SPECIFICATIONS FOR SECANT PILE
PART I
1. GENERAL
1.1. DESCRIPTION
This section includes drilling and installation of secant pile, drilled piers including locations, diameters of shafts, bottom elevations, and details of construction. This provision governs the construction of “Secant Piles” also known as Drilled Piers and Drilled Shafts. Secant Piles and Drilled Piers are a reinforced concrete section, cast‑in‑place against in-situ material or temporary steel casing. Secant Piles and Drilled Piers are a straight vertical shaft type.
The term “secant pile wall” shall include, but not be limited to, steel secant piles, concrete filled drilled shafts, cast-in-place concrete facing, and drainage. The secant pile wall shall be constructed using a tangent system of overlapping drilled shafts built using top down construction techniques with a permanent cast-in-place concrete facing.
Work shall include design and construction of the secant pile system, excavation method and excavation support system; material disposal; control and disposal of ground, surface, and construction water; and site restoration. Work areas shall be fenced and barricaded from public access. Construction of the drilled piers shall be in accordance with the details and dimensions shown on the plans and this provision.
1.2. DESIGN REQUIREMENTS
The design of a secant pile wall excavation support system must be able to withstand earth pressures, hydrostatic pressures, bottom heave, equipment loads, applicable traffic and construction loads, and other surcharge loads; to allow safe construction without movement or settlement of the ground; and to prevent damage to or movement of adjacent structures, streets, and utilities. This design must be compatible with the geologic conditions and any anticipated ground behavior.
Ø Design each member or support element to support the maximum loads that can occur during construction, with appropriate safety factors.
Ø Design the support system to minimize horizontal and vertical movements and to protect adjacent properties, facilities, and utilities from damage. Design support systems to maintain the stability of the excavation against sliding and bottom heave.
Ø Design excavation support systems in accordance with all State and Federal safety requirements.
1.2.1. Works In Accordance With Specifications
Unless otherwise stated, concrete, reinforcement and formwork shall be in accordance with the requirements in the relevant specifications.
In the event that the provisions of other specification clauses cause ambiguity or conflict with the requirement of these specification clauses, the latter shall take precedence unless otherwise approved by the Engineer.
1.2.2. Survey of Secant Pile Locations
The Contractor shall be required to employ an approved Licensed Surveyor who will set up the positions of the secant piles as shown in the pile layout plans of the detailed design. A certified copy of the survey, lines, and levels shall be established. Secant pile centerline locations staked and maintained by the Licensed Surveyor or engineer provided by the Contractor.
The Contractor will be responsible for the accuracy of location and positioning of each pile. Any errors in setting out and any consequential loss to the Client will be made good by the Contractor to the satisfaction of the Engineer.
1.2.3. Tolerances
Construct secant pile drilled piers at the locations shown on the plans and within the tolerances specified herein. If tolerances are exceeded, the Engineer may require corrective measures to meet the tolerances specified. Construct the drilled piers such that the axis at the top of the piers is no more than 75 mm (3 in) in any direction from the position shown in the plans. Build secant drilled piers within 2% of the plumb deviation for the total length of the pier. Verify the plumbness of the drilled pier excavations by an accurate procedure, such as an inclinometer on the kelly bar or other approved techniques. Unless a plan note requires the construction joint to be moved below the ground line, construct the finished top of pier elevation between 25 mm (1 in) above and 75 mm (3 in) below the top of pier elevation shown on the plans.
1.2.4. Correction
Should piles be installed outside these tolerances affecting the design and appearance of the structure, the Contractor shall propose and carry out immediate corrective measures to the approval of the Engineer at his own time and cost.
1.3. PREQUALIFICATION AND EXPERIENCE REQUIREMENTS
Use a Secant Pile Contractor pre-qualified by the client. Submit documentation that the Secant Pile Contractor has successfully completed at least 3 drilled pier projects within the last 3 years with diameters, lengths, and subsurface conditions similar to those anticipated for this project. Documentation should include the General Contractor and Owner’s name and current contact information with descriptions of each past project. Also, submit documentation of experience with dry and wet placement of concrete and the use of temporary casing or slurry.
PART 2
2. PRODUCTS AND MATERIAL REFERENCES
2.1. Publications listed below form a part of this specification to extent referenced. Publications are referenced in text by basic designation only.
2.1.1. American Society for Testing and Materials (ASTM)
A36/A36M-05............ Standard Specification for Carbon Structural Steel
A283/A283M-03........ Standard Specification for Low and Intermediate Tensile Strength Carbon Steel Plates
A615/A615M‑06a...... Standard Specification for Deformed and Plain Carbon‑Steel Bars for Concrete Reinforcement
A929/A929M-01........ Standard Specification for Steel Sheet, Metallic-Coated by the Hot-Dip Process for Corrugated Steel Pipe
A996/A996M-06a...... Standard Specification for Rail‑Steel and Axle-Steel Deformed and Bars for Concrete Reinforcement
C33-03....................... Standard Specification for Concrete Aggregates
C94/C94M-05............. Standard Specification for Ready-Mixed Concrete
C150-05..................... Standard Specification for Portland Cement
C494/C494M-05a....... Standard Specification for Chemical Admixtures for Concrete
C618-05..................... Standard Specification for Coal Fly Ash and Raw or Calcined Natural Pozzolan for Use in Concrete
C989-05..................... Standard Specification for Ground Granulated Blast-Furnace Slag for Use in Concrete and Mortars
C1017/C1017M-03..... Standard Specification for Chemical Admixtures for Use in Producing Flowing Concrete
2.1.2. American Concrete Institute (ACI)
211.1-91 (2002)......... Standard Practice for Selecting Proportions for Normal, Heavyweight and Mass Concrete
301-05........................ Specifications for Structural Concrete
315-99........................ Details and Detailing of Concrete Reinforcement Structures.
