SECTION 845 — DRILLED SHAFTS — DRILLED SHAFTS
845.01 Description.
The work includes the construction of steel cased, cast-in-place, concrete-filled, straight drilled shafts with steel reinforcement and the excavation, backfilling, dewatering, and disposal of obstructions encountered within the limits of the drilled shaft construction, at the required locations, lines and grades. The drilled shafts will be advanced into soil or bedrock to support the structure and design loads.
845.02 Materials.
Concrete. Provide a concrete mix that complies with Class XX modified as a SCC mix as specified in SECTION 601. Grout. Provide a cement water grout mix using Type II cement and water. Use a cement grout mixture that has a minimum seven-day compressive strength (f’ c) of 5000 psi. Reinforcing Steel. Use galvanized reinforcing steel that conforms to Subsection M05.06. Crosshole Sonic Logging Tubes. Provide access tubes for crosshole sonic logging (CSL) that are 2 in. ID, Schedule 40 steel pipe conforming to ASTM A53, and Grade A or B, Type E, F, or S. Permanent Drilled Shaft Casing. Use high strength steel conforming to Subsection M05.05.1. Slurry. Provide a slurry that is a stable suspension of mineral or polymer in potable water. Do not use polymer-mineral/bentonite blended slurries. Do not use mineral/polymer blended slurries. Excavation Monitoring Devices. Use the Shaft Inspection Device (SID) as manufactured by GPE, Inc., of Gainesville, Florida or approved equivalent.
Part 800 — Bridge Structures August 2025
SECTION 845 — DRILLED SHAFTS 800-223 Permanent Steel Casings. Provide permanent steel casing that conforms to ASTM A252 Grade 3 steel. Use permanent casing wall thickness as specified, but not less than ⅜ in.
845.03 Construction.
Lines and Grades.
a.Benchmarks. The Engineer will provide benchmarks located on or close to the site. Maintain and protect the benchmarks and all location stakes.
b.Loc ation. Employ a Professional Land Surveyor registered in the State of Rhode Island to establish the lines and levels. Establish the location of the drilled shafts with the approval of the Engineer. Identify the location of the center of completed drilled shafts on an engineering drawing relative to the design location and submit to the Engineer within two working days after completing the unit. Ensure that the drawings certified by the Contractor’s surveyor include: ● Baseline and north arrow ● Drilled shafts clearly identified ● Deviation in inches, to the nearest ½ in., from plan location at cutoff elevation Submittals.
a.General. Do not initiate any work until the Engineer has received, reviewed, and approved in writing each required submittal.
b.S ubmittal Documentation. Submit for review the names and qualifications of the Contractor/Subcontractor’s engineers and superintendents responsible for the work specified. Document, by resume and project lists, that each proposed individual has a minimum of five years’ experience for the work specified. In the submitted resumes and project lists, include a description of the formal training and experience, including a general description of subsurface soils encountered and drilling equipment used and a list of a minimum of three projects successfully drilled to the diameter range and depth required on the project in the last five years.
c.S hop Drawings. Submit Shop Drawings according to Subsection 105.02.
d.Site Plan. Submit a site plan including the method to access the site (timber cribbing, etc.), proposed equipment laydown area, method to secure the area from unauthorized access, and method to temporarily support equipment. The plan will be subject to permit agency review and acceptance. If requested by the permitting agencies, modify the proposed methods at no additional cost to the Project. Submit a detailed description of work that, at a minimum, addresses each of the following items of work: • Details of proposed equipment • M ethods and sequence of operations to be used to install casings
Part 800 — Bridge Structures August 2025
800-224 SECTION 845 — DRILLED SHAFTS • Excavat ing soil and maintaining a stable excavation • R emoving and disposing of obstructions within the limits of the shaft excavation • C leaning the shaft walls and bottom s o that less than 3 in. of loose, soft material remains • M onitoring the diameter and plumbness of shafts • P roducing, maintaining, mixing, circulating, and reclaiming slurry to maintain a clean bottom and to remove soil cuttings from the borehole • I nstalling reinforcing steel without damaging the excavated sidewalls of the drilled shaft • P lacing concrete by continuous tremie methods s o that no defects or voids occur in the concrete column • Using means and methods reviewed and approved by the Engineer in writing to separate the drill slurry from the concrete during tremie pours • B ackfilling Ensure that the submittal includes provisions for protecting any existing bridges, adjacent residential structures and property, and nearby utilities during drilled shaft installation. In addition, submit the following: • T he type of proposed access tubes and associated materials to prepare drilled shafts for CSL • T he type and installation of any jointing section to extend CSL tubes or instrumentation housings • S hop Drawings detailing the installation of materials • P rocedures and S hop Drawings detailing proposed means of protecting and maintaining the specified spacing of CSL access tubes and instrumentation housings during drilled shaft installation, especially in the rock socket below the bottom of the reinforcing cage
e.Welding Procedures. Submit welding procedures and qualifications of welders and tackers as specified in AWS D1.5 for casing steel and AWS D12.1 for reinforcing steel.
f.S lurry Data . Submit the following: • S lurry data from the supplier identifying the recommended physical and chemical properties of the slurry, the proposed slurry mix design and additives, if any, and the details and description of slurry equipment and overall plant operation • During construction, the results of quality control tests performed on the slurry promptly after the tests are completed • R ecord copies each week • S hop Drawing details for the management of slurry disposal • I nformation on the proposed off-site facility for the disposal of spent slurry
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SECTION 845 — DRILLED SHAFTS 800-225
g.Test Reports and Installation Logs. Submit test reports and installation logs as specified herein and in Subsection 845.03.4 . Submit proposed installation log forms for acceptance.
h.S haft Monitoring. Submit a description of the monitoring method, such as with the Shaft Inspection Device (SID) or equivalent, and the method of providing and checking the cleanliness of shaft bottoms and identifying the type of bearing material for consistency with design assumptions before placing concrete.
i.Dr illed Shafts . Submit the method of monitoring and continuously maintaining slurry level in the drilled shafts.
j.S haft Excavation. Submit the method of monitoring verticality of the shaft excavation in two principal perpendicular planes during excavation, and submit the details of proposed corrective measures to be implemented as necessary. For personnel who will perform verticality monitoring, submit documentation of training by the manufacturer in the use of the device or instrumentation to monitor verticality.
k.S haft Diameter. Submit the method of measuring the diameter of the shaft excavation in the rock socket after excavation (such as sonic caliper technology or equivalent). For personnel who will perform the diameter monitoring, submit documentation of training by the manufacturer in the use of the device or instrumentation to monitor the diameter with shaft depth.
l.C entering Shaft. Submit the method of placing, securing, and maintaining the position of steel reinforcing centered in the drilled shaft.
m.C oncrete Placement. Submit the method of placing concrete, including number, location, and details of tremie pipes.
n.R emedial Action Plan. Submit the remedial action plan, including calculations, methods, and materials necessary to complete corrections for out-of-tolerance drilled shaft foundations.
o.O bstruction. Submit the details of proposed equipment, methods, and sequence of operations to remove and dispose of obstructions.
p.C oncrete Mix . Submit the concrete mix design, trial batch reports, and laboratory test data. Prepare the submittal on Department forms according to SECTION 601. Submit the grout mix design, trial batch reports, and laboratory test data. Prepare the submittal on Department forms according to SECTION 601.
q.E xcavated Material . Submit the plan for handling, controlling, and managing on-site and off-site excavated soils, rock, and groundwater and their disposal site.
r.C ompleted Drilled Shaft Location Plan. At the completion of drilled shaft operations, and at least five working days before removal of drilled shaft equipment from the site, submit a final, as-installed drilled shaft location plan indicating:
Part 800 — Bridge Structures August 2025
800-226 SECTION 845 — DRILLED SHAFTS ● Surveyed location ● Shaft designation ● Shaft bottom elevation ● Permanent steel casing tip elevation and cutoff elevation as certified by a Registered Professional Engineer licensed in the State of Rhode Island.
s.Hydrostatic Pressures . Use appropriate means to satisfactorily manage hydrostatic conditions to minimize impacts to the work during foundation installation. Tolerances.
a.Drilled Shaft Diameter. Ensure that the minimum diameter is not less than specified, and that the maximum diameter does not exceed the specified diameter by more than 3 in.
b.Dr illed Shaft Rock Socket Diameter. Ensure that the minimum diameter is not less than specified, and that the maximum diameter does not exceed the specified diameter by more than 3 in.
c.Dr illed Shaft Rock Socket Bearing Elevation. Drill r ock sockets to within 6 in. of the specified bearing elevation as determined by the Engineer using the construction phase boring data.
d.Ma ximum Variation from Vertical . 1 percent.
e.Elevation of the Top of Shaft. Within 3 in. of the preliminary cut-off elevation.
f.Steel Cage. After all concrete is placed, ensure that the top of the reinforcing steel cage is no more than 6 in. above and no more than 3 in. below the required position.
g.C ompleted Shaft. Design the excavation equipment and methods so that the completed shaft excavation will have a planar bottom. Ensure that t he cutting edges of excavation equipment used to prepare the final drilled shaft tip configuration is normal to the vertical axis of the equipment within a tolerance of ±⅜ in. per foot of diameter.
h.C oncrete Volume. Compare the v olume of concrete placed to the theoretical volume required to fill a unit length of shaft. Make the comparison at the top of the rock socket and at the third point along the length of the shaft. Use the top of shaft as the final point of comparison. Report the actual versus theoretical rise in concrete level immediately to the Engineer. The Engineer will evaluate the dimension and quality of concrete by CSL testing.
i.R einforcing Steel . Ensure that t he reinforcing steel in the shaft is tied and supported so that the reinforcing steel will remain within allowable tolerances until the design seven-day concrete strength is verified. Use c oncrete spacers or other approved non-corrosive spacing devices at sufficient intervals (within 1 ft of the bottom and at intervals not exceeding 10 ft vertically up the shaft) to ensure concentric spacing for the entire cage length. Construct spacers of approved material equal in strength, quality , and durability
Part 800 — Bridge Structures August 2025
SECTION 845 — DRILLED SHAFTS 800-227 to the concrete specified for the shaft. Ensure that the spacers have adequate dimension to ensure the required clearance. Record Information.
a.Drilled Shaft Installation Log. For each drilled shaft installed, record on the drilled shaft installation log the: ● Identification number of drilled shaft ● Location ● Alignment ● Dimensions (plan & as-built) ● Elevations of top and bottom (plan & as-built) ● Depth of bearing stratum penetration ● Description of materials encountered at all elevations ● Elevation of water table and drilling fluid during excavation ● Condition of bottom of excavation ● Method of construction ● Slurry test data (indicate elevation of bottom of hole at time of introduction) ● Concrete data (slump & sample identification) ● Time & date of concreting ● Verticality and deviation from plan location ● Other data called for on the report form or pertinent to the drilled shafts Include the results of the bottom shaft, diameter, and verticality monitoring. Record the theoretical volume of excavation, volume of concrete placed vs . depth, and total volume of concrete placed. Provide a plot of actual concrete volume vs. theoretical volume and actual rise of concrete in the shaft. Report observed irregularities to the Engineer within 24 hours of discovery.
b.Draft Information. Submit the draft record information for each completed drilled shaft weekly. Submit the final record drawings for each drilled shaft no more than one week after completion of the work.
c.D aily Job Records . Maintain daily job records of mineral or polymer slurry testing performed under Subsection 845.03.5. Submit records on a weekly basis and more frequently if variations occur. Control Testing of Slurry.
a.Testing Control. Perform control testing of mineral slurry according to API Standard RP 13B, Standard Procedure for Testing Drilling Fluids as witnessed by the Engineer and submit a Certificate of Compliance. If polymer slurry is used, modify the parameters according to the slurry manufacturer ’s recommendations. Demonstrate experience in testing on at least three projects, and submit a summary to the Engineer for written approval.
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800-228 SECTION 845 — DRILLED SHAFTS
b.Slurry Testing. Test the slurry using the specified apparatus to determine the following: ● Freshly Mixed Slurry. Measure density, pH, and Marsh Cone viscosity of freshly mixed slurry. Perform API fluid loss test on freshly mixed mineral slurry and: ○ Calibrate density measuring devices at the start of the P roject and monthly thereafter or more often if there is evidence of needed calibration to an accuracy of ±0.05 lb/cu ft. ○ Perform API fluid loss test according to American Petroleum Institute Standard 13A. Ensure that fluid loss does not exceed 25cc in 30 minutes. ● Slurry Inside Excavation . Perform the tests specified below to verify that the slurry properties inside excavations are within the specified limits. Obtain samples from the top, middle, and bottom of the shaft, and perform the following tests once every four hours: ○ Density, by mud density balance ○ Viscosity, by Marsh Cone Method ○ pH ○ Sand content ● Perform fluid loss measurements in the shaft at the beginning or end of every shift. ● Perform the API fluid loss test for polymer slurry once every three days at times directed by the Engineer. Ensure that fluid loss does not exceed 25cc in 30 minutes.
c.Slurry in Excavation Before Placing Concrete. Immediately before placing concrete, take slurry samples using a sampling tool approved by the Engineer and test for density, Marsh Cone Viscosity, pH, and sand content. Extract slurry samples from the base of the shaft and at intervals not exceeding 10 ft up the slurry column in the shaft until two consecutive samples produce acceptable values for density, viscosity, and pH. Circulate and clean the slurry using an airlift and desanding unit. Modify or replace the slurry in the shaft if the test parameters exceed the limits specified. A nticipate encountering soil fill, potentially contaminated groundwater, and other agents that may be deleterious to the slurry. Modify the slurry mix as required to maintain a stable suspension at all times.
d.Los s of Fluid. Limit the f luid loss in the open borehole to a drop in the slurry level of no greater than one in. per hour per 20 ft of excavation depth, and no more than 2 ft total in a 24-hour period. For areas subject to recurring fluctuations (e.g., tidal areas), document this in the test results.
e.M ineral Slurry. Premix mineral slurry with potable water. Use mineral slurry of the high swelling, pure, premium grade sodium, bentonite-based type. Do not use the slurry mix until the bentonite mix has been allowed to swell and hydrate according to the time recommendations provided by the mineral manufacturer. Use slurry tanks of adequate capacity for slurry circulation, storage, and treatment. Desand the equipment as necessary to control slurry sand content to less than 4 percent by volume at any point
Part 800 — Bridge Structures August 2025
SECTION 845 — DRILLED SHAFTS 800-229 in the borehole at the time the slurry is introduced. Prevent the slurry from “setting up” in the shaft. Such methods may include, but are not limited to: ● Agitation ● Circulation ● Adjusting the properties of the slurry Properly dispose of all slurry at an off-site location. Conduct control tests using a suitable apparatus on the mineral slurry to determine density, viscosity, and pH. An acceptable range of values for those physical properties is as follows: ● A suspension of powdered Wyoming or Dakota bentonite, attapulgite, or approved equivalent ● Density of slurry in the excavation ― 65 to 75 lb/cu ft ● Density of slurry before concrete placement ― 65 to 70 lb/cu ft ● Viscosity of slurry in the excavation ― 30 to 45 seconds per quart by Marsh Cone Method ● pH of slurry in the excavation ― 8.0 to 11.0 ● Yield ― 90 barrel per ton, minimum ● Dwell time in the mixer ― 10 minutes, minimum ● Storage time to allow hydration ― 6 hours, minimum ● Sand content ― Less than 1 percent by volume measured within 12 in. of the bottom of the drilled shaft immediately before concrete placement ● Fluid loss ― 25cc maximum in 30 minutes using a filter press by API 13A. Note: ○ Perform tests only when the slurry temperature is above 4.5 degrees Celsius (40 degrees Fahrenheit). ○ If desanding is required, ensure that the sand content does not exceed 4 percent by volume at any point in the borehole as determined by the American Petroleum Institute sand content test (API RP 13B-1) when the slurry is introduced. Perform tests to determine density, viscosity, and pH value during the shaft excavation to establish a consistent working pattern. Conduct a minimum of four sets of tests, at least one test every two hours, during the first eight hours of slurry use . When the results of four consecutive tests show consistent behavior, the testing frequency may be decreased to one set every four hours of slurry use.
f.Polymer Slurry. Use polymer slurry that consists of either natural or synthetic materials. Submit the polymer data to the Engineer for approval. Ensure that the slurry properties at
Part 800 — Bridge Structures August 2025
800-230 SECTION 845 — DRILLED SHAFTS the time of mixing and at the time of concreting conform to the written recommendations of the manufacturer , except that the sand content at the base of the drilled shaft excavation shall not exceed 1 percent when measured by Method API 13B-1, Section 5, immediately before concreting. Submit for review and approval by the Engineer a detailed report specific to the Project prepared and signed by a qualified slurry consultant describing all slurry materials, mix proportions, mixing methods, and quality control methods. Ensure that t he submittal includes all properties and ranges for density of slurry in the excavation, viscosity of slurry in the excavation, and pH of slurry in the excavation. Property Requirement Test Density (lb/cu ft) during drilling Just before placing concrete Less than or equal to
64.0 lb/cu ft
Mud Weight (Density) API 13B-1 Viscosity (sec/qt) during drilling just before placing concrete 32-108 less than or equal to 60 lb/cu ft Marsh Funnel and Cup API 13B-1 Section 2.2 pH 8.0 to 11.0 Glass electrode, pH meter or pH paper Sand Content (%) By volume Before final cleaning Just before placing concrete Less than or equal to
1.0 %
Sand Content Kit API 13B-1 Section 5 When approved by the Engineer, slurry may be used in salt water. The allowable density may be increased up to 2 lb/cu ft. The slurry temperature must be at least 40º Fahrenheit (4º Celsius) when tested. Excavation.
a.General. ● Excavate for the drilled shaft using non- displacement methods to advance the excavation through overburden materials and to maintain a stable excavation. Form the rock socket by methods such as coring, rotary drilling, chiseling, or other methods. ● Do not allow vibration or excessive wheel loads to affect the drilled shaft during construction. ● Seat permanent surface steel casing in bedrock by vibratory, drilling, or driving methods reviewed and approved by the Engineer.
Part 800 — Bridge Structures August 2025
SECTION 845 — DRILLED SHAFTS 800-231 ● During excavation, prevent instability or displacement of the surrounding earth, excessive water intrusion, or damage from construction operations. ● Ensure that the completed shaft excavation has a planar bottom around the perimeter of the shaft tip. Ensure that t he bottom of the shaft slopes uniformly and is free of depressions exceeding 0.25 ft deeper than the adjacent surfaces. Ensure that t he cutting edges of excavation equipment are normal to the vertical axis of the equipment within a tolerance of ⅜ in. per foot of diameter. ● Evaluation of the shaft installation at any stage may be made by the Engineer. Measure the depth to the bottom of the shaft bearing stratum at the request of the Engineer to determine compliance with the specification requirements. If the Engineer concludes that the bedrock at the foundation bearing level cannot support the design load, the Engineer may request the Contractor to drill deeper. Do not concrete the drilled shafts until the hole has been observed, evaluated, and approved by the Engineer in writing. ● Upon initial contact with bedrock, regardless of the depth and rock quality, cease drilling and notify the E ngineer, who will determine the actual depth. ● If an obstruction is encountered, notify the Engineer immediately. Obstructions are defined as natural, man-made, or man-placed objects, materials, or structures (e.g., granite blocks, concrete, timber, logs, piles, cobbles, boulders) encountered at or below ground surface that unavoidably and completely halt the progress of the shaft excavation or subsurface drilling work for more than one hour per incident as determined by the Engineer. These efforts include adjustment of drilling rate, down pressure, change of drill tools, and use of chisel tools to break past or remove the obstruction. Probe to locate the extent of any obstruction and propose a method of passing or removing it. ● Do not consider as obstructions any d rilling tools that are lost in the excavation. Remove these tools. Repair the hole when removal operations cause damage. Tool removal and hole repairs will be at no additional cost to the Department.
b.Groundwater Control. ● Provide groundwater control using drilling slurry and permanent casing, if necessary. ● If dewatering is required, coordinate with RIDOT, the Rhode Island Department of Environmental Management (RIDEM), all utility companies, and municipal or other agencies, including agencies governing the discharge of water from dewatering operations.
c.Inspection. ● The approximate design bottom elevation of the drilled shafts is based on design criteria developed by the Engineer using subsurface conditions shown on the boring logs. The Engineer may adjust the required bottom elevation based on the elevation and quality of the bearing material encountered during drilling of more recent test
Part 800 — Bridge Structures August 2025
800-232 SECTION 845 — DRILLED SHAFTS borings and during installation of the drilled shafts. The Engineer will be the sole judge for classifying the material encountered. ● Sound, measure, and record the depth to the final bottom of shaft in the presence of the Engineer to verify that soil or sediment from the sides of the shaft has not fallen into the shaft and collected on the shaft bottom. Ensure that the maximum depth of sediment does not exceed 1½ in. with at least 50 percent of the base with no more than ½ in. of sediment. Perform depth measurements at the following times: ○ Immediately after excavation has been performed to the final depth. ○ Immediately after the excavation has been cleaned of all loose material and has been desanded. ○ Immediately before placing reinforcing steel in the slurry-filled shaft. ○ During installation of the reinforcing cage through dedicated access tubes, location, and type to be proposed by the Contractor and reviewed by the Geotechnical Engineer. ○ Immediately before concrete placement. ● Ensure that the average measured depth at each stage does not vary by more than +0.1 ft or -0.2 ft. Record and average a minimum of six, equally spaced soundings to determine the depth. The Engineer will investigate the measurements that exceed the tolerances. Complete any additional cleaning or drilling until the measurements satisfy the specified tolerances. Ensure that water at the base of the shaft does not exceed 3 in. before the placement of concrete. ● Before placement of reinforcing steel and concrete, ensure that loose material from the bottom and sides of the excavation has been removed and that the shaft is within the specified tolerances. Remove all loose material at the bottom of shaft. Document the drilled shaft excavation dimensions vs. depth and verticality using the specified monitoring device to verify that the shaft is within the specified tolerances.
d.Monitoring. Provide monitoring devices and qualified technicians for monitoring the following: ● Shaft Bottom Cleanliness. Use the Shaft Inspection Device (SID) as manufactured by GPE, Inc. of Gainesville, Florida or approved equivalent. ● Shaft Verticality Measurement Device. Provide equipment and a qualified technician for monitoring the dimensions and verticality of drilled shaft excavations. At a minimum, take measurements using equipment attached to the top of the drill rig (Kelly bar). ● Shaft Diameter Measurement Device. Provide equipment and a qualified technician for monitoring the dimensions of drilled shaft excavations. Provide sonic caliper technology or approved equivalent.
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SECTION 845 — DRILLED SHAFTS 800-233
e.Mineral Slurry Level. M aintain the level of mineral slurry at not less than 4 ft above the highest observed piezometric pressure head at all times during excavation.
f.P olymer Slurry . Maintain the level of polymer slurry at a level not less than 6 ft above the highest observed piezometric head. Installation of Casings.
a.Permanent Casing. Furnish and install permanent casing that will remain in place and is included in the design of the drilled shaft. Permanent casing may be oversized up to 3 in. if necessary to facilitate temporary casing installation. Comply with the following: ● Use permanent casing on all drilled shafts, unless otherwise stipulated in the Contract. ● Ensure that permanent casing is continuously joined. ● Advance the permanent surface casing and seat in bedrock. ● Stabilize the sidewalls of the shaft by slurry, steel casing, placement and redrilling of concrete fill, or other means, as proposed and after review and approval by the Engineer. ● Use permanent steel casing that complies with ASTM A252, Grade 3 steel. Ensure that the permanent casing wall thickness is as required to support soil and water pressures, handling, installation, construction, and transportation loads, but not less than ⅜ in. ● Ensure that the permanent casing has a minimum diameter as indicated on the Plans. ● For vertical and horizontal joints in permanent casings, provide full penetration welds that conform to AWS Dl.5 requirements.
b.Temporary Casing. When stipulated 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 pre vent 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 ft unless synthetic slurry is bei ng used. During casing extraction, maintain a sufficient level of fluid in the casing to counteract external hydrostatic pressures but no less than 5 ft 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 represent a defect in the drilled shaft. Correct defective shafts using approved methods at no cost to the Department. Corrective action may include the following: ● Removing the drilled shaft concrete and extending the drilled shaft deeper to compensate for the loss of frictional capacity to the cased zone
Part 800 — Bridge Structures August 2025
800-234 SECTION 845 — DRILLED SHAFTS ● Providing straddle drilled shafts to compensate for capacity loss ● Providing a replacement drilled shaft Installation Requirements for Crosshole Sonic Logging.
a.Preparation of Crosshole Sonic Logging (CSL) Access Tubes. Install the access tubes as shown on the approved Shop Drawings. Fasten the tubes at 3- ft intervals to the interior of the reinforcement cage in a parallel manner. Immediately after concrete placement of the drilled shafts, fill the tubes with clean water and cap the tubes. Wait a minimum of 24 hours after concrete placement before completing CSL. Repair or replace (by coring) damaged or blocked tubes.
b.Tube Criteria. Install the access tubes in the drilled shafts in a regular, vertical, symmetric pattern so that four tubes are equally spaced.
c.M easurement . Record the spacing between the centerline of adjacent at the third points of the reinforcing cage to an accuracy of 0.25 in. Provide measurements to the Engineer before placement of the steel reinforcing cage in the shaft.
d.A ccess Tubes. Ensure that the access tubes for Crosshole Sonic Logging (CSL) are 2 in. ID, Schedule 40 steel pipe conforming to ASTM A53, Grade A or B, Type E, F, or S. Ensure that the access tubes extend the entire length of the shaft to the shaft tip (bottom of drilled shaft/rock socket), and have a round, regular internal diameter free of defects and obstructions in the tube and at joints to permit free, unobstructed passage of the source and receiver probes. Ensure that the tubes are watertight and free from corrosion, with clean internal and external surfaces to ensure good bond between the concrete and tubes. Construct the tubes with threaded steel caps at top and bottom ends. Ensure that the tubes are vertical over their entire length. Provide additional reinforcing/carrier cage to the bottom of the drilled shafts to stabilize and position the access tubes.
e.I nspection . Before the placement of the drilled shaft concrete, inspect the CSL tubes to confirm that they are continuous and properly installed. If they require any remedial work, perform this work before the placement of concrete at no cost to the Department.
f.Tes ting. Ensure that all drilled shafts are CSL tested. Before CSL testing by the Engineer, ensure that the test probes can pass through every tube to the bottom. If a tube is obstructed, clear the tube by an acceptable means to allow passage of the probe the full length of the tube. If the tube cannot be cleared, core a hole within the shaft near the obstructed tube that is large enough to accommodate the probe for the full length of the drilled shafts. Perform all of this at no additional cost to the Department. Installation of Reinforcing Steel.
a.Delivery. If it is not practical to deliver the assembled reinforcing steel to the jobsite as a complete unit ready for installation, make splices on site before lowering the assembly into the hole.
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b.Cleaning. Before installation, inspect and clean reinforcing steel of materials that prevent effective bonding of concrete on steel.
c.P lacement . Place reinforcing steel in the excavation shaft immediately after cleaning the bottom.
d.R einforcing Steel. If the shaft cannot be completely concreted within eight hours of the completion of excavation, do not place the reinforcing steel in the excavation. Recirculate and reclean the slurry using airlift equipment and a desanding unit immediately before placement of the reinforcing steel and concrete.
e.C entralizers . Equip reinforcing steel with non- corrosive, non- metallic centralizers that have sufficient strength to resist any loads they will be subjected to during construction and to maintain the specified minimum concrete cover. Space centralizers at intervals necessary to maintain the specified cover but do not provide a vertical spacing greater than 20 ft. Do not drop or force reinforcing steel into the shaft. If the reinforcing steel does not smoothly enter the excavation, due to misalignment of the reinforcing cage, steel casing, open borehole, or obstructions, remove the cage and adjust and clean the excavation as specified until the reinforcing fits smoothly.
f.S ediment . After installation of reinforcing steel and immediately before concrete placement, the Engineer will measure the bottom of the excavation to determine if sediment has accumulated on the shaft bottom in excess of the requirements. If excess sediment is found to have accumulated on the shaft bottom, clean the bottom of the excavation with equipment that can remove the sediment. Placing Concrete.
a.Timing. Place concrete immediately after inspection and approval by the Engineer of the completed excavation and placement of reinforcement. If the shaft is not concreted within eight hours after completion of excavation, recirculate and reclean the slurry usi ng airlift equipment and a desanding unit to maintain slurry uniformity throughout the depth of the shaft before placing concrete.
b.Tr emie Pipe Sections. Ensure that the tremie pipe inside diameter is not less than 10 in. Replace any pipe sections showing signs of wear or defects. Secure tremie pipe joints with power equipment. Secure pipe sections with safety chains.
c.P lacement . Place concrete in one continuous operation through a tremie pipe directly from the concrete truck or from a concrete pump. Ensure that no concrete is allowed to free fall when placed. Use a disposable plug, reviewed and approved by the Engineer, to separate the slurry from the concrete at the top of the tremie pipe. Ensure that the plug provides continuous separation between the slurry and the concrete for the entire length of the tremie pipe. Ensure that the bottom of the tremie pipe or the concrete pump pipe is at the bottom of the open borehole before pumping concrete. If during the placement of concrete, any of the following occur: ● There is a sudden drop in concrete level is detected ● The tremie seal is compromised
Part 800 — Bridge Structures August 2025
800-236 SECTION 845 — DRILLED SHAFTS ● The tremie placement is suspended for more than two hours ● The theoretical volume of concrete deviates more than 10 percent from actual then, core the shaft at a minimum of four plan locations selected by the Engineer to detect potential voids, unacceptable concrete, or other defects. Perform the coring and the remedial actions needed to correct any voids, unacceptable concrete, or other defects. Additional Requirements for Slurry Displacement Method.
a.Transport. Use equipment that produces a stable suspension and provides mechanical agitation. Transport slurry by means of a temporary pipeline between tank locations and the drilled shafts.
b.R emoval . Use drilling clean-out buckets and slurry screening equipment that can remove soil and rock drilling spoil material from the slurry.
c.S lurry Level . Maintain the mineral slurry level to a minimum of 3 ft or polymer slurry level to a minimum 3 ft above the groundwater level or surface water level to prevent caving or sloughing of earth.
d.S lurry Consistency. Test the slurry to verify satisfactory characteristics before concrete placement is started. Place concrete within the time the excavation remains stable and clean. Pump the displaced slurry to holding tank(s) sufficient to store the entire displaced volume of the drilled shaft. Do not spill slurry on the site or in the surface water and do not use excavated holding pits. When no longer needed, properly dispose of slurry at an off-site location.
e.C oncrete Placement . Place concrete through a tremie pipe directly from the concrete truck or from a concrete pump. Ensure that the bottom of the tremie pipe or the concrete pump pipe is at the bottom of the open borehole before pumping concrete. Use a minimum 10-in. inside diameter tremie pipe. Do not use aluminum components. Clean and smooth the inside and outside surface of the tremie pipe to permit both the flow of concrete and the unimpeded withdrawal during concreting. In addition: ● Place a spherical separator or other device approved by the Engineer in the tremie pipe immediately before the introduction of concrete to positively separate the concrete from the slurry. The m ethods acceptable for review are vermiculite plugs, commercially available plastic, and rubber inflatable or non-inflatable plugs. Do not use paper or plastic bags to separate the slurry and the concrete. ● Keep the bottom of the tremie pipe within 10 in. of the excavation bottom until the separator floats to the surface of the shaft. Retrieve the separator plug from the excavation, or submit documentation, for the Engineer’s written approval, that the plug material will not cause a shaft defect if it remains. ● Keep the tremie pipe embedded at least 5 ft below the top of the concrete/slurry interface throughout the concrete placement. If the tremie pipe is raised above the fluid concrete level, the Engineer will reject the shaft.
Part 800 — Bridge Structures August 2025
SECTION 845 — DRILLED SHAFTS 800-237 ● Remove and dispose of the upper portion of concrete, contaminated with slurry, that reaches the top of the shaft. The Engineer will observe the depth to which contaminated concrete has been removed. The Engineer will determine if sufficient contaminated concrete has been removed or if additional contaminated concrete requires removal. Alternative methods of concrete placement that limit the mixing of slurry with concrete may be proposed for review and approval by the Engineer in writing. Acceptance and Rejection of Drilled Shafts.
a.Acceptance Tests. The drilled shafts will be accepted for payment only after the CSL tests and the results of concrete tests provide verification of the structural integrity of the drilled shafts, as approved by the Engineer in writing. If the CSL record is complex or inconclusive, drill coreholes in the drilled shaft for evaluation of the drilled shaft. When a defect is confirmed by coring, perform the coring and subsequent grouting of the defect and corehole at no additional cost to the Department. However, if no defects are found, the Department will pay for the coring costs, including pressure grouting of the coreholes.
b.R emedial Action. If the Engineer determines that the drilled shafts are unacceptable, submit a plan for remedial action to the Engineer for review and approval. Ensure that calculations and working drawings for the remedial action plan are stamped by a Registered Professional Civil Engineer in the State of Rhode Island.
c.Fi nal Acceptance. Following final acceptance of the drilled shafts by the Engineer, tremie grout the CSL access tubes with a minimum 5000 psi cement grout.
845.04 Method of Measurement.
Drilled Shaft – Furnish and Install in Soil will be measured by the linear foot for the total length in place from the bottom of the permanent casing to the drilled shaft cut off elevation as accepted by the Engineer. Transportation, processing, and proper off-site disposal of excavated materials will be measured for separately under the applicable provisions of PART 200. Drilled Shaft – Obstruction Removal will be measured by the linear foot for the length of obstruction removed as follows: • Measurement for obstruction drilling will begin at the larger of the following rates of advance: ○ When the rate of advance of the drilled shaft excavation using customary soil excavation tools and equipment has slowed to less than 10 percent of the average measured and computed rate of advance for the same soil strata encountered at the site, or ○ When the rate of advance has decreased to less than 0.5 ft per hour. The time spent drilling obstructions will not be included in the determination of the average rate of advance in the strata.
Part 800 — Bridge Structures August 2025
800-238 SECTION 845 — DRILLED SHAFTS • Measurement for obstruction drilling will end when the rate of advance exceeds 20 percent of the average rate of advance in the strata. • All material between obstructions, defined by the above, will not be measured for payment under this item but will be measured under Drilled Shaft – Furnish and Install in Soil. Drilled Shaft – Furnish a nd Install Rock Socket will be measured by the linear foot for the total length in place from the bottom of the accepted drilled shaft rock socket tip elevation to the bottom of the permanent casing as accepted by the Engineer.
845.05 Basis of Payment.
The Department will pay for the completed and accepted quantities as follows. Pay Item Pay Unit Drilled Shaft – Furnish and Install in Soil LF Drilled Shaft – Obstruction Removal LF Drilled Shaft – Furnish and Install Rock Socket LF Payment at the Contract unit price is full compensation for all resources necessary to complete the item of work , i ncluding costs for engineering, mobilization, and demobilization, set -up, equipment, labor, and materials, and for additional engineering services and remedial work required due to drilled shafts not installed according to the Contract. The following incidental items will not be reimbursed: • Any dewatering operations • C onstructing diameters larger than the diameter shown in the Contract Documents • Making an embedment below the specified bearing elevation as determined by the Engineer using all data available at the time of construction • Obstructions for any item whose penetration, demolition, removal, or excavation is included clearly and expressly in the work of any other pay item • All costs due to lost tool removal and replacement , including costs associated with hole degradation due to obstruction removal operations or the time the hole remains open • Remedial measures, including engineering analysis and redesign, to correct for out -of- tolerance drilled shaft construction • The design, labor, and materials necessary to perform the remediation
Referenced in this section
Drilled Shafts in other states
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Source: Standard Specifications for Road and Bridge Construction (Blue Book), 2022 (Aug 2025 compilation) Edition. Pages 591–607 of 951. View official source ↗