Reference/Code: BS-EN-14844
Safety:
- WARNING: Erecting concrete elements is a high risk activity. Adequate safety controls must be in place in conformance with legislation and codes of practice.
- A risk assessment must be carried out by the contractor identifying all risks/hazards and measures to control or eliminate the identified risks/hazards. A safe work method statement (SWMS) must be prepared before the high risk construction activity commences.
- The appropriate personal protective equipment (safety eyewear, gloves, hardhats, hi-visibility vests and safety footwear) is to be worn during all stages of installation of concrete elements.
- Equipment shall be fit for its intended purpose and operating conditions and shall be designed to a recognized standard.
Offloading / Handling
- The box culvert should be visually inspected on the truck when it arrives at the jobsite before it is unloaded to ensure that no damage has occurred during transit.
- When handling concrete products, it is important to remember that, as concrete is a heavy and somewhat brittle material, bumps or shock loads of any description are liable to damage the product. This applies particularly to sharp edges.
- All offloading areas provided must be level, hard, drained and free of debris.
- Any culvert is damaged during transit or offloading should be marked and set aside.
- Damaged ends, chips or cracks which do not pass through the wall can easily be repaired. These products should be clearly marked to ensure that the necessary repairs are done before installation.
- Culverts can be offloaded with conventional lifting. However, specialized equipment with safe lifting capacity is recommended.
- The culvert is provided with lifting holes. The most common lifting device consists of a sling with a lifting eye and spreader bar.
- Culverts should only be lifted using the holes provided. A single sling under the deck of a large span portal combined with rough handling can cause cracking along the top of the deck.
- The offloading of culverts must be controlled to prevent collision with other culverts or hard objects.
- If culverts have to be moved long distances from the storage area to the site where they are to be installed, they should be transported in the same way as AOCP delivered them to site.
Storage/Stacking
Double handling should be avoided. However, where the site conditions do not permit, a storage yard away from the laying site will have to be established. The product may then be received at the storage yard and transported to the laying site when required.
The storage area should be level, firm and clear of any objects that may cause damage to the products.
Storage area clear of combustible materials and free from storm water flooding should be selected.
Any storage of products should be as near as possible to where the products will be installed.
If culverts have to be moved long distances from the storage area to the site where they are to be installed, they should be transported in the same way as the AOCP delivered them to site.
Site Preparation
In all circumstances site activity should be conducted in a safe manner. All ancillary materials and equipment should be readily available on site prior to commencement of work, including lifting provisions. Trenches should be wide enough to ensure safe installation and allow for compaction of backfill to box sides.
Bedding: The box culvert foundation is typically referred to as bedding. The bedding under the box culvert must be able to support the full load of the installed box culvert, its contents, and the loading above the box culvert. The bottom of the excavation should be free of irregularities and local hard or soft areas, which should be removed and brought up to level with well-compacted granular material. Bedding will be of granular material with adequate thickness and good leveling. Special circumstances, e.g. low ground bearing capacity, may lead to other forms of foundation.
The minimum thickness of the bedding material is six inches, or it can be greater if required by the project specifications. The bedding, made up of medium granular material, should be installed and compacted to provide uniform support for the full length and width of each box culvert section. A two inch minimum thickness leveling course of fine granular base material can be used as required to achieve a level bedding surface. The final grading for the bedding should be done with a laser or level and grade stakes. For the final grading, the granular material should be screeded using a screed board as long as the width of the outside span of the box. If properly done, the final grading will allow an easier installation while setting the box culvert sections. Improper bedding could prevent the tongue of the box from being properly started into the groove. It is very important that time be spent to ensure the box culvert bedding preparation is done correctly.
Product Installation
Laying: A box culvert line is usually laid from the downstream end. For box culverts with sockets, the sockets are usually placed at the upstream end to receive the next box culvert to be laid.
Before laying the box culverts they should be inspected to ensure that they are clean and undamaged.
Lower the box culvert carefully on to the prepared base aligning the spigot with the socket of the unit already laid.
Prevent loose surface bedding material from entering the joint space during positioning of the unit.
If any adjustment to level is necessary, remove the box culvert and adjust the surface layer of the bedding. Do not use local packing such as stones, wooden pieces to adjust the level.
Accumulation of water in the excavation should be prevented by appropriate dewatering methods. Units should be laid by specialist contractors/installers in accordance with the manufacturer's instructions. Special care to be taken while pushing the adjacent boxes so that edges are not broken.
Drainage sheets at the bottom of the excavation and lateral drainage may be used if water could affect the completed construction.
Joints: Box culverts are carefully lowered into the trench on a well compacted gravel base or blinding concrete where applicable. The edges of boxes to be joined are cleaned using a cloth or nylon wire brush. The annular gap between male and female ends should be adequately spaced to receive cement grout or mastic sealant as joint material.