2.1.3. American Welding Society (AWS)
D1.1 (2006)................ Structural Welding Code – Steel
2.2. MATERIALS
SPEC WRITER NOTE: Delete this Article if un-reinforced concrete drilled piers are used.
2.2.1. Steel Reinforcement: ASTM A 615/A 615M, or 996, Grade 60, deformed
2.2.2. Portland Cement: ASTM C 150, Type I or II
SPEC WRITER NOTE: Select mineral or cementitious admixtures from two subparagraphs below if permitted. Ready-mix plant blends fly ash or slag with Portland cement.
2.2.3. Fly Ash/Slag
A Fly Ash Admixture: ASTM C 618, Class C or F
B Ground Granulated Blast Furnace Slag: ASTM C 989, Grade 100 or 120.
2.2.4. Normal Weight Aggregate: ASTM C 33, uniformly graded, 19 mm (3/4 in) maximum aggregate size.
2.2.5. Water; Portable, complying with ASTM C 94/C94 M requirements.
2.2.6. Admixtures: Certified by manufacturer to contain not more than 0.1 percent water soluble chloride ions by mass of cementitious material and to be compatible with other admixtures and cementitious materials. Do not use admixtures containing calcium chloride.
SPEC WRITER NOTE: If desired, select admixtures from subparagraphs below.
A Water-Reducing Admixture: ASTM C 494, Type A.
B Water Reducing and Retarding Admixture: ASTM C 494, Type D.
C High-Range, Water-Reducing Admixture: ASTM C 494, Type G.
D Plasticizing and Retarding Admixture: ASTM C 1017, Type II
2.2.7. Concrete Mix: Prepare design mixes according to ACI 211.1 and ACI 301 for each type and strength of concrete determined by either laboratory trial mix or field test data bases. Use a qualified testing agency for preparing and reporting proposed mix designs for laboratory trial mix basis. Proportion mixes according to ACI 211.1 and ACI 301 to provide normal-weight concrete with the following properties.
A Compressive Strength (28 days): 34.5 MPa (5000 psi)
B Minimum Slump: Capable of maintaining a slump of 125 mm (5 in) plus or minus 25 mm (1 in).
C Do not air-entrain concrete for secant piles.
D Limit water soluble, chloride-ion content in hardened concrete to 0.15/0.3 percent by weight of cement.
E Concrete-mix design adjustments may be considered if characteristics of materials, project conditions, weather, test results, or other circumstances warrant. Resubmission and approval of proposed changes to concrete mix proportions is the responsibility of the Contractor.
2.2.8. Concrete Mixing: Measure, batch, mix, and deliver concrete according to ASTM C 94/C 94M, and furnish batch ticket information. Do not add water to concrete mix after mixing, unless a procedure following ACI 301 is submitted to, and approved by, the Engineer. Maintain concrete temperature less than 32 degree Celsius (90 degree Fahrenheit).
2.3. SUBMITTALS
Whether the Contractor designs only the secant piles or redesigns the wall, within 60 days after receiving Notice to Proceed, the Contractor/Subcontractor, pre-qualified for the design and construction of the secant pile wall, shall submit design calculations and working drawings prepared, stamped, and signed by a Professional Engineer registered in the state of the project. The working drawings shall show all details clearly to allow an expeditious review of the proposed design and construction procedure by the Engineer.
The wall shall be designed to safely support all earth, water pressure, and existing building loads, and protect utilities, traffic or construction loads and all permanent loads without permitting undesirable wall deflections and ground settlements behind the wall.
2.3.1. Submit Samples and Shop Drawings
A Before beginning work, submit a detailed location plan and description of the proposed method of secant pile installation, all of which shall be subject to the review and approval of the Engineer.
B Shop Drawings shall comply with ACI 315, “Details and Detailing of Concrete Reinforcement”. Furnish shop drawings prepared by a Professional Engineer licensed in the State of the project for detailing, fabricating, bending, and placing concrete reinforcement.
2.3.2. Reports
A Secant Pile Record: Data as specified.
B Rock Excavation: Data as specified.
C Certified, “Secant Pile Field Record” for each secant pile recording actual elevation of bottom, elevation of rock (if applicable), final centerline, location of top, variation of shaft from plumb, result of all tests and observations performed, material type and actual allowable bearing capacity of bottom, depth of socket into rock, levelness of bottom, seepage of water, still water level ( if allowed to flood), variation of shaft diameter (from those shown); and evidence of seams, voids, or channels below bottom.
