2013 - Week_4_- Notes

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15 Νοε 2013 (πριν από 3 χρόνια και 4 μήνες)

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Week 4 Notes

Page
1


CROSS SECTIONS

Road
Cross section sheet layout




OVERVIEW


Cross sections in Engineering Survey
Sites
and C
onstruction
Design
drawing
s

are invariably
drawn

in conjunction with
the Long section

so that an accurate assess
ment of the ground may
be made, and

consequently we can continue on to calculate volumes.



The Long section
profile forms the levels in the major direction.

Cross sections profiles
record the profile of the ground at right angles to the main road center line traverse.


Cross sections and
profiles are therefore complementary and together supply the three
dimensions to obtain cubic quantities.


Week 4 Notes

Page
2


While it is noted that p
rograms such as 12d, Civil3d and Mx
-
roads have been
developed over
the years to impor
t Survey Data and extrapolate Sections,
Long Sections and Volumes from
a
road design, there
are
two
main
important reasons why we need to un
derstand the basics of
drawing s
ections and working out volumes manually


It is important to recognise mistakes

and

incorrect extrapolation from any 3d prog
ram before
the model is passed on for
construction
.
It is also important to
have
good Engineering

knowledge and experience, in order to

determine where there is a potential design issue. A
computer 3D guru with no Engineering background and no knowledge of

what
he is

drawing,
can potentially cost the co
mpany a lot in money, and also

time fixing mistakes that could
have been avoided with basic Engineering
knowledge
and drafting skills


Often decisions on jobs are required instantly. There is often no time to

survey a new area or
extension and take this data
into a 3D program.
Also there is

often no time to create a 3D
model and export profiles and volumes. Some very important site decisions are worked out in
the site shed with a pencil and scale rule, or in
A
utoCAD

on a laptop using contours in

an
image format in the background
.


FIELD OBSERVATIONS (Surveying

History
)


Surveying has
also changed

dramatically
over the years
and is
still changing
all the time.



From

1900
-
1960
the most common way of recording R
oad Cross Sections was using
an
Abney level
and tape were

common place in a surveyors backpack
.

This was similar to early
instruments used by sailors to navigate by the stars. It was surprisingly accurate and very
quick to gain approximate ground lines in
steep terrain.


From the

19
3
0



1980 the most common way of recording Road Cross Sections was

a
T
heodolite and chain,
used along side a level
, staff

and
tape

for more accurate surveys.


In the 1980’s
the most common way of recording Road Cross Sections was

using
digital
Theodolites
and

Total stations took over recording data digitally and this was eventually
processed through a program like Civilcad and imported into AutoCAD


By the
19
90’s aerial photography was advancing enough to allow rough contours to b
e taken
on land forms without forest or dense bush. These eventually became good enough to do
rough estimates when bidding for work.


2000

-

present
Digital survey has now advanced to a point where they have laser levels and
GPS units with high levels of a
ccuracy and advanced accurate contours to 0.2
-
0.5m from
Satellite data.



200
5

-

present
LIDAR
s
urvey data is collected and used as survey Data


LIDAR
-

AIRBORNE LASER SCANNING


NZAM
has significant experience in LiDAR (Light Detection and Ranging) acquisition with
data collected throughout NZ since 2005. LiDAR is a cost effective alternative to
conventional ground surveying for medium to large scale terrain
modeling

projects and
accur
acies achievable are far superior to photogrammetric mapping.


Week 4 Notes

Page
3



LiDAR collects highly dense sets of discrete elevation points that represent a sampling of the
surface. Light is transmitted out to the target which is reflected back to the instrument where
i
t is analysed. The change in the intensity of the light enables some properties of the target to
be determined. The time for the light to travel out to the target and back to the LiDAR is used
to determine

the range to the target.




LI
DAR data is used to

produce:




spot heights




DEM, DTM, DSM




contours




feature extraction




building footprints and heights




vegetation measurements




breakline definition




road centre
-
line location and road surface modelling



LI
DAR data
produces value
-
added products such as:




hydrologically enforced terrain models




data fusion




view shed analysis




virtual reality / augmented reality




3D fly
-
through



Additional use of LIDAR data.


The applications possible from LiDAR include accurate flood
modeling
, corridor mapping,
wireless
network planning, road and engineering design, power line mapping, hazard
clearance, natural resource assessment, demographic profiling and urban planning, to name a
few.