For grout fill, use of polythene sheet of at least 200mm wide and wrap on 3 sides of the box outer periphery like a diaper and tie the ends with wire straps is recommended. Top end of the joint will be left open for pouring of grout. Close the inner periphery of the joint with wood strips on all sides. The annular space of the joint is now ready to receive the grout.
For mastic sealant no such polyethylene sheet is required
Preparation of grout and placing:
Pre- Soaking: All concrete surfaces should be saturated with clean, fresh water prior to grouting. Immediately before grouting takes place, any free water should be removed.
Mixing: Add 4-4.5 litres water for flow consistency of the mix for a 25 kg bag. Measure out appropriate quantity of clean water into the mixer.
Slowly add the full pack of grout material to the water and mix continuously for 3 to 5 minutes, until a smooth, free flowing consistency is obtained.
Pouring: Pour the grout from one end so that the flow covers all three sides. After this, pour the grout on top end of the joint. Allow 3 hours for the grout to solidify. Cut the wire straps and remove the polythene diaper and inner wood strips for reuse.
Backfilling: Backfill shall be placed uniformly on each side of the precast concrete box sections. The backfill material to be placed, the percent of compaction, the depth of layers, etc., shall be as required by the contract specifications.
Key Notes & Precautions
- Improper bedding: Most joint annular spaces are Ό-inch to ½-inch. If the bedding is irregular, lining up the tongue with the receiving groove will be difficult. Because boxes are wide and flat, any irregularities in the bedding can prevent the tongue of the box from being properly started into the groove. If this is apparent before attaching the winches and anchors, pull the box out of the way and properly prepare the bedding.
- Use of granular material with an excess percentage of fines: If the trench is wet, the fines will not provide a stable work area.
- Standing water in the trench: It is difficult to judge the grade and uniformity of the granular bedding, to properly dig an adequate groove hole, and to ensure that no dirt or granular material is in the groove when water is standing in the trench.
- Boxes do not hang plumb: This may be caused by improper cable or rigging location. If using a four-part sling, longer or shorter clevises may help alleviate the problem. Be consistent in hooking the rigging to the box culvert.
- Pulling the box into the home position unevenly: Care should be taken to ensure that both vertical portions of the tongue get started evenly into the groove of the previously set box.
- Ensure that adequate inspection / examination and maintenance of the equipment have been carried out prior to its use.
- The crane or lifting equipment operator should be competent and suitably trained and must be experienced to carry out all relevant duties.
Gallery
Tunnels
Storm Water Conveyance
Tunnel & Escape Routes
Reference/Code: ASTM C 1479-10
Safety:
- WARNING: Erecting concrete elements is a high risk activity. Adequate safety controls must be in place in conformance with legislation and codes of practice.
- A risk assessment must be carried out by the contractor identifying all risks/hazards and measures to control or eliminate the identified risks/hazards. A safe work method statement (SWMS) must be prepared before the high risk construction activity commences.
- The appropriate personal protective equipment (safety eyewear, gloves, hardhats, hi-visibility vests and safety footwear) is to be worn during all stages of installation of concrete elements.
- Equipment shall be fit for its intended purpose and operating conditions and shall be designed to a recognized standard.
Offloading / Handling
- The Pipe should be visually inspected on the truck when it arrives at the jobsite before it is unloaded to ensure that no damage has occurred during transit.
- When handling concrete products, it is important to remember that, as concrete is a heavy and somewhat brittle material, bumps or shock loads of any description are liable to damage the product. This applies particularly to sharp edges.
- All offloading areas provided must be level, hard, drained and free of debris.
- Any Pipe is damaged during transit or offloading should be marked and set aside.
- Damaged ends, chips or cracks which do not pass through the wall can easily be repaired. These products should be clearly marked to ensure that the necessary repairs are done before installation.
- Pipe can be offloaded with conventional lifting. However, specialized equipment with safe lifting capacity is recommended.
- The offloading of Pipe must be controlled to prevent collision with other Pipe or hard objects.
- If Pipe have to be moved long distances from the storage area to the site where they are to be installed, they should be transported in the same way as AOCP delivered them to site.
Storage/Stacking
Double handling should be avoided. However, where the site conditions do not permit, a storage yard away from the laying site will have to be established. The product may then be received at the storage yard and transported to the laying site when required.
The storage area should be level, firm and clear of any objects that may cause damage to the products.
Storage area clear of combustible materials and free from storm water flooding should be selected.
Any storage of products should be as near as possible to where the products will be installed.
If Pipe have to be moved long distances from the storage area to the site where they are to be installed, they should be transported in the same way as the AOCP delivered them to site.
