503.01 503-1 SECTION 503 DRILLED SHAFTS DESCRIPTION
503.01 This work consists of furnishing all materials, labor, tools, equipment, services and
incidentals necessary to construct the drilled shafts (also referred to as drilled caissons, drilled piers, cast -in-place -drilled -holes, or cast -in-situ piles) per the Contract Documents and this Specification. SUBMITTALS AND MEETINGS
503.02 Submittals. At least 30 days before the start of drilled shaft construction, the
Contractor shall submit to the Engineer an electronic file of a project reference list verifying the successful completion by the Contractor of at least three separate foundation projects within the last five y ears with drilled shafts of similar size (diameter and depth) and construction difficulty to those shown on the Plans in similar subsurface geotechnical conditions. A brief description of each project and the project ow ner's contact name and current phone number shall be included for each project listed. Work shall not begin until all required submittals have been received by the Engineer.
a.Experience and Personnel. The personnel assigned to the project shall have the following minimum experience:
1.On-site supervisors shall have a minimum of two years of experience in supervising construction of drilled shaft foundations of similar size (diameter and depth) and installation method to those shown on the Plans and similar geotechnical conditions to those described in the geotechnical report. The work experience shall be direct supervisory responsibility for the on -site drilled shaft construction operations. Project management level positions indirectly supervising on -site drilled shaft construction operations are not acceptable for this experience requirement.
2.Drill rig operators shall have a minimum of one year of experience in construction of drilled shaft foundations. The Engineer may request a list identifying on -site supervisors and drill rig operators assigned to the project for review. The list shall contain a detailed summary of each individual's experience in drilled shaft excavation operations. The Contractor sh all inform the Engineer in writing of changes to field personnel.
b.Drilled Shaft Installation Plan . At least 30 days before the start of drilled shaft construction the Contractor shall submit an electronic file of a Drilled Shaft Installation Plan narrative. In preparing the narrative, the Contractor shall reference the available subsurface geotechnical data provided in the Co ntract and any geotechnical reports prepared for this project. This narrative shall provide at a minimum the following information:
1.Description of overall construction operation sequence and the sequence of drilled shaft construction when in groups or lines.
2.A list, description, and capacities of proposed equipment including but not limited to cranes, drills, augers, bailing buckets, final cleaning equipment and drilling unit. As appropriate, the narrative shall describe why the equipment was selected and suit ability to the anticipated site and subsurface conditions. 503.02 503-2 3. Details of drilled shaft excavation methods, including proposed drilling methods, methods for cleanout of the bottom of the excavation hole and a disposal plan for excavated material including drilling slurry (if applicable). This shall include means and m ethods to address subsurface geotechnical conditions including boulder and obstruction removal techniques if such are indicated in the Contract subsurface geotechnical information or Contract Documents . Details of the methods to be used to ensure drilled shaft hole stability (i.e., prevention of caving, bottom heave, etc. using temporary casing, slurry, or other means) during excavation and concrete placement.
4.Detailed procedures for mixing, using, maintaining, storing, and disposing of the slurry shall be provided if applicable. A detailed mix design (including all additives and their specific purpose in the slurry mix) and a discussion of its suitability to th e anticipated subsurface geotechnical and site conditions shall also be provided for the proposed slurry.
5.The submittal shall include a detailed plan for process control of the selected slurry including property tests, test methods, and minimum and maximum property requirements that must be met to ensure that the slurry functions as intended for the anticipated subsurface conditions and shaft construction methods per the slurry manufacturer's recommendations and these specifications.
6.When casings are proposed or required, casing dimensions and detailed procedures for casing installation, removal, advancing the casing, and excavating the drilled shaft hole per subsection 503.1 2 (b) shall be provided. When removing casing, detail the method to extract the casing to maintain shaft reinforcement in proper alignment and keep concrete workable during casing extraction.
7.Details of concrete placement including proposed equipment and procedures for delivering concrete to the drilled shaft, placement of the concrete into the shaft, placement and raising of the tremie or pump line during placement, size of tremie and pump lin es, operational procedures for pumping, and a sample uniform yield form to be used by the Contractor for plotting the volume of concrete placed versus the depth of shaft for all shaft concrete placement. Describe the method to be used to form a horizontal construction joint during concrete placement. Include details of procedures to prevent loss of slurry or concrete into waterways, and other areas to be protected.
8.Describe the method and materials that will be used to fill or eliminate all voids below the top of shaft between the plan shaft diameter and excavated shaft diameter, or between the shaft casing and surrounding soil if permanent casing is specified.
9.Details of any required load tests or shaft integrity tests including equipment, instrumentation, procedures, calibration data for test equipment, calculations and drawings.
10.Details and procedures for protecting existing structures, utilities, roadways and other facilities during drilled shaft installation. The stability of the existing structures is the responsibility of the C ontractor. Any new drilled shaft that is placed next to existing structures/drilled shafts with the potential to affect stability shall be considered 503.03 503-3 safety critical work and shall follow the submittal requirements as specified in subsection 107.06.
c.Slurry Technical Assistance. If slurry is to be used to construct the drilled shafts, the Contractor shall provide or arrange for technical assistance from the slurry manufacturer as specified in subsection 503.1 2 (b)5(A). The Contractor shall submit three copies of the following to the Engineer at least 14 days before the start of drilled shaft construction:
1.The name and current phone number of the slurry manufacturer's technical representative assigned to the project.
2.The names of the Contractor’s personnel assigned to the project and trained by the slurry manufacturer’s technical representative in the proper use of the slurry. The submittal shall include a signed training certification letter from the slurry manufacturer for each individual including the date of the training.
d.Logs of Shaft Construction. The Contractor’s Quality Control staff shall prepare inspection logs using CDOT Form 1333 – Inspector’s Report of Caisson Installation documenting each shaft construction activity. In addition, the Contractor shall prepare and submit the logs documenting a ny subsurface investigation borings or rock core holes performed by the Contractor at drilled shaft foundation locations. In addition to the information required on the Form 1333, the Contractor shall provide the following information: type and dimensions of tools and equipment used, any changes to the tools and equipment; type of drilling fluid if used, the results of slurry tests, any problems encountered, and metho d used for bottom cleaning. In addition to the information required on the Form 1333, concrete placement records shall include at least the following information: tremie tip elevation during concrete placement, and concrete yield curve (volume versus concrete elevation, actual and th eoretical). A complete set of shaft inspection logs for an individual drilled shaft shall be submitted to the Engineer within 48 hours of the completion of concrete placement at the shaft.
