558.01 Description
This work is constructing reinforced concrete shafts cast in cylindrically excavated holes that extend into soil or rock to support the structure and externally applied loads at the locations and to the lines and grades shown in the contract.
558.02 Materials
558.02.1 Drilled Shaft Concrete
Use Drilled Shaft Concrete for all concrete placed between the bottom of the shaft and the top of the casing, unless otherwise shown in the contract. Obtain the Project Manager’s approval before using a SCC mix design.
558.02.2 Permanent Drilled Shaft Casing
Furnish casing in accordance with the size and thickness requirements specified and casing material that meets the requirements of AASHTO M 270, Grade 36. Furnish, fabricate, and inspect casing materials in accordance with Section 556.
558.02.3 Reinforcing Steel
Furnish all reinforcing steel in accordance with Section 555 and Subsection 711.01.
558.03 Construction Requirements
558.03.1 Submittals
Submit the following information.
A.Drilled Shaft ASC and WN outlining:
1.Bent and shaft construction sequence. If more than one shaft is worked on at any time, include that information in the submittal.
2.Method of shaft excavation.
3.Method to clean shaft excavation including details for air-lift systems.
4.Temporary and permanent casing installation and removal methods. Include casing top and bottom elevations and diameters.
5.The effects of hydrostatic pressure differentials that may occur during excavation and shaft construction. Include a description of procedures relating to hydrostatic effects that will be used to ensure that the stability of the excavation is not compromised.
6.Method of concrete placement. State the planned initial elevation of the bottom of placement pipe. Provide descriptions of methods or devices used to prevent the injection of air or water into the drilled shaft concrete when starting concrete placement and in the event the placement is stopped and restarted. Include descriptions of methods or devices that will be used to control the rate of concrete discharge in order to minimize turbulence that could result in concrete washout or other detrimental effects.
7.Time necessary for complete concrete placement.
B.Name and experience record of Contractor, and Superintendent and driller(s) that will perform the drilled shaft work on this project. Include all experience in the last 10 years.
C.List of proposed drilling equipment to be used, including any cranes, drills, augers, bits, temporary casings, and cleaning tools. Include diameter of augers and cleaning buckets. 558 – DRILLED SHAFTS 2020 EDITION V5.1 558-2
D.Proposed size and location of all reinforcing steel used to support or maintain the shape of the reinforcing steel cage.
558.03.2 Shaft Pre-construction Meeting
Schedule a shaft pre-construction meeting with the Project Manager for a time 7 to 14 calendar days prior to drilling. The minimum required attendees are the superintendent, concrete supplier, and Project Manager. The purpose of the meeting is to review the requirements of this specification, discuss the drilled shaft installation plan, and to discuss logistical and contingency plans.
558.03.3 Geotechnical Logging
The Department may provide a geotechnical representative on-site during drilling and installation operations to log the excavation. Notify the Project Manager at least 7 calendar days prior to start of drilled shaft excavation so that the Project Manager may schedule the on-site representative.
558.03.4 Shaft Excavation
Use excavation methods that provide contact with firm, undisturbed soil or rock with the sides and bottom of the drilled shaft. Do not excavate holes larger than the outside diameter of permanent casings.
558.03.5 Shaft Locations, Alignment and Tolerances
Drill all shafts to the bottom elevations specified or as directed by the Project Manager. Construct the shaft so the vertical centerline axis of the finished shaft is within 3 inches (75 mm) of the plan location at the top of the shaft. Drill all shafts to within 2% of vertical the entire depth of the shaft excavation.
558.03.6 Sloughing and Caving
Use tools and tool withdrawal rates that will not cause suction effects that result in soil intrusion or instability of the excavation. Use construction methods that will ensure no sloughing or caving of the shaft side walls. In the event any sloughing or caving does occur, remove all sloughed material. Ensure that concrete completely fills the shaft. If caving occurs during placement of drilled shaft concrete, immediately stop the flow of concrete, and undertake corrective measures to completely remove the sloughed materials from the shaft. If necessary, to facilitate material removal, remove the concrete and reinforcing steel already placed in the shaft.