Site Preparation
Site preparation can significantly influence progress of the project. The amount and type of work involved in site preparation varies with the location of the project, topography, surface conditions, and existing utilities. Commonly included are:
- Detours and traffic control signing
- Access roads
Clearing and grubbing
- Tree relocation or protection
- Stripping and stockpiling topsoil
- Pavement and sidewalk removal
- Management of excess material
- Relocation of existing natural drainage
- Notifications and protection of existing structures and all utilities
- Environmental considerations, such as temporary erosion and sediment control.
Product Installation
Line and Grade
For sewer construction, where the pipe is installed in a trench, line and grade are usually established by one, or a combination of the following methods:
- Control points consisting of stakes and spikes set at the ground surface, and offset a certain distance from the proposed sewer centerline
- Control points established at the trench bottom, after
- The trench is excavated
- Trench bottom and pipe invert elevations established while excavation and pipe installation progresses
- Global Positioning System (GPS)
Important
Line and grade should be checked as the pipe is installed, and any discrepancies between the design and actual alignment and pipe invert elevations should be corrected prior to placing the backfill or fill over the pipe.
Obtaining manhole invert levels for the preparation of as- built drawings, combined with visual inspection of the sewer or culvert, provide an additional check that settlement has not occurred during backfill or fill operations.
Where control points are established at the surface and offset, lasers, transits, batter boards, tape and level, or specially designed transfer instruments, are used to transfer line and grade to the trench bottom. Regardless of the specific type of transfer apparatus used, the basic steps are:
- Stakes and spikes, as control points, are driven flush with the ground surface at 7.5 to 15m intervals for straight alignment, with shorter intervals for curved alignment.
- Offset the control points 3m, or another convenient distance, on the opposite side of the trench from which excavated material will be placed.
- Determine control point elevations by means of a level, transit or other levelling device. Drive a guard stake to the control point, and mark the depth of the control point from the control point to the trench bottom or pipe invert.
- After the surface control points are set, a grade sheet is prepared listing reference points, stationing, offset distance and vertical distance from the control points to the trench bottom or pipe invert.
Transferring the line and grade along the trench bottom is achieved by using a laser system, or a batter board system.
The laser system, the most commonly used system, uses a transit or level to set the starting point on the trench bottom. As with any surveying instrument, the initial setting is most important. Once the starting point is established, the laser can be set for direction and grade. Lasers can be used for distances up to 300 m (average runs for pipe installations are 90 to 150 m). The projected beam is intercepted along the trench bottom with a target, placed in the bell that accepts the light.
Temperature can affect the trueness of the laser beam; therefore, it is helpful to keep the line well ventilated. The laser instrument can be mounted in a maintenance hole, set on a tripod or placed on a solid surface to project the light beam either inside, or outside the pipe. A workman with any ordinary rule, or stadia rod, can measure offsets quickly and accurately, generally within 2 mm or less.
There are two types of batter board systems. One type is incorporated for narrow trenches, the other for wide trenches.
For narrow trenches, a horizontal batter board is spanned across the trench, and adequately supported at each end. The batter board is set level at the same elevation as the string line, and a nail driven in the upper edge, at the centre line of the pipe. In many cases the batter board is used only as a spanning member, with a short vertical board nailed to it at the pipe centerline. A string line is pulled tight across a minimum of three batter boards, and the line transferred to the bottom by a plumb bob cord held against the string line. Grade is transferred to the trench bottom by means of a grade rod, or other suitable vertical measuring device.
Where wide trenches are necessary, due to large pipe sizes or sloped trench walls, the batter board may not be able to span the width of excavation. In such cases, the same transfer principle is used, except that the vertical grade rod is attached to one end of the batter board, and the other end set level against the offset string line. The length of horizontal batter board is the same as the offset distance. The length of the vertical grade rod is the same as the distance between the pipe invert and the string line.
Specially designed instruments are available which incorporate a measuring tape, extendible arm and levelling device. These instruments are based on the same principle, but eliminate the need to construct batter boards and supports.
Equipment
Several types of excavating equipment are available. Selection of the most efficient piece of equipment for a specific excavation operation is important, since all excavating equipment has practical and economic limitations. Considerations include the type and amount of material to be excavated, depth and width of excavation, dimensional limitations established in the plans, pipe size, operating space and spoil placements. Basic equipment can usually be modified or adapted for use in most excavating operations.
Excavation
For sewer construction, the scope of operations involved in general excavation includes trenching, tunnelling, backfilling, embankment construction, soil stabilization, and control of ground water and surface drainage. Adequate knowledge of subsurface conditions is essential for any type of excavation.
This is accomplished through soil surveys and subsequent soil classification. Soil borings are usually obtained for design purposes, and the information included on the plans, or made available to the contractor in a separate document. This soil boring information is useful in evaluating unsuitable subsoil conditions requiring special construction. If the subsoil information on the plans is not sufficiently extensive, it is normally the responsibility of the contractor to obtain additional test borings.