503.03 Meetings The Engineer will evaluate the Drilled Shaft Installation Plan for
conformance with the Contract within10 working days after receipt of the submission. At the option of the Department, a Shaft Installation Plan Submittal Meeting may be scheduled following review of the Contractor’s initial submittal of the Plan. Those attending the Shaft Installation Plan Subm ittal Meeting, if held, shall include the following: The superintendent, on - site supervisors, and other Contractor personnel involved in the preparation and execution of the Drilled Shaft Installation Plan.
1.The Project Engineer and Owner’s personnel involved with the structural, geotechnical, and construction review of the Drilled Shaft Installation Plan together with Owner’s personnel who will provide inspection and oversight during the drilled shaft constru ction phase of project. The Contractor shall submit to the Engineer updates or modifications to the Drilled Shaft Installation Plan whenever such updates or modifications are proposed. The Engineer will evaluate the new information for conformance with the Contract Plans and Specifications and respond within 10 working days after receipt of the submission. A shaft P re-construction meeting shall be held at least five working days before the Contractor beginning any shaft construction work at the site to discuss investigative boring information, construction procedures, personnel, and equipment to be used, and other 503.04 503-4 elements of the accepted Shaft Installation Plan as specified in subsection 503.02(b). If slurry is used to construct the shafts, the frequency of scheduled site visits to the project site by the slurry manufacturer’s representative shall be discussed. Those attending shall include:
2.The superintendent, on -site supervisors, and other key personnel identified by the Contractor as being in charge of excavating the shaft, placing the casing and slurry as applicable, placing the steel reinforcing bars, and placing the concrete. If slurry is used to construct the shafts, the slurry manufacturer's representative and a Contractor’s employee trained in the use of the slurry, as identified to the Engineer per subsection 503.04(c)4(1), shall also attend. The Engineer , key inspection personnel, and appropriate representatives of the Department. If the Contractor’s key personnel change, or if the Contractor proposes a significant revision of the approved Drilled Shaft Installation Plan, an additional confere nce may be held at the request of the Engineer before any additional shaft construction operations are performed.
503.04 Control and Disposal of Materials. The Contractor shall collect and properly dispose
offsite all slurry and water displaced during final cleaning and concrete placement. Open pits for collection of materials may be allowed during construction activities for later disposal. Control all excavated material, slurry, water, and other matter so that at no time it enters or encroaches upon the adjacent travel lanes, railroad, water ways, and environmentally sensitive or restricted areas as shown on the plans. All environmental regulations for handling, discharge, and disposal of all construction materials shall be followed. MATERIALS
503.05 Concrete. Concrete used in the construction of drilled shafts shall be Class BZ per
Section 601. If the concrete does not meet the requirements of Section 601, price reductions shall be applied to the drilled caisson pay item. The Contractor may elect to use Self Consolidating Concrete (SCC) Class BZ.
503.06 Reinforcing Steel. Reinforcing steel shall be per Section 602. When necessary,
vertical bars shall be bundled in order to maximize clear space between vertical reinforcement. Rolled hoops or bundled spirals shall be used in order to maximize the clear space between horizontal reinforcement. Reinforcing steel cages for drilled shafts with varying shaft and socket diameters shall be designed with a single, uniform diameter. At all times, the reinforcing bars and fabricated steel reinforcing cage shall be supported off the ground surface and shall be protected from contamination of mud, oils and solvents, and other deleterious materials. The steel shall be free of excessive rust (flaking, peeling, and thick coating) at the time of cage placement into the hole. Any contaminati on or excessive rust shall be cleaned and removed by the Contractor to the Engineer’s acceptance before placement.
503.07 Casings . All permanent structural casing shall be of steel conforming to ASTM
A36/A36M or ASTM A252 Gr 2 unless specified otherwise on the Plans. All splicing of permanent structural casing shall be per AWS D 1. 1 Bridge Welding Code. All casing shall be watertight and clean before placement in the excavation. Where the minimum thickness of the casing is specified on the Plans, it is specified to satisfy structural design requirements only. The Contractor shall increase the casing thickness from the minimum specifi ed thickness, as necessary and accepted by the Engineer, to satisfy the construction installation requirements. 503.08 503-5 All permanent casing shall be of ample strength to resist damage and deformation from transportation and handling, installation stresses, and all pressures and forces acting on the casing. For permanent nonstructural casing, corrugated casing may be used. The diameter of permanent casing shall be as shown on the Plans unless a larger diameter casing is approved by the Engineer. When a larger size permanent casing is approved by the Engineer, no additional payment will be made for the increased weight of casing steel or the increased quantity of drilled shaft excavation and concrete. All temporary casing shall be a smooth wall structure steel except where corrugated metal pipe is shown on the Plans as an acceptable alternative material. All temporary casing shall be of ample strength to resist damage and deformation from transportation and handling, installation and extraction stresses, and all pressures and forces acting on the casing. The casing shall be capable of being installed and removed without deforming and causing damage to the completed shaft and without disturbing the surrounding soil. Temporary casing shall be completely removed, unless otherwise shown on the Plans or approved by the Engineer. The outside diameter of temporary casing shall not be less than the specified diameter of the shaft.
