D&H Underground Tanks – speciﬁcations and installation · D&H Underground Tanks – speciﬁcations and installation ... British Standard BS 6297: 1983 recommends that sewage

D&H Underground Tanks –specifications and installation

Guidance on the selection, installation andhandling of D&H Tankstor® undergroundtanks, including D&H Separators.Please also consult the relevant section forguidance on specific products.

© D&H Products, Maple House, Hamlin Way, Kings Lynn, Norfolk. PE30 4NG T. +44 (0)1553 819590 F. +44 (0)845 2703334 E. [email protected]

D&H Separators (Stormceptor® by-pass separators, Puraceptor® class 1 separators and full

retention class 2 separators) and D&H Tankstor® underground tanks, (septic/settlementtanks, cesspools and stormwater attenuation tanks, etc.) must be installed according to theseinstructions.

The local authority and the local region of the Environment Agency should also be consulted asto whether any particular code applies to installation. Failure to follow these installationinstructions will make void our warranty and may result in tank failure.

Site access and conditions

It is the responsibility of the contractor toensure suitable access to good hard groundthat is safe and suitable for off-loading.

Wide/long loads

Where the tank is of such size that police/private escort is required delivery times givenare estimates only. In the event of delaysoutside our control eg. police re-routing orescort delays, the extra charges that result willbe forwarded to the contractor.

Off-loading/handling

The contractor is responsible for off-loading.Tank handling during off loading must becarried out with care to prevent rolling offthe vehicle. Care must also be exercised toprevent accidental damage from impact orcontact with sharp objects.

Tanks should be lifted using slings, notchains or wire ropes. Do not drag tanks alongthe ground for any distance and avoid jarringor bumps. Do not lift with water in the tank.(See page 4.2).

Note: Where transport height restrictionsprevent the tank being loaded in the verticalposition on the transport vehicle, the tank willbe loaded at 45 degrees or as required to keepwithin the restrictions. In such cases it will benecessary for the tank to be off loaded onto alevel area or well supported planks positionedadjacent to the ‘lift’ points and to support atleast four ribs. The area must allow room toenable the tank to be rolled into the verticalposition before lifting the tank intothe excavation.

Storage

Set tank on smooth ground free of bricks andsharp objects. Chock/tie down to preventmovement in high winds. (See page 4.2).

Tank dimensions

Dimensions given on drawings andliterature shall be subject to manufacturingtolerances and should be checked physicallyprior to installation.

Installation procedures

The alternative methods of installation dependon the ground conditions, water table, the tank’slocation and whether the tank is fitted with feetor not.

Installation should be carried out by a competentcontractor in accordance with the aboveprocedures, Health & Safety at Work legislationand good building practice.

It is not possible to cover every condition inthese instructions, therefore if in doubt contactus.

Tank specification

Check that you have received the correctspecification tank.

D&H underground tanks are available inspecifications to suit invert depths, concreteor pea gravel surround and ground waterconditions; standard, heavy, extra heavy andspecial. (See pages 4.3 and 4.4).

For most applications the standard orheavy specifications are adequate. If thetank invert depth and/or water table depthis outside the range we shall be pleased toadvise accordingly.

Siting D&H septic tanks

British Standard BS 6297: 1983 recommendsthat sewage treatment works should be as farfrom habitable buildings as is economicallypracticable. The direction of the prevailing windshould be considered in relation to anyproperties when siting the works.

In accordance with the Building Regulations2000. H2 2002 edition D&H septic tanks shouldbe sited at least 7m from any habitable parts ofbuildings, and preferably downslope.

The tank should not be installed near a road ordriveway, where it could be subjected to highexternal loads, unless the installation is designedto withstand such loadings so they are nottransferred to the tank shell.

Information contained in this data sheet is approximate andfor general guidance only. In accordance withthe company’s policy of constant improvement anddevelopment D&H Products reserves the right to changethe specification without prior notice.

Where the tank is to emptied using a tanker, itshould be sited within 30m of a vehicle accessprovided that the invert level of the septic tankis no more than 3m below the level of thevehicle access. This distance may need to bereduced where the depth to the invert of the tankis more than 3m. There should also be a clearroute for the hose such that the tank can beemptied and cleaned without hazard to thebuilding occupants and without the contentsbeing taken through a dwelling or place ofwork.