Excavated Material
The placement of excavated material is an important consideration in sewer construction, and may influence the selection of excavating equipment, the need of providing sheathing and shoring, and backfill operations.
In trench installations, the excavated material is usually used for backfill, and should be placed in a manner that reduces re-handling during backfilling operations. As a general rule, for unsupported trenches, the minimum distance from the trench to the toe of the spoil bank should not be less than one half the trench depth. For supported trenches, a minimum of one metre is normally sufficient.
Stockpiling excavated material adjacent to the trench causes a surcharge load, which may cave in trench walls.
The ability of the trench walls to stand vertically under this additional load depends on the cohesion characteristics of the particular type of material being excavated. This surcharge load should be considered when evaluating the need to provide trench support. It may be necessary, where deep or wide trenches are being excavated, to haul away a portion of the excavated soil, or spread the stockpile with a bulldozer, or other equipment. If the excavated material is to be used as backfill, the stockpiled material should be visually inspected for rocks, frozen lumps, highly plastic clay, or other objectionable material.
If the excavated soil differs significantly from the backfilled material set forth in the plans, it may be necessary to haul the unsuitable soil away and bring in selected backfill material.
Spoil placement for culvert installations is usually not as critical as trench installation. If the excavated material is suitable for the embankment construction, it can be immediately incorporated into the embankment adjacent to the culvert. If using imported materials, care must be taken so that the frost susceptibility is the same as the native material. Top soil, or other highly organic soils, are usually stockpiled outside the top of the embankment slope, and used for dressing the slopes after the embankment is constructed.
Dewatering
Dewatering of trenches and excavations should be undertaken in order to keep the excavation stable and free of water. Dewatering efforts must be monitored for impacts such items as settlement and ground water usage. When dewatering efforts are no longer required they must be arrested such that no disturbance to the pipe will occur.
Water from dewatering operations must be disposed of in accordance with local regulations. Pumped water requires that it be filtered through a sediment control device and disposed of such that it does not impact public health or safety, property or the environment. Water should not be directed over pavements or sidewalks or effect the functionality of settling ponds and sediment basins.
Excavation Limits
It is the contractor's responsibility to adhere to all Occupational Health and Safety Act requirements for excavations. The sloping requirements for Soil shall follow as per drawings.
In general no more than 15 m of trench be open in advance of the completed pipe system.
The most important excavation limitations are trench width and depth. As excavation progresses, trench grades should be periodically checked against the elevations established on the sewer profile.
Improper trench depths can result in high or low spots in the line, which may adversely affect the hydraulic capacity of the sewer, and require correction, or additional maintenance, after the line is completed. If the trench depth is excavated beyond the limits of the required excavation, granular material should be placed and compacted in the trench to reinstate the required trench limits prior to backfilling the trench.
The backfill load transmitted to the pipe is directly dependent on the trench width at the crown of the pipe. To determine the backfill load, the designer assumes a certain trench width, and then selects pipe strength capable of withstanding this load. If the constructed trench width exceeds the maximum trench width specified in the design, the pipe may be overloaded and may require the use of a stronger pipe or a higher class of bedding, or both. Where maximum trench widths are not indicated in any of the construction contract documents, trench widths should be as narrow as possible, with side clearance adequate enough to ensure proper compaction of backfill material at the sides of the pipe.
When unstable soil conditions are encountered, sheathing or shoring can be used, or the banks of the trench can be sloped to the natural angle of repose of the native soil. If the trench sides are allowed to slope back, the pipe should be installed in a shallow sub trench excavated at the bottom of the wider trench. The depth of the sub trench should be at least equal to the vertical height of the pipe.
For a confined trench installation, the following trench widths at the top of the pipe are recommended:
| CLEARANCE TABLE |
Pipe Inside Diameter
(mm) |
Clearance
(mm) |
| 900 or less |
300 |
| Over 900 |
500 |
Sheathing and Shoring
Trench stabilization is usually accomplished through the use of sheathing and shoring. The structural requirements of sheathing and shoring depend on numerous factors such as:
- Depth and width of excavation
- Characteristics of the soil
- Water content of the soil
- Weather conditions
- Proximity to other structures
- Vibration from construction equipment or traffic
- Soil placement or other surcharge loads
- Code requirements
Accurate evaluation of all of these factors is usually not possible, so the design and application of temporary bracing systems varies considerably. However, certain methods of stabilizing open trenches have evolved and can be used as a general guide.
Shoring for trenches is accomplished by bracing one bank against the other; structural members which transfer the load between the trench sides are termed struts. Wood planks placed against the trench walls to resist earth pressure, and retain the vertical banks, are termed sheathing. The horizontal members of the bracing system, that forms the framework bearing against the sheathing or termed whalers or stringers, and the vertical members of the bracing system are termed strong backs.
