21010: Surveying II

Instructor: Dr. Debasis Roy, Office: 1st Floor, S.R. Sengupta Geotechnical Laboratory. Telephone: 3456 (office), 3457 (home), 220214 (home). E-mail: debasis@civil.iitkgp.ernet.in

Introduction: Ground rules, grading policy, attendance…

Lecture Hours: Mondays, 10:30a to 11:30a at CE 205; Tuesdays, 7:30a to 9:30a at CE 205.

Resources: No single resource would cover the entire curriculum: resources will be used as reference depending on suitability. They include:

Chandra, A.M. 2002. Higher Surveying. New Age International Publishers: New Delhi De, A. 2000. Plane Surveying. S. Chand and Company Ltd.: New Delhi Kanetkar, T.P., and Kulkarni, S.V. 1966. Surveying and Levelling. A.V.G. Prakashan:

Poona. Punmia, B.C. 1981. Surveying, Volumes I and II. 7th Edition. Standard Book House. US Army Corps of Engineers. 2002. Structural Deformation Surveying. Engineer

Manual EM 1110-2-1009. http://www.usace.army.mil/pubs.htm

LECTURES 1 AND 2: JANUARY 6 & 7, 2004

INTRODUCTION Surveying from an engineer’s perspective is determination relative positions of points on above or beneath the earth surface. It essentially involves linear and angular measurements and elevation difference between two points. In all surveying measurements emphasis is on minimization and estimation of errors. Linear measurements are typically carried out by: • Pacing

• Engineer’s chain (and accessories, e.g., arrow, poles, pegs and offset rods)

• Tachemetry or telemetry (distances are using the principles of optics and a telescope and accessories, e.g., stadia rods): to be covered in this course

• Electronic Distance Measurement (based on reflection of electro-magnetic signals): to be covered in this course

• Astronomical measurements

Horizontal and vertical angular measurements are typically carried out from astronomical observations, or by using a magnetic compass or a theodolite (also known as a transit) or a Total Station (with or without Automatic Target Recognition or ATR capability).

DEFINITIONS PRECISION, ACCURACY AND BIAS: See Figure 1.

Figure 1. Accuracy, Precision and Bias

SYSTEMATIC AND RANDOM ERROR: Systematic error is repeatable under the same condition, while random error is not. Random error is governed by the notion of probability.

CHAINAGE AND OFFSET: The location of a point is often fixed with respect to a survey line using chainage and offset. Chainage is a linear measurement to a given point on the

survey line typically expressed in ?+?? or ?+??? format proceeding in a certain direction. Offset is the perpendicular distance from the point of interest to the survey line.

CONDITIONING OF DATASET: If the results are very sensitive to a small change in measurement, the dataset is ill-conditioned. Otherwise, it is well-conditioned (see Figure 2).

Figure 2. Ill- and Well- Conditioned Triangles

CLASSIFICATION OF ENGINEERING SURVEY 1. Classification based on Geometry of the problem. Plane survey: applies plane

geometry neglecting curvature of earth. Geodetic survey: applies spherical geometry accounting for the curvature of the earth.

2. Classification based on location of measurements. Land Survey, Hydrographic Survey or Astronomical Survey

3. Classification based on the objective. Municipal Survey, Route Survey (pipeline, road, railway), Mine Survey, Soil Survey

4. Classification based on instrument used. Taping, Tachemetry, Aerial Survey, EDM Survey

GOOD PRACTICES • Redundancy (repetitive measurement)

• Working from whole to part