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Independent Concrete Pipe

Installation Information | Box Culverts

TOOLS AND EQUIPMENT

  • (2) - 3Tn chain winches w/min. of 3' of chain, and handles
  • (4) - 8"x8" timbers or equivalent I beams,  2' longer than the outside vertical dimension of the box
  • 3/8" x 20' chains - (quantity depends on length of the culvert)    
  • 4-way spreader cable - if not already w/ crane
  • Buckets
  • Burke 8 T lifting equipment, if Rapid Lift anchors are used
  • Cable chokers, 3/4" or 5/8" - pairs of 4, 6, and 8 foot lengths
  • Concrete Nails
  • Hoe
  • Level
  • Manhole cables and spoons
  • Re-bar stakes
  • Shims
  • Shovels
  • Sledge Hammer
  • String
  • Tool Bag
  • Trowels
  • Two screw shackles 1/2"
  • Two screw shackles 5/8"

MATERIALS

  • Bags of Mortar Mix
  • Joint Material
  • Joint Wrap
  • Patching Material
  • Plugs for lift holes
  • Sealing Material

DELIVERY

Scheduling

Be certain to know the weight of each box section, the number of sections to be hauled on each load, what joint and/or wrap material is to be used and delivery schedule of that material. 10x8 and larger boxes require lo-boy trailers which may require advance scheduling.

Unloader

The unloader should have adequate capacity to handle the weight of the units and the necessary mobility to lift and set box down w/the lifting assembly.  Crawler or truck crane, or backhoe of sufficient size must be available.

Unloading & Placing

When direct placement from truck trailer to final location is required, a crane w/stabilizers should be used.  Crawlers w/out outriggers, or backhoes, may not have the stability or accurate movement necessary to line up the units for proper installation.

Sequence 

Joints of the standard box sections have been matched at the plant and must be installed in order.  Any required special sections are shipped in order of placement from downstream to upstream, unless otherwise advised.  Place units bell upstream.  Unloading should take 5-10minutes for each unit depending on job conditions. The unloading to placement should take 30-50 minutes, if no problems are encountered.

SITE PREPARATION

Water

If the water table is in the trench zone, appropriate de-watering methods must be employed.  The engineer must consider the effects of future water table levels as it applies to the backfill material around the precast concrete box as well as the box construction itself. Migration of bedding and backfill material should be prevented. 

Several methods may be employed such as pumping, ditching and/or piping the water around the box location. All pumping operations should be through a filtered discharge

One method to control water in the bedding material is to place a 55gal drum perforated with 1/4" holes, at the upstream end of the culvert.  It may be necessary to place the perforated drums at several different locations to obtain the desired results. 

Bury the drum in the ground with the bottom at least 2' to 3' below the final bedding elevation. Place the necessary suction pumps in the drum and outlet the water further downstream. If using #2's, open graded or granular bedding material, the water will drain very easily to the drum.

Grade

Box culverts provide a broad bearing surface on the bedding and, therefore, normally do not settle, nor can they be forced down to grade. It is important to have a good level grade established prior to box placement. Base material should be fine to medium granular material.  Coarse materials are harder to fine grade. 

The boxes should be aligned accurately prior to pulling home.  A small transverse trench (shovel width wide x depth of granular material x width of box) shall be formed at the end of the last installed box section to allow granular material to fall into when the next box section is slid into place.  Experience suggests it also helps to hold the grade slightly low as the boxes have a tendency to rise during the joining process due to the flat bottom surface. If necessary pack material under the box to maintain grade.

Box sections placed on drop walls or wing wall footings can be accomplished if final inlet footing is appropriate to allow for deviations in line, grade, box length, and joint variations. With care, footing excavation and installation can normally be accomplished after the box is in place.  Normal joint creep in the line will be 1/2" to 1" per joint.  Allow for joint length (5"), when necessary

Bedding

The minimum thickness of the bedding material shall be 6". The bedding material can be 310 or 57's.  If 57's are used they should be topped w/310. This facilitates screening and draining of the bedding material.

603.03 ODOT Construction and Material Specifications:            
The foundation for the conduit bed shall be firm for its full length. Where unstable material is encountered below the plan foundation it shall be removed to the depth directed by the Engineer under the conduit and to the width of the trench and replaced w/granular material. Rock boulders encountered at the conduit bed shall be removed at least 6" below the bottom of the conduit and replaced with granular material. 

The final grade for the bedding shall be established by using a laser (or level) and grade stakes placed as often as necessary.  Final grading should be accomplished by screening the granular material. The screed board should be as long as the width of the box (span + 2x the wall thickness).  Attach a 4' level to the top of the screed board. Starting at the downstream end, workers should screed the granular material, filling in low spots and leveling off high spots. Special attention to the final grading will speed the setting of the box culverts.

An alternative method is to set timber or light steel beam screeds with the tops at the elevation of the outside bottom of the box. .

ALIGNMENT

Installation of the first few box sections should be done with care as it will influence the line and grade to follow.  Line and grade can be controlled with laser, string line, batter boards, transit and level, etc. Note air temperature differential effect on laser.  If using a string line, once the center-line of the culvert has been established, locate a string line to the one side of the culvert.  Locate it about 2" from the outside wall.  This dimension is equal to 1/2 the span, plus the wall thickness, plus 2 inches.

