Section 565 — Drilled Shafts

Description

565.01This work consists of providing and constructing reinforced concrete drilled shafts.

Material

565.02Conform to the following Subsections: Neat hydraulic cement grout 701.04(a) (2) Reinforcing steel 709.01 Slurry (d rilling fluids) 725.13 Steel pipes 717.06 Structural carbon steel 717.01(a) Water for cementitious materials 725.01(a)

Construction Requirements

565.03Qualifications. At least 30 days before starting drilled shaft work , submit the following for approval:

(a)On-site supervisor. A résu mé for the on-site supervisor describ ing at least 5 years ’ experience supervising construction of drilled shafts of similar lengths and scope to those shown in the plans and in similar geotechnical conditions described in the geotechnical report. Include experience as the direct supervisor responsible for on-site construction operations;

(b)Drill operator. A résumé for each drill operator describ ing at least 2 years’ experience in the construction of drilled shafts ;

(c)Professional engineer or geologist. A résumé for a professional engineer or professional geologist with at least 5 years’ experience in the design and construction of drilled shafts and logging shaft excavations;

(d)Geotechnical engineer or geologist. If applicable, a résumé for a geotechnical engineer or engineering geologist working under the direct supervision of the professional engineer or professional geologist described in Subsection 565.03(c) , to maintain the boring log. Show at least 2 year s’ experience in the design and construction of drilled shafts and logging shaft excavations; and

(e)Crosshole sonic logging (CSL) engineer. A résumé for a CSL engineer describ ing at least 5 years ’ experience in the testing of drilled shafts.

565.04Construction Plan. At least 30 days before starting drilled shaft work, submit the following according to Subsection 104.06:

(a)Proposed drilled shaft construction schedule and sequence. Schedule shaft installation to avoid interconnection or damage to shafts in which placed concrete has not attaine d final set. 566 (b) Proposed drilling, hole cleaning, hole preparation, and bottom inspection method; and reinforcement and concrete placement equipment and procedures for the ground conditions expected to be encountered. Provide specific shaft drilling and concreting procedures to mitigate problems associated with ground water, surface water bodies, or both. Demonstrate an understanding of the subsurface conditions at the site by referencing available subsurface data shown in the boring logs. Indicate procedures to minimize disturbance to the construction site or overlaying or adjacent structure or services. Discuss potential drilling difficulties and indicate means and methods that will be used to remove obstructions from the excavation.

(c)Proposed drilled shaft excavation and construction methods used to ensure shaft stability during construction and reinforcement and concrete placement. Include proposed shaft drilling procedures for maintaining required horizontal and vertical shaft alignment. Include disposal plan for excavated material. If shaft casing is required, provide casing dimensions and detailed procedures for permanent casing installation or temporary casing installation and remov al.

(d)Proposed methods for mixing, testing, circulating, using, maintaining, and disposing of slurry, if used. Provide a detailed slurry mix design and its suitability to the subsurface conditions. Include the name and telephone number of the slurry manufact urer’s representative.

(e)Details of reinforcement placement. Include bracing, centering, centralizers, and lifting and support methods.

(f)Proposed structural concrete mix design conforming to Section 552, except as shown in Table 565- 4.

(g)Concrete placement methods. Include proposed operational procedures for free -fall, tremie, or pumping methods. (h) The method used to form an emergency horizontal construction joint during concrete placement.

(i)Inspection forms and charts for logging subsurface conditions during excavation and concrete volume placement. Include examples of populated forms. Conform to the installation and construction plan requirements for drilled shafts in FHWA -NHI-18-024, Drilled Shafts: Construction Procedures and LRFD Design Methods .

