nhbc standards chapter 4 foundations april 2010

8/18/2019 Nhbc Standards Chapter 4 Foundations April 2010

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a substance or groupof substances withthe potential to cause

significant harm

a route by which a source could reacha target

that which could be significantly harmed by the source

source

p a t h w a y

target


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NO

NO

HAZARDS

KNOWN OR

SUSPECTED?

YES

YES

NO

YES

NO

NO

YES

BASIC

INVESTIGATION

DETAILED

INVESTIGATION

INITIAL ASSESSMENT

Y

ALKOVER SURVEY TS

FURTHER

INVESTIGATION

REQUIRED?

FURTHER

INVESTIGATION

REQUIRED?

ARE

HAZARDS

FOUND?

DOCUMENTATION

AND VALIDATION

COMMENCE

CONSTRUCTION

UNFORESEEN

HAZARDS?

COMPLETE

CONSTRUCTION

MANAGE

HAZARDS


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‘A few years back

there was a tip inthe area.’

WATER LANE


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°


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µ

µ µ

µ

µ


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mature height

50% mature height

In this range useH = mature height

as listed in Appendix 4.2-B

In this range useH = actual height

Figure 1 should be used when:


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T equal to or greater than B

B

acceptablefoundationdepth

depthgreater than3/4 X

depth X determined assuming

soil is shrinkable

n o n

s h r i n k a b l e

s o i l

s h r i n k a b l e

s o i l

°


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0.5 m 0.5 mlevel formation

raft foundation

angle ofrepose of

infill material

ground level

1.25m max.depth (measured in accordance withSitework clause S3)

fully compacted infill material


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Foundation details

Tree details

Site Details

Unaltered

High

0.00

0.00

Volumechangepotential:

Ground level:

Groundlevelalteredby(m):

Climatezonedepth

reduction(m):

NextHelp Climatezones

Site Details

Unaltered

High

0.00

0.00

Volume change potential:

Ground level:

Ground level altered by

(m):

Climate zone depth

reduction (m):

NextHelp Climate zones

NHBC Standards

Chapter 4.2

Building near trees

Electronic foundation

depth calculator

Help Continue

tree to remain

tree to remain

original ground level

Use the lower of:a: foundation depth based on appropriate

tree height (see Figure 8)b: foundation depth based on mature height of tree

a

bb

tree to be removed

tree to be removed


Use the lower of:a: foundation depth based on appropriate

tree height (see Figure 8)b: minimum foundation depth (see Table 8)

a

ab

proposed tree proposed tree


bb a

Use the lower of:a: minimum foundation depth (see Table 8)b: foundation depth based on mature height of tree

mature height

50% mature height

In this range useH = mature height

as listed in Appendix 4.2-B

In this range useH = actual height

Figure 8 should be used when:

line of trench bottom

step not greaterthan 0.5m

foundation depth

ground level


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backfill

500mm

450mmmax

vertical face tofoundation

compressible material(see Table 9)

Void (see Table 9 or 10)

It is essential that:

and the foundation excavation has a vertical face.

concrete overspill it may be necessary to consult an Engineer.

backfill

embedment of anchorage bars tobe 40 bar diametersor designed by anEngineer (see Technical Requirement R5)

compressible material to sides of piers(see Table 9)

compressible material or void former toinside face of external ground beams(see Table 9)

compressible material or void former beneathground beams(see Table 9)

void (see Table 9 or 10)

500mm

It is essential that heave material is provided to the entireareas shown. Particular care should be taken to ensure that thefull width of the ground beam is protected.

backfill

embedment of pile tensionreinforcement to be 40 bar diameters or designed by an Engineer (see Technical Requirement R5)

optional rigid slip liner

pile length toEngineer's design

compressible material or void former toinside face of external ground beams(see Table 9)

compressible material or void former beneath ground beams (see Table 9)

Void (see Table 9 or 10)

It is essential that heave material is provided to the entire areas shown. Particular care should be taken to ensure that the fullwidth of the ground beam and the areas around the pilesare protected.


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0 0.2 0.4 0.6 0.8 1.0 1.2

0

0.5

1.0

1.5

2.0

2.5

Minimum depth 1.0m

F o u n d a t i o n d e p t h s ( m )

D/H

L o w

M o d e r a t e

M o d e r a t e

H i g h

H i g h

TREE WATER DEMANDS

Broad leafed trees Coniferous treesHigh

Moderate

Low

High

Moderate


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D/H

L o w

M o d e r a t

e

M o

d e r a t e

H i g h

H i g h


0.2 0.4 0.6 0.8 1.0 1.2

0

0.5

1.0

1.5

2.0

2.5

TREE WATER DEMANDS

Broad leafed trees Coniferous trees

High

Moderate

Low

High

Moderate

Minimum depth 0.9m

0


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D/H

L o w

M o d e r a t

e

M o d

e r a t e

H i g h

H i g h


Minimum depth 0.75m

0.2 0.4 0.6 0.8 1.0 1.2

0

0.5

1.0

1.5

2.0

2.5

0

TREE WATER DEMANDS

Broad leafed trees Coniferous treesHigh

Moderate

Low

High

Moderate


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36 0.9m minimum foundation depth