Siting D&H cesspools

D&H cesspools should be sited at least 7m fromany habitable building and preferablydownslope. They should however be sitedwithin 30m of a sludge removal tanker accessand at such levels and position to operate andwithout hazard to the building occupants.

Extension access shafts

Check if extension shafts are required.

These are available in 500mm high increments.

Note: Where coalescer units or pumps areincorporated that require guide rails, or laddersare fitted, the height of the extension accessshaft/s should be measured accurately beforeordering.

Health and safety

Installation should be carried out by acompetent contractor in accordance with theabove procedures, Health & safety at Worklegislation and good building practice.

A warning notice should be visible at thetop of each access shaft – ‘danger, harmfulfumes’ and ‘respirators must be worn inthis tank’. Before entering persons must bequalified in accordance with ‘confined space’requirements.


D&H underground tanks

Lifting, handling and storage

25ºmaximum

minimum of 1/4 x length

Lifting and handling – preferablemethods

• Do not roll or drop tanks. Only movetanks by lifting. Rolling tanks coulddamage fittings.

• Tanks can be lifted using slings/webbing straps as illustrated.

• Where necessary a spreader barshould be used.

• Guide the tank with guide lines.• Never use chains or steel cables

around tank shell.• Do not drag tanks along ground for

any distance.• Avoid jarring or bumps.• Do not lift with liquid in the tank.• Set tanks on smooth ground, free of

rocks or other sharp objects.

Do not roll or drop tank.

Storage – preferable methods

If tanks have to be stored temporarily prior toinstallation, they should be located:

• in an area where the chance of accidentaldamage or vandalism will be minimised.

• on a flat surface free from small or sharpobjects.

• with efficient temporary anchorage to

Tie down against high winds.

Prevent any movement.

Preferred methods of lifting.

Never drag along the ground or lift unevenly. Place tanks on smooth, level ground.

D&H septic tanks 240,000 litre for ScottishWater Solutions.


D&H underground tanks – 200,300 and 400 seriesSpecifications to suit invert depths and ground water conditions – pea gravel and concrete surrounds

X depth ofwater table

Y maximumdepth

Well drained groundHigh water table

Standard tanks


Y maximumdepth


Heavy, extra heavy and special tanks

300 series with pea gravel surround

2

4

6

8

2 3 41

Depth of water table X (metres)

Maximum depth Y (metres)

STANDARD TANK

HEAVY TANK

EXTRA HEAVY TANK

SPECIAL TANK

300 series with concrete surround

2

4

6

8

2 3 41



STANDARD TANK

HEAVY TANK

EXTRA HEAVY TANKSPECIAL TANK


2


4

6

8

2 3 41


STANDARD TANKHEAVY TANK

EXTRA HEAVY TANK

SPECIAL TANK


2

4

6

8

2 3 41



STANDARD TANK

HEAVY TANK

EXTRA HEAVY TANK

SPECIAL TANK

Burial depths for 200 series withconcrete surround

Standard specification tanks

Maximum burial depthto bottom of tank 4m

Maximum height of watertable above bottom of tank 1m

Heavy specification tanks

Maximum burial depthto bottom of tank 6m

Maximum height of watertable above bottom of tank 2m


D&H underground tanks – 500 and 600 seriesSpecifications to suit invert depths and ground water conditions – pea gravel and concrete surrounds


Y maximumdepth


Standard tanks


Y maximumdepth


Heavy, extra heavy and special tanks


2

4

6

8

2 3 41


EXTRA HEAVY TANK

SPECIAL TANK

STANDARD TANK

HEAVY TANK



2

4

6

8

2 3 41


10

EXTRA HEAVY TANK

SPECIAL TANK

STANDARD TANK

HEAVY TANK



2

4

6

8

2 3 41


EXTRA HEAVY TANK

SPECIAL TANK

STANDARD TANK

HEAVY TANK



2

4

6

8

2 3 41


10

EXTRA HEAVY TANK

SPECIAL TANK

STANDARD TANK

HEAVY TANK


© D&H Products, Maple House, Hamlin Way, Kings Lynn, Norfolk. PE30 4NG T. +44 (0)1553 819590 F. +44 (0)845 2703334 E. [email protected] Assured Company BS EN ISO 9001:2008