565.05Trial Drilled Shafts. If trial drilled shafts are required, perform the work according to the applicable requirements of Subsection 565.06. Before drilling holes for production shafts, demonstrate that the proposed methods and equipment are adequate by drilling a trial drilled shaft adjacent to the production shafts at an approved location. Make the center -to-center spacing between the trial shaft and production shafts at l east three shaft diameters or two bell diameters, whichever is larger. Construct the trial drilled shaft to the same size and to the tip elevation of the deepest production shaft shown in the plans. When bells are specified for production shafts, include a bell in the final trial shaft to verify the feasibility of belling in the specified bearing stratum. Install casing if caving occurs or the hole deforms sufficient to encroach upon the planned placement of the reinforcement cage with specified minimum con crete cover. Seat the casing to prevent caving and to allow dewatering of the hole when required. Remove material from inside the hole. Keep casing in place at least 4 hours while attempting to remove water in the hole. Record the rate of groundwater seepa ge into the hole. After this 4 -hour period, fill the hole with saturated sand while the casing is removed to simulate the concreting operation and casing removal for the production drilled shafts. Concrete or reinforcing steel is not required in the trial drilled shaft. Modify methods and equipment if the trial drilled shaft does not meet performance requirements. Submit a new installation plan and drill a new trial shaft for approval.

565.06Shaft Drilling.

(a)Drilling. Drill holes according to the approved construction plan. Excavate structural footings supported on drilled shafts and construct fills before initiating shaft drilling. Provide equipment and tooling able to drill shafts of the specified diameter and lengths 20 percent longer than those specified. Comply with tolerances shown in Table 565-1.

(1)Boring log. Provide a geologist or an engineer to mainta in a boring log of material excavated from the drilled shaft. Include the following information:

(a)Description and approximate top and bottom elevation of each type of soil or rock ma terial encountered and the date and time the soil or rock material was enco untered;

(b)Elevation and approximate rate of seepage or groundwater encountered;

(c)Equipment used to drill the shaft, time required to complete the shaft, bit changes, breakdowns, and other drilling difficulties encountered; and

(d)Remarks.

(2)Drilling methods. Use the uncased dry construction method where groundwater level and soil conditions are suitable to construct the shaft in a relatively dry -stable excavation and may be visually inspected before placing concrete. Use casing construction method, wet constructio n method, or both for shafts that do not meet the requirements for the dry construction method.

(a)Dry construction method. Drill the shaft, remove accumulated water and loose material from the excavation, place the reinforcing cage, and concrete the shaft in a relatively dry excavation. The dry construction method may be used when the excavation meets the following:

(1)Less than 12 inches of water accumulates above the base of the hole during a 1-hour period without pumping; (2) The sides and bottom of the hole remain stable without caving, sloughing, or swelling for 4 hours after excavation or over -reaming; and

(3)Loose material and water can be satisfactorily removed before inspection and before reinforcement and concrete placement. 568 (b) Wet construction method. Use water or slurry to maintain shaft stability with a fluid head inside the shaft excavation higher than the on- site static water elevation while advancing the excavation to final depth, placing the reinforcing cage, and concreting the shaft. Perform the following:

(1)Desand and clean drilling slurry;

(2)Final cleaning of the excavation using a bailing bucket, submersible pump, or other approved devices;

(3)Place shaft concrete with a tremie or concrete pump, starting at the shaft bottom; and

(4)Maintain pressure inside the shaft higher than outside at all times. Maintain inside fluid head elevation at least 5 feet higher than outside water head elevation. Table 565-1