The first box is critical to establishing a straight line of box sections.  Mark a start point at the downstream end of the culvert. By using the string line and the start point, place the box lightly onto the bedding material.  Check that the distance between the string and the outside wall of the box is equal along the full lay length of the box. Finally, let the box section down until the full weight of the box in on the bedding. Check that the box is positioned correctly

SETTING

Joint Material

Place the joint material on the bottom half of the bell of the box last placed.  The balance of the joint material shall be placed on the spigot of the box to be set.  If the joint material is preformed butyl rubber, place the rubber strip about 1" from the leading edge of the bell and spigot.

Remove the granular material 6" in front of the bell of the previously set box to a depth of about 3". This prevents the granular material getting into the joint as the boxes are pulled together.  

In cold weather it may be necessary to heat the joint material with hot water bath, bottle gas torch, or both. Storing joint material in a sunny location will allow heat absorption and make it more workable. Different grades of joint material are available for use depending on temperature

When installing filter fabric or an external wrap at joints, slip material under box joint prior to setting the box in place, or position just prior to pulling home.  Roll excess material, to be used for the sides and top, up in bundles to each side of the box until the box is in the home position, then finish the joint material installation.  It is desirable to place external joint wrap in one continuous strip.  If short strips are used, the joint wrap across the top slab joint should be continuous and extend 12" down the vertical sides, overlapping the vertical side wall strips.

Pick up the box to be placed and line up as close as possible with box in place and start the joint.  Take care so the joint material does not contact before you start the joint. This may cause the joint wrap to loosen and sag. Hold the box in this position and hook up your tugging device to the pulling assembly.

The person giving crane directions should position themselves on top of the box culvert previously set.  This person should be able to clearly see the operator.

When joining box sections together, chains or winches should be used.  Construction equipment, such as backhoes, front end loaders, etc., must "NOT" have direct contact with the precast box sections.  Using such equipment to push the box sections together should be avoided because of the force applied can damage the box. 

Bring the box section to be installed to rest on grade about 18 to 30 inches from box in place.  Check joint alignment, make the adjustment on lifting device as necessary.  Clean joints and install joint sealant material. Direct the crane operator to bring the spigot end of the box to a position in front of the receiving bell.  Keep the top slab of the box about 2' above the top slab of the box previously set.

Looking down the vertical face of the spigot and the bell, direct the crane operator to move the box sideways until the spigot is lined up with the receiving bell.  Slowly let the box down until the top to the spigot slips into the receiving bell.  At this point, keep most of the weight of the box on the crane hook. 

Winches

Hook up pulling devices to pull the joint home.  Place 8”x 8” wood timbers or adequately sized I beams vertically at the ends of the culvert.  Position the timbers even with the bottom haunches of the box. 

Using high tensile chains, wrap one end of the chain around the bottom of the timber.  In the bell of the box being set, place 8”x 8” timbers vertically even with the bottom haunches.  Using two, 3T chain winches, connect the chains and timber anchors to each other. Each chain and winch will be located in the two bottom corners of the box.  Using the chain winch, gradually tighten the chains until they are snug. Check the safety of the system. With the majority of the box weight still on the crane hook, gradually winch the boxes into the home position. This should be done evenly. Keep an eye on the distance from the string line to the outside wall of the box.  Gradually, let the box down onto the bedding. 

Repeat previous steps. 

COMPLETION

Lift holes, where permitted, are to be plugged with masonry plugs furnished, by forcing down sealant-coated plug from the top until flush with the box ceiling.  Fill balance of lift hole with grout.

Force the excess joint material into joints as required. Trim excess joint material from inside box.  Allow for mortar pointing when required. 

Seal the precast box section joints with either mastic (preformed or trowelable), a butyl closed-cell rubber extrusion gasket joint wrap, or cement grout, as specified for the project. 

The place between consecutive precast box sections, as measured on the inside surfaces, shall be in accordance with the manufacturer's recommendations and/or contract specifications.

Box sections may be used in parallel for multi-cell installations if means of position lateral bearing by continuous contact between the sides of adjacent boxes are provided. Compacted earth fill, granular backfill, or grouting between the units are considered means of providing such positive bearing.

Backfill shall be placed uniformly on each side of the precast concrete box sections as installation progresses. The backfill material to be placed, percent of compaction, depth of layers, etc. shall be required by the contract specifications.

Common Problems that Occur:

Improper preparation of bedding.
Most joint annular spaces are 1/4"to 1/2".  If the bedding is irregular, lining up the tongue into the receiving bell will be difficult. Because boxes are wide and flat, any irregularities in bedding can cause the tongue of the box not to be properly started into the bell.  If this is apparent before attaching the winches and anchors, pull the box out of the way and check the bedding again.

Use of granular material that has a large 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 evenness of the granular bedding and to properly dig an adequate bell hole when water is standing in the trench.  

Boxes do not hang plumb.  This may be caused by improper anchorage 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 its home position unevenly. Care should be taken to ensure that both vertical portions of the tongue get started evenly into the bell of the box previously set.

Not allowing for joint creep.  If footers or headwalls are specified consult the supplier to determine if the actual lay length of the individual boxes plus joint creep will be greater than the culvert length shown on the design plans.

Inadequate crane capacity. A representative of the crane rental company should visit the site and determine what the crane size should be.