CMT100S Chapter 1 Earthworks

8/17/2019 CMT100S Chapter 1 Earthworks

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Construction Methodsfor Civil Engineering

Chapter 1

Earthworks

Presented by: Reinholdt J

Loots



1.1Introduction_______________________________________

Earthworks in modern engineeringconstruction interpreted in a variety ofways, depending on where one is

involved in the process:A Geotechnical (Soils) Engineer will

interpret earthworks as dealing with

soils in generalA Structural Engineer and Building

Contractor will interpret earthworks with

reference to foundations



Before Earthworks Start

!denti"cation of site

Site and its #oundaries are esta#lished

Surveyor places #oundary pegs

Site cleared and levelled

Space made for parking, roads, delivery of

goods, accommodation of engineering



Site Clearance

Site cleared of all o#structions

$emolition

%anual&mechanical

Construction plant' %achinery used on site

Stockpiles away from

construction site

' op soil

' nusa#le materials



Setting out a site

*orks #oundaries

+ dierent from site #oundaries

$one #y surveyor

$atum level

+ "-ed point set in concrete



Bearing capacity Bearing pressure

Settlement

Back"ll

Self'weight loads

!mposed loads

$ierential settlement

1.2Definitions_______________________________________



.oundations

Shallow

foundations

$eep

foundations

1.3Foundations_______________________________________



.oundation types

Strip.oundatio

n

/aft.oundatio

n

0ad&isolated

.oundations

0ile.oundatio

nsCaissons

Shallow $eep

1.4Foundation Types_______________________________________





*hich factors will determine the choice offoundation type1

he otal 2oad of the #uilding

he nature and #earing capacity of the soil he settlement of the soil

otal load 3 Self weight 4imposed loads

1.5Choosing Foundation Types_______________________________________



Exercise

Activity 1.3: Calculation of self'weight load (5&m run)

for wall, given wall (2 3 67m, B 3 78m, 9 3 7m) and 3 877kg& ;3< =77kg&>

!mposed 2oad (varies #etween < and kg&m?)

Solution:

$ensity 3 mass & volume (kg&) ;or >

@olume 3 2 - B - 9 3 67m - 78m - 7m 3 4.0

%ass 3 density - volume 3 877kg& - 87 3 9 600g

*eight 3 mass - gravitational acceleration 3 77kg - <m 3 8 <=kgm 3 94 !"6 #

Self'weight load &m run 3 Self'weight concreteload&length of wall

3 8 <= 5 & 67m 3 !$ $%&.'0 #(m r)n



Soil Bearing Capacity

he nature and bearing capacity of the soil can #edetermined #y:

rial holes and trial pits

Boreholes and core analysis 2ocal knowledge

Soil testing methods eg CB/, nuclear

penetrometer

!n situ "eld tests eg plate loading, S0, $C0,

etc

2a#oratory testing tria-ial test



Foundation design

Activity 1.4: Calculating the minimum width ofthe strip foundation (eg for houses) reuired tosupport a load worked out as follows:

Fiven: otal load per meter 3 <7k5

Bearing capacity of the soil 3 < 77 k5&

%inimum width reuired3 7=7m

So, width of the foundation strip must #e=77mm



1.6Excavations

Small contracts:

rench dug #y hand or e-cavator

2ends itself to application of la#our'enhanced construction

seen as a form of employment creation (see Chapter<)

Large contracts:

%ore economical to use some form of mechanical

e-cavator



1.7Timbering

Struts, planking, shuttering G shoring

temporarily supports the sides of e-cavations

(deeper than <6 m) on sta#le soils

nsta#le soils always to use

tim#ered supports

!tHs purpose11 0age <

Activity <6

(homework)



Timbering (cont)

Purpose o timbering supports:

prevent the sides from collapsing

prevent the inIow of loose material

prevent damage to the adJoining property

keep the e-cavation open #y acting as a retaining wall

to the sides of the trench

keep the workers in the trench safe from collapsing soil

Activity 1.! try for homework

i i i



1.8Basic timberingexcavation terminology

0oling #oards

*alings

Struts

Sheeting

/unners

0uncheons



1.9Trench ExcavationSafety

Activity 1.": Safety in Construction Froup poster

*hat are some of the reasons why trenches collapse1

%ention where in the chapter on Safety is pointed out

the safety measures related to e-cavation

E-plain the recommended precautions when working

in trenches



Reasons why trenches collapse

%aterials too close to the sides

E-cavation plant and euipment too close to the edge

nsta#le su#soil material

Changes in the moisture content of the soil

@i#rations from compaction plant or passing vehicles

he soil is una#le to support its own weight

nsta#le nature of the soil



Trench ExcavationRegulations

< *here trenches are close to the pu#lic, the followingprecautionary measures are taken:

renches protected #y a fence

/ed warning lights placed at regular intervals to

warn pu#lic

5o workers allowed in trenches deeper than<6m

without sides protected or #raced

? All #racing supported #y cross #racing

8 Bracing strong enough to support soils



Trench ExcavationRegulations (cont)

