Usually KAST performs foundation excavation and backfill on an hourly basis because subcontractors forced to put a lump sum number on the excavation will be too high.
If there is excess material, at a minimum we should be able to have someone provide free trucking to remove the fill. If market conditions are light, you may get $l/cy plus trucking for fill.
In excavations below water table, we may have to over excavate and put l' - 2' of ballast rock at the bottom of the excavation. This will provide a better working surface and will help minimize any turbidity from the excavation process.
In extreme dewatering conditions, the pile caps can be backfilled with ballast rock, which then acts as a filter through which contaminated water can be run through.
Over excavation may be desired at pile caps so the pile butt chips can be left in the hole in lieu of removing by hand.
When estimating a job, a site may appear balanced, but in a tight downtown site it may require that excavated material be brought off-site and when pile caps are stripped, fill be imported. This can add significant dollars to the estimate, but may help the schedule by reducing the amount of material to be handled and stored on site. This needs to be studied by all KAST staff prior to finalizing Owner budget.
Obtain a copy of the NPDES Generic Permit and NOI for the project. If site is greater than 5 acres, weekly and post rainfall (within 24 hours of rainfall greater than 0.5”) inspections must be performed by a state certified stormwater inspector.
FIELD & QC ITEMS:
Because excavation is being done on an hourly basis, KAST field supervision must log all hours and verify we are getting our monies worth with a competent operator.
A typical condominium deficiency is car parking spaces not matching the plan. If there are any as-built discrepancies, the plans must be changed. Adjust car stops to keep cars from hitting any pipes or wall mounted items.
Settlement of a hi-rise building is a very real possibility. Consult with Structural and Geotechnical Engineer. The slab on grade or adjacent garage structure may not be able to be poured until enough settlement has occurred.
Are test piles required? If so, allow 30 days for completion of test pile installation and results.
Are test piles to be installed from working grade?
Will rig remain on site until production pile installation? Account for number of mobilizations with buy.
If site needs cut down with rig on-site, leave rig in best possible location to keep it out of the way. It will most likely need relocated on site one time.
Verify required length and diameter
Is length based on depth from existing grade or from bottom of pile cap?
Negotiate unit prices for excess grout due to unforeseen conditions, additional and deleted piles, and differences in depth, all by pile type.
Will piles be installed from existing grade, or will site need excavated first?
If site conditions allow, cut site to working grade first (top of pile cap or other based on cut/fill analysis, concrete displacement and fill storage availability) in order to minimize pile cut-off.
Layout and as-builts can be bought from independent surveyor or from pile subcontractor. Pile numbering plan to be prepared by whoever performs surveying.
How many mobilizations will be required?
Pilings shall be staked with #3 rebar x 18” stakes to mark the center of pile driven flush to the ground with a flag indicating the pile number.
Buy 120% of total pile quantity for layout due to losses during installation.
Expected durations:
16” piles 170-210 piles per week
18” piles 70-90 piles per week
24” piles 50-70 piles per week
Review number of mobilizations required
Review Geo-Tech report for required grout ratio and compare to the ratio included in subcontractor bids. Recommend buying 1.8 times theoretical volume, depending on site location and soil conditions. Contact Geotechnical engineer to see if pile installation was completed on a nearby site. If so, request actual data from engineer regarding grout ratio.
Include piles for tower crane(s) and buck hoist(s) as required.
Verify if piles are required for on-grade pool structure or other site improvements
Will rock layer be encountered? Verify blows from Geo-tech report (N-value).
A dewatering plan and narrative is required for a permit.
Permits required:
City (verify with city if permit is required, even if you’re not discharging)
SFWMD, SWFWMD
DEP
State DEP permit when working east of CCCL
Is the subcontract performance based (e.g. dry hole) or equipment rental (wellpoints and pumps for a specific duration).
Determine who bears risk of dewatering costs
Subcontractor – performance rental from supplier or subcontractor
KAST – equipment rental from supplier or subcontractor
Owner – dewatering allowance?
Where is the water being discharged to?
City storm system
Adjacent river, lake or other waterway
On site detention basin
How is turbidity being handled?
Settling tanks
Chemical drip
Settling basin / pond
Turbidity screen on outfall into public waterway
Is salt water intrusion an issue?
If so, are recharge wells required?
Who provides monitoring wells and monitoring?
Is settlement of adjacent structures or roads a potential?
Who monitors adjacent groundwater levels and settlement?
What types of soils are present?
Organic soils will lead to turbidity
Limestone will cloud water and provide discharge problems
Sand is best soil to work with
Review elevations of rock layers
Penetration of rock layers can bring aquifer to the surface
Pre-drilling for well points may be required if well points need to penetrate the rock layer
Site should be cut down as low as possible before installation of well point header. This will minimize head pressure required.
Dewatering systems
Perimeter well points
Two stage well points may be required for deeper dewatering
System pressure should be minimum of 20psi. If not, there will be leaks in system which will reduce effectiveness.
Sock drains
Useful for interior dewatering when perimeter well points are not completely effective
Coordinate location with foundations and other below ground elements
Installation depth will not be exact and will vary
Open pumping
Effective for small isolated areas
Turbidity can be a problem because surface water is being discharged
Typically this water cannot be discharged into public waterway without settling out solids first
Pumping into deep well
May be the only option in tight downtown locations
If deep well is to be used for permanent storm systems it will have to be re-drilled
This must be permitted
Preference is electric pumps for wellpoint systems with diesel pumps for back-up (be sure to size temporary electric service accordingly)
For 24-hour pumping, dewatering pumps should be equipped with a pressure / electric switch and solenoid which would activate a call to a security service upon loss of the vacuum pump. The service would call the dewatering subcontractor and/or KAST personnel until contact is made.
Depending on the extent and how critical the dewatering operation, a night watch guard service or pump machine is often required.
The subcontract is normally bought for duration with a per diem for additional rental.
If discharge into public waterway, a floating boom(s) is recommended to contain any turbidity.
Failure to implement an effective dewatering plan with no adverse impact to public waterways can result in fines to KAST in excess of $100,000.
Coordinate if plumber or irrigation sub brings water feed to each planter:' Preference is plumber so sleeves can be coordinated while structure is being erected.
Irrigation lines should be fed off of a separate water service from the domestic meter along with the cooling tower and pool so Owner does not pay sewer impact fees on this water use.
Buy tagging of specimen trees in the nursery by Landscape Architect, AHJ, and Owner, or get photographs if trees are out of area.
FIELD & QC ITEMS
Sleeve to all elevated planters for irrigation. All sleeves go through sidewall, not bottom to minimize waterproofing issues. Ensure sleeves in planters (i.e. Conduit & irrigation sleeves are as high as possible (but below grade) in the planter box, and on the side wall.
Sometimes large trees need to install early due to crane logistics. If so, early operation of irrigation system is required.
Landscape material should be inspected by the Landscape Architect, AHJ, and Owner the day it is delivered to the site. This is the only way to properly classify the material as FL Fancy, FL #1, etc.
When budget allows buy drip irrigation systems in planters to minimize water on stucco planter tops.
