506Drilled Shaft Foundations

Drilled Shaft Foundations

506.1DESCRIPTION

1 This section describes the requirements for constructing drilled shaft foundations.

506.2MATERIALS

1 Provide materials in accordance with the following:

Material Subsection Admixtures 801.4 Aggregate for Concrete 803 Fly Ash 801.2 Portland Cement 801.1 Reinforcing Steel 811.1 Water 814.1

506.3EQUIPMENT

1 Ensure that equipment meets the following requirements:

Equipment Subsection Batch Plant 513.3.1 Mixers 513.3.2 Placing Equipment 513.3.3

2 Provide a power-driven rotary auger or, if required, rock drilling equipment. Provide a rig of sufficient size and capacity and equipped to produce holes of the diameter and depth specified.

506.4CONSTRUCTION

506.4.1 Drilled Holes

1 At least 30 calendar days prior to the start of drilled shaft construction, submit four copies of the Drilled Shaft Excavation and Installation Form E-151 for acceptance to the engineer, with a copy to the Geology Program. The department will evaluate the Drilled Shaft Excavation and Installation Form E- 151 for conformance with the contract and specifications within ten working days after receipt of the submission. At the option of the department, a Drilled Shaft Installation P lan Meeting may be scheduled following review of the contractor's initial submittal of the form. Do not begin work until the Drilled Shaft Excavation and Installation Form E-151 is accepted in writing by the engineer.

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2 Drill shafts to within 3 in [75 mm] of their specified locations, measured at the top of the center axis. Drill vertical shafts no more than 1.5 percent of their length from plumb for their full length.

3 Drill holes deep enough to meet design requirements. The engineer may change the specified elevation of the bottom of a drilled hole depending on where satisfactory material is encountered.

4 Blasting of bedrock in the drilled shaft hole will not be permitted.

5 Use removable segmental casing, when necessary, to prevent caving or water seepage. Ensure that such casing is smooth, watertight, and made of metal strong enough to resist hydrostatic pressure, concrete pressure, and surrounding earth pressure. Ensure that the casing is clean, extends to the top of the drilled shaft excavation, and has an outside diameter not less than the specified diameter of the drilled hole. When the top of the drilled shaft is below ground level, use a removable oversize casing or other approved forming method from the ground surface to the shaft as required to control caving.

6 If caving conditions are encountered, stop drilling and change methods.

7 Do not use water for drilling mud or slurry without prior approval of the engineer.

8 If encountered, remove subsurface obstructions at the drilled shaft locations. Such obstructions may include man- made materials such as old concrete foundations and natural materials such as boulders. Employ special procedures or tools to clear the hole if it cannot be advanced with conventional augers, drilling buckets or other tools . Such special procedures/tools may include, but are not limited to: chisels, boulder breakers, core barrels, air tools, or hand excavation.

9 Promptly remove drilling tools that are lost in the excavation. Removal of lost tools and repair of hole degradation due to removal operations or the excessive time that the hole remains open will be at no additional cost to the department.

10 As approved by the engineer, dispose of excavated material not used as backfill around the completed structure.

11 Sequence drilled shafts as shown in the contract. Do not construct adjacent shafts within 24 hours after placement of concrete and only when the concrete has reached a minimum compressive strength of 1800 psi [12.5 kPa] in the newly poured drilled shaft.

12 Do not leave drilled shaft excavations open overnight unless cased full depth or otherwise protected against sidewall instability. An open excavation is defined as a drilled shaft that has not been filled with concrete, or temporarily backfilled with a material approved by the engineer . Protect the walls and bottom of the drilled shaft excavation so that side wall caving and bottom heave is prevented from occurring, and so that the

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soil adjacent to the drilled shaft is not disturbed. Th e contractor bears full responsibility for execution of the method(s) of stabilizing and maintaining the drilled shaft excavation.

506.4.2 Cleaning and Inspection

1 Do not place reinforcing steel or concrete before the engineer has inspected the drilled shaft excavation for tolerances, satisfactory bearing material, plumbness, and lack of debris and loose material. The department will consider a hole sufficiently dry if water depth can be kept at 3 in [75 mm] or less while placing concrete.

2 Measure final shaft depths with a suitable weighted tape or other approved methods after final cleaning. Shaft cleanliness will be determined by the engineer. Ensure there is less than 0.5 in [10 mm] of sediment over a minimum of 50 percent of the base at the time concrete is placed. Ensure the maximum thickness of sediment or debris at any place on the base of the shaft does not exceed 1.5 in [35 mm].

506.4.3 Reinforcing Steel

1 Assemble the reinforcing steel cage completely and place as a unit. R igidly brace the reinforcing cage to retain its shape for lifting, or lift the cage in a manner that does not cause racking or distortion. Show bracing and any extra reinforcing steel required for fabrication of the cage on the submitted shop drawings. Remove cross bracing during cage placement unless otherwise approved by the engineer.

2 Anchor the reinforcing cage adequately to prevent movement after installation. During concrete placement, provide positive support from the top for the reinforcing steel cage. Maintain the top of the reinforcing steel cage at the elevation shown in the contract.

3 Extend the bars in the lower portion of the shaft to the bottom of the hole if the shaft is lengthened and full-depth reinforcement is specified. Lap-splice the bars to proper length in accordance with Subsection 514.4.5, Placing and Fastening, and Table 506.4.3-1, Lap Lengths for Drilled Shaft Reinforcing Steel.

