E4014 Construction Surveying Pavement Setout. Road Construction Consists of a number of sequential...

E4014 Construction Surveying

Pavement Setout

Road Construction

• Consists of a number of sequential steps– clearing– earthworks– drainage works– pavement construction– road furniture

Road Construction - Clearing• When

– occurs prior to commencement of earthworks

• Where– 1.5metres outside road formation

• How– remove all trees and other vegetation

Road Construction - Clearing• Surveyor’s Role

– mark limits of road formation– batter points + 1.5metres– stakes with flagging or flag trees– use plans and tables

Road Construction - Clearing• Existing Survey Control

– baseline survey marks and offsets– permanent marks & bench marks

• Accuracy of Setout– probably ±0.5metre horizontal

Road Construction - Drainage• When

– before major earthworks• keep construction site dry

– after major earthworks• to keep subgrade dry

Road Construction - Drainage

Surface Drains• Where

– catch drains– catch surface water flow over adjacent natural

surface and divert it into the drainage system – 2metres from edge of cutting– maybe construct bank rather than cut surface

drains

• When– before major earthworks



– Table Drains• collect surface water draining off the road

pavement• wide and deep enough to collect and hold all

surface water• deep enough to intercept any subsoil

moisture close to the surface• discharge onto natural surface or into

culverts every 100 metres

• When– after major earthworks - before subgrade construction


Surface Drains• Where– Levy Drains

• used on hills to collect run-off from pavement area and direct it into flumes which carry the water down the embankment

• prevents scouring of the batters in fill

• When• before and after major earthworks



– kerb & Gutter• urban form of table drain• also used in rural road cuttings• normally constructed by an extrusion machine

• When• after major earthworks and pavement

construction


Subsoil Drains• Where– constructed to prevent damage by

underground water from• water seeping down through the pavement• water rising in springs• water flowing downhill in the upper soil layers– control is achieved by

– intercepting ground water before it reaches the roadway

– lowering the water table by providing outlets for reservoirs surrounded by impervious barriers

– subsoil pipes are usually located– in the shoulder between the pavement and the table

drain– under the edge of pavement


Subsoil Drains• Where– Culverts

• carry water from one side of the road formation to the other

• pre-cast concrete pipes, pre-cast concrete boxes, insitu concrete boxes, corrugated steel pipes and arches

• When– after construction of sub-grade, before

placing the sub-base

Road Construction - Earthworks• Proper construction involves

– clearing– stripping of topsoil– drainage of swampy areas– removal of poor materials– compaction of natural surfaces– benching of steep slopes– spreading and compaction of fill materials

Road Construction - Earthworks• Preparation of site

– clear all timber

– utilities• re-location of existing utilities• conduits for future utilities will save cost

and damage to road formation at a later time

Road Construction - Earthworks• Preparation of site, cont

– access through the site for current traffic• away from construction site• in rugged country locate the side-track in

the position of the final catch drain on the up-hill side of cuttings


– Removal of topsoil• valuable commodity to be conserved for later

landscaping• wasted in fills and destroyed by having fills

placed over it• removal of top soil ensures firmer foundation

of fills• stockpiled in heaps of less than 1 metre in

height– if buried for long periods fertility is lossed


– Removal of material too weak to support fill• highly organic clays, saturated clays in

swamps, silt and mud

– compact the natural surface of fill sites by rolling


– Cuttings and Fills• eventual aim of all fill work is to position

the the subgrade underlying the pavement layers in the right location and at the correct level and to provide drainage to maintain its condition


– earthworks operation comprises the following operations• formation of cutting by excavating through

the high ground• formation of embankments by filling over

the low ground• shaping the ground or finished surface to

true formation levels• excavation for drainage works


– earthworks operation will involve• excavating or loosening natural material• loading the material into haulage units• transporting the material from cuttings or

borrow pits to fill sites• dumping the material• compacting the material


– Cuttings• Through Cuts

– may be through a small hill or over the top of a large hill to lower the grade of a road

– prior to construction the material type must be identified and the angle of repose estimated

• Side Hill Cuts– part of the road in cut and part in fill– enables balancing of earthworks– embankment portion tends to move downhill,

better to be full cut


– Fills• material should be obtained from as near

to the embankment site as possible• material should be stable, high bearing

strength and a free draining nature• sand gravel mix, sand clay mix and sand

silt mix are suitable fill materials when correctly placed


– Cut & Fills• often the largest task in road works• often the most costly operation in terms

of total sums of money involved• speed and efficiency depends largely on

the quantity and types of earthmoving plant available

– initial plant selection for a site will effect the its overall progress


– Cut & Fills, cont• in most materials except rock the factor

governing the speed of work is likely to be transporting of the material and not the excavation itself

• capacity of the haulage system must equal the maximum digging output

• it follows that the haul should be kept as short as possible


– Sequence of operations in CUT• excavate to reach formation level or to

remove alll unsuitable material• transport away from site the undesirable

soils – organic top soil, heavy highly plastic water-

logged clays, loose sand

• haul suitable material from cuts to fill areas


– Sequence of operations in FILL• drain water from hollows and holes,

dispose of sludge before filling is begun• spread the fill material into horizontal

layers not more than 250mm deep• thoroughly compact these layers to

maximum density

Road Construction - Bases and Sub-Bases• After the earthworks and

compaction of fills, subgrade is brought tp the correct formation and trimmed

• Road Pavement– sub-base layer, maybe– base course layer

Road Construction - Bases and Sub-Bases• Road Pavement

– sub-base layer, maybe• stronger than the underlying subgrade

– base course layer• stronger than the sub-base

– surface course• stronger than the base course

• wheel loads which are most intense near the surface are taken by materials which are able to accept the load without significant deformation

Road Construction - Bases and Sub-Bases• Base Course

– Rigid• cement concrete with or without the

addition of a separate wearing course• used in roads effected by flooding or

subjected to heavy traffic loads

Road Construction - Bases and Sub-Bases• Base Course, cont

– Flexible bases• natural materials which deflect slightly

under loads• common in Qld are soil aggregate, crushed

rock and uncrushed stone• level control required as the material is

placed in layers deep enough to ensure required compaction can be achieved

• if tests have not been done on the material the loose layer should be placed 25% thicker than the desired final compacted layer

Road Construction - Bases and Sub-Bases• Base Course, cont

– Flexible bases• natural materials which deflect slightly under

loads• common in Qld are soil aggregate, crushed

rock and uncrushed stone• level control required as the material is placed

in layers deep enough to ensure required compaction can be achieved

• if tests have not been done on the material the loose layer should be placed 25% thicker than the desired final compacted layer

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E4014 Construction Surveying Pavement Setout. Road Construction Consists of a number of sequential...

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