6

Knly materials reuired for e-ecution of work allowed intrench

0rovide all trenches L <6m deep with safe access, eg

ladder

= nderground services investigated G located #efore

e-cavation

/egular inspection of trenches daily, weekly or monthly

intervals, or after #ad weather and rain

!nspection carried out #y a responsi#le and competent person

+ prefera#ly person in charge of shift or e-ecution of work



1.10Excavating Basements

Perimeter trench

sed in weak soil perimeter trench is dug

around new #asement e-cavation

#ase of trench covered with 67'=6 mm weakconcrete #linder or #linding layer



Excavating Basements (cont.)

Ra#ing struts E-cavated in sections

.irm su#soil

*ide e-cavation




$o%erdams

emporary structure pumped dry to e-pose

#ottom of water #ody

.or construction purposes

!nterlocking steel sheet

piles #raced with tie rods E-cavation then takes place

#ehind the coerdam




&iaphragm 'alls /etaining wall or structure used to retain large

masses of soil

se a #entonite slurry

techniue

Basic procedure M5K*

(see ne-t slide)




&iaphragm 'alls ( Basic procedure of method:

E-cavated spoil material replaced with #entonite slurry

*hen applied to the sides of the e-cavation, the slurry

forms a soft gel that penetrates slightly into the soil

his acts like a stopper, keeping sides sta#le Ggroundwater out

0anels to support the sides of e-cavation can #e inserted G

e-cavation to reuired depth can continue in this manner

Knce reuired depth reached, reinforcing cage is lowered

into the hole G "-ed in position

A high slump concrete is pumped into trench G displaces

slurry which is either pumped away or recycled



1.11Retaining Walls

/etains soil at an angle greater than that soil would naturally

assume (ie at Nangle o reposeO), to resist soil and waterpressures

&esigned to prevent Kverturning

Sliding

Soil not overloaded

Construction materials used not

overstressed

)actors that need to be ta#en

into account: 5ature G type of Soil

* height

Su#soil water movements

ype of wall

Construction materials used in wall



Reinforced Earth

Strengthening of soil used as "ll material throughaddition of strong tensile reinforcement in form of

strips + frictional forces

Soil is compacted in layers

/einforcing strips placed #etween layers



Types of Retaining Walls

Fravity /* Cantilever /*

0recast concrete /S

Concrete #lock /*



Construction 0lant

Earth%oving0lant

E-cavation0lant

Compaction 0lant

1.12Construction Plant

BulldoPerAngledoPerScrapersFraders ractor Shovel

.ront'end 2oader

Skimmer.ace ShovelBackactor$ragline%ulti'purposeE-cavator

Static weight roller@i#ratory roller0neumatic roller%ini vi#ratingroller

@i#rating plate



1.13Excavation Plant

Consists of power unit (diesel engine) ande-cavating attachment

Skimmer

.ace shovel

Backactor $ragline

%ulti'purpose e-cavator

rencher



1.14Earth-moving Plant

*ulldo+er,Angle do+er

Q 9igh'powered tractor on tracks "tted with ablade

on the front and a ripper at the #ack

Q 0ushes loose material ahead

Q sed to level a site & #ack"lling & ripping &

grading

Scrapers + stripping, levelling, cut'and'"ll

Graders + road construction Cuts & grades soil to reuired level

-ractor shovel + scoop loose material

)ront(end loader +

%ost versatile machine



1.15Compaction plant

)unction: @i#ratory, dead'weight, kneading

(manipulation) actions

-ypes:

Static weight roller

@i#ratory roller

0neumatic roller

%ini'vi#rating roller

@i#rating plate

!mpact plate



Which factors influence the compactiveeffect of a roller? Static weight

5o of vi#rating drums

.reuency and amplitude of vi#ration

/oller speed

/atio #etween frame and drum weight

$rum diameter $riven or non'driven drum

5um#er of passes



*+,E-+R:

RK S9K2$ A5S*E/ A22 SE2.'E@A2A!K5ES!K5S A5$ $K A22 AC!@!!ESTTT

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CMT100S Chapter 1 Earthworks