LIDAR DERIVED DTM AND CONTOURS
-

AUCKLAND REGION


During the 2005/06 flying season NZAM flew the Auckland region with an
airborne LiDAR
scanner

to develop digital terrain models for a range of applications.

I
nternet Link
-

http://dev918.webgurus.co.nz/services/lidar/



The terrain data was captured to achieve a vertical accuracy of +/
-

0.25m (1 sigma
confidence) in the urban and intertidal areas an
d +/
-

0.50m (1 sigma confidence) in rural
areas. The data will be used for a wide variety of applications, including flood hazard
mapping, hydrological studies and ortho
-
correcting aerial photography throughout the region.


0.25m
-

0.36m resolution (grou
nd sample distance) imagery was captured concurrently and
orthorectified over some of the project extent.


However there are
also

important
things an Engineer

need
s

to understand

before requesting a
survey for Profile drawings and Earthworks calculations


Cost of
obtaining
the data

(the time factor in obtaining the data can be important here)



The Extent of the Job

Week 4 Notes

Page
4




The Contour interval accuracy needed



The nature of the terrain (is there tall trees or dense bush everywhere?)



The time factor involved in obtain
ing the data


Normally at the start of a large job
, the

time factor
is not considered in choosing the type of
survey data required.

Normally a complete digital survey is used.


Satellite contours or aerial photograph Contours are
being used more and more
to save costs,
but this depends on the exact natu
re of the Civil Engineering job and the nature of the terrain.


Cost can play a part in the decision of what data to us
e,
if the terrain is steep or dense bush.
This will mean
the

local site survey cost will

increase and quick cheap
er

aerial data may be
preferred?


E
XAMPLES



Job One : The job is in steep terrain and involves a platform for a Large wind farm with a
rough gravel road to site (use aerial or Satellite date)


Job Two : The job is a highway shape
correction over 600m (use a digital site survey with
accurate levels)


There is also another Scenario, where a quick Quality check is required on site before
proceeding or you need to check set out points or levels before or after the subcontract
or

has
bee
n on site. The companies digital survey equipment is being used on other bigger jobs.


This is where a level, staff and tape may quickly solve your problem. Or if you have one a
digital
Theodolite
, tape and staff
.



If there is a time factor involved then
a level staff and tape may be used to


(i)

Level, tape and staff
-

Gives high accuracy and can usually be done concurrently with
the long section. It is a suitable method for fairly flat country and where the sections extend
considerable distances out from

the main traverse. A series of R.L.’s can be obtained in the
normal way, or alternatively, the horizontal axis of the instrument (height of collimation)
forms a local datum for each cross
-
section.


(ii
) Theodolite, tape and staff


(suitable on steep grou
nd). Set up over centre
-
line peg and
measure height of collimation. At right angles to the main traverse set an inclined line of
sight roughly parallel to the ground. Staff inter sections are read as before.


S
CALES


Cross sections are drawn to natural sca
le although for special purposes distorted scales have
been used occasionally. The choice of scale may depend upon the nature or extent of the
particular work or project. Common scales are: 1:50, 1:100 and 1:200; the most common
being 1:100. Others may be
employed as required.





Week 4 Notes

Page
5


BATTER SLOPES


Batter Slopes design is first investigated by
Geologists
. They pass the borehole, lab test
reports and geological data on to a

Geotechnical Engineers

for Batter Design.


H
ere are some reasons why the design of the b
atter slopes may change and the method to the
geotechnical design approach.


The slopes at, or steeper than, 1 to 1 in cuttings and 1.5 to 1 on fills are to be adopted only
when stability can be assured from experience or soil tests. There will be many cas
es where
the nature of the material will demand flatter slopes even on high cuts and fills, while in some
cases certain materials such as pumice or loess will be more stable in cutting at a slope almost
vertical than when battered on a flatter slope.


In c
uttings, the top of th
e cutting should be rounded off,
except in spec
ial materials such as
pumice.


In high cuttings, benching is often advisable. 3m wide benches every 6.1m of vertical height
is common practice.


On high embankment with slopes steeper the
n 2 to 1 in clay, provision should be made for a
1m bench every 3m to 4.6m of vertical height, and a layer of scrub or similar treatment
provided along each bench.


Both as a safety measure and a means of improving the appearance of the road and
facilitati
ng maintenance, the batters in shallow cuts and fills should be as flat as reasonably
possible.



The attached table gives examples of the limiting batter slopes to be adopted in cuttings and
on embankments of varying depths.