Drilled Shaft Construction Tolerances

Drilled Shaft Attribute Allowable Variance Top elevation 1 in above to 3 in below the elevation shown in the plans Axial alignment Within 1.5% of plumb in soil Within 2.0% of plumb in rock Rebar stick -up 6 in above to 3 in below the elevation shown in the plans Diameter At least the diameter shown in the plans Horizontal location at t op-of-shaft elevation Shaft diameter less than or equal to 2.0 ft 3 in Shaft diameter greater than 2.0 ft and less than 5.0 ft 4 in Shaft diameter 5.0 ft or larger 6 in If drilled shaft excavations and completed drilled shafts are out of tolerance or defective, submit correction procedures for approval before correcting the deficiencies. Correct unacceptable shaft excavations and completed shafts to the satisfaction of the CO. Maintain the drilled hole to the specified nominal diameter before placing reinforcement elements and concrete. Increase the hole diameter at least ½ inch to a maximum of 3 inches when approved if ground softening, swelling or slurry cake buildup occurs. Case the hole, use a slurry during drilling, or both if the drilled hole continues to degrade and encroach upon the planned placement of the reinforcement cage with specified minimum concrete cover. Extend exterior casings from above the waterline to a subsurface elevation to protect against water action during placement and curing of the concrete when drilled shafts are located in open waters. Install the exterior casing to provide a positive seal at the bottom of the casing and prevent piping of water or entry of other material from the shaft excavation behind the casing. Remove drill cuttings and other loose debris from the bottom of the hole upon completion of drilling. Clean the drilled hole leaving no more than 2 inches of sediment on the bottom of the hole. Reduce the depth of a ccumulated water to less than 3 inches before placing concrete in shafts constructed using the dry method. Use a Shaft Inspection Device (SID) to visually verify that the magnitude of sediment is within tolerance unless otherwise specified. Provide a SID f or the inspection that is equipped with a high- resolution video camera with recording capability. Use the SID to measure the amount of sediment in the bottom of the drill hole in multiple locations totaling no less than 1 location per foot of drilled shaft diameter. Provide 3 days' notice before performing the SID camera work and provide live video feed. Provide video recordings within 1 week. Do not drill additional shafts, allow wheel loads, vibration -inducing equipment, or other construction activities within 15 feet or 3 shaft diameters, whichever is greater, of a newly constructed shaft for at least 20 hours. Fill rejected drill holes with flowable backfill.

(b)Slurry. Premix slurry with potable water according to the slurry manufacturer’s instructions to allow for hydration before introduction into the shaft excavation. Use slurry tanks of adequate capacity for slurry circulation, storage, and treatment. Do not use excavated slurry pits or the shaft excavation to mix the slurry. Do not add slurry component directly into the shaft excavation. Provide desanding equipment to limit slurry sand content as shown in Tables 565-2 and 565-3, at any point within the shaft. Verify sand content immediately before placing concrete. Desanding is not required for setting temporary casings, sign posts, or lighting mast foundations. Maintain the level of slurry in the excavation at least 5 feet above the highest expected adjacent piezometric water pressure head for mineral slurry, or 10 feet above the highest expected piezometric water pressure head for polymer or water slurry. Stop drilling and take corrective measures when there is a sudden loss of slurry from the hole. Prevent the slurry from setting up in the shaft. Discontinue the use of slurry and use an approved alternative method if the slurry construction method fails to produce the desired results. Maintain density, viscosity, and pH of the mineral or polymer slurry throughout shaft excavation and concre te placement according to Tables 565-2 and 565-3. Take slurry samples using an approved sampling tool. Extract slurry samples from the base of the shaft and 10 feet up from the base of the shaft. Perform 4 sets of tests during the first 8 hours of slurry use. The testing frequency may be decreased to one test set for every 4 hours of slurry use when results are acceptable and consistent. Comply with the manufacturer’s recommendations and Table 565-3 for polymer slurry. 570 Table 565-2 Acceptable Range of Values for Mineral Slurry

Property In Hole at

Time of Test

Concreting Method

Density , pounds per cubic foot(1) 64 to 72 Density balance API 13B -1, Section 1(2) Viscosity, seconds per quart 28 to 50 Marsh Funnel AP 13B- 1, Section 2.2(2) pH 8 to 11 pH paper or meter Sand content, % 4.0 maximum API 13B -1, Section 5(2)

(1)Density values shown are for fresh water. Increase density values 2 pounds per cubic foot for saltwater. Perform tests when slurry temperature is above 40 ° F.

(2)American Petroleum Institute, API 13B- 1, Recommended Practice for Field Testing Water -based Drilling Fluids . Table 565-3 Acceptable Range of Values for Polymer Slurry

Property In Hole at

Time of Test

Concreting Method

Density, pounds per cubic foot(1) 64 maximum Density balance API 13B -1, Section 1(2) Viscosity, seconds per quart 32 to 135 Marsh Funnel AP 13B- 1, Section 2.2(2) pH 8 to 11 pH paper or meter Sand content, % 1.0 maximum API 13B -1, Section 5(2)

(1)Density values shown are for fresh water. Increase density values 2 pounds per cubic foot for saltwater. Perform tests when slurry temperature is above 40 ° F.