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Rev 09.09

Typical installationsWith concrete base and concrete/pea gravel surround

Excavation details for concrete surround Series 100/200 Series 300 Series 400 Series 500 Series 600 Max. burial

depths (m) Standard dry excavation 4.0 4.0 5.0 5.7 6.2

Heavy dry excavation 6.0 5.6 6.00 7.25 7.3 high water table – 3.0 3.75 5.0 5.2

Extra heavy dry excavation – 6.5 7.0 8.0 8.4

Special dry excavation – 7.3 8.0 9.2 10.2

Minimum hardcore (mm), dependent on ground conditions 150 200 250 300 300

Concrete base slab (mm) Slab thickness 100-150 150 220-240 240-300 250-300

Concrete surround (mm), dependent on ground conditions 100-150 150 200-250 250-300 250-300

Maximum Initial water fill depths, prior to backfilling (mm) 200 300 400 500 500

Tank internal diameter (mm) 1250/1200 1800 2600 3500 4000

Tank external diameter (mm) 1300/1225 1875 2700 3650 4150

For your specificrequirements refer toburial depth and watertable depth charts onpages 3 and 4

Installation with feet/chocks

Installation without feet

200mm minimumthickness concretesurround

Tank length

Buria

l dep

th

Pea gravel or similarfree flowing cleanrounded aggregate orselected non-cohesivematerial

600mm diameteraccess shaft can becut to length on site

Manhole cover and frame,set in flush with finishsurface, as required

Concrete cradleto support 1/3circumference(minimum 200mm)250-300mm hardcore

Excavation minimum length Overall diameter

Internal diameter

Inve

rt to

suit

Installation of D&HTankstor tank whereground overinstallation is notrequired to be vehicle

Wet or clayground

Dry, well-drained ground

Manhole cover and frame,set in flush with finishsurface, as required

Type 1 MOT stone,well compacted

Reinforced concretecover slab designed totake vehicle loading

Installation of D&HTankstor tank with feetand a load bearingcover slab.

Ensure concreteslab is cleanready for placingconcrete surround.Surround should beplaced within48hrs of casting thebase slab

Concrete surround

250-300mm hardcore

For pea gravel surround see burial depth charts on pages 4.3 and 4.4.


Typical installation of D&H tank without feet

Hardcore Concretesurround

Concrete cradle to supportone third of circumference

Reinforced concreteslab designed to takevehicle loading

Well compactedtype 1 sub baseMOT stone

Installation of tanks surrounded in concrete

Typical installation of D&H tank with chocks & wedges

HardcoreConcretebase slab

Timberwedges



Concretesurround

Chocks

Preliminary

Determine the size of the excavation from thedimensions of the tank and the incoming draininvert depth allowing for a minimum of 200-250mm (250-300mm for 500/600 Series tanks)of concrete all round the tank. Where difficultground conditions or the possibility of externalloading exist, the concrete surround should bedesigned accordingly, ie. extra thickness and/orthe use of reinforcing.

Excavation

Excavate allowing for easy placing of thetank and concrete and for consolidating concretearound the bottom half of the tank whenbackfilling.

Allowance should be made for any timbering orsheeting that may be required.

If the base of the excavation is of unstableground – loose gravel, running sand, landfilltype areas, peat, swamp or in clay areas subjectto swelling/shrinking etc., excavateto allow for 250-300mm of hardcore and coverwith a polythene membrane prior to placingconcrete.

Procedure with feet/chocks

Feet and chocks can be provided duringmanufacture to enable the tank to be placed on aflat concrete base and levels checked prior tosurrounding with concrete.

Feet are not load bearing and minimal watershould be placed in the tank prior to placingbackfill concrete.

1. Pour concrete base to correct depthand level off. Base to be reinforced asnecessary.

2. When this concrete has set sufficiently, placethe tank in position, check for levelsincluding inlet/outlet inverts and fill withwater in accordance with table on page 4.5.Ensure concrete slab is clean readyfor placing concrete surround. Surroundshould preferably be placed within 48hrs ofcasting the base slab. Proceed to 3.

An alternative to feet for stabilising the tank arechocks. These are mounted each end of the tankto enable the tank to be maintained in a verticalposition on a flat concrete slab. The procedure isas follows.

