Article 1 — Description
Construct foundations consisting of reinforced or non-reinforced concrete drilled shafts .
Article 2 — Materials
Use materials that meet the requirements of the following Items. Item 421, “Hydraulic Cement Concrete” Item 440, “Reinforcement for Concrete” Item 448, “Structural Field Welding” Use concrete for drilled shafts that meets the requirements shown i n Table 1 unless otherwise shown on the plans. Table 1 Concrete for Drilled Shafts Drilled Shaft Type Concrete Non-reinforced Class A Reinforced Class C Slurry and underwater concrete placement Class SS Use coarse aggregate Grade 4, 5, or 6 for drilled shaft concrete in reinforced drilled shafts. Grade 2 or Grade 3 may be used if the shaft is dry and reinforcing steel has a 5 in. minimum clear spacing. Use a water -reducing, retarding admixture in accordance with DMS -4640 , “Chemical Admixtures for Concrete,” in all concrete when using casing that will be pulled or when placing shafts under water or under slurry. Use concrete with slump that meets the requirements shown in Table 2 as deter mined in accordance with Tex-415-A . Table 2 Slump Requirements Placement Type Min Acceptable Placement Slump (in.) Recommended Design and Placement Slump (in.) Max Acceptable Placement Slump (in.) Dry 5-1/2 6-1/2 7-1/2 Underwater and under slurry 7 8 9 Perform a slump loss test in accordance with Tex -430-A before beginning work when casing is to be pulled or concrete is to be placed underwater or under slurry. Provide concrete that will maintain a slump of at least 4 in. throughout the entire anticipated time of concrete placement. Time of concrete placement is in accordance with Section 416.3.6., “Concrete,” and Section 416.3.7., “Additional Requirements for Slurry Displacem ent or Underwater Concrete Placement Methods.” Note the temperature of the concrete mix at the beginning of the slump loss test. Place the concrete if its temperature at the time of placement into the drilled shaft is no more than 10°F higher than the slump loss test temperature. Use ice or other concrete-cooling ingredients to lower concrete temperature or run additional slump loss tests at the higher temperatures. Slump loss testing will be waived if anticipated time of concrete placement is less than 90 min. 501 Use mineral drilling slurry that meets the requirements shown in Table 3, as determined in accordance with Tex-130-E . Deter mine pH of slurry in accordance with Tex-128-E or using pH paper strips. Table 3 Mineral Slurry Requirements Before Introduction into Excavation Sampled from Bottom of Excavation Before Concreting Specific Gravity Sand Content pH Specific Gravity Viscosity (sec.) Sand Content ≤1.10 ≤1% 8–11 ≤1.15 ≤45 ≤4% Use mineral slurry consisting of processed bentonite or attapulgite clays mixed with clean fresh water. Do not use partially hydrolyzed polyacrylamide (PHPA) polymeric slurry or any other fluid composed primarily of a polymer solution. If approved, water may be used as the drilling fluid. In this case, all the provisions shown in Table 3 must be met, except that the maximum specific gravity is not to exceed 1.12. Sample slurry from the bottom of the hole, before placing concrete, and test it in accordance with Tex -130-E . Use a pump or air lift to remove slurry that does not meet the requirements shown in Table 3 while adding fresh clean slurry to the top of the hole to maintain the slurry level. Continue this operation until the slurry sampled from the bottom of the hole meets the requirements.