(2)American Petroleum Institute, API 13B- 1, Recommended Practice for Field Testing Water -based Drilling Fluids . Correct slurry if sample does not meet the requirements shown in Table 565-2 or 565-3. Do not place concrete until the results of the resampling and retesting are approved.

(c)Casings. Install temporary casing to prevent sloughing of the top of the shaft excavation, unless it can be satisfactorily demonstrated to the CO that surface casing is not required. Install temporary casing regardless of excavation method when sidewall conditions warrant additional stabilization or mitigation of excessive groundwater infiltration. Use smooth, clean, watertight, steel casings of sufficient stren gth to withstand handling, installation stresses, concrete placement, and surrounding earth pressures. Casing diameters are outside diameters when shown in the plans. Comply with American Petroleum Institute tolerances applicable to regular steel pipe for permanent casing diameter. Provide casings with the outside diameter at least the specified size of the shaft. Install casings to produce a positive seal at the bottom of the shaft to prevent piping of water or other material into or out of the excavated h ole. Stabilize the excavation with slurry, backfill, or other approved methods if it becomes necessary to remove a casing. Maintain an adequate head of water or slurry inside the casing to prevent piping or sloughing of material at the bottom of the hole w hen drilling below the water table. Subsurface casings are to be considered temporary unless designated as permanent casing. Remove temporary casing concurrent with concrete placement. Maintain the concrete within the casing so 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 practically removed are considered to be a defect in the drilled shaft. Correct defective shafts using approved methods. Corrective action may consist of, but is not limited to, the following:

(1)Removing the shaft concrete and extending the shaft deeper to compensate for loss of frictional capacity in the cased zone;

(2)Providing straddle shafts to compensate for capacity loss; or

(3)Providing a replacement shaft. Cut permanent casing off at the required elevation and leave in place.

(d)Obstructions. If obstructions, such as boulders, logs, or man -made objects are encountered during shaft excavation, notify the CO. Remove, bypass, or break-up obstructions according to the approved construction plan and Section 203. If methods in the approved construction plan are not effective, submit alternative plans for approval. Drilling tools and other construction material and equipment lost in the excavation will not be considered as obstructions. Promptly remove tools, material, or equipment from the excavation and repair degradation of the shaft.

565.07Reinforcing Steel and Crosshole Sonic Logging Access Tubes Placement. Perform reinforcing steel work according to Section 554. Securely wire together contact reinforcing steel lap splices. Tie and support the reinforcing steel so it remains within the required tolerances. Securely tie concrete spacers or other approved spacing devices at fifth points around the cage perimeter and space at intervals no more than 10 feet along the length of the cage. Use spacers of approved material at least equal in quality and durability to the shaft concrete. Install steel CSL access tubes for each drilled shaft at locations specified and according to ASTM D6760. Extend access tubes at least 24 inches above shaft top and no more than 3 inches above shaft bottom. Use 1½-inch nominal diameter, Schedule 40, standard black pipe conforming to ASTM A53 for CSL access tubes. Provide a watertight end plug at the lower end of the pipe and make joints watertight. Fill the CSL access tubes with potable water before placing concrete in the drilled shaft. Temporarily cap the top of the tubes to prevent debris or concrete from entering the tubes. Place the reinforcing steel cage as a unit immediately after the drilled hole is inspected, accep ted, and before concrete placement. Remove cage when directed for re -inspection if concrete is not placed immediately. Avoid distortion or racking of the steel when handling reinforcing cages. Provide positive support at the top for the reinforcing steel cage during concrete placement. 572 Do not proceed with installation of subsequent shafts until CSL testing has been completed on the first drilled shaft and the results have been approved in writing. Approval to proceed with the construction of subsequent shaf ts, before receiving approval of the first shaft will be based on observations of workmanship during construction of the first shaft and the following:

(a)Compliance with the approved shaft installation plan;

(b)Contractor’s daily reports and inspector’s daily logs of excavation, reinforcement, and concrete placement; and