1. Pour concrete base to correct depthand level off. Base to be reinforced asnecessary. Work to full slab thickness– see table on of page 4.5.

2. When this concrete has set sufficiently, placethe tank in position and check for levelsincluding inlet/outlet inverts. Also check theribs are firmly seated on the concrete slab, or,at least every third rib. Those ribs standingfree of the slab support with a tapered timberwedge (50mm wide tapered 10º-15º). Wherea number ofribs are unsupported place wedges fromalternate sides.

3. Place backfill concrete (ST4 mix) up to thedepth of the water in the tank ensuring theconcrete is properly consolidated under thetank to prevent voids. Consolidate by hand– Do not use vibrating pokers.

4. Continue by placing concrete around the tankat the same time filling with waterto equalise pressure and resist floatation.Where the tank is divided into chambersensure all chambers are filled equally.

5. Connect up pipework, seat access shaft intosocket and apply waterproof mastic/adhesive, or as applicable.

6. Top up the tank with water to inlet/outletinvert level and place remainder of concreteto a depth of approximately 250mm abovethe top of the tank. Where extension accessshafts are fitted, these can be surrounded inconcrete once the main tank surroundconcrete has set.Important: Before surrounding circularor rectangular shafts with concrete,shutter internally to support the sides andsafeguard against distortion.

7. Where the concrete slab over the tank is totake vehicle loading, it should be reinforcedin accordance with good practice to take themaximum load and should be extended ontounexcavated ground. It is important thatvehicle loading is not transferred to the tankitself.

8. Incorporate inspection cover frames in thenormal manner.


Installation of tanks surrounded in concrete

Typical installation of D&H tank without feet



Concrete cradle to supportone third of circumference

Concretesurround

Hardcore

Cesspool tanks/silage tanks etc.

When the concrete surround has fully cured, cesspools should be

Procedure without feet

1. Place concrete along the centre of theexcavation base and lower the tank intoposition ‘puddling’ it into the concrete toform cradle. Consolidate under the tank toprevent voids. Consolidate by hand– Do not use vibrating pokers.

2. Check the tank is truly vertical and leveland that inlet/outlet invert levels are correct.

3. After the concrete has reached its initial set,fill with water in accordance with table onpage 4.5.

4. Continue by placing concrete around the tankat the same time filling with waterto equalise pressure and resist floatation.Where the tank is divided into chambers

5. Connect up pipework, seat access shaft into socket and applywaterproof mastic/adhesive, or as applicable.

6. Top up the tank with water to inlet/outlet invert level and placeremainder of concrete to a depth of approximately 250mm above thetop of the tank. Where extension access shafts are fitted, these can besurrounded in concrete once the main tank surround concrete hasset.Important: Before surrounding circular or rectangular shafts withconcrete, shutter internally to support the sides and safeguard againstdistortion.

7. Where the concrete slab over the tank is to take vehicle loading,it should be reinforced, in accordance with good practice, to take themaximum load. The reinforcing should be extended ontounexcavated ground. It is important that vehicle loading is nottransferred to the tank itself.

8. Incorporate inspection cover frames in the normal manner.

Venting D&H septic tanks and cesspools

Adequate ventilation of the septic tank and theinlet pipework shall be provided to prevent theaccumulation of fermentation gases.

Venting D&H Separators

D&H Separators should be vented inaccordance with BS EN 752 (BS8301:1985Building Drainage) or Health and SafetyGuidance Notice HS (G) 41 for filling stations,subject to local authority requirements.

In multiple chamber separators, vent pipeworkmust not be combined into a common stackbelow a point where pollutants contained couldbe transferred to other chambers.

D&H Separator automatic alarm/monitoring system

(Requirement of the Environment Agency’s Pollution PreventionGuidelines PPG3)

The D&H automatic alarm/monitoring system provides continuousmonitoring of the separator contents by sensing when the light liquidwithin the separator has filled to a predetermined level (with design safetymargins), and provides a simple audio-visual warning to alert the operatorthat the separator needs to be emptied.

The system comprises 2 parts: a compact control unit and aprobe unit.

The control unit is installed in a non-hazardous area remote fromthe probe. It is self-contained and requires only a normal 240v ACelectrical supply. The control incorporates a ATEX approved intrinsicallysafe circuit, which enables the probe unit to be used in Zone ZeroEnvironments. For technical and installation details see page 4.13.


