Surveying Practical Lab 3
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CEVB 211 SURVEYING PRACTICAL TRAININGLABORATORY EXPERIMENT NO. 4INTRODUCTION TO DIGITAL THEODOLITE
MUHAMMAD FIKRIL AZIM BIN ABDUL SANICE094946
DATE OF LABORATORY SESSION : 16 NOVEMBER 2015DATE OF REPORT SUBMISSION : 3 NOVEMBER 2015LAB INSTRUCTOR : DR. AL MAHFOODH ALI NAJAH AHMED
TABLE OF CONTENTCONTENT PAGE
Table of Content2
Introduction & Objective3-4
Materials or Equipments 4
Results & Calculations 5-8
PROBLEM STATEMENTAs a civil engineer, I am required to apply the knowledge of levelling to establish a contour map for a new project site using Grid Method.
The contour is the relative position of points in a plan that is represented by a map. Contouring is defined as a contour line joining points of equal heights or altitude. The vertical distance between successive contours is known as the vertical interval. Contour lines are continuous lines and cannot meet or cross any other contour line, nor can any one line split or join any other line, except in the case of a cliff.The height between the successive contours is called the vertical interval or contour interval and is always constant over a map or plan.
For the method of Contouring, the Grid Method is one of the preferable methods for contouring of plains or gently sloping grounds such as hills. A contour plan gives an idea of the altitudes of the surface features as well as their relative positions in plan serves the purpose of both, a plan and a section.
In this method the points located and surveyed are not necessarily on the contour lines but the spot levels are taken along the series of lines laid out over the area. The spot levels of the several representative points representing hills, depressions, ridge and valley lines and the changes in the slope all over the area to be contoured are also observed. Their positions are then plotted on the plan and the contours are drawn by interpolation. This method of contouring is also known as contouring by spot levels where the Grid Method is classified as one of the Indirect Method of Contouring.
OBJECTIVE To produce contour plan using application Surfer8 using Grid Method.
Apparatus1. Automatic Level (1 unit)2. Tripod (1 unit)3. Levelling Staff (2 units)4. Staff Bubble (2 units)5. Hammer, nails and spray
Procedure1. Grid lines are produced at 10 m interval. The points are marked at the grid intersection by using pegs or arrows.2. Observation from a known reference point, nearest Bench Mark (BM) or Temporary Bench Mark (TBM) is begun. A reference point is selected to be BM and the RL to be assumed as 100.000 m.3. Notes: The observations are normally taken as Intermediate Sight (IS).4. All observations shall be booked in the provided levelling form. Only booking by pen is accepted.
= 8.788 = 8.849= 2716.235 = 2704.36
Table 2: Levelling Form
Figure 1: Grid Method for finding Northing and Easting
Figure 2: Contour map on 40m x 40m
DiscussionThere are differences between plan data, profile data and cross-sectional data used in the construction surveys for routes. The plan data is a view from above. It shows a view of the route if you were in a plane looking down onto route itself. For the profile data, it is a view you will see from the side. It gives us the existing ground elevation and its relationship to the proposed ground elevation. A cross sectional data is a data you will see the end areas and surface dimensions for the calculation of the route.
There are 27 readings including the BM (Benchmark). Each reading have been given a remark. Every remark has its own coordinate based on the north axis and east axis. The value of misclosure is 0.061. The reduce levels were corrected before the data being copied into Surfer8. Based on the contour map, the highest peak is in coordinate (30, 30). It is noted that the closer the contour line with each other, the steeper the actual area.
Parallax occurs when the focusing screw and the eyepiece is done incorrectly. This condition can be detected by moving the eye to different parts of the eyepiece when reading the staff. If different readings are obtained then parallax is present.
To remove parallax, hold a sheet of paper in front of the object and adjust the eyepiece so that the cross hairs are in focus. Then remove the sheet of paper and bring the staff into focus using the focusing screw. Once again check for parallax by moving your eye around the eyepiece. If parallax is still occurring repeat the adjustment procedure.
Commonly, the error involves the level rod not vertical enough, leveling rod not fully extended or incorrect length. Besides that, level instrument may not be leveled properly for all readings and the instrument may be out of adjustment. The environment conditions also may affect the readings including wind and heat.
So, to reduce the error, tripods leg is anchored firmly. The bubble level also needed to be checked before and after each reading. Take the least time as possible between BS and FS. Also, we need to keep the distance to the BS and the FS to be equal. There must be a rod person with a level for the rod.
Conclusion Basically, the Grid Method is the most precise and preferable method in constructing the contour graphically. Based on the data, there might be some error committed during the experiment based on the discussion that might be slightly affect the view of the contour map from the Surfer8 applications.