Table 506.4.3-1 Lap Lengths for Drilled Shaft Reinforcing Steel Bar Size (No.) Length Bar Size (No.) Length 4 [13] 1 ft 4 in [410 mm] 8 [25] 3 ft 7 in [1100 mm] 5 [16] 1 ft 8 in [510 mm] 9 [29] 4 ft 6 in [1380 mm] 6 [19] 2 ft 0 in [610 mm] 10 [32] 5 ft 9 in [1780 mm] 7 [22] 2 ft 9 in [840 mm] 11 [36] 7 ft 0 in [2140 mm]

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5 Make spiral reinforcement full-depth on extensions. Ensure additional spliced bars and spiral reinforcement is placed at bottom of the drilled shaft . Use spliced bar extensions with sufficient stability to withstand lifting, placing, and downward forces of wet concrete without slippage. If necessary to ensure stability, tack weld the lap splice extension, along with tie wire, for a distance no more than 24 in [600 mm] from the bottom of the initial reinforcement, and tack weld the spiral to the longitudinal reinforcement.

6 Use spacers or centralizers, securely locked to the reinforcing cage that do not possess any openings or voids when in place. Ensure the spaces or centralizers maintain the minimum clearance between the reinforcing steel cage and shaft face shown in the contract. Do not use block or wire type spacers or centralizers. Ensure no metallic elements will be within the concrete annular space. Use a minimum of 1 non corrosive spacer per 30 in [ 750 mm] of circumference of the reinforcing steel cage. Place the spacers within 2 ft [0.5 m] of the bottom and top, and at intervals not to exceed 10 ft [3 m] vertically. Use one of the following spacers or centralizers or an approved alterative.

506.4.4 Concrete

1 Use classS concrete in accordance with Subsection 513.4.4, Mix Design, except use a slump of 8 in ± 1 in [200 mm ± 25mm].

2 Prior to concrete placement, provide results of a trial mix test conducted by an approved testing laboratory using approved methods to demonstrate that the concrete retains its 8 in ± 1 in [200 mm ± 25mm] slump throughout the 2-hour placement limit. Place concrete as soon as possible after completing the drilled shaft excavation and inspection by the engineer. Place concrete by a method which prevents segregation of aggregates. Continuously place concrete from the bottom to the top of the shaft. Continue concrete placement after the shaft excavation is filled until good quality concrete is evident at the top of the shaft . Ensure the elapsed time from the beginning of concrete placement in the shaft to the completion of placement does not exceed 2 hours. Place in vertical dry holes, without dropping more than 25 ft [7 m]. Do not drop concrete if it strikes the reinforcing steel or the sides of the hole. In holes deeper than 25 ft [7 m] place concrete with an enclosed chute or pump. Where dewatering of the hole cannot maintain a static water depth of 3 in [75 mm] or less, discharge concrete below the water. Immerse the discharge end of the tremie pipe at least 5 ft [1.5 m] in concrete at all times after starting the flow of concrete. Clearly mark the tremie pipe in 1.0 ft [0.3 m] increments, starting at the bottom of the tremie tube, to ensure the minimum embedment of the tremie pipe in the concrete is maintained.

3 Ensure tremie pipe has a hopper at the top that empties into a watertight tube at least 10 inches [250 mm] in diameter. If a pump is used, use a watertight tube with a minimum diameter of 4 in [100 mm].

4 At the discharge end of the tube on the tremie or concrete pump line, include a device to seal out water while the tube is first filled with concrete. In lieu of a seal at the discharge end of the pipe, a “Pig” or “Rabbit” device may be placed in the hopper prior to concrete

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placement, which moves through the tremie when pushed by the concrete, forcing water or slurry from the tremie pipe.

5 If at any time during the concrete pour the tremie or pump line orifice is removed from the fluid concrete column and discharges concrete above the rising concrete level, the shaft will be considered defective. In such case, remove the reinforcing cage and concrete, complete any necessary sidewall removal directed by the engineer, and repour the shaft. All costs to replace defective shafts are the responsibility of the contractor.

6 If the concrete placement operation is interrupted, the engineer may require proof by core drilling or other tests that the drilled shaft contains no voids. If testing reveals voids repair them or replace the drilled shaft at no additional expense to the department. Responsibility for coring and testing costs, and calculation of time extension, will be approved or rejected by the engineer.

7 Complete a concrete yield plot for each wet shaft poured by tremie methods. Submit this yield plot to the department within twenty four hours of completion of the concrete pour.

8 V ibrate the top of the concrete in accordance with Subsection 513.4.11, Placing Concrete, for a depth equal to two shaft diameters. Do not vibrate concrete when the static water level is near or within the top portion to be vibrated. Remove displaced water and any concrete that may have an excessive water/cement ratio prior to vibrating and finishing the top surface of the drilled shaft.

506.4.5 Casing Removal

1 Remove the casing while concrete is workable but after all concrete has been placed, unless otherwise approved by the engineer. As necessary, to facilitate the casing ’s upward movement use an initial short pull (or “jerk”), rotation, downward pressure, or tapping. Thereafter, lift vertically at a slow, uniform rate while keeping the casing aligned with the hole. Telescoping, outer and inner, or jointed casings may be pulled in stages. In all cases of removal, maintain at least 5 ft [1.5 m] of fluid concrete above the bottom of the casing.

506.5MEASUREMENT and PAYMENT

1 The engineer will measure:

the shaft to the top of the shaft.

payment, but will be considered incidental to the Drilled Shaft Foundation.

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Foundation excavations will be considered incidental to the Drilled Shaft Foundation bid item.

2 The department will pay as follows:

Pay Item

Pay Unit Measure to the Nearest Pay to the Nearest Drilled Shaft Foundation____in [mm]

FT [m] 0.1 ft [0.05m] FT [0.5m]