Excavating – general

Excavate allowing for easy placing of the tankand backfill and for consolidating backfillaround the bottom half of the tank. Allowanceshould be made for any timbering or sheetingthat may be required.

Filter fabric

Where there is a risk of the migration of peagravel with the native soil, an approved filterfabric/geotextile is recommended.

Filling tanks

Do not fill tanksuntil backfill is totop of the tank.(Exception; WetHole see page 4.9).

Where the tank is divided into chambers ensureall chambers are filled equally.

Note: Where the chambers may require tobe separated by load bearing partitions toaccommodate different liquid levels the tankmust be surrounded in concrete.

Installation of tanks surrounded with pea gravel backfill

450mm minimum450-500mm minimum

Special placement and compaction required

1

2

3

Crushed rock3mm-16mm

Pea gravel3mm-20mm

If you have an installation situation that isnot covered by this installation bookletplease contact our technical servicesdepartment.

It is important that only properly trainedand experienced contractors perform thismethod of installation.

Backfill material

Pea gravel or crushed rock is preferred asbackfill material.

Clean and washed sand may be used.Sand must be compacted in 300mm liftsto above the tank top.

Requirements for backfill material are:

• Clean and washed.• Non-cohesive, inert material.• Pea gravel or crushed rock.• Particle not larger than 20mm.• Material free from rocks, ice, snow or

organic material.

Excavation size, backfill and compaction

Depth of cover for standard and heavyspecification tanks

No vehicle loads

100/200/300/400 series tanks aredesigned for a minimum cover of 600mm ofbackfill or 300mm plus 100mm reinforcedconcrete slab.

500/600 series 1100mm backfill or 900mmbackfill plus 100150mm reinforced concreteslab.

Vehicle loads

100/200/300/400 series tanks subjectedto vehicle loading must have a minimum coverof 600mm of backfill plus a minimum 150mmreinforced concrete slab designed to take themaximum load without such loadings beingtransferred to the tank itself.

500/600 series as above but 1000mm backfillplus a minimum 150mm reinforced concreteslab as above.

The maximum depth of the cover is governedby the maximum drain invert depth andperiodic high water table when encountered.

Depth of cover for extra heavy and specialspecification tanks, contact our technicalservices department.

Approved backfill material for tanks and pipes


Installation of tanks surrounded with pea gravel backfill

1. Dry hole backfill bed

300mm bed

Curved, long handled probe toreach underside of the tank

Second 300mmlayer of backfill

2. Dry hole place backfill around tank.

3. Dry hole complete backfill.

300mm bed

Dry hole procedure

Excavation size – stable ground conditions

Determine the size of the excavation from

the dimensions of the tank and the incomingdrain invert depth, allowing for a minimum of450mm of backfill between the tank sides andthe ends of the excavation.

Excavation size – unstable ground conditions

Where the ground is unstable, eg. landfill typeareas, peat, swamp or in clay areas subjectto swelling/shrinking, the width of the backfillmust be increased to a minimum of half the tankdiameter between the tank sides and the ends ofthe excavation.

If the base of the excavation is also of unstableground, allow for 250-300mm of hardcore.After placing the hardcore, consolidate to ensurea firm base for the backfill.

Installation

1. Place a minimum of 150-300mm ofapproved backfill over the excavationbottom. Refer to table below.

2. Position tank carefully onto backfill bed andcheck for levels including inlet/outlet inverts.

3. Place first 300mm lift of backfill evenlyaround the tank by shovelling and pushingbeneath the tank bottom, between ribs andend domes to ensure complete supportand to eliminate voids. (Where access isconfined, long handled probes, curved toenable reaching the underside of the tank, canbe used). Place and compact further 300mmlifts as above to a minimum depth of 1/3rdtank diameter. The remainderof the backfill can be poured withoutconsolidation except where required tosupport a cover slab.

4. Connect up inlet, outlet and vent pipework,seat access shaft into socket and applywaterproof mastic/adhesive, or as applicable.

5. Where a concrete slab is to be constructedover the tank to take vehicle loading, itshould be reinforced in accordance with goodpractice to take the maximum load andshould be extended onto unexcavated ground.It is important that vehicle loading is nottransferred to the tank itself. Important:Before surrounding circular or rectangularshafts with backfill, shutter internally tosupport the sides and safeguard againstdistortion.