558.03.7 Permanent Casing
1.Furnish and install permanent casing when specified in the contract. Permanent casing remains in place and is included in the design of the drilled shaft. The Contractor may elect to oversize the permanent casing diameter up to 3 inches (75mm).
2.Limit the excavation in advance of the casing tip to no more than 10 feet (3 m) unless synthetic slurry is being used.
3.If field welding, submit the weld procedures.
4.Provide corrosion protection for all permanent casing. Galvanize the permanent casing to AASHTO M 111 and ASTM A653 specifications or paint. If painting, meet the following requirements:
a.Furnish paint in accordance with Subsection 710.02(B)(3) .
b.Prepare in accordance with the paint manufacturer’s recommendations. 2020 EDITION V5.1 DRILLED SHAFTS – 558 558-3
c.Apply paint to the casing from the top of exposed steel to the ordinary low water level for casing installed in a water channel and from the top of exposed steel to 1 foot (0.3 m) below ground elevation for casing installed outside of a water channel.
d.Apply the first 2 coats of paint to produce a minimum 12 mil (305µm) dry film thickness. Verify the dry film thickness using SSPC PA-2. Appy the finish coat using the same paint or compatible paint approved by the paint manufacturer, with the first 2 coats. Provide a finish coat with a minimum 3 mil (75 µm) dry film thickness. Verify the dry film thickness using SSPC PA-2. Provide the finish coat paint that meets SAE-AMS-STD 595, pigment code 36440 (concrete gray). If applied in the shop, submit a copy of the painter’s certification that the paint was applied following the manufacturer’s recommendations and the paint coat thickness on the casing.
e.Repair paint damage caused by transport, handling, welding, and installation following the paint manufacturer’s recommendations at no cost to the Department. Submit a copy of the paint manufacturer’s recommendations.
558.03.8 Excavation Stability
Do not use slurry construction methods as an alternative to or in conjunction with temporary casing unless specified in the contract. Use casing to facilitate shaft construction and prevent sloughing and caving of the shaft sidewalls. The contract may specify temporary casing minimum elevations. Place the temporary casing deeper, if necessary, to prevent material from entering the shaft excavation. Use casing with an outside diameter no less than the specified diameter of the shaft. Limit the excavation in advance of the casing tip to no more than 10 feet (3
m.unless synthetic slurry is being used. During casing extraction, maintain a sufficient level of fluid in the casing to counteract external hydrostatic pressures but no less than 5 feet (1.5 m) of positive head. Maintain an adequate level of concrete within the casing to ensure that fluid trapped behind the casing is displaced upward and discharged at the ground surface without contaminating or displacing the shaft concrete. Temporary casings that have become bound or fouled during shaft construction and cannot be removed are considered to be a defect in the drilled shaft. Correct defective shafts using approved methods at no cost to the Department. Corrective action may consist of, but is not limited to, the following:
1.Removing the drilled shaft concrete and extending the drilled shaft deeper to compensate for the loss of frictional capacity to the cased zone.
2.Providing straddle drilled shafts to compensate for capacity loss.
3.Providing a replacement drilled shaft.
558.03.9 Obstructions
An obstruction is defined as a specific object (including, but not limited to, boulders, logs, and man-made objects) encountered during the shaft excavation which prevents the advance of the shaft excavation. If an obstruction is encountered promptly notify the Project Manager. Submit a proposed obstruction removal method for approval within 2 business days of encountering the obstruction.
558.03.10 Cleaning
Remove all loose or disturbed material from the bottom of the shaft excavation immediately prior to placing reinforcing steel and concrete. After cleaning, no more than 1-inch (25 mm) of loose or disturbed material is permitted in the bottom of the shaft. For wet shafts founded in rock, use an air lift to demonstrate that the shaft is clean. Use an air-lift system meeting the following requirements:
1.Sufficient length to discharge outside of the shaft.
2.Minimum of 4-inch (100 mm) diameter. 558 – DRILLED SHAFTS 2020 EDITION V5.1 558-4
3.Compressed air input line located within 12 inches (305 mm) of the bottom of the lift pipe.
4.Air compressor capable of producing 185 CFM at 100 psi (5.2 m3/min at 6.9 bar); and
5.Meet all applicable environmental requirements relating to discharge. During final cleanout and until concrete placement is complete, maintain the fluid level within the shaft at a level of 5 feet (2 m) or more higher than the water level present outside of the shaft.