Improper removal of sheathing can reduce the frictional effects, and increase the backfill load on the pipe, so sheathing should be removed in increments, as the backfill is placed. Additional compaction of the backfill material may be necessary to fill the voids behind the sheathing, as it is removed. The four common sheathing methods are:
- Open sheathing
- Close sheathing
- Tight sheathing
- Trench shields or boxes
Open Sheathing
Open sheathing consists of a continuous frame, with vertical sheathing planks placed at intervals along the open trench. This method of sheathing is used for cohesive stable soils, where groundwater is not a problem.
Close Sheathing
Close sheathing consists of a continuous frame, with vertical sheathing planks placed side by side to form a continuous retaining wall. This method of sheathing is used for non-cohesive and unstable soils.
Tight Sheathing
Tight sheathing is similar to closed sheathing, except the vertical sheathing planks are interlocked. This method of sheathing is used for saturated soils. Steel sheet piling is sometimes used instead of wood planking.
Trench Boxes
Trench boxes, or shields, are heavily braced boxes of steel, or wood, which can be moved along the trench bottom as excavation and pipe laying progress. Trench boxes are used to protect workers installing pipe in stable ground conditions, where the trenches are deep and not sheathed. Trench shields are also used in lieu of other methods of shoring and sheathing for shallow excavations
where the sides of the shields can extend from the trench bottom to ground surface. When trench shields are used, care should be taken when the shield is moved ahead, so as not to disturb the bedding or pull the pipe apart.
Foundation Preparation
A stable and uniform foundation is necessary for satisfactory performance of any pipe. The foundation must have sufficient load bearing capacity to maintain the pipe in proper alignment and sustain the mass of the backfill, or fill material placed over the pipe. The trench bottom foundation should be checked for hard or soft spots, due to rocks or low load-bearing soils. Where undesirable foundations exist, it should be stabilized by ballasting, or soil modification.
Ballasting requires removal of the undesirable foundation material and replacing it with select materials such as sand, gravel, crushed rock, slag, or suitable earth backfill. The depth, gradation, and size of the ballast depend on the specific material used and the amount of stabilization required, but usually the ballast should be well graded.
Soil modification involves the addition of select material to the native soil. Crushed rock, gravel, sand, slag, or other durable inert materials with a maximum size of 75 mm, is worked into the subsoil to the extent necessary to accomplish the required stabilization.
In rock, shale or other hard, unyielding soils, the excavation should be continued below grade, and the over-excavation replaced with select material to provide a cushion for the pipe.
Pipe Bedding
Once a stable and uniform foundation is provided, it is necessary to prepare bedding in accordance with the bedding requirements set forth in the plans, specifications or standard drawings.
An important function of the bedding is to level out any irregularities in the foundation, and assure uniform support along the barrel of each pipe section. The bedding is also constructed to distribute the load bearing reaction, due to the mass of the backfill or fill material, around the lower periphery of the pipe. The structural capacity of the pipe is directly related to this load distribution, and several types of bedding have been established to enable the specification of pipe strengths during the design phase.
The following general requirements should be followed:
- When bell and spigot pipe is to be laid, recesses should be shaped to receive the bells.
- Bedding material placed in the haunches must be compacted prior to continued placement of cover material.
- Bedding requiring compacting should be placed inlayers not exceeding 200 mm in thickness, loose measurement, and compacted to 95% of the max. Density before a subsequent layer is placed.
- Bedding on each side of the pipe should be completed simultaneously. At no time should the levels on each side differ by more than the 200 mm uncompacted layer.
For trench installations, where space is limited, tamping or pneumatic and mechanical impact tampers kneading action, are primarily useful for soils containing clays. Granular soils are most effectively consolidated by vibration. Compaction equipment can generate significant dynamic forces capable of damaging installed pipe.
Bell holes should be excavated to accommodate projecting joints, and to provide support along the barrel of the pipe.
Bedding Materials
Materials for bedding should be selected on the basis that uniform contact can be obtained between the bed and the pipe. Since most granular material will shift to attain this uniform contact as the pipe settles, an ideal load distribution can be realized.
Bedding material is Granular in 25 mm or less in size, or unshrinkable fill, as specified in the Contract documents.
Class B Bedding
Granular Foundation:
- A granular foundation without shaping is used only with circular pipe.
- The pipe is bedded in compacted granular material placed on the flat trench bottom.
- The granular bedding has a minimum specified thickness, and should extend at least half way up the pipe at the sides.
- The remainder of the side fills, and a minimum depth of 300 mm over the top of the pipe, should be filled with densely compacted material.
Shaped Sub grade:
- For a shaped sub grade with granular foundation, the bottom of the excavation is shaped to conform to the pipe surface but at least 50 mm greater than the outside dimensions of the pipe.