(c)Concrete placement logs and volume curves. The CO will furnish written notification to proceed with subsequent shaft construction within 24 hours after completion of the first shaft. If the CO determines the first shaft to be of questionable quality, discontinue all shaft construction until the CSL test results of the first shaft are received and reviewed and the shaft accepted in writing. After the first drilled shaft has been accepted , do not change construction methods, equipment, or material used to construct subsequent shafts, unless otherwise approved. 565.08 Concrete for Drilled Shafts. Use a removable form or other approved means to form the shaft to at least 24 inches below finished ground when the top of shaft is above ground. Forms may be removed according to Subsection 562.08 if the shaft concrete has not been exposed to saltwater or moving water for 7 days. Strip the forms without damaging the concrete. Remove the top portion of the drilled shaft concrete before continuing with column construction when it is determined the concrete has been affected by underwater placement. Place concrete immediately after excavation is complete and the reinforcing steel cage with CSL access tubes is in place. Provide concrete conforming to Section 552, except as shown in Table 565-4. Table 565-4

Concrete for Drilled Shafts

Method Class Slump

Shafts constructed without

drilling fluid A(1) 7±1 inches

Shafts constructed with

drilling fluid A(1) 8±1 inches

Shafts for underwater

placement S –

(1)Use Class A(AE) concrete on portions of the drilled shaft above the finished ground-line unless otherwise noted. Do not use seal concrete above the freeze- thaw or wet -dry zone of the hole. Place underwater concrete according to Subsection 552.08(d) , except as modified in this Section and as approved. Adjust approved admixtures for project conditions to ensure that the concrete has the minimum required slump for at least 2 hours. Submit trial mix and slump loss test results for concrete at ambient temperatures appropriate for site conditions. Place each load of concrete within 2 hours of batching. Longer placement time may be allowed if the concrete mix maintains the minimum required slump for longer than 2 hours. Do not retemper concrete that has developed its initial set. Place concrete in one continuous operation from bottom to top of the shaft. Continue placing concrete after the shaft excavation is full and until acceptable quality concrete is evident at the top of shaft. Consolidate the top 10 feet of the shaft concrete using acceptable vibratory equipment before initial concrete set. Finish the top of the shaft to the required elevation shown in Table 565-1. Consolidate shaft concrete only when water or slurry above the finish concrete level has been removed. Place concrete using the following methods:

(a)Free- fall. Use free- fall placement only in dry holes. Ensure the concrete falls directly to the shaft base without contacting either the rebar cage or shaft sidewall. Drop chutes may be used to direct placement of free -fall concrete. Drop chutes consist of a smooth tube of either one -piece construction or sections that can be added and removed. Support the drop chute so that the maximum height of free -fall of the concrete measured from the bottom of the chute is 25 feet. Reduce the height of free -fall or rate of concrete flow into the excavation if concrete placement causes the shaft excavation to cave or slough or strikes the rebar cage or sidewall. Use tremie or pumping to place the concrete if placement cannot be satisfactorily accomplished by free-fall placement.

(b)Tremies. Use tremies for concrete placement in either wet or dry holes. A tremie consists of a hopper and tube of sufficient length, mass, and diameter to discharge concrete at the shaft base. Do not use tremies that contain aluminum parts that will come in contact with the concrete. Provide a tremie tube with clean and smooth inside and outside surfaces and sufficient wall thickness to prevent crimping or sharp bends. Provide tubes with an inside diameter at least six times the maximum size of aggregate used in the concrete mix, but at least 10 inches. Use a watertight tremie according to Subsection 552.08(d) for wet holes. Construct the discharge end of the tremie to allow free radial flow of concrete during placement. Place the tremie discharge at the shaft base elevation. Place the concrete in a continuous flow. Keep the tremie discharge immersed at least 10 feet below the surface of the fluid concrete. Maintain a positive head of concrete in the tremie at all times. If the tremie discharge is removed from the fluid concrete column and discharges concrete above the rising concrete surface into displaced water; remove the reinforcing c age and concrete, complete necessary sidewall removal as directed, and reconstruct the shaft.

(c)Pumps. Use pumped concrete placement in either wet or dry holes. Use a 4- inch minimum diameter discharge tube with watertight joints. Place the discharge tube at the shaft base elevation. Use a sealed discharge tube according to Subsection 552.08(d) for wet holes. If a plug is used, remove it from the hole or use a plug made from approved material that will prevent a defect in the sha ft if not removed. Place the concrete in a continuous flow. Keep the pump discharge tube immersed at least 10 feet below the surface of the fluid concrete. Remove the reinforcing cage and concrete if the discharge tube is removed from the fluid concrete co lumn and discharges concrete into displaced water. Complete necessary sidewall removal as directed and reconstruct the shaft. 574 565.09 Crosshole Sonic Logging Integrity Testing. Provide a n on- site CSL engineer during testing.

(a)Testing. Perform integrity testing on production drilled shafts according to ASTM D6760. Test drilled shafts between 4 and 14 days after concrete placement. Submit drilled shaft bottom and tip elevations, access tube lengths, surveyed tube positions, and date of concrete placement befor e testing to the CO. Perform tests between all tube pairings in the shaft, including adjacent perimeter access tubes and diagonally between tubes. If an access tube is unacceptable for testing, drill a plumb core hole to the appropriate depth and install a fully -grouted replacement tube or propose an alternative integrity test method that is acceptable to the CO. Tremie fill access tubes with neat hydraulic cement grout after integrity testing, inspection and data analysis are completed and accepted.

(b)Test results and reporting. Submit preliminary results for each shaft tested before CSL test personnel leave the site. Submit a detailed CSL report within 5 days of testing. Allow 5 days for review of the data before continuing construction on the tested shaft. Include the following in the CSL report:

(1)Project identification and dates of CSL testing;

(2)Table and a schematic showing shafts tested with identification of tube coordinates and collar elevation;

(3)Names and affiliations of personnel who performed the CSL te sts and interpretations;

(4)Type of equipment used for testing;

(5)Data logs and waterfall diagrams;

(6)X-Y plots of first arrival times, amplitude, and velocity versus shaft depth; and

(7)Interpretations, analyses, and results. Identify and provide detailed discussion of each anomalous zone detected by the CSL. Anomalous zones are zones where velocity reduction exceeds 15 percent of the average velocity of properly placed and cured shaft concrete at the time of testing or reductions in measured relative energ y are greater than 9 dB of the local average value of relative energy. Collect and process additional data sufficient to construct 3D color -coded tomographic images with two -dimensional cross -sections between tubes within identified anomalous zones.

565.10Acceptance. Material for drilled shafts will be evaluated under Subsections 106.02 and 106.03. Construction of drilled shafts will be evaluated under Subsections 106.02 , 106.03, and 106.04 as follows:

(a)Drilled shafts exhibiting velocity reductions less than or equal to 15 percent of the average velocity of properly placed and cured shaft c oncrete at the time of testing and reductions in measured relative energy less than 9 dB of the local average value of relative energy are acceptable.

(b)Where velocity reductions exceed 15 percent of the average velocity of properly placed and cured shaft co ncrete at the time of testing or reductions in measured relative energy are greater than 9 dB of the local average value of relative energy, provide additional imaging and other data required in Subsection 565.09(b) to enable fu rther evaluation of the shaft. Drill at least two core holes to intercept the anomalous zone and obtain core samples from the suspect area when required. The CO will evaluate the crosshole sonic logging data, the tomographic imaging data, and the retrieved core data and determine if substantive defects are present .

(c)Removal of obstructions will be evaluated under Subsection 106.02. Concrete will be evaluated under Section 552, except concrete will be sampled at the point of discharge from the truck. Reinforcing steel will be evaluated under Section 554.

Measurement

565.11Measure the Section 565 pay items listed in the bid schedule according to Subsection 109.02 and the following as applicable: When measuring drilled shafts by the linear foot, measure from the plan top elevation to the approved tip. Do not measure portions of shafts extending deeper than approved. When measuring trial drilled shafts by the linear foot, measure from the approved tip elevation to the ground surface at the center of the shaft.

Payment

565.12The accepted quantities will be paid at th e contract price per unit of measurement for the Section 565 pay items listed in the bid schedule, except the drilled shaft contract price will be adjusted according to Subsection 106.05. Payment will be full compensation for the work prescribed in this Section. See Subsection 109.05. Payment for drilled shafts will be made at a price determined by multiplying the contract price by the structural concrete comp ressive strength pay factor.