Article 3 — Construction
Submit d rilled shaft installation plan for review no later than 1 mo. before drilled shaft construction. Include the following in the plan: name and experience record of the drilled shaft superintendent who will be in charge of drilled shaft operations for the project ; list of proposed equipment to be used, including cranes, drills, augers, bailing buckets, final cleaning equipment, de- sanding equipment, slurry pumps, core- sampling equipment, tremies or concrete pumps, and casing; details of overall construction operation sequence and the sequence of shaft construction in bents or groups ; details of shaft excavation methods ; when the use of slurry is anticipated, details of the slurry mix design and its suitability for the subsurface conditions at the construction site, mixing and storage methods, maintenance methods , and disposal procedures ; details of methods to clean the shaft excav ation; details of reinforcement placement, including support and centralization methods ; details of concrete placement, including proposed operational procedures for free- fall, tremie , or pumping methods; and details of casing installation and removal methods. The installation plan will be reviewed for conformance with the plans, specifications , and special provisions. The Contractor will be notified within 14 days of receipt of the installation plan of any additional information required or changes necessary to meet the C ontract requirements. All procedural approvals will be subject to trial in the field and will not relieve the Contractor of the responsibility to satisfactorily complete the work as shown on the plans and in conformance with s pecifications . Place the shaft to within the following tolerances . Vertical plumbness : 1 in. per 10 ft. o f depth Center of shaft located under column: 1 in. of horizontal plan position 502 Center of shaft located under footing: 3 in. of horizontal plan position Complete the embankment at bridge ends before installing drilled shafts that pass through the fill. Ref er to Item 423, “Retaining Walls,” for provisions for drilled shafts passing through the structural volume of retaining walls.
3.1 Excavation . The plans indicate the expected depths and elevations for encountering satisfactory bearing
material. Excavate as required for the shafts through all materials encountered to the dimensions and elevations shown on the plans or required by the site conditions. Removal of man- made obstructions not shown on the plans will be paid for in accordance with Article 9.7., “Payment for Extra Work and Force Account Method.” Adjust the bottom of the shaft or alter the foundation if satisfactory founding material is not encountered at plan elevation, as approved, to satisfactorily comply with design requirements. Blasting is not allow ed for excavations. Stop drilling if caving conditions are encountered and adopt a construction method that stabilizes the shaft walls. Do not excavate a shaft within two shaft diameters (clear) of an open shaft excavation, or one in which concrete has been placed in the preceding 24 hr. Dispose of material excavated from shafts and not incorporated into the finished project as shown on the plans and in conformance with federal, state, and local laws. Provide suitable access, lighting, and equipment for proper inspection of the completed excavation and checking of the dimensions and alignment of shaft excavation.
3.2 Core Holes . Take cores to determine the character of the supporting materials if directed. Use a method that
will result in recovery of an intact s ample adequate for judging the character of the founding material. Such cores should be at least 5 ft. deeper than the proposed founding grade or a depth equal to the diameter of the shaft, whichever is greater. Take these cores when the excavation is complete.
3.3 Casing . Use casing when necessary to prevent caving of the material, excluding groundwater, when slurry is
used for hole stabilization, or when required in conformance with the Contractor ’s safety plan. Provide casing with an outside diameter not les s than the specified diameter of the shaft. The portion of shaft below the casing may be as much as 2 in. smaller than the specified shaft diameter. No extra compensation will be made for concrete required to fill an oversized casing or oversized excavation. Use casing strong enough to withstand handling stresses and pressures of concrete and of the surrounding earth or water, and that is watertight, smooth, clean, and free of accumulations of hardened concrete. Use construction methods that result in a minimal amount of disturbed soil trapped outside the casing. This does not apply to temporary undersized casings used to protect workers inside shafts or to drilled shafts designed for point bearing only. Leave casing in place only if authorized or s hown on the plans. Extract casing only after placing the concrete to an appropriate level. Always m aintain enough concrete in the casing to counteract soil and water pressure. Rotate or move the casing up or down a few inches if necessary before and during concrete placement to facilitate extraction of the casing.
3.4 Requirements for Slurry Displacement Method . When soil conditions warrant, use the slurry displacement
method to construct drilled shafts , unless otherwise shown on the plans. Use this method to s upport the sides of the excavation with processed mineral slurry that is then displaced by concrete to form a continuous concrete shaft. Install surface casing to at least 10 ft. below existing ground before introducing slurry. Do not use casing other than surface casing. Do not use surface casing longer than 20 ft. without approval. Do not extract the surface casing until after placing the concrete. 503 Pre-mix slurry in a reservoir with enough capacity to fill the excavation and for recovery of the slurry dur ing concrete placement. Do not mix slurry in the shaft excavation or other hole. Allow adequate time for hydration of the slurry before introduction into the excavation. Maintain a head of slurry in the shaft excavation at or near ground level or higher, as necessary, to counteract groundwater pressure during and after drilling. Use an air lift or proper size cleanout bucket, just before placing reinforcing steel, to remove any material that may have fallen from the sides of the excavation or accumulated on the bottom after the completion of drilling. Use a cleanout bucket if material is too large to be picked up using an air lift. Re-process the hole using the auger as directed if concrete placement is not started within 4 hr. of the completion of the shaft excavation. Then clean the bottom using an air lift or cleanout bucket and check the slurry at the bottom of the hole for compliance with slurry requirements in accordance with Article 416.2., “Materials.” Agitate the congealed slurry to liquefaction if t he slurry forms a gel before concrete placement, and whenever directed. Recover and dispose of all slurry as approved, and in conformance with all federal, state, and local laws. Do not discharge slurry into or in close proximity to streams or other bodies of water.
3.5 Reinforcing Steel . Completely assemble the cage of reinforcing steel and place it as a unit immediately
before concrete placement. The cage consists of longitudinal bars and lateral reinforcement (spiral reinforcement, lateral ties, or horizontal bands). Connect individual segments with couplers or by lapping steel as approved if overhead obstacles prevent placement of the cage as a single unit. Extend the reinforcing steel cage as follows if the shaft is lengthened beyond plan length, unless dir ected otherwise. Extend the cage to the bottom for shafts supporting structures other than bridges. Extend the cage to 25 ft. or to the bottom, whichever is shorter, for bridge shafts with plan lengths less than 25 ft. Do not extend the cage for bridge shafts with plan lengths at least 25 ft. that are lengthened less than 33% of plan length. Extend the cage as directed for bridge shafts with plan lengths at least 25 ft. that are lengthened more than 33% of plan length. If the cage does not reach t he bottom of the shaft, it may be suspended, or a portion of the longitudinal steel may be extended to support the cage on the bottom of the shaft. Bars used to extend or support the cage may be lap spliced or welded by a qualified welder. Place the extens ion at the bottom of the shaft. Tie spiral reinforcement to the longitudinal bars at a spacing no more than 24 in., or as required for a stable cage. Ensure lateral reinforcement is not welded to longitudinal bars unless otherwise shown on the plans. Center the reinforcing steel cage in the excavation using approved “roller” -type centering devices unless otherwise approved. Use concrete or plastic chairs to keep the reinforcing cage off the bottom of the hole. Use centering devices starting at 1.5 ft. off from the bottom of the cage and spaced vertically at intervals not exceeding 10 ft. Use at least three centering devices per level at a spacing not to exceed 30 in. Flat or crescent -shaped centralizers (“sleds”) are not allowed. Support or hold down the cage to control vertical displacement during concrete placement or extraction of the casing. Use support that is concentric with the cage to prevent racking and distortion of the steel. 504 Check the elevation of the top of the steel cage before and after concret e placement or after casing extraction when casing is used. Downward movement of the steel up to 6 in. per 20 ft. of shaft length and upward movement of the steel up to 6 in. total are acceptable. Maintain the minimum length of steel required for lap with column steel. Use dowel bars if the proper lap length is provided both into the shaft and into the column. Locate and tie all dowel bars into the cage before placing concrete. Locate and tie anchor bolts when required before placement of concrete. Use templates or other devices to assure accurate placement of anchor bolts.
3.6 Concrete. Perform all work in accordance with Item 420, “Concrete Substructures.” Provide concrete with
maximum placement temperatures as shown in Table 4. Provide thermal analysis to show, and temperature- recording devices to verify, maximum concrete core temperature requirements are met in accordance with Section 420.4.7.14, “Mass Placements,” for shafts with diameter exceeding 7 ft. Instrument the first shaft for each size shaft exceedi ng 7 ft. diameter, and as directed if results do not meet specifications and when the concrete mix design changes. Table 4 Max Concrete Placing Temperature Shaft Size Mix Design Options 1 –5 Mix Design Options 6 –8 Diameter <5 ft. 95°F 95°F 5 ft. ≤ diameter ≤ 7 ft. 95°F 85°F 7 ft. < diameter 85°F 75°F Form portions of drilled shaft that project above natural ground. Remove loose material and accumulated seep water from the bottom of the excavation before placing concrete. No more than 3 in. of water should be present within the base of the excavation at the time of concrete placement. The rate of inflow should be conf irmed by observation to be less than 12 in. per hour. Place concrete using underwater placement methods if seepage exceeds the tolerable levels cited above. Place concrete as soon as possible after all excavation is complete and reinforcing steel is placed. Provide workable concrete that does not require vibrating or rodding. Vibrate formed portions of drilled shafts. Place concrete continuously for the entire length of the shaft. Limit free fall of concrete to 25 ft. for dry shafts of 24- in. or smaller diameter. Use a suitable tube or tremie to prevent segregation of materials. Use a tube or tremie in sections to provide proper discharge and permit raising as the placement progresses. For dry shafts more than 24- in. diameter, concrete may be allowed to free fall an unlimited distance if it does not strike the reinforcing cage or sides of the hole during placement. Provide a hopper with a minimum 3- ft. long drop- tube at the top of the shaft to direct concrete vertically down the center of the shaft when free fall is used. Do not use a shovel or other means to simply deflect the concrete discharge from the truck. Always m aintain enough head of concrete for cased shafts above the bottom of the casing to overcome hydrostatic pressure. Extract casing at a slow, uniform rate with the pull in line with the axis of the shaft. Monitor the concrete level in the casing during extraction. Stop the extraction and add concrete to the casing as required to ensure a completely full hole upon casing removal. The elapsed time f rom the mixing of the first concrete placed into the cased portion of the shaft until the completion of extraction of the casing must not exceed the time for which the concrete maintains a slump of more than 4 in. in accordance with Article 416.2., “Materi als.” Modify the concrete mix, the construction procedures, or both for subsequent shafts if the elapsed time is exceeded. Cure the top surface and treat any construction joint area in accordance with Item 420.
3.7 Additional Requirements for Slurry Displaceme nt or Underwater Concrete Placement Methods. Place
concrete on the same day the shaft is excavated and as soon as possible after all excavation is complete 505 and reinforcing steel is placed. Rework the hole by overdrilling a minimum 1/2 in. on all sides on t he same day that concrete is placed when drilling of a hole is performed on multiple days if approved. Use an air lift or cleanout bucket of the proper size to clean the bottom of the excavation before placing the reinforcing steel cage and concrete. Place concrete through a closed tremie or pump it to the bottom of the excavation. The minimum tremie diameter will be at least six times the maximum size of aggregate used in the concrete mix , but not less than 10 in. Initially seal the tremie or pump line to positively separate the concrete from the slurry or water. Place concrete continuously from the beginning of placement until the shaft is completed. Always keep the tremie full of concrete and well submerged in the previously placed concrete if using a tremie. Raise the tremie as necessary to maintain the free flow of concrete and the stability of any casing used. Always keep the discharge tube submerged in the previously placed concrete if using a pump. Place additional concrete to ensure the removal of any contaminated concrete at the top of the shaft. Allow the top portion of concrete to flush completely from the hole at the completion of the pour until there is no evidence of slurry or water contamination. Do not attempt to remove this concrete using shovels, pumps, or other means. Level the top of shaft with hand tools as necessary. Use a sump or other approved method to channel displaced fluid and concrete away from the shaft excavation. Recover slurry and dispose of it as approved. Do not discharge displaced fluids into or near streams or other bodies of water. Provide a collar or other means of capturing slurry and the top portion of concrete flushed from the shaft for pours over water. Remove the tube, reseal it at the bottom, penetrate with the tube into the concrete already placed by at least 5 ft., and recharge it before continuing if concrete placement is interrupted due to withdrawal of the submerged end of the tremie or pump discharge tube before completion. If this condition exists, notify the Engineer and note the elevation and circumstances related to the loss of seal on the drilled shaft log. The elapsed time from the mixing of the first concrete placed until the completion of concrete placement, including extraction of the casing, must not exceed the time for which the concrete maintains a slump of more than 4 in. in accordance with Article 416.2., “Materials.” Modify the concrete mix, the construction procedures, or both for subsequent shafts if the elapsed time is exceeded.
