plotted dotes After of method to determine which Scanlinethere Survey. Before ofconducting thisthen job, calculated. there is some that, anotherpreparation tracing paper was we used plot theprocedure contour. By using this kind of plotting contour the is slope stability and preliminary before doto the right smoothly. The discontinuities surveymethod, data sheet prepared which the failure of slope can data be determined. The of slope whether planar, wedge, circular or toppling. is containing all of the that we need to failure measure on theissite.
FACULTY : CIVIL & ENVIRONMENTAL ENGINEERING DEPARTMENT : GEOTECHNICAL & TRANSPORTATION ENGINEERING LABORATORY : ENGINEERING GEOLOGY & GEOPHYSIC LABORATORY TOPIC : PLOTTING POLES AND CONTOURING OF STRUCTURAL GEOLOGY DATA (LAB 4a)
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6/9 LAB 4a
EFECTIVE DATE : AMENDMENT DATE:
8.0 CONCLUSION This experiment is about plotting poles and contouring of structural geology data. From this experiment, the students should able to measures the dip and dip direction of any planes, plotting poles of structural geological data, and able to plot contour from the structural geology data. In this experiment, we are using equal-area for plotting poles and great circles, equal-area polar net, kalsbeek counting net, tracing paper and pencil to come to the experiment objectives. From this experiment that we have done in geology lab, we should know how to plot poles and carry out contouring of the structural geology data now. Poles can be plotted on the polar stereonet on which the dip direction is indicated on the periphery of the circle and the dip is measured along racial lines wih zero degrees at the center. It should be noted that the stereonet is the lower hemisphere plot in which the direction scale starts at the bottom of the circle and increase following the clockwise directionwith the north arrow corresponding to the dip diection of 180°. There is reason why do we set the scale in this way is that if the field reading as measured with structural compass are plotted directly on the stereonet, the poles are correctly plotted on the lower hemisphere plot. Then all the datas are being used to make the projection and form the contour on the tracing paper using all the requirements that we have. The procedure for plotting is lay a sheet of tracing paper on the printed polar net and mark the north direction and each quadrant position around the edge of the outer circle. A mark is then made to show the pole that represents the orientation of each discontinuity as defined by its dip and dip direction. Poles for shallow dipping discontinuities lie close to the center of the circle and poles of steely dipping discontinuities lie close the periphery of the circle.