503.08 Mineral Slurry . Mineral Slurry shall be used per the quality control plan specified in
subsection 503.02(b)(5). Mineral slurry shall conform to the following requirements: Table 503 -1 DRILLED CAISSON MINERAL SLURRY REQUIREMENTS Property Test Requirement Density (pcf) Mud Weight (Density) API 13B -1, Section 1 64.3 to 72 Viscosity (seconds/quart) Marsh Funnel and Cup API 13b -1, Section 2.2 28 to 50 pH Glass Electrode, pH Meter, or pH Paper 8 to 11 Sand Content (%) API 13B-1, Section 5 4.0 max . immediately before placing concrete
503.09 Polymer Slurry . Polymer slurries, either natural or synthetic, shall be used per the
manufacturer's recommendations, and shall conform to the quality control plan specified in subsection 503.02(b)(5). The polymer slurry shall conform to the following requirements: 503.10 503-6 Table 503 -2 DRILLED CAISSON POLYMER SLURRY REQUIREMENTS Property Test Requirement Density (pcf) Mud Weight (Density) API 13B -1, Section 1 64.3 max Viscosity (seconds/quart) Marsh Funnel and Cup API 13b -1, Section 2.2 32 to 135 pH Glass Electrode, pH Meter, or pH Paper 8 to 11.5 Sand Content (%) API 13B -1, Section 5 1.0 max . immediately before placing concrete The sand content of polymer slurry before final cleaning and immediately before placing concrete shall be less than or equal to 1.0 percent, per American Petroleum Institute API 13B-1, Section 5. Slurry temperature shall be at least 40 °F when tested.
503.10 Water Slurry . Water may be used as slurry when casing is used for the entire length
of the drilled hole, or to stabilize the bedrock below the temporary casing provided that the method of drilled shaft installation maintains stability at the bottom of the shaft excavation. Water slurry shall conform to the following requirements: Table 503 -3 DRILLED CAISSON WATER SLURRY REQUIREMENTS Property Test Requirement Density (pcf) Mud Weight (Density) API 13B -1, Section 1 64 max Sand Content (%) API 13B -1, Section 5 1.0 max
503.11 Access Tubes for CSL Testing. Access tubes for CSL testing shall be steel pipe of
0.145- inch minimum wall thickness and at least 1.5 inches inside diameter. The access tubes shall have a round, regular inside diameter free of defects and obstructions, including all pipe joints, in order to permit the free, unobstructed passage of 1.3 inches’ maximum diameter source and receiver probes used for the CSL tests. The access tubes shall be non - galvanized, watertight, free from corrosion, and with clean internal and external faces to ensure good bond between the concrete and the access tubes. The access tubes shall be fitted with watertight threaded caps on the bottom and the top. Grout for filling the access tubes at the completion of the CSL tests shall be a neat cement grout with a maximum water/cement ratio of 0.45. Drilled shafts for structures as shown on the CDOT S -Standard drawings shall be excluded from this testing, except as noted on the plans. CONSTRUCTION REQUIREMENTS
503.12 Drilled Shaft Excavation. The excavation and drilling equipment shall have
adequate capacity, including power, torque and down pressure to excavate a hole of both the maximum diameter and to a depth of 20 feet or 20 percent beyond the maximum shaft length shown on the Plans, whichever is greater. Blasting will only be permitted if specifically stated on the Plans or authorized in writing by the Engineer. Once the excavation 503.12 503-7 operation has been started, the excavation shall be conducted in a continuous operation until the excavation of the shaft is completed except for pauses and stops. Pauses or interruptions during this excavation operation will not be allowed except for casing installation, casing splicing and removal of materials or obstructions. Drilled shaft excavation operation interruptions not conforming to this definition shall be considered stops. The Contractor shall provide temporary casing at the site in sufficient quantities to meet the needs of the construction method. If the drilled shaft excavation is not complete at the end of the shift or series of continuous shifts, the drilled shaft excavation operation may be stopped provided the Contractor protects the shaft as indicated in subsection 503. 12(b) before the end of the workday . If slurry is present in the shaft excavation, the Contractor shall conform to the requirements of subsection 503. 12 (b)5(2) regarding the maintenance of the minimum level of drilling slurry throughout the stoppage of the shaft excavation operation and shall recondition the slurry to the required slurry properties per subsections 503.09, 503.10, and 503.11 before recommencing shaft excavation operations. Sidewall over -reaming shall be performed when the time for shaft excavation exceeds 24 hours (measured from the beginning of excavation below the casing when casing is used). Sidewall over-reaming shall also be performed when the sidewall of the hole is determined by the Engineer to have softened due to the excavation methods, swelled due to delays in the start of concrete placement, or degraded because of slurry cake buildup. Over -reaming thickness shall be a minimum of 1/2 -inch or as directed by the Engin eer. Over -reaming may be accomplished with a grooving tool, over -reaming bucket, or other equipment approved by the Engineer. If over-reaming is required as a result of the excavation time exceeding the time limit specified, the Contractor shall bear the c osts associated with both sidewall over -reaming and additional drilled shaft concrete related to over -reaming. Excavation to the foundation cap elevation shall be completed before drilled shaft construction begins unless otherwise noted in the Contract Documents or approved by the Engineer. Any disturbance to the foundation cap area caused by shaft installation shall be repaired by the Contractor before placing the cap concrete. When drilled shafts are to be installed in conjunction with embankment construction, the Contractor shall construct drilled shafts after placement of the embankment fill unless otherwise sho wn on the Contract Documents or approved by the Engineer. Drilled shafts installed before the completion of the embankment fill shall not be capped until the fill has been placed to the bottom of cap level.
a.Dry Construction Method. The dry construction method consists of drilling the shaft excavation, removing accumulated water and loose material from the excavation, placing the reinforcing cage, and concreting the shaft in relatively dry excavation. The dry construction method ma y only be used if the shaft excavation demonstrates that the following conditions are met: less than 12 inches of water accumulates above the base of excavation over a period of one hour when no pumping is performed, the sides and bo ttom of the hole remain stable without detrimental caving, sloughing, or swelling between the completion of excavation and concrete placement, all loose material and water can be satisfactorily removed before inspection and concrete placement (no more than 2 inches of water will be permitted in the bottom of the shaft excavation at the time of concrete placement), and the Engineer can visually inspect the sides and bottom of the shaft before placing the concrete. The drilled shaft excavations shall not be left open overnight unless cased full depth or otherwise protected against sidewall instability. An open excavation is 503.12 503-8 defined as a drilled shaft that has not been filled with concrete, or temporarily backfilled with a material approved by the Engineer per subsection 503. 12(b) or protected per subsection 503.1 2 (b). The use of slurry to protect a drilled shaft during a drilling stoppage or overnight shutdown shall be approved by the Engineer. The excavation shall be protected with a suitable cover that will prevent persons or materials from falling into the hole. Casing of drilled shafts in stable rock formations during stoppages is not required if accepted by the Engineer unless shown on the Plans or specified .
b.Protection Methods . The Contractor bears full responsibility for selection and execution of the methods of stabilizing and maintaining the drilled shaft excavation. The walls and bottom of the drilled shaft excavation shall be protected so that sidewall caving and bottom h eaves are prevented from occurring. For shafts where the soils above the bedrock do not contribute to the bearing calculations as shown on the Plans, the soils surrounding the temporary casing may be disturbed during the installation of t emporary casing using uncontrolled in -situ slurries. Acceptable protection methods include the use of casing, drilling slurry, or both:
1.Temporary Casing Construction Method. The Contractor shall conduct casing installation and removal operations and drilled shaft excavation operations such that the adjacent soil outside the casing and drilled shaft excavation for the full height of the dr illed shaft is minimally disturbed. For shafts where the soils above the bedrock do not contribute to the bearing calculations as shown on the Plans, the soils surrounding the temporary casing may be disturbed during the installation of temporary casing us ing uncontrolled in- situ slurries. If the Contractor is utilizing casing that is sealed into the underlying bedrock, water may infiltrate the shaft below the casing. Excavation of the bedrock may continue without the use of casing or slurry if the shaft remains stable. The Contractor shall remove all temporary casings from the excavation as concrete placement is completed, unless approval has been received from the Engineer to leave specified temporary casings in place. As the temporary casing is withdrawn, sufficient he ad of fluid concrete must be maintained to ensure that water or slurry outside the temporary casing will not breach the column of freshly placed concrete. Casing extraction shall be at a slow, uniform rate with the pull in line with the shaft axis. Excessi ve rotation of the casing shall be avoided to limit deformation of the reinforcing steel cage.
2.Permanent Casing Construction Method. After the casing has been filled with concrete, all void space occurring between the casing and drilled shaft excavation shall be filled with a material that approximates the geotechnical properties of the in-situ soils, per the Drilled Shaft Installation Plan specified in subsection 503.02(b). Tops of permanent casings for the drilled shafts shall be removed to the top of the drilled shaft or finished ground line, whichever is lower, unless the top of permanent casing is shown in the Plans at a different elevation. For those drilled shafts const ructed within a permanent body of water, tops of permanent casings for drilled shafts shall be removed to the low water elevation unless otherwise shown on the Plans or directed by the Engineer. Casing used for forming shafts installed through a body of wa ter shall not be removed. 503.12 503-9 3. Alternative Casing Methods. When approved by the Engineer , installation of casing using rotating or oscillating methods will be permitted. Use of this alternative casing method shall be per the equipment and procedures shown in the approved Drilled Shaft Installation Plan and shall comply with all other requirements specified. Drilled shaft casing shall be equipped with cutting teeth or a cutting shoe and installed by either rotating or oscillating the casing.
4.Uncontrolled In- Situ Slurry. The uncontrolled in- situ slurry consists of in -situ soils from the drilled shaft mixed with water. For shafts where the soils above the bedrock do not contribute to the bearing calculations as shown on the Plans, the Contracto r may use uncontrolled in- situ slurry to install temporary casing. For shafts where the soils above the bedrock do contribute to the bearing calculations, the use of uncontrolled in- situ slurry to install temporary casing shall not be allowed. Slurry per subsections 503.08, 503.09, and 503.1 0 or temporary casing per subsection s 503.07 and 503.12 is required if the drilled shaft does not remain stable using uncontrolled in- situ slurry.
5.Slurry. The Contractor may use slurry per subsections 503.0 8, 503. 09, and 503.1 0 to maintain a stable excavation during drilled shaft excavation and concrete placement operations once water begins to enter the drilled shaft excavation and remain present. The Contractor may use slurry to maintain stability during drilled shaft excavation and concrete placement operations in the event that water begins to enter the drilled shaft excavation at a rate of greater than 12 inches per hour, or if the Contractor is not able to restrict the amount of water in the drilled shaft to less than 3 inches before concrete placement, or to equilibrate water pressure on the sides and base of the drilled shaft excavation when groundwater is encountered or anticipated based on t he available subsurface data.
A.Slurry Technical Assistance If slurry is used, the manufacturer's representative, as identified to the Engineer per subsection 503.02(c), shall provide technical assistance for the use of the slurry. The manufacturer’s representative or the Contractor’s employee trained in the use of the slurry, as identified to the Engineer per subsection 503.02(c), shall be present at the site throughout the shaft slurry operations for this project to perform the duties specified above.
B.Minimum Level of Slurry in the Excavation When slurry is used to maintain a stable excavation, the slurry level in the excavation shall be maintained to obtain hydrostatic equilibrium throughout the construction operation at a height required to provide and maintain a stable hole, but not less than 5 feet above the water table. Slurry levels shall be as follows:
1.Not less than five feet above the water table for mineral slurries
2.Not less than 10 feet above the water table for water slurry and uncontrolled in - situ slurries
3.Not less than 10 feet above the water table for polymer slurries, except when a lesser dimension is specifically recommended by the slurry manufacturer for the site conditions and construction methods. 503.13 503-10 The Contractor shall provide casing, or other means, as necessary to meet these requirements. The slurry level shall be maintained above all unstable zones a sufficient distance to prevent bottom heave, caving, or sloughing of those zones. Throughout all stops in drilled shaft excavation operations, the Contractor shall monitor and maintain the slurry level in the excavation the greater of the following elevations:
1.No lower than the groundwater level elevation outside the drilled shaft
2.Elevation as required to provide and maintain a stable hole.
C.Cleaning Slurry The Contractor shall clean, re- circulate, de- sand, or replace the slurry , as needed, in order to maintain the required slurry properties. Sand content will only be required to be within specified limits immediately before concrete placement.
503.13 Obstructions. When obstructions are encountered, the Contractor shall notify the
Engineer promptly. An obstruction is defined as a specific object not identified on the Plans or Geotechnical Report per subsection 102.05 (including, but not limited to, boulders, logs, and manmade objects) encountered during the drilled shaft excavation operation that prevents or hinders the advance of the drilled shaft excavation. When efforts to advance past the obstruction to the design drilled shaft tip elevation result in the rate of advance of the drilled shaft drilling equipment being significantly reduced relative to the rate of advance for the portion of the drilled shaft excavation in the geological unit that contains the obstruction, then the Contractor shall remov e, bypass or break up the obstruction under the provisions of subsection 503. 23(a) . Blasting will not be permitted unless approved in writing by the Engineer. Drilling tools that are lost in the excavation will not be considered obstructions and shall be promptly removed by the Contractor. All costs due to lost tool removal will be borne by the Contractor including, but not limited to, costs associated with the repair of hole degradation due to removal operations or an excessive time that the hole remains open.
503.14 Protection of Existing Structures and Drilled Holes . The Contractor shall control
operations to prevent damage to existing structures and recently drilled holes, utilities, roadways and other facilities. Preventative measures shall include, but are not limited to, selecting construction methods and procedures that will prevent excessive caving of the drilled shaft excavation and monitoring and controlling the vibrations from the driving o f casing or sheeting, drilling of the shaft, or from blasting, if permitted.
503.15 Slurry Sampling and Testing. Mineral slurry and polymer slurry shall be mixed and
thoroughly hydrated in slurry tanks, lined ponds, or storage areas. The Contractor shall draw sample sets from the slurry storage facility and test the samples for conformance with the appropriate spec ified material properties before beginning slurry placement in the drilled hole. Slurry shall conform to the quality control plan included in the Drilled Shaft Installation Plan per subsection 503.02(b)(5) and approved by the Engineer . A sample set shall be composed of samples taken at mid -height and within 2 feet of the bottom of the storage area. 503.16 503-11 The Contractor shall sample and test all slurry in the presence of the Engineer, unless otherwise approved by the Engineer . The date, time, names of the persons sampling and testing the slurry, and the results of the tests shall be recorded. A copy of the recorded slurry test results shall be submitted to the Engineer at the completion of each drilled shaft, and during construction of each drilled shaft when requested by the Engineer. Slurry samples shall be taken at mid -height and within 2 feet of the bottom of the drilled shaft and tested during drilling as necessary to verify the control of the properties of the slurry. As a minimum, sample sets of polymer slurry shall be taken and tested at least once every four hours after beginning its use during each shift. Sample sets of all slurry shall be taken and tested immediately before placing concrete.
503.16 Drilled Shaft Excavation Inspection . The Contractor shall use best methods such as a
cleanout bucket, air lift, or hydraulic pump to clean the bottom of the excavation of all drilled shafts. For wet drilled shaft excavation in soils, the base of the excavation shall be covered with not more than 3 inches of sediment or loose or disturbed material just before placing concrete. For dry drilled shaft excavations in soils, the base of excavation shall be covered with not more than 1.5 inches of sediment or loose or disturbed material just befor e placing concrete. For wet and dry drilled shaft excavations in rock, the base of the excavation shall be covered with not more than 0.5 inch for 50 percent of the base area of sediment or loose or disturbed material just before placing concrete. The excavated drilled shaft will be inspected and approved by the Engineer before proceeding with construction. The bottom of the excavated drilled shaft shall be sounded with an airlift pipe, a tape with a heavy weight attached to the end of the tape, a borehole camera with visual sediment depth measurement gauge , or other means acceptable to the Engineer to determine that the drilled shaft bottom meets the requirements in the Contract. The Contractor shall supply all needed equipment required to inspect the drilled shaft excavation.
503.17 Assembly and Placement of Reinforcing Steel . The Contractor shall show bracing and
any extra reinforcing steel required for assembling, transportation, or placement of the cage on the shop drawings. The Contractor shall be responsible for engineering the temporary support and bracing of the reinforcing cages to ensure that they maintain their planned configuration during assembly, transportation, and installation. The reinforcing cage shall be rigidly braced to retain its configuration during handling and construction. Individual or loose bars will not be permitted. All intersections of vertical and horizontal bars shall be tied. At least four vertical bars of each cage, equally spaced around the circumference, shall be tied at all reinforcement intersections with double wire ties. The remaining reinforcement intersections in each cage shall be tied with single wire ties. The reinforcement shall be carefully positioned and securely fastened to provide the minimum clearances specified or shown on the Plans, and to ensure that no displacement of the reinforcing steel cage occurs during placement of the concrete. Splicing of the reinforcement cage during placement of the cage in the shaft excavation will not be permitted unless otherwise shown on the Plans or approved by the Engineer. If the reinforcing cage is spliced during placement of the cage into the drilled shaft excavation, the splice details and location of the splices shall be per the Plans and the accepted Drilled Shaft Installation Plan. In additio n, the work shall be performed within the time limits specified in subsection 503.1 2. 503.17 503-12 The steel reinforcing cage shall be securely held in position throughout the concrete placement operation. The reinforcing steel cage shall be supported from the top during the placement of the concrete to achieve the clearances shown on the Plans. Setting the cage on the bottom of the hole will not be permitted. The support system shall be concentric to prevent racking and displacement of the cage. The reinforcing steel in the drilled shaft shall be tied and supported so that the location of the reinforcin g steel will remain within allowable tolerance. Concrete spacers or other approved non -corrosive spacing devices shall be used at sufficient intervals (near the bottom, the top, and at intervals not exceeding 10 feet vertically) to ensure concentric spacing for the entire cage length. The number of spacers required at each level will be one spacer for each foot of excavation diameter, with a minimum of four spacers at each level. The spacers shall be of adequate dimension to ensure an annular space between the outside of the reinforcing cage and the side of the excavation along the entire length of the drilled shaft as shown on the Plans. Acceptable feet made of plastic or concrete (bottom supports) shall be provided to ensure that the bottom of the cage is maintained at the proper distance above the base of the excavation unless the cage is suspended from a fix ed base during the concrete pour. Concrete cover for the reinforcing steel shall be 3 inches at the bottom of the drilled shaft. Minimum concrete cover on the sides of the reinforcing steel shall be as follows: Table 503 -4 DRILLED CAISSON MINIMUM CONCRETE SIDE COVER OVER REINFORCING STEEL Drilled Shaft Diameter Minimum Concrete Side Cover Less than or equal to 3 feet 3 inches Greater than 3 feet and less than 5 feet 4 inches Greater than or equal to 5 feet 6 inches Drilled shafts for structures as shown on the CDOT S -Standard drawings shall be excluded from the minimum cover concrete requirements, except as noted on the plans. If concrete placement does not immediately follow the cage placement, the Engineer may order the steel to be removed from the excavation so that the integrity of the excavation, including the presence of loose material in the bottom of the hole, and the surface condition of the reinforcing steel may be determined by inspection. Bracing steel that constricts the interior of the reinforcing cage shall be removed after lifting the cage if freefall concrete or wet tremie methods of concrete placement are to be used. The elevation of the top of the steel cage shall be checked before and after the concrete is placed. If the upward displacement of the rebar cage exceeds 2 inches, or if the downward displacement exceeds 6 inches, the drilled shaft shall be considered defe ctive. No additional drilled shafts shall be constructed until the Contractor has modified the rebar cage support in a manner satisfactory to the Engineer. 503.18 503-13 503.18 Concrete Placement, Curing, and Protection . Concrete placement shall be per Section 601 and shall commence as soon as possible after completion of drilled shaft excavation by the Contractor and inspection by the Engineer. Immediately before commencing concrete placement, the drilled shaft excavation and the properties of the slurry (if used) shall be per subsections 503.0 8, 503.09 , and 503.1 0. The CSL access tubes shall be filled with potable water before concrete placement and the top watertight threaded caps shall be reinstalled. Concrete placement shall be one continuous placem ent to the top of the drilled shaft, or as shown on the Plans. If water is not present the concrete shall be deposited through the center of the reinforcement cage by tremie, pump or free -fall preventing segregation of aggregates. The concrete shall be placed such that the free- fall is vertical down the center of the drilled shaft without hitting the sides or steel reinforcing cage. If water exists in amounts greater than 2 inches in depth or enters at a rate of more than 12 inches per hour, then the drilled shaft concrete shall be placed per subsection 601.12(f). Before placing any fresh concrete against concrete deposited in water or slurry (construction joint), the Contractor shall remove all scum, laitance, loose gravel, and sediment on the surface of the concrete deposited in water or slurry, and chip off any h igh spots on the surface of the existing concrete that would prevent any steel reinforcing bar cage from being placed in the position as shown on the Plans. The Contractor shall not perform foundation piling driving or casing installation using oscillation method within a radius of 20 feet or drilled shaft excavation operations within a clear distance of 3 diameters of a newly poured drilled shaft until a minimum of 24 hours has passed after the placement of concrete and the concrete has reached a minimum compressive strength of 1 ,800 psi. For any portion of the caisson socketed in fine grained bedrock susceptible to slaking and degradation such as, but not limited to, claystone, siltstone, or shale and provided the proper slurry properties have been achieved. If the concrete is not placed within four hours of drilling, the Contractor shall drill into the bedrock an additional 1/3 of the plan specified rock socket before placing the concrete. The reinforcing cage shall extend to the new tip elevation. For the use of polymer slurry this requirement will be waived.
503.19 Drilled Shaft Construction Tolerances . Drilled shafts shall be constructed so that the
center of the poured shaft at the top of the drilled shaft or mudline, whichever is lower, is within the following horizontal tolerances: Table 503 -5 DRILLED CAISSON MAXIMUM HORIZONTAL DISTANCE TOLERANCE S Drilled Shaft Diameter Maximum Horizontal Tolerance Less than or equal to 2 feet 3 inches Greater than 2 feet and less than 5 feet 4 inches Greater than or equal to 5 feet 6 inches 503.20 503-14 Drilled shafts in soil and rock shall be within 1.5 percent of plumb. Plumbness shall be measured from the top of poured drilled shaft elevation or mudline, whichever is lower. During drilling or excavation of the drilled shaft, the Contractor shall make frequent checks on the plumbness, alignment, and dimensions of the drilled shaft. Any deviation exceeding the allowable tolerances shall be corrected with a procedure approved by the Engineer. Drilled shaft steel reinforcing bars shall be no higher than 6 inches above or 3 inches below the plan elevation. The reinforcing cage shall be concentric with the drilled shaft excavation within a horizontal tolerance of 1 -1/2 inches. The top elevation of the completed drilled shaft shall have a tolerance of plus 1 inch or minus 3 inches. The diameter of the drilled shaft shall not be less than the diameter shown on the Plans. Tolerances for casings shall be per American Pipe Institute tolerances applicable to regular steel pipe. Drilled shaft excavations and completed drilled shafts not constructed within the required tolerances will be considered defective. The Contractor shall be responsible for correcting all defective drilled shafts to the satisfaction of the Engineer. Materia ls and work necessary, including engineering analysis and redesign, to complete corrections for out -of-tolerance drilled shafts shall be furnished without cost to the Owner or an extension of the completion date of the project. The Contractor shall submit redesign drawings electronically sealed by the Contractor’s Engineer. TESTING AND VERIFICATION
503.20 Integrity Testing. Crosshole Sonic Log (CSL) testing shall be performed per ASTM
D6760. The minimum number of shafts tested shall be indicated on the plans. CSL testing shall be performed on shafts constructed using tremie concrete placement methods and drilled shafts selected by the Engineer. Drilled shafts for structures as sho wn on the CDOT S - Standard drawings shall be excluded from this testing, except as shown on the plans. The Engineer may increase the number of shafts tested as deemed necessary. The Contractor shall accommodate the CSL testing by furnishing and installing access tubes per subsection 503.12. The Contractor shall install access tubes for CSL testing in drilled shafts as shown on the plans selected by the Engineer to permit access for the CSL test probes. If the condition of the drilled shaft excavation permits drilled shaft construction in the dry, the Engineer may specify that the testing be omitted. The Contractor shall securely attach the access tubes to the interior of the reinforcement cage of the drilled shaft. One access tube shall be furnished and installed for each foot of drilled shaft diameter, rounded up to the nearest whole number, unless otherwise shown on the Plans. A minimum of three tubes will be required. The access tubes shall be placed around the drilled shaft, inside the spiral or hoop reinforcement and 3 inches clear of the vertical reinforcement, at a uniform spacing measured along the circle passing through the centers of the access tubes. If these minimums cannot be met due to close spacing of the vertical reinforcement, then the access tubes shall be bundled with the vertical reinforcement. 503.20 503-15 If trimming the cage is required and access tubes for CSL testing are attached to the cage, the Contractor shall either shift the access tubes up the cage or cut the access tubes, provided that the cut tube ends are adapted to receive the watertight cap as specified. The access tubes shall be installed in straight alignment and as near to parallel to the vertical axis of the reinforcement cage as possible. The access tubes shall extend from 1 to 2 inches below the bottom of the reinforcing steel to at least 2 feet above the top of the drilled shaft. Couple tubes as required with threaded couplers, such that inside of tube remains flush. The Contractor shall clear the access tubes of all debris and extraneous materials before installing the access tubes. Care shall be taken to prevent damaging the access tubes during reinforcement cage installation and concrete placement operations in the drilled shaft excavation. The access tubes shall be filled with potable water before concrete placement, and the top watertight threaded caps shall be reinstalled. Before performing CSL testing operations, the Contractor shall remove the concrete at the top of the drilled shaft down to sound concrete. The Contractor shall engage a qualified Specialty Engineer to perform the CSL testing. The qualified CSL Specialty Engineer shall have a minimum three years of experience of CSL testing and have a Colorado Licensed Professional Engineer supervising the collection and interpretation of data. The Contractor shall provide all necessary assistance to the CSL Specialty Engineer to satisfactorily perform the testing. The testing shall be performed after the drilled shaft concrete has cured at least 96 hours. Additional curing time before testing may be required if the drilled shaft concrete contains admixtures, such as set retarding admixture or water reducing admixture. The additional curing time before testing required under these circumstances shall not be grounds for additional compensation or extension of time to the Contractor. No subsequent construction shall be performed on the completed drilled shaft until the CSL tests are approved and the drilled shaft accepted by the Engineer . After placing the drilled shaft concrete and before beginning the CSL testing of a drilled shaft, the Contractor shall inspect the access tubes. Each access tube that the test probe cannot pass through shall be replaced, at the Contractor’s expense, with a 2 -inch diameter hole cored through the concrete for the entire length of the drilled shaft. Unless directed otherwise by the Engineer, cored holes shall be located approximately 6 inches inside the reinforcement and shall not damage the drilled shaft rein forcement. Descriptions of inclusions and voids in cored holes shall be logged and a copy of the log shall be submitted to the Engineer. Findings from cored holes shall be preserved, identified as to location, and made available for inspection by the Engin eer. The Engineer will approve the continuation of drilled shaft construction before approval and acceptance of the first shaft if the Engineer’s observations of the construction of the first shaft are satisfactory, including, but not limited to, conformance to the Drilled Shaft Installation Plan as approved by the Engineer, and the Engin eer’s review of Contractor’s daily reports and inspector’s daily logs concerning excavation, steel reinforcing bar placement, and concrete placement. Drilled shafts with velocity reduction exceeding 30 percent are not acceptable without additional offset CSL testing and three -dimensional (3 D) Tomography analysis. 503.21 503-16 If subsequent testing at a drilled shaft indicates the presence of a defect in the drilled shaft, the testing costs and the delay costs resulting from the additional testing shall be borne by the Contractor. If this additional testing indicates that the drilled shaft has no defect, the testing costs and the delay costs resulting from the additional testing will be paid by the Owner. If the drilled shaft construction is on the critical path of the Contractor’s schedule, a time extension equal to the delay created by the additional testing will be granted. If the Engineer determines a drilled shaft is unacceptable based on the CSL tests and tomographic analyses, or observes problems during drilled shaft construction, coring of the shaft to allow further evaluation and repair shall be required, or the shaft shall be replaced. If coring to allow further evaluation of the shaft and repair is chosen, one or more core samples shall be taken from each unacceptable shaft for full depth of the shaft or to the depth directed by the Engineer. The Engineer will determine the number, location, and diameter of the cores based on the results of 3D tomographic analysis of offset and horizontal CSL data. The Contractor shall provide an accurate log of cores, label and place the cores in a crate showing the shaft depth at each interval of core recovery, transport the cores along with five copies of t he coring log to the Engineer, and perform strength testing by an AASHTO certified lab on portions of the cores that exhibit questionable concrete as determined by the Engineer. If the coring or testing indicates the shaft is defective, the Contractor shall propose remedial measures for approval by the Engineer, repair all detected defects, and conduct post repair integrity testing using horizontal and offset CSL testing, and 3D tomographic imaging as described. The coring costs and remedial measure costs shall be borne by the Contractor. If the additional coring indicates that the drilled shaft has no defect, the coring costs resulting from the additional coring will be p aid by th e Owner. If the drilled shaft construction is on the critical path of the Contractor’s schedule, a time extension equal to the delay created by the additional testing will be granted. All access tubes and cored holes shall be dewatered and filled with a 4,000- psi grout after tests are completed and the drilled shaft is accepted. The access tubes and cored holes shall be filled using grout tubes that extend to the bottom of the tube or hole or into the grout already placed.