- The width should be sufficient to allow 0.6 times the outside pipe diameter for circular pipe, 0.7 times the outside span for arch and elliptical pipe, and the full bottom width of box sections to be bedded in fine granular fill placed in the shaped excavation.
- Densely compacted backfill should be placed at the sides of the pipe to a depth of at least 300 mm above the top of the pipe.
Class C Bedding
Granular Foundation:
- Used only with circular pipe, the pipe is bedded in loosely compacted granular material, or densely compacted backfill placed on a flat bottom trench.
- The bedding material should have a minimum specified thickness, and should extend up the sides for a height of at least 0.15 times the outside diameter.
- For trench installations, the side fill and area over the pipe to a minimum depth of 150 mm should be filled with compacted backfill.
Shaped Sub grade:
- The pipe is bedded with ordinary care in a soil foundation, shaped to fit the lower part of the pipe exterior with reasonable closeness for a width of at least 0.5 times the outside diameter for a circular pipe, 0.15 times the outside pipe rise for elliptical pipe, and full bottom width of box units
- For trench installations, the sides and area over the pipe are filled with lightly compacted backfill to a minimum depth of 150 mm above the top of the pipe.
- For embankment installations, the pipe should not project more than 90% of the vertical height of the pipe above the bedding.
Cover
- Cover material is Granular 25 mm or less in size, or native material, as specified in the Contract Documents.
- Cover material should be placed so that damage to or movement of the pipe is avoided.
- Cover material requiring compacting should be placed in layers not exceeding 200 mm in thickness, loose measurement, and compacted to 95% of the maximum dry density before a subsequent layer is placed.
- Cover material should be placed on each side of the pipe and should be completed simultaneously. At no time should the levels on each side differ by more than the 200 mm uncompacted layers.
When single cell boxes are used in parallel for multi-cell installations, positive lateral bearing must be provided between the sides of adjacent units. This is accomplished with grout to fill the 50mm annular space.
Backfill
- Backfill material is Granular 25 mm or less in size, or native material, as specified in the Contract Documents.
- Backfill material should be placed in uniform layers not exceeding 300 mm in thickness for the full width of the trench and each layer should be compacted to 95% of the maximum dry density before a subsequent layer is placed.
- Backfill should be placed to a minimum depth of 900 mm above the crown of the pipe before power operated tractors or rolling equipment should be used for compacting. Uniform layers of backfill material exceeding 300 mm in thickness may be placed with the approval of the Contract Administrator.
- If the contract specifies native backfill material, acceptable earth backfill material may be substituted with the approval of the Contract Administrator.
- In areas within the roadway, for a depth equal to the frost treatment, the earth backfill material should have frost susceptible characteristics similar to the adjacent material.
Handling
Proprietary lifting systems are used for various precast concrete products, including pipe, maintenance holes, and box units. These systems offer a positive lifting connection to the pipe for added safety, and since the anchors are embedded, patching is not required.
Important
The work procedures for material handling, worker safety, the modification of backhoes for use as cranes and all components of any lifting assembly must comply with the Occupational Health and Safety Act requirements for Construction Projects. A competent person designated by the contractor should inspect all lifting assemblies and attachment hardware prior to each use. Any damage or defective equipment must be immediately removed from service. All other safety procedures and recommended operating practices by the manufacturer of the lifting equipment must be followed. Failure to observe the above warnings may lead to property damage, personnel injury and death.
Load-Carrying Capacity of Lift Anchors
The MAXIMUM safe working load is clearly visible on the head of the anchor for easy recognition of the appropriate hardware and accessories for-use with the lift anchor. However the safe working load of any lift anchor may be drastically reduced due to several factors, such as:
- Length of anchor, or embedment depth
- Distance to edges, corners or openings
- Concrete compressive strength at time of initial lift
- Number of lifting points and type of rigging used
- Direction of pull (cable or sling angle)
- Impact or dynamic loads
Handling Pipe
In pipe, anchors are placed laterally along the top of the pipe. These anchors can accommodate pipe diameters from 975mm to 3600mm. Because the pipe is lifted by two points, stability during lifting is established.
How to Use Lift Anchors for Setting Pipe
Lift anchors in concrete pipe can be used to "home" or pull the product into its final position with a special chain sling such as the P-74-S Pipe Laying Sling by Dayton Superior, shown below.
1. The pipe is first transported to the installation site with the symmetrical sling and lowered close to the already placed pipe.
2. The long leg of the Pipe Laying Sling is attached to the farthest anchor on the previously laid pipe. The free leg is attached out of the way on the clevis link provided.
3. Locate the center of lift over the closest anchor of the previously laid pipe. This will properly align the direction of pull.
4. The pipe is pulled into position by slowly raising the boom on the crane or backhoe without moving the boom forward or backward.
