Section II

Applications of Measurements

3. Control

4.Cnstruction Surveys

Control• To start any surveying project, surveyors need to

start measurements from known points: points of

known coordinates.

• In the vertical, one benchmark is enough.

• In the horizontal (X, and Y) you need at least two

points

• onsite of known presicse elevation, we call it a

benchmark.

Vertical control

Elevations• For any elevation measurements onsite:

• a backsight is recorded at the benchmark;

• the height of instrument si computed: HI =

EBM + BS

• The elevation of any point = EBM – (FS or IS)

• Therefore, you have to have at least one point.

• A set of benchmarks ar established around the

site before any construction design or activity

by measurements from government provided

benchmarks

Horizontal Control

• To measure (X, Y) horizontal coordinates, you need to

occupy one know point say (A), aim at another known

point, say (B). The unknown point is C

• Calculate the azimuth of the line AB = tan-1 X/ Y

• Measure the angle BAC and the distance L to the

unknown point C

• Calculate the azimuth of the line AC

= Azimuth of AB ± angle BAC

Calculate X and Y for the line AC

Calculate the coordinates of C:

Xc = XA + X and Yc = YA + Y

Example 1

Calculate the azimuth of AB if the azimuth of

AB = 40 and the angle BAC = 25

Answer:

= 65

N

40 C25

AZ AC

A

B

Given that the coordinates

of point A (543.12,

341.67)m. The azimuth of

the line AB in the figure

below = 65 (that is 65

degrees) and the

horizontal length between

points (A) and (B) is

145.23 m. Calculate the

coordinates of point (B).

6

Coordinate Computations

Example 2

Answer:

XAB

= L sin() = 145.23 sin (65) = 131.62 m

YAB

= L cos() = 145.23 sin (65) = 61.38 m

Then;X

B= X

A+ X

AB= 543.12 + 131.62 = 674.74

YB

= YA

+ YAB

= 341.67 + 61.38 = 403.05 m

Coordinate ComputationsExample 2

• Therefor, you need at least two known points

to calculate a reference azimuth, such as the

azimuth of AB in the previous example.

• Note that we do not measure azimuth as it is

very difficult to figure out where north is, but

we need the azimuth to compute coordinates.

• We solve the problem by measuring angles

between lines, compute the azimuth of one of

them, and then use the measured angle to

compute the needed azimuth.

Horizontal Control

Summary• In summary, we need to have points of precise

coordinates around the site to measure from.

• For elevations, the vertical, we establish

“benchmarks” by measurements of elevations from

government provided benchmarks.

• For X and Y, horizontal coordinates, we establish

horizontal control points by:

• Measurements from other known points; or

• Using GPS (explained later in this course)

Construction Surveys

Stages and Measurements of CS

• Design stages: topographic Surveying, and site maps

• Construction stage:

• Setting-out and positioning works. 60% of surveying hours.

• involves establishing lines and grades by means of stakes and string lines to guide the contractor

• During and after construction: as built drawings, a record and a check.

• Measurements involved: Horizontal and vertical angles, elevations, horizontal distances.

CS Equipment• Laser Instruments:

– to create a visible line, or plane of known elevation or tilt

– The line or plane could be horizontal, vertical, or tilted.

– Single beam lasers will project visible string lines or plumb lines

– Rotating beam lasers: a rotating single beam to create a plane.

– Examples:

» Laser levels, laser theodolite and total stations, hand-held EDM instruments (Figures 23-1 to 23-4)

» Recent technology of prism-less total stations and EDMs.

» Machine Guidance

Laser is used to guide the blade

•Total Stations: the ones designed for CS are of lower angular resolution(10” or 20”), and shorter ranges(500 m)

•Relative GPS: sub-centimeter accuracy with real time kinematic GPS in horizontal, few cm in vertical. Must maintain visibility with satellites

•Levels

Staking out a Building

• First step is to locate the building by boundary surveying. Stakes are placed temporarily at the corners as a check.

• In a small size building, a set of batter boards and reference stakes are first set. The boards are around the building corners and nailed at a certain elevation above the footing base or at first floor elevation.

• Nails are driven into the batter board tops so that a string connecting them will define an outside wall

• In a larger building, radial methods are used using a total station

Batter Boards هالخنزير؟ماهى الخنزيرة أو الشبلونة

ربع هى هيكل خشبى مؤقت يتم اعداده على شكل م:تعريف الخنزيرة

أو مستطيل أو طبقا لشكل المبنى على الأرض المطلوب أقامة

.زيرةالمشروع عليها بهدف توقيع المحاور الخاصة بالمنشأ على الخن