Wet hole procedure

Where there is water entering the excavation,the water level should be maintained below thefoundation level by pumping with or withoutthe aid of a pump well in one corner of theexcavation.

Wet hole backfill.

If the water level cannot be lowered you willneed to ballast the tank very carefully. Place thetank in the excavation adding only enough waterballast to sink it. The water level in thetank must never exceed the water level inthe excavation. While adding ballast use onlylifting strap to keep the tank in position.

It is essential the backfill is distributed evenlyround the base of the tank and thoroughlyconsolidated with the aid of long handledprobes to eliminate any voids as set out in point3 ‘Dry hole procedure’.

To prevent flotation, mechanical anchoringmay be required. See pages 4.11 and 4.12.

Backfill bed

Please refer to this table for the minimumamount of approved backfill to be used over theexcavation bottom for your series tank.

Tank min backfill bed

100 series 150mm

200 series 150mm

300 series 200mm

400 series 250mm

500 series 300mm

600 series 300mm


Installation of tanks into wet concrete cradle with pea gravel

This method of installation combines the economy of pea gravel backfill and the safety of aconcrete cradle. For the less experienced contractor this is a safer option than bedding on peagravel.

Excavation size – stable ground conditions

Determine the size of the excavation from the dimensions of the tank and the incoming draininvert depth, allowing for a minimum of 200-250mm (ST4 mix) concrete and for a minimum of450mm between the tank and the excavation.

Excavation size – unstable ground conditions

Where the ground is unstable, eg. landfill type areas, peat, swamp or in clay areas subject toswelling/shrinking, the width of the backfill must be increased to a minimum of half the tankdiameter between the tank sides and the ends of the excavation.

If the base of the excavation is also of unstableground, allow for 250-300mm of hardcore.After placing the hardcore, consolidate andcover with a polythene membrane prior toplacing concrete.

Note: If mechanical anchoring is required,sinkers will need to be cast into the concretecradle. See mechanical anchoring on page 4.11and 4.12.

1. Place concrete along the centre of theexcavation base and lower the tank intoposition ‘puddling’ it into the concrete toform cradle. Consolidate under the tank toprevent voids. Consolidate by hand– do not use vibrating pokers.

2. Check the tank is truly vertical, level andinlet/outlet invert levels are correct.

3. Place first 300mm lift of backfill evenlyaround the tank by shovelling and pushingaround the tank sides, between ribs and enddomes to ensure complete supportand to eliminate voids. (Where accessis confined long handled probes, curvedto enable reaching the underside of the tank,can be used). After placing first lift ofbackfill the remainder of the backfillcan be poured without further consolidationby hand.

4. Connect up inlet, outlet and vent pipework,seat access shaft into socket and applywaterproof mastic/adhesive, or as applicable.

5. Where the concrete slab is to be constructedover the tank to take vehicle loading itshould be reinforced in accordance withgood practice to take the maximum load andshould be extended onto unexcavatedground. It is important that vehicle loading isnot transferred to the tank itself.


Note: Where the tank is divided into chambersensure all chambers are filled equally. Wherethe chambers may require to be separatedby load bearing partitions to accommodatedifferent liquid levels the tank must besurrounded in concrete.

Pea gravel or other similar,freeflowing, clean roundedaggregate or selected non-cohesive material

600mm diameter access shaft canbe cut to length on site. Manholecover and frame, set in flush withfinish surface as required

250-300mm hardcoreConcrete cradle to supportone third of circumference


Pea gravel surround2475 (300 series)4250 (500 series)

Ratchet and sinker

3300 (400 series)4750 (600 series)

Concrete anchor pad

100-120

300

600 (300 series)850 (400 series)

1150 (500 series)1300 (600 series)

GRP strap locators

Webbing strap

Water table

300

D&H underground tanksMechanical anchoring

Tank Dia. No cover 150mm coverseries (mm) slab (mm) slab (mm)

300 1800 1200 1100

400 2600 1500 1400

500 3500 1800 1700

Minimum burial depth

The following table shows minimumburial depths when mechanical anchoring is

D&H mechanical anchoring system

Mechanical anchoring is required where thetank is to be surrounded in pea gravel and wherewater could enter into the excavation(underground water table, rainwater run-off etc.)or where the tank is to be surrounded inconcrete and it is imperative the tank does notshift during the placement of this concrete.