Table of Batter Slopes
-

Limi
ting Batter Slopes



















In C
uttings


In rock and conglomerate : up to
0.125 to 1

In other materials


over 4.6m high : 1 to 1


1.8m
-

4.6m high : 1.5 to 1


0
-
1.8m high : 2 to 1


In Embankments

Over 7.6m high

: 1.5 to 1

1m
-

7.6m : 2 to l

Under lm : 4 to l

Week 4 Notes

Page
6


CIVIL DRAWING TERMINOLOGY

USED ON CROSS SECTIONS


(
common terms and abbreviations.
)


Base course material

Graded aggregate used for the principal supporting layers of a pavement.


Batter poles (or pegs)

Poles or peg
s set out to

mark the position of the top or foot of an inclined surface to be
formed.


Benching

Cutting a step or shelf in a sloping bank.


Bench mark

A well defined mark or peg whose level is known and which is used to establish the level of
other poin
ts


Berm

A horizonta
l ledge or margin formed at the top or bottom of an earth slope or intermediately.


Camber

The convexity given to the cross
-
section of a roadway; normally 3%


5%.




C
rossfall


Week 4 Notes

Page
7



The uniform slop
e

of the pavement normally from one
shoulder edge to the other





Formatio
n

The surface of the ground in its final shape after the completion of the earthworks.



Formation level

The level of a particular point of that part of the surface of the completed earthworks
designed to support
the pavement (see diagram).



Formation width

Se
e diagrams below


Cross

section on straight


Cross

section on straight


Week 4 Notes

Page
8


Cross section on a curve



Cross section on a curve



Cross section
on tangent





Highway

A general term denoting a road or stre
et primarily for through traffic, usually on a continuous
route.



Highway street or road

A general term denoting a public way for purposes of vehicular travel, including the entire
area within th
e right
-
of
-
way


In urban areas use
Motorway,
highway or st
reet in rural areas use highway or road


Median

The portion of a divided highway separating the travelled ways for traffic moving in opposite
directions. They can be depressed, raised as islands, grassed or const
ructed in permanent
materials.


Motorway

A

divided arterial highway for through traffic with full control of access and generally with
grade separations at intersections.


P
avement


a)

a general term for a paved surface. The superficial covering of an area s
uch as a street
or road, consisting of as
phalt, bitumen, tar or the like.

b)

a term applied specifically to the whole construction in a road made to support

t
raffic
above the subgrade.


Shoulder

The portion of the roadway contiguous with the travelled way for

accommodation of stopped
vehicles, for
emergency use, and for lateral support of base and surface courses.


Week 4 Notes

Page
9


Sub
-
base

Material used for lower pavement layers, where reduced quality is acceptable.


Subgrade

That part of the earthworks located immediately below
formation level.


Superelevation

The inward title or transverse inclination given to the surface of a road
-

way throughout the
length of a horizontal curve to reduce the effects of centrifugal force on a moving vehicle.



Typical section details



Week 4 Notes

Page
10




The road structures (cross section
on a straight section of road)



The pavement layers

from top down




The surfacing, which is always waterproof on important roads and is then called seal
or paving



The basecourse



The sub
-
base



The cutoff or drainage layer (used on clay subgrades or in wet co
untry)







Week 4 Notes

Page
11


Platform Cross

section
s





Week 4 Notes

Page
12







CROSS SECTIONS


Check List


a)

Have you
shown

a datum line for each cross section.

b)

Have you
dimensioned the
platform
?


c)

Have you shown critical levels for top of cut and bottom of batter

d)

Have you shown levels f
or existing ground

e)

Have you shown levels for the design platform?

f)

Always indicate with section marks where the cross section is on the proposed plan

g)

Extend the cross section far enough to pick up important features like trees, swamps,
paths etc.

h)

Indicate e
xisting ground which is being removed with a dashed line

i)

Show topographical features(trees, fences, boundaries), Environmental features
(swamps, native trees) cultural (
Maori
), hydro
graphic (pipes) and surfaces features
(retaining wall, buildings, paths)
on the cross section if their positions are known
provided they fall within the extents of the cross section

j)

Show setout levels below the cross section

for top of cut and bottom of batter

k)

Label all relevant
features with notes and leader lines

l)

Provide cut
and fill areas where relevant

m)

Chainage or distance

measured from one end or from the centerline of the Platform

n)

Design batter slopes

o)

Existing ground indicated in a different linetype in cut