5. When the pipe has been pulled into position, the load is released and the Pipe Laying System is moved to the next pipe, and the process is repeated.
Warning: Anchors can become overloaded and fail if the crane or back hole continues to apply load after the connection has been completed.
Jointing
Pipe should be lowered into the trench, or set in place for embankment installations, with the same care as when the pipe was unloaded from the delivery trucks.
In laying the pipe, it is general practice to face the bell end of the pipe in the upstream direction. This placing helps prevent bedding material from being forced into the bell during jointing, and enables easier coupling of pipe sections.
Jointing Materials
Several types of joints and sealant materials are utilized for concrete pipe, to satisfy a wide range of performance requirements. All of the joints are designed for ease of installation. The manufacturer's recommendations regarding jointing procedures should be closely followed to assure resistance to infiltration of groundwater and/or backfill material, and exfiltration of sewage or storm water.
The most common joint sealants and joint filers used for sanitary sewers, storm sewers, and culverts are:
- Rubber gasket attached or separate
- Mastic, bulk or preformed
- Mortar
Rubber Compound
Rubber gaskets are of three basic types:
- Pre-lubricated gasket for single offset joints, with one flat side, which is placed on the pipe spigot. This is the gasket type most commonly used for standard concrete gravity pipe.
- Profile gasket for single offset joints, with one flat side, which is placed on the pipe spigot
- O-ring, which is recessed in a groove on the spigot, and confined by the bell, after the joint is completed
For all gasket types, dirt, dust, and foreign matter must be cleaned from the joint surfaces. Except for pre-lubricated type, the gasket and bell should be coated with a lubricant recommended by the manufacturer. The lubricant must be clean and be applied with a brush, cloth pad, sponge or glove. In some cases, a smooth round object, such as a Screwdriver shaft should be inserted under the gasket and run around the circumference two or three times, to equalize the stretch in the gasket, before jointing.
Rubber gaskets are required to be stored in a sheltered cool dry place. They need to be protected from prolonged exposure to sunlight, extreme heat in the summer, and extreme cold in the winter. Proper care of the gaskets prior to the installation will ensure maximum ease of installation, and maximum sealing properties.
Gaskets are generally formulated for maximum sealing performance in a standard sewer installation carrying
Primarily storm water or sanitary sewage. Custom rubber formulations are available for special situations, where specific elements are being carried in the effluent. Some common examples of where a custom formulation would be required are where resistance is needed against hydrocarbons, acids, UV rays, ozone, and extreme heat.
Mastic Sealant Jointing
Mastic sealants consist of bitumen or butyl rubber and is usually cold applied. The joint surfaces must be thoroughly cleaned, dried and prepared in accordance with the manufacturer's recommendations.
Typically supplied in pre-formed coils, the flexible rope style sealant should be properly sized based on the width of the annular joint space being sealed.
During cold weather, better workability of the mastic sealant can be obtained if the mastic and joint surfaces are warmed.
Mortar
Mortar for joints is composed of one part normal Portland cement and two parts mortar sand, wetted with only sufficient water to make the mixture plastic.
The joint surface is thoroughly cleaned and soaked with water immediately before the joint is made. A layer of mortar is placed in the lower portion of the bell end of the installed pipe and on the upper portion of the spigot end of the pipe section to be installed. The spigot is then inserted into the bell of the installed pipe until the sealant material is squeezed out. Any annular space within the pipe joint is filled with mortar, and the excess mortar on the inside of the pipe is wiped and finished to a smooth surface.
Regardless of the specific joint sealant used, each joint should be checked to be sure all pipe sections are in a homed position. For joints sealed with rubber gaskets, it is important to follow the manufacturer's installation recommendations to ensure that the gasket is properly positioned, and is under compression.
External Bands
External bands may be used in addition to any jointing material to serve two functions:
- Prevent fine materials from entering the joint
- Prevent infiltration of groundwater
If the prevention of bedding material from entering the conveyance system is the primary objective, filter fabric, while allowing the groundwater to infiltrate, will stop the bedding backfill material from entering.
To prevent the infiltration of water, external extruded rubber gaskets are utilized. The gasket must be of sufficient width to cover the joint, and must be installed with some tension applied, according to the manufacturer's recommendations. As the joint is backfilled, pressure is applied to the gasket as it is pressed against the structure, providing a seal at the joint.
Jointing Procedures
Joints for pipe sizes up to 600 mm in diameter can usually be assembled by means of a bar and wood block. The axis of the pipe section to be installed should be aligned as closely as possible to the axis of the last installed pipe section, and the tongue, or spigot, end inserted slightly into the bell, or groove. A bar is then driven into the bedding and wedged against the bottom bell, or groove, end of the pipe section being installed. A wood block is placed horizontally across the end of the pipe to act as a fulcrum point, and to protect the joint end during assembly. By pushing the top of the vertical bar forward, lever action pushes the pipe into a home position.