558.03.11 Installation of Cross-hole Sonic Logging (CSL) Tubes
Use 1½-inch (38 mm) nominal diameter schedule 40 steel CSL access tubes. Provide an end plug at the lower end of the pipe and make all joints watertight. Install the CSL access tubes evenly spaced around the reinforcing cage and inside of hoops and spiral reinforcing steel shown in the contract, using connectors that will allow the tubes to slide through them when force is applied. Position the connectors so that couplings will not prevent the tubes from sliding. Ensure tubes extend to the shaft bottom. After inserting the shaft reinforcing steel, drive each tube down until contact is made with the shaft bottom. Fill the CSL access tubes with potable water prior to or immediately after placing concrete in the drilled shaft. Temporarily cap the top of the tubes to prevent debris or concrete from entering the tubes.
558.03.12 Reinforcing Steel
Tie bars at all intersections. After inspection and approval of the drilled shaft excavation by the Project Manager, place the reinforcing steel cage into the shaft as one unit. Support the steel cage from the top so that racking and distortion are prevented. Remove internal stiffeners as necessary as the steel cage is placed in the excavation to prevent interference with the placement of concrete. Use non-corroding, roller-type spacers or other non-corroding devices as approved by the Project Manager along the steel cage length and around the steel cage perimeter to align and maintain clearance from reinforcing cage to edge of casing during concrete placement. Begin placing the drilled shaft concrete immediately after the Project Manager has inspected and approved the location and alignment of the cage within the drilled shaft. Remove the steel cage and re-inspect the excavation as directed by the Project Manager if the concrete placement is not started within 3 hours of placing the steel cage in position.
558.03.13 Concrete Placement Record
Complete the Department’s Drilled Shaft Concrete Placement Log. Accurately record all data required on the form as the concrete is placed. After the drilled shaft concrete has been placed and before the end of the day submit the completed form. The Department will provide copies to the Contractor upon request.
558.03.14 Drilled Shaft Concrete
Place concrete in the drilled shaft as specified for either dry excavations or wet excavations.
A.Dry Excavations. Place concrete by gravity tremie tube or pumping. Concrete may free fall into the shaft if the concrete can be directed so that it does not strike the reinforcing steel, the excavation wall, or any other obstruction during the fall.
B.Wet Excavations.
1.Place all drilled shaft concrete by tremie tube, pumping, or other approved method to avoid separation and segregation of the concrete mix components.
2.Separate the first concrete placed from the fluid in the excavation using a plug in the tube, or other approved device.
3.Begin concrete placement in a manner that minimizes mixing of the concrete with the water and material in the shaft. 2020 EDITION V5.1 DRILLED SHAFTS – 558 558-5
4.Maintain a minimum of 10 feet (3 m) of tremie pipe embedment and continuously place drilled shaft concrete to ensure upward displacement of all contaminated concrete. If at any time during the placement, it is necessary to temporarily stop or the tremie pipe orifice is removed from the concrete, stop, and restart concrete placement in a manner that ensures that air, water, or other undesirable material is not allowed to be mixed into the concrete or incorporated into the drilled shaft. Concrete that is discharged above the rising concrete level in the shaft is considered undesirable material.
5.Once concrete has reached the top of the drilled shaft, remove, and dispose of the top layer of concrete and any concrete contaminated with mud or fluid from the drilled shaft. Remove sufficient concrete to fully expose sound, homogeneous and uncontaminated concrete in the shaft.
558.03.15 Shaft Testing and Acceptance
A.Cross-Hole Sonic Logging. The Project Manager may use CSL to check the structural soundness of any completed drilled shaft. The CSL testing will be performed when the concrete has cured sufficiently to give consistent test readings. Schedule construction activities to allow twelve calendar days from the time concrete is placed in the shaft until the shaft is tested. Provide a stable 110-Volt AC or a 12-Volt DC electrical supply if requested. When the CSL testing access tubes are no longer needed for testing, as determined by the Project Manager, cut off the tubes flush with the top surface of the drilled shaft. Remove water and fill CSL tubes with grout. Protect tubes from freezing until water is removed. The Project Manager will accept or reject the shaft based on the CSL testing or a subsequent drilled core sample. For any drilled shaft determined by CSL testing to be of uncertain quality, drill core samples with a minimum diameter of 2 ½ inches (65 mm), at locations and to depths specified by the Project Manager. Use a core drilling method that provides complete core recovery and minimizes abrasion and erosion of the core. Grout all core holes when directed by the Project Manager.
B.Corrective Action. If the CSL or subsequent coring identifies any defect in the shaft that compromises the capacity of the shaft; repair the shaft by a method approved by the Project Manager. Submit a repair plan no later than 14 calendar days after notification. Include calculations and working drawings, stamped by a professional engineer licensed in Montana. Furnish all materials and work necessary to correct shaft defects at Contractor expense. Prior to constructing other shafts, submit a written proposal that describes changes in construction methods or materials designed to avoid defects in subsequent drilled shafts.
558.04 Method of Measurement
558.04.1 Drilled Shaft
Drilled shaft will be measured by the linear foot (m) of shaft between the actual bottom elevation of the drilled shaft and the top of shaft elevation shown on the contract.
558.04.2 Drilled Shaft Concrete
Drilled shaft concrete will be measured by the cubic yard (m
3.of concrete placed calculated from the planned cross-sectional area times the as built length of the drilled shaft.
558.04.3 Reinforcing Steel
Drilled shaft reinforcing steel will be measured by the pound (kg) in accordance with Subsection 555.04. 558 – DRILLED SHAFTS 2020 EDITION V5.1 558-6
558.04.4 Drilled Shaft Casing
Permanent drilled shaft casing will be measured by the pound (kg) of permanent casing installed as shown in the contract or as directed by the Project Manager in writing. If the Contractor elects to oversize the casing diameter, measurement will be based on the diameter shown in the contract.
558.04.5 Temporary Casing
When the Contract contains the pay item Temporary Drilled Shaft Casing, temporary drilled shaft casing will be measured by the linear foot (m) of temporary casing measured from the higher of the ground or water surface elevation down to the bottom elevation of the installed temporary casing.
558.04.6 CSL Tubes and Testing
Include all costs associated with furnishing and installing, and grouting CSL access tubes and any required extensions and providing a power source in the Drilled Shaft pay item. No measurement or payment will be made for construction delays resulting from the initial CSL drilled shaft testing. The Department will extend the contract time by 1 day for each day over 12 calendar days required to complete the CSL drilled shaft testing. The Department will pay the costs for the initial CSL drilled shaft testing. If a defect is found based on the CSL drilled shaft testing, coring, or other physical investigation, the contractor is responsible for all costs associated with the physical investigation, engineering design, shaft repairs and any construction delay costs. Pay the costs of CSL drilled shaft retesting of the repaired drilled shafts. If no defect is found in the drilled shaft based on the physical investigation, the investigation will be considered extra work and paid for in accordance with Subsection 109.04 , and considered for time adjustment in accordance with Subsection 108.07.
558.05 Basis of Payment
Payment for the completed and accepted quantities is made under the following: Pay Item Pay Unit Drilled Shaft Linear Foot (m) Reinforcing Steel Pound (kg) Drilled Shaft Casing Pound (kg) Drilled Shaft Concrete Cubic Yard (m3) Temporary casings remain the property of the Contractor. If the Contract contains the pay item Temporary Drilled Shaft Casing, all costs associated with temporary casing including, but not limited to, procurement, fabrication, transportation, installation, and removal, are included in the pay item Temporary Drilled Shaft Casing. If the Contract does not contain the pay item Drilled Shaft Temporary Casing, no measurement or payment will be made. Include all costs associated with temporary casing including, but not limited to, fabrication, providing, transporting, installation and removal in the Drilled Shaft pay item. Payment for obstruction removal will be made on a force account basis. Air-lifting is not measured separately for payment. Include costs for all airlifting in the Drilled Shaft Item.
Drilled Shafts in other states
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Source: Standard Specifications for Road and Bridge Construction, 2020 (v5.1) Edition. Pages 369–374 of 611. View official source ↗