PART 3
3. EXECUTION
3.1. GENERAL
Wall elements for the secant pile wall designed and constructed in conformance with this Specification and as shown on the plans shall be, rebar cages or structural steel beams that are placed vertically in predrilled holes that are alternately backfilled with structural concrete;
or,
reinforcing steel which will conform to Section ____ of the Standard Specifications. Completely assemble a cage of reinforcing steel, consisting of longitudinal and spiral bars and place it in the drilled secant pier excavation as a unit immediately after the proper condition of the excavation is demonstrated to the Engineer. When concrete placement does not follow immediately after cage placement, remove the steel from the pier excavation unless the Engineer directs otherwise. If the cage is removed, recheck the pier excavation for cleanliness in accordance with this provision before reinstalling the cage.
The primary secant piles will be installed at the spacing shown on the plans. After a section of primary piles has been installed and the concrete fill allowed to set for a minimum of one (1) day, then the adjacent secondary piles will be installed so that sufficient overlap between the secondary and primary piles is obtained as shown on the plans. Do not allow the concrete to fully set in the primary piles before placing the secondary piles or it may be difficult to remove the portion of concrete necessary to construct the secondary pile. This will mean that the secant pile wall will need to be completed in several sections until the entire wall is complete.
3.1.1. Size: Minimum sizes and types of secant piles are shown. Proposal to use secant pile piers of sizes and types different from those shown may be accepted if submitted in writing to the Engineer for approval and provided the following conditions are met:
A Least dimension of secant pile is equal to or greater than least dimension shown.
SPEC WRITER NOTE: Consult Structural Engineer for bearing value required in following paragraph.
B If volume of secant pile as constructed is greater than that shown, bearing area at base is increased so that additional weight is distributed to bearing material at no more than _____ kPa (______ ksf).
C Entire secant receives full lateral support from surrounding material.
3.1.2. Changes: Requests for change in size or type of secant pile from those shown shall be accompanied by calculations and other documentation necessary to show that proposed changes will meet load requirements. Do not proceed with changes before receiving written approval from Engineer.
3.1.3. Temporary Steel Casings: Install casings for protection of workers and inspection personnel, for prevention of cave-ins or displacement of earth walls, and for retention of groundwater (when applicable), and flowing soils.
3.1.4. Defective Casings: Do not install buckled, distorted or otherwise damaged casings. Replace casings damaged or disturbed during construction, casings that are not mud-tight or otherwise not in accordance with drawings or specifications, at no additional cost to the Owner.
3.1.5. Survey: Registered Professional Land Surveyor or Registered Civil Engineer, specified in Section, GENERAL REQUIREMENTS, shall establish lines and levels and stake secant pile locations.
3.2. EXCAVATION
3.2.1. Excavation and construction methods shall result in minimum disturbance of surrounding material and full lateral support of secant piles by surrounding material.
3.2.2. If materials with satisfactory bearing strength occur at elevations higher or lower than those shown, place bottom of secant piles at higher or lower elevations, subject to approval of Engineer.
SPEC WRITER NOTE: Delete following paragraph if not required.
3.2.3. Percussion test drill a test hole 50 mm (2 in) in diameter to depth equal to twice secant pile diameter, but not less than 1.83 m (6 ft) deep, in bottom of each secant pile which has been excavated to rock to determine if rock seams are underlain by soil seams or voids.
3.2.4. Excavate secant piles to dimensions and required bearing strata or elevations shown on contract drawings. Maintain sidewall stability during drilling. Excavate holes for closely spaced secant piles, and those occurring in fragile strata, only after adjacent holes are filled with concrete and allowed to set. Secant pile drilling equipment shall have the minimum torque capacity and downward force capacity for the contract site conditions. Bottoms of secant piles shall be cleaned of loose or soft materials and leveled. If bottoms are sloping rock, excavate to a level plane or step with maximum step height less than ¼ the width or diameter of the bearing area. All material removed from the secant pile holes shall be removed from the ground around the casing before concrete placement is started and shall be disposed of by the Contractor offsite in areas submitted to, and approved by, the Engineer.
3.2.5. Excavations for utilities, support of excavations, or other purposes shall be kept a minimum distance of two shaft diameters away from the outer edge of the secant pile.
3.3. PLACING CONCRETE
3.3.1. Before placing concrete, the tip of the secant pile shall be observed and approved by a qualified testing agency registered and licensed in the state. The testing agency shall be retained by the Contractor and approved by the Engineer. The shaft shall be inspected, cleared of mud, water, loose material, and debris.
3.3.2. Place concrete using a down pipe to direct flow of concrete. Except in the presence of water, concrete may fall freely, up to a maximum height of 1.82m (6.0 ft) provided the concrete does not hit the sides of the secant pile. Use a tremie pipe or pump, if the distance is greater than 1.82 m (6.0 ft).
3.3.3. Withdraw casing, as concrete is deposited, constantly maintaining top surface of concrete at least 1.83 m (6 ft) above lower end of casings. Place concrete to form a monolithic cylindrical shaft having full lateral support from surrounding undisturbed materials. Strