a substance or groupof substances withthe potential to causesignificant harm

a route by which asource could reacha target

that which could besignificantly harmedby the source

source

pat

hw

ay

target

NO

NO

HAZARDSKNOWN ORSUSPECTED?

YES

YES

NO

YES

NO

NO

YES

BASICINVESTIGATION

DETAILEDINVESTIGATION

INITIAL ASSESSMENTY

ALKOVER SURVEYTS

FURTHERINVESTIGATION

REQUIRED?

FURTHERINVESTIGATION

REQUIRED?

AREHAZARDSFOUND?

DOCUMENTATIONAND VALIDATION

COMMENCECONSTRUCTION

UNFORESEENHAZARDS?

COMPLETECONSTRUCTION

MANAGEHAZARDS

‘A few years backthere was a tip in

the area.’

WATER LANE

°

μ

μ

μ

μ

μ

mature height

50% mature height

In this range useH = mature height

as listed inAppendix 4.2-B

In this range useH = actual height

Figure 1 should be used when:

T equal to orgreater than B

B

acceptablefoundationdepth

depthgreaterthan3/4 X

depth Xdeterminedassumingsoil isshrinkable

no

n s

hri

nka

ble

so

ilsh

rin

kab

le s

oil

°

0.5 m 0.5 m level formation

raft foundation

angle of repose of

infill material

ground level

1.25m max.depth (measuredin accordance withSitework clause S3)

fully compactedinfill material

Foundation details

Tree details

Site Details

Unaltered

High

0.00

0.00

Volume change potential:

Ground level:

Ground level altered by(m):

Climate zone depthreduction (m):

NextHelp Climate zones

Site Details

Unaltered

High

0.00

0.00

Volume change potential:

Ground level:

Ground level altered by(m):

Climate zone depthreduction (m):

NextHelp Climate zones

NHBC Standards

Chapter 4.2

Building near trees

Electronic foundationdepth 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

ab

b

tree to be removed

tree to be removed

original ground level

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 treeproposed tree

original ground level

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 inAppendix 4.2-B

In this range useH = actual height

Figure 8 should be used when:

line of trench bottom

step not greater than 0.5m

foundation depth

ground level

backfill

500mm

450mmmax

verticalface to foundation

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 ofanchorage bars tobe 40 bar diametersor designed by anEngineer (see TechnicalRequirement R5)

compressible materialto sides of piers(see Table 9)

compressible materialor void former toinside face of externalground beams(see Table 9)

compressible materialor 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 the full width of the ground beam is protected.

backfill

embedment of pile tensionreinforcement to be 40 bardiameters or designed byan Engineer (see TechnicalRequirement R5)

optional rigidslip liner

pile length toEngineer's design

compressible materialor void former toinside face of externalground beams(see Table 9)

compressible materialor void formerbeneath groundbeams (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 full width of the ground beam and the areas around the piles are protected.

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

Fou

nd

atio

n d

epth

s (m

)

D/H

Low

Moder

ate

Mod

erat

e

Hig

h

High

TREE WATER DEMANDS

Broad leafed trees Coniferous trees

High

Moderate

Low

High

Moderate

D/H

Low

Moderate

Mod

erat

e

Hig

h

High

Fou

nd

atio

n d

epth

s (m

)

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

D/H

Low

Moderate

Mod

erat

e

Hig

h

High

Fou

nd

atio

n d

epth

s (m

)

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 trees

High

Moderate

Low

High

Moderate

36 0.9m minimum foundation depth

37

38

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

WorcesterBirmingham

Stafford

Stoke on Trent

ChesterLiverpool

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)

μ

100l’p = 36 x 100 = 36%

μμ

μμ

μ

Lombardy Poplarmature height 25m

zone of influenceof Lombardy Poplar1.25 x 25 = 31.25m

zone of influenceof Sycamore 0.75 x 22 = 16.5m

Sycamorematureheight 22m

8m

10mhouse

H 25D = 10 = 0.4

H 22D = 8 = 0.36

HD= 0.4,

HD= 0.36,

trench length

trenchlength

distance from boundary

trenchwidth

boundary

diagonals

finished ground level

at least 450mm

vertical sidesand steps horizontal

land drainsdiverted tosuitableoutfall

diversion

50mm gap all round

maskedopening

flexiblejoint

granularbackfillaround pipe

lintel

flexiblejoint

flexible materialaround pipe

pegs helpto ensurecorrect levels

at least 75mmcover75mm

sidecover

joint using reinforcing bars

joint withexpandedmetal lath

joint using corrugatedmetal former

joint with expandedmetal lath

overlap

TS

S

overlap

T

The minimum thicknessof the foundation (T)should either be P or150mm, whichever is greater.

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

dpc

at least225mm

GROUNDBEAM

dpc

at least 150mm

weephole

RAFTFOUNDATION

trench length

trenchlength

distance from boundary

trenchwidth

boundary

diagonals

boundary

distance from boundary

diagonals

alignment

alignment

°

100

90

80

70

60

50

40

30

20

10

0

CLAYFine Medium

SILT

Coarse Fine Medium

SAND

Coarse Fine Medium

GRAVELCOBBLES

Coarse

6 20 60 200 600 2 6 20 60 200 mm2

Micr

on

PERC

ENTA

GE

PASS

ING

63 150

212

300

425

600

mm

1.18

2 3.35

5 6.3

10 14 20 28 37.5

50 63 75

Zone Adeepcompaction

Zone Bstonecolumns

settlementof fill

layers withhigh organiccontent

stone column acting as vent for dangerous gases

interaction ofadjacent foundations

house A house B

stone column acting as soakaway

adjacentbuilding

newbuilding

stone column

original water level

depressed water leveldry process

adjacentbuilding

newbuilding

stone column raised water level

original water level

wet process

depth in accordance with Chapter 4.2

structural load from design

ground bearing capacity and settlement potential

brick reinforcementand movementjoints in walls if required

excavation and drain/servicetrenches shouldbe above 45º line

45º

reinforced concretestrip foundation

raft orsemi-raftfoundation

maximumcentres

2m max centres

2m 2m 2m

missing stonecolumn - new column required

stone column mis-aligned by more than 150mm - new column requiredin correct position

stone column mis-aligned by 150mm or less - no action needed

depth 25%greater thananticipated

50% more backfill than anticipated

anti

cip

ated

dep

th

mini zonetest using skips

zone test

excavation and drain/servicetrenches shouldbe above 45º line

45º

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

Micr

on

PERC

ENTA

GE

PASS

ING

63 150

212

300

425

600

mm

1.18

2 3.35

5 6.3

10 14 20 28 37.5

50 63 75

Zone Adeepcompaction

Zone Bstonecolumns

clean, hardinert stone

void is formed asvibrator displaces the ground

compressed air

stone backfill isplaced into void during withdrawalof vibrator

continuous stonecolumn formed

waterflushing

stone backfill is placedinto the void during withdrawal of vibrator - water assists instabilising the hole

continuous stonecolumn formed

clean, hardinert stone

void is formed as vibrator displaces the ground

water jet

compactedcolumn

granularmaterial

compacted zone

vibrator displaces the ground

granular material is placed into the depressionaround vibrator

existing groundis compacted