surveying practical lab 2

9
CEVB 211 SURVEYING PRACTICAL TRAINING LABORATORY EXPERIMENT NO. 2 LEVELLING – ESTABLISHING A TEMPORARY BENCH MARK (TBM) SECTION: 03 NAME ID MUHAMMAD FIKRIL AZIM BIN ABDUL SANI CE094946 DATE OF LABORATORY SESSION : 5 NOVEMBER 2015 DATE OF REPORT SUBMISSION : 19 NOVEMBER 2015 LAB INSTRUCTOR : DR. AL MAHFOODH ALI NAJAH AHMED 1

Upload: fikrilazimabdulsani

Post on 12-Apr-2016

58 views

Category:

Documents


4 download

DESCRIPTION

Surveying

TRANSCRIPT

Page 1: Surveying Practical Lab 2

CEVB 211 SURVEYING PRACTICAL TRAINING

LABORATORY EXPERIMENT NO. 2

LEVELLING – ESTABLISHING A TEMPORARY BENCH MARK (TBM)

SECTION: 03

NAME IDMUHAMMAD FIKRIL AZIM BIN ABDUL SANI CE094946

DATE OF LABORATORY SESSION : 5 NOVEMBER 2015

DATE OF REPORT SUBMISSION : 19 NOVEMBER 2015

LAB INSTRUCTOR : DR. AL MAHFOODH ALI NAJAH AHMED

1

Page 2: Surveying Practical Lab 2

TABLE OF CONTENT

CONTENT PAGE

Table of Content 2

Summary/Abstract 3

Introduction 4

Materials or Equipments 5-13

Discussion 14

Conclusion 14

References 14

2

Page 3: Surveying Practical Lab 2

PROBLEM STATEMENT

As a civil engineer, you are required to apply the knowledge of levelling to establish a temporary benchmark for a new project site.

ABSTRACT/SUMMARY

Basically, the equipment that will be discussed in this report will help me in establishing the temporary benchmark for an easier way and more accurate method for levelling.

It has no relevance to property lines, right-of-ways, or other surveyed features, and is only used to complete the survey.

A temporary benchmark (TBM) is a fixed point with a known elevation used for level control during construction works and surveys. Nails in road seals, or marks on kerb & channel are commonly used as temporary benchmarks.

Basically, the equipments are the main key for the practical training. Even though we already know the basic concepts of the devices and the procedure of the levelling for example, without the equipments, we cannot carry out the practical training since it is the most crucial components for this practical course.

In addition, we need learn and must be exposed to the usage and how to handle the equipments itself. In other words, we need to identify the apparatus and their usage to be able to carry out the surveying procedure.

INTRODUCTION

3

Page 4: Surveying Practical Lab 2

A temporary benchmark in surveying is a control point that is set by a surveyor to base other points off of. They will assign it an elevation, and other points that are surveyed off of that point will have a relative elevation rather than an absolute elevation. 

A marking, or location, with a known elevation. These markings are not usually permanent. They are used by a person doing leveling work as intermediary points when carrying a known elevation from one point to another. TBMs can as simple as the top of the ground surface where you drag your foot to mark the spot. They could also be the top of a rock or wooden stake, or even an "X" or "+" scratched into concrete or rock. It is desirable for TBMs to be something that can be found at a later time so that elevations can be rechecked.

The students need to minimize the errors by first, identifying the error sources and the procedures. It is the main component of this course. In addition, it is important for the students to acquire surveying data during laboratory periods, applying fundamental concepts for data adjusting and developing a preliminary route plan, all by cooperative efforts among the students, individually and grouping.

OBJECTIVE

To establish a new Temporary Bench Mark (TBM)

4

Page 5: Surveying Practical Lab 2

Apparatus

1. Automatic Level (1 unit)2. Tripod (1 unit)3. Levelling Staff (2 units)4. Staff Bubble (2 units)5. Hammer, nails and spray

Procedure

1. The experiment is began from a known reference point, nearest Bench Mark (BM) or TBM. Otherwise, a reference point to be BM is selected and the RL to be assumed as 100.000 m.

2. Change point (CP) is established along the levelling route to the new TBM.3. The distance between the Backsight (BS) and Foresight (FS) should be almost equal

(not more than 60 meters)4. The loop to the starting point is closed (known as reference point)5. When closing the levelling loop to the starting point, the same established points (CP)

are observed.6. The misclosure is calculated and accordingly distributed.7. The allowable misclosure is 0.017 mm.8. All the observations shall be booked in the provided levelling form. Only booking by

pen is accepted.

5

Page 6: Surveying Practical Lab 2

DISCUSSION

WHAT IS THE DIFFERENCES BETWEEN THEODOLITE AND TOTAL STATION?

TheodolitesA Theodolite is an instrument for measuring both horizontal and vertical angles, as used in triangulation networks. It is a tool used in the surveying and engineering industry, but theodolites have been adapted for other specialized purposes as well. A theodolite consists of a telescope mounted movably within two perpendicular axes, the horizontal axis, and the vertical axis.

Total StationsTotal station is an optical instrument used in modern surveying. It is a combination of an electronic theodolite (transit), an electronic distance measuring device (EDM) and software running on an external computer, such as a laptop or data collector.

LevelsThe builder's level is often mistaken for a transit, but is actually a type of inclinometer. It measures neither horizontal nor vertical angles. It simply combines a bubble level and telescope which allows the user to visually establish a level line of sight along a plane.

6

Page 7: Surveying Practical Lab 2

Basically, the total station can simultaneously measure the vertical, horizontal angles and slope distances, then it can be transferred to a computer to generate map. But, for the theodolite, it can be used for measuring both horizontal and vertical angles only.

Discussion

Precision of levelling As with all techniques used in engineering surveying it is important to estimate how accuracy of the measurements taken. An assessment of the quality of levelling can be made by calculating the misclosure for a line of levels. This is determined by comparing the reduced level of the closing bench mark with the level obtained for it by calculation from the staff readings. On construction sites and other engineering projects, levelling is usually carried out over short distances and it can involve a lot of instrument positions. The allowable misclosure for a line of levels is given by:

Allowable misclosure =

Where, m is a constant and n is the number of instrument positions used. The value most often used for m is 5mm ±m n

When the misclosure obtained from staff readings is compared to the allowable misclosure, if miscloure is greater than the allowable value the levelling is rejected and must be repeated. If the misclosure is less than the allowable value, then the levelling is accepted and adjusted. The value of m depends on the site conditions. For example if the levels found are to be used for earth work excavations m might be 30mm. For setting out steel and concrete structures excavations m might be 3mm. In some cases m is specified in the contract documents.

Conclusion

The primary purpose of this report is to identify the usage of all equipments used for surveying procedure, thus enable me to use the equipments properly based on what I have learnt from the class and the further investigation about those equipments.

7

Page 8: Surveying Practical Lab 2

References

http://www.tcd.ie/civileng/Staff/Brian.Caulfield/3A1/3A1%20Lecture%205.pdf

8