When jointing medium diameter pipe, a chain or cable is wrapped around the barrel of the pipe behind the tongue, or spigot, and fastened with a grab hook, or other suitable connecting device. A lever assembly is anchored to the installed pipe, several sections back from the last installed section, and connected by means of a chain, or cable, to the grab hook on the pipe to be installed. By pulling the lever back, the tongue, or spigot, of the pipe being jointed is pulled into the bell, or groove, of the last installed pipe section. To maintain close control over the alignment of the pipe, a laying sling can be used to lift the pipe section slightly off the bedding foundation.
When jointing larger diameter pipe, and when granular bedding is used, mechanical pipe pullers are required. Several types of pipe pullers, or "come along" devices, have been developed, but the basic force principles are the same.
Large diameter pipe can be joined by placing a "dead man" block inside the installed pipe, several sections back from the last installed section, which is connected by means of a chain or cable to a strong back placed across the end of the pipe section being installed. The pipe is pulled home by lever action similar to the external assembly. Mechanical details of the specific apparatus used for pipe pullers, or come along devices, may vary, but the basic lever action principle is used to develop the necessary controlled pulling force.
Note: The excavating equipment must not be used to push pipe sections together or to adjust pipe to the final grade. The force applied by such equipment can damage pipe joints.
Summary of Jointing Procedures for Pre- lubricated Gasket for Single Offset Joints
The unique design of the pre-lubricated pipe gasket requires no field lubrication and no equalization after installation.
Installation:
1. Ensure that bell and spigot are free from cracks, chips, or other defects.
2. Brush loose dirt, debris and foreign material from the inside surface of the bell, the spigot and the
gasket.
3. Stretch gasket around the spigot, with the nose against the step, and the tube laying flat against the spigot.
4. Align the spigot with the bell, and thrust the spigot home using suitable mechanical means. The Homing process will cause the lubricated tube to "roll" over itself, above the compression section, allowing the pipe to slide forward.
Once the pipe is fully homed,
- The compression section seals the total annular space
- The rolling tube comes to rest within the small annular space acting as a cushion against side loads
- The serrations act to resist pipe pull-out.
Summary of jointing procedure of Rubber Gasket
Service Connections
Service connections to the main pipe sewer should be made using factory made tees or wyes, strap-on-saddles, or other approved saddles. Factory made tees or wyes should be used for all service connections where the diameter of the main pipe sewer is:
- Less than 450 mm, or
- Less than twice the diameter of the service connection.
Holes in the main pipe sewer should be cut with approved cutters and should be the minimum diameter required to accept the service connection. If mortar-on saddles are used, the inside of the pipe should be mortared at the connection.
Where existing service connections are to be connected to new pipe sewers or service connections, proper jointing procedures must be used.
Changes in Alignment
Maintenance holes should be used when there is a need to change alignment, grade or size of a pipeline. Alignment
Changes in concrete pipe sewers can also be incorporated into the line through the use of deflected straight pipe, radius pipe, or bends. Since manufacturing and installation feasibility are dependent on the particular method used to negotiate a curve, it is important to establish the method prior to excavating the trench.
- For deflected straight pipe, the joint of each pipe section is opened on one side while the other side remains in the home position. The difference between home and opened joint space is generally designated as the pull. The maximum permissible pull must be limited to that opening which will provide satisfactory joint performance. This varies for different joint configurations and is best obtained from the pipe manufacturer.
- When establishing alignment for radius pipe, the first section of radius pipe should begin one half of a radius pipe length before the beginning of curve, and the last section of radius pipe should extend one half of a radius pipe length beyond the end of curve.
- When extremely sharp curves are required, deflected straight pipe or radius pipe may not be suitable. In such cases, bends or elbows may be used.
One or more of these methods may be employed to meet the most severe alignment requirements. Since manufacturing processes and local standards vary, local concrete pipe manufacturers should be consulted to determine the geometric
Key Notes & Precautions
- Improper bedding: Most joint annular spaces are Ό-inch to ½-inch. If the bedding is irregular, lining up the Bell with the receiving Spigot will be difficult.
- Use of granular material with an excess percentage of fines: If the trench is wet, the fines will not provide a stable work area.
- Standing water in the trench: It is difficult to judge the grade and uniformity of the granular bedding, to properly dig an adequate groove hole, and to ensure that no dirt or granular material is in the groove when water is standing in the trench.
- Pulling the pipe into the home position unevenly: Care should be taken to ensure that both portions of the Bell get started evenly into the Spigot of the previously set Pipe.
- Ensure that adequate inspection / examination and maintenance of the equipment have been carried out prior to its use.
- The crane or lifting equipment operator should be competent and suitably trained and must be experienced to carry out all relevant duties.
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