503.21 Drilled Shafts Load Tests . Test shafts shall be installed at the locations shown on
the Plans unless otherwise directed or approved by the Engineer. Test shafts shall be installed to the same dimensions, details, and elevations shown on the Plans, and shall be installed using the same equipment and installation procedures proposed for installation of the foundation drilled shafts. If the methods or procedures are changed following the completion of load testing, the Contractor shall install additional load test shafts and conduct additional load tests as directed by the Engineer at no additional cost to the Owner. An electronically sealed report of load test results shall be submitted within five business days of the testing completion. Load testing results will be evaluated by the Engineer before installing any production drilled shafts, to allow for design modifications based on the load test results. Load test data as reported shall conform to the Drilled Shaft Foundation Testing (DSHAFT ) and be available in electronic form at the project website. 503.22 503-17 (a) Static Load Tests. Static load tests shall be performed per the procedures specified in ASTM D1143.
b.Force Pulse (Rapid) Load Tests. Force pulse (rapid) load tests shall be performed per the procedures specified in ASTM D7383. METHOD OF MEASUREMENT
503.22 Drilled shafts will be measured by the linear foot from the elevation shown on the plans
to the bottom of the hole as drilled. Each approved splice of the reinforcing cage for additional length of shaft will be measured as 1/2 linear foot of additional length of drilled shaft. BASIS OF PAYMENT
503.23 The unit price of drilled shafts shall be full compensation for making all excavations;
hauling and disposal of excavated material; provision and disposal of slurry, performing all necessary pumping; furnishing and placing required concrete and reinforceme nt steel, including the reinforcement projecting above the tops of the drilled shafts necessary for splicing and any intermediate reinforcement splices; furnishing and placing of CSL tubes; all backfilling; furnishing, placing, and removing temporary casings; furnishing permanent casing if required to complete the work; and for furnishing all tools, labor, equipment, and incidentals necessary to complete the work. Costs associated with repairing defects found in the drilled shaft shall be included in the c ost of the drilled shaft.
a.Payment. The accepted quantities for drilled shafts will be paid for at the Contract unit price per linear foot except for price adjustments allowed in (b) below. Payment will be made under: Pay Item Pay Unit Drilled Shaft ( Inch) Linear Foot Drilled Shaft Load Test Each CSL Testing Each Obstruction Encounter and Removal will not be measured and will be paid for per subsection 109.04 under Force Account item Obstruction Encounter and Removal.
b.Price Adjustments. When the Engineer orders holes to be drilled to a lower elevation than shown on the plans, compensation for additional depth will be as follows: 503.23 503-18 Table 503 -6 DRILLED CAISSON ADDITIONAL LENGTH COMPENSATION Additional Length Compensation Less than or equal to 5 feet Contract Unit Price Greater than 5 feet and less than 15 feet Contract Unit Price plus 15% Greater than or equal to 15 feet As provided in subsection 109.04 Additional compensation will not be paid for the portions of a drilled shaft that are extended due to the Contractor's method of operation, as determined by the Engineer. 504.01 504-1 SECTION 504 WALLS DESCRIPTION
504.01 This work consists of constructing a Concrete Panel Facing Mechanically Stabilized
Earth (MSE) Retaining Wall System at the locations and to the lines and grades shown on the plans. Either metallic or geosynthetic reinforcement (woven fabrics or geogrids) as specified in this specification may be used as MSE reinforcement in the reinforced struct ure backfill zone. The retained structure backfill zone is the structure backfill retained by the reinforced structure backfill zone as shown on the plans. This work consists of constructing a permanent soil nailed retaining wall (also referred to as ground nail wall), with complete details starting in subsection 504.2 3. MATERIALS
504.02 Shop Drawings. The Contractor shall submit one electronic submittal of shop drawings
and certified material test reports for review before construction of the wall. See subsection 504.07, for a complete list of submittal requirements. Shop drawings shall be submitted per subsection 105.02. The shop drawings shall provide the details necessary to demonstrate compliance with the Contract, including :
a.Wall Layouts. Wall layouts shall conform to lines and grades on the plans including start, corner, and end stations, leveling pad step breaks, total number of panels, and top and bottom of wall elevations. For walls with rail anchoring slabs, the top of panel elevati ons shall be within 8 inches of the elevation shown on the plans measured from the bottom of the anchoring slab. The construction batter required to achieve the batter shown on the plans shall be shown on the shop drawings. If temporary walls ar e required for the construction of the permanent wall, the permanent wall vendor shall provide the shop drawings and certified material test reports for temporary walls.
b.Panel and Reinforcement Locations . Unless otherwise shown on the plans, each layer of soil reinforcement shall be connected to the back of each facial panel and the panel numbering and placement sequence shall be shown. The back of each panel shall be logically numbered with its location . Panel to panel, panel to reinforcement connection detail, and limits of special panels at curved wall corner shall be shown.
c.Wall Elevations. Except for the top of the leveling pad, wall elevations given on the plans are based on the desirable wall height. The actual panel and reinforcement elevations shall be marked on the shop drawings by taking into account the supplied panel as well as spe cial panel heights for matching the front and top finished grade.
d.Soil Reinforcement Material . The soil reinforcement type, Minimum Average Roll Value of the Ultimate tensile strength TULT (MARV ) for geosynthetic soil reinforcement or yield strength for metallic soil reinforcement, spacing, lengths, elevations, and the corresponding wall design height shall be shown on the shop drawings. The starting and ending stations for change in grade of reinforcement materi al shall be shown for walls with
Source: Colorado Standard Specifications for Road and Bridge Construction, 2023 Edition. Pages 423–440 of 943.