37

38


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Thurso

Wick

Dingwall

Inverness

Fort William

Oban

Pitlochry

Perth

Glasgow

Ayr

DumfriesLondonderry

Belfast

Douglas

Blackpool

Holyhead

Conwy

Shrewsbury

Aberystwyth

Lancaster

Edinburgh

Dunbar

Berwick Upon Tweed

Newcastle Tynemouth

MiddlesbroughDarlington

Carlisle

Montrose

Peterhead

Cardigan

Pembroke

Ilfracombe

ExeterTaunton

Bristol

Salisbury

Poole

WeymouthPlymouth

Penzance

Brecon

Worcester

Birmingham

Stafford

Stoke on Trent

Chester

Liverpool

Manchester

Lincoln

Derby

LeicesterKings Lynn

Norwich

Skegness

Grimsby

Hull

York

Scarborough

Leeds

Yarmouth

Cambridge

Banbury

Cheltenham

Oxford

SwindonReading

Winchester

Southampton

Hastings

Dover

MargateLondon

Chelmsford

Colchester

Portsmouth

Brighton

Newport

Cardiff

St. Austell

Swansea

Enniskillen

Barrow-in-Furness

Aberdeen

Lowestoft

Ipswich

Barnstaple

0.50m (500mm)

0.45m (450mm)

0.40m (400mm)

0.35m (350mm)

0.30m (300mm)

0.25m (250mm)

0.20m (200mm)

0.15m (150mm)

0.10m (100mm)

0.05m (50mm)


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µ

100

l’p = 36 x 100 = 36%

µ

µ

µ

µ

µ

Lombardy Poplar mature height 25m

zone of influenceof Lombardy Poplar 1.25 x 25 = 31.25m

zone of influenceof Sycamore0.75 x 22 = 16.5m

Sycamorematureheight 22m

8m

10mhouse


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H 25

D=

10= 0.4

H 22

D=

8= 0.36

H

D= 0.4,

H

D= 0.36,


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trench length

trenchlength

distance from boundary

trenchwidth

b o u n d a r y

d i a g o n a l s

finished ground level

at least450mm

vertical sidesand steps horizontal

land drainsdiverted to

suitableoutfall

diversion


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50mm gapall round

masked opening

flexible joint

granular backfill around pipe

lintel

flexible joint

flexible material

around pipe

pegs helpto ensurecorrect levels

at least75mmcover 75mm

sidecover

joint usingreinforcing bars

joint withexpanded metal lath

joint usingcorrugated metal former

joint withexpanded metal lath


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overlap

T S

S

overlap

T


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The minimum thicknessof the foundation (T)

should either be P or150mm, whichever isgreater.

foundation widthshould be not lessthan the appropriatedimension in Table 10

wall should becentral on foundation

Diagram 24 Foundation dimensions

P PW

T

Trench fill foundations may be used as analternative to strip foundations


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dpc

at least 225mm

GROUND

BEAM

dpc

at least150mm

weephole

RAFT FOUNDATION


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trench length

trenchlength


trenchwidth

b o u n d a r y

d i a g o n a l s

b o u n d a r y


diagonals

alignment

alignment


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°


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100

90

80

70

60

50

40

30

20

10

0

CLAYF in e M ed iu m

SILT

Coarse F in e M ed iu m

SAND

C oa rs e F in e M ed iu m

GRAVELCOBBLES

Coarse

6 20 60 200 600 2 6 20 60 200 mm2

M i c r o n

P E R C E N T A G E P A S S I N G

6 3

1 5 0

2 1 2

3 0 0

4 2 5

6 0 0

m m

1 . 1

8

2 3 . 3

5

5 6 . 3

1 0

1 4

2 0

2 8

3 7

. 5

5 0

6 3

7 5

ZoneAdeepcompaction

Zone Bstonecolumns

settlement of fill

layers withhigh organic content


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stone column acting as ventfor dangerous gases

interaction of adjacent foundations

house A house B

stone column actingas soakaway

adjacent building

new building

stone column

original water level

depressed water level dry process

adjacent building

new building

stone column raised water level

original water level

wet process

depth in accordancewith Chapter 4.2


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structural loadfrom design

ground bearing capacityand settlement potential

brick reinforcement and movement

joints in wallsif required

excavation anddrain/servicetrenches should be above 45º line

45º

reinforced concrete strip foundation

raft or semi-raft foundation


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maximumcentres

2m maxcentres

2m 2m 2m

missing stonecolumn - newcolumn required

stone columnmis-aligned bymore than150mm - newcolumn required in correct position

stone column mis-alignedby 150mm or less -no action needed

depth 25%greater thananticipated

50% morebackfill thananticipated

a n t i c i p a t e d

d e p t h


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mini zonetest using skips

zone test

excavation anddrain/servicetrenches should be above 45º line

45º


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100

90

80

70

60

50

40

30

20

10

0

CLAYFine Medium

SILT

Coarse Fine Medium

SAND

Coarse Fine Medium

GRAVELCOBBLES

Coarse

0.006 0.02 0.06 0.2 0.6 2 6 20 60 200 mm0.002

M i c r o n

P E R C E N T A G E P A S S I N G

6 3

1 5 0

2 1 2

3 0 0

4 2 5

6 0 0

m m

1 . 1

8

2 3 . 3

5

5 6 . 3

1 0

1 4

2 0

2 8

3 7

. 5

5 0

6 3

7 5

Zone Adeepcompaction

Zone Bstonecolumns


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clean, hard inert stone

void is formed asvibrator displacesthe ground

compressed air

stone backfill is placed into voidduring withdrawal of vibrator

continuous stonecolumn formed

water flushing

stone backfill is placed into the void duringwithdrawal of vibrator -water assists in

stabilising the hole

continuous stonecolumn formed

clean, hard inert stone

void is formed as vibratordisplaces the ground

water jet

compacted column


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granular material

compacted zone

vibrator displacesthe ground

granular materialis placed intothe depressionaround vibrator

existing ground is compacted


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nhbc standards chapter 4 foundations april 2010

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