3.8 Test Load . Load test shafts, if required, in accordance with Item 405, “Foundation Load Test.”
3.9 Trial Shaft . When required on the plans, construct trial shafts to the depth and diameter shown on the plans.
Trial shafts include drilling the hole, placement of the rebar cage (unless otherwise stated), and placement of the concrete. When trial shafts are required, delay start of production shafts until successful completion of trial shafts.
Article 4 — Measurement
4.1 Drilled Shaft . Drilled shaft foundations will be measured by the foot to the bottom of the shaft .
4.1.1 Interior Bents and Piers. Shafts will be measured from a point approximately 6 in. below the finished
earthwork elevation at the center of each shaft, unless specific elevations or dimensions are shown on the plans or unless otherwise directed to meet unusual conditions. The bent height shown on the plans is for estimating purposes only and does not control the top- of-shaft measurement.
4.1.2 Abutment Bents and Retaining Walls . Shafts will be measured from the bottom of footing or cap elevation.
4.1.3 Other Non- Bridge Structures . Shafts, including trial shafts, will be measured from the top of the shaft.
4.2 Core Hole . Core holes will be measured by each core hole drilled.
Article 5 — Payment
The unit prices bid for the various classifications of drilled shafts are full compensation for excavation; furnishing, placing, and removing casing; furnishing, processing, and recovering slurry; furnishing and 506 placing reinforcing steel; pumping; furnishing and placing concrete, including additional concrete required to fill an oversize casing or oversize excavation; conducting slump loss tests; backfilling; disposing of cutti ngs and slurry; and materials, tools, equipment, labor, and incidentals. When the bottom of a drilled shaft is placed at an elevation below plan grade, no direct payment will be made for extra reinforcement placed to support the cage. The extra reinforcement will be subsidiary to the unit price bid per foot of shaft. No extra payment will be made for casings left in place, unless specified on the plans . No payment will be made for “Drilled Shaft” until the concrete has been placed.
5.1 Drilled Shaft . The work performed and materials furnished in accordance with this Item and measured as
provided under “Measurement” will be paid for at the unit price bid for “Drilled Shaft,” “Drilled Shaft (Non -Reinforced),” “Drilled Shaft (Sign Mounts),” “Drilled Shaft (High Mas t Pole),” “Drilled Shaft (Roadway Illumination Pole),” or “Drilled Shaft (Traffic Signal Pole)” of the specified diameter, subject to the limitations for overruns authorized by the Engineer in accordance with Section 416.5.1.1., “Overrun.”
5.1.1 Overrun . Payment for individual completed shaft lengths up to and including 5 ft. more than the maximum
plan length shaft, in accordance with Section 416.5.1.2., “Maximum Plan Length Shaft,” will be made at the unit price bid per foot of the specified diameter. Payment for the portion of individual completed shaft length more than 5 ft. and up to and including 15 ft. more than the maximum plan length shaft, in accordance with this Item, will be made at a unit price equal to 115% of the unit price bid per foot of the specified diameter. Payment for the portion of individual completed shaft length greater than 15 ft. more than the maximum plan length shaft, in accordance with Section 416.5.1.2., “Maximum Plan Length Shaft,” will be made at a unit price equal to 125% of the unit price bid per foot of the specified diameter.
5.1.2 Maximum Plan Length Shaft . Payment described in the previous Sections is subject to the following
provisions for extra depth drilling. For bridge structures, the maximum plan length shaft is the maximum length shaft, regardless of diameter, for any drilled shaft on that specific bridge. For retaining walls, the maximum plan length shaft is the maximum length shaft, regardless of diameter, for any drilled shaft on that specific retaining wall. For ov erhead sign structures, the maximum plan length shaft is the maximum length shaft, regardless of diameter, for any overhead sign structures included in the Contract. For high mast illumination poles, the maximum plan length shaft is the maximum length shaf t, regardless of diameter, for any high mast illumination pole included in the Contract. For roadway illumination poles, the maximum plan length shaft is the maximum length shaft, regardless of diameter, for any roadway illumination pole included in the Contract. For traffic signal poles, the maximum plan length shaft is the maximum length shaft, regardless of diameter, for any traffic signal pole included in the Contract.