D&H mechanical anchoring straps are availablefor all tanks. These are located over thedesignated ribs and held in position by locatorspositioned over the said ribs. Cables or strapsshould not be used between the ribs on the tank.

It is the responsibility of the tank owner orhis technical representative to determine ifmechanical anchoring is required for a specificinstallation.

If water could enter the excavation(underground water table, rainwater run-off etc.)we recommend the tank is mechanicallyanchored unless the minimum depth from tanktop is, as in table on left.

The weight of over burden on top of the concreteanchor pad provides the anchoring force.

The pad is to prevent buoyancy but should bedesigned taking into account soil conditions eg.thickness and reinforcement.

Anchor points should be spaced equal to thetank diameter plus 300mm on each side of thetank regardless of tank diameter. The anchorpoints must be aligned in accordance with thedesignated ribs plus or minus 25mm.

All anchor straps must be uniformly tightenedwith the ratchets. Straps should be a tight, snugfit to the ribs but must not cause the tank todeflect. It is recommended that the ratchets arepositioned on alternate sides of the tank toensure the tank remains vertical duringtensioning.

Check the tanks internal diameter before andafter tensioning the straps with a gauge rod toensure against deflection.

Do not fill with product or water until backfill islevel with top of tank except when backfillingwith concrete.

When backfilling with concrete, we advise thatthe tank is filled with water to a correspondinglevel with the concrete to equalise pressure.Where the tank is divided into chambers, ensureall chambers arefilled equally. See installation procedure forsurrounding in concrete.

Straps must not be placed between the ribs orpassed over from one side to the other asstress will be transferred to the weakest partof the tank wall. Unless the D&H system isused and positioned correctly the 25 yearwarranty will be nullified.

Do not strap here

X X


190

100-120

250

Strap locatorNeoprenenon-slip pad

Strong reinforcing ribs

Strap

Removablebolt

Ratchet

Short lengthof webbing

Galvanisedsinker

Loop to end ofwebbing loop topoint outwards

D&H underground tanksMechanical anchoring

Procedure for ‘anchoring’ tanks down

1. Check contents of kit.

2. Install the galvanised sinker into the pre- castpockets of the concrete base. These must lineup with the ribs of the tank. The ‘holdingdown’ ribs are indicated on the tank by a‘strap’ label.

3. Using the ‘short’ length of webbing, pass theloop of the webbing through the sinkerbringing it back on itself, then pass theremaining webbing through the loop and pulltight. (Sketch 1).

4. Taking the ratchet, remove the bolt. Place thetop loop of the ‘short’ length of webbingbetween the opening from where the bolt hasbeen removed and replace the bolt. (Sketch2). Note the arm of the ratchet should befacing outwards.

5. Attach the ‘long’ length of the webbing tothe opposite galvanised sinker in a similarway to that described in Stage 3. Then throwthe remaining length of webbing over thetank, making sure that the webbing is nottwisted.

6. Slide the GRP strap locators on to the ‘long’length of webbing and position the locatorsas shown in the drawing (see previous page).

7. Taking the end of the ‘long’ length ofwebbing, thread it through the slot of theratchet and tighten up using the ratchet armto give required tension.

8. On completion the ratchet tensioners shouldbe well wrapped in ‘DENSO’ or similar tapefor long-term protection ifthe tank is surrounded in pea gravel orsimilar backfill.

Sketch 1 Sketch 2

Sketch 3Anchoring kit contents for300 series:Short length of webbing x 1

Long length of webbing x 1

Galvanised sinker x 2 Ratchet

x 1

GRP strap locators x 3

Anchoring kit contents for400,500 and 600 series:

Short length of webbing x 1

Long length of webbing x 1

Galvanised sinker x 2 Ratchet

x 1

GRP strap locators x 5

Galvanised sinker

Top of sinker shouldprotrude 100-120mm aboveconcrete slab.

Documents

D&H Underground Tanks – speciﬁcations and installation · D&H Underground Tanks – speciﬁcations and installation ... British Standard BS 6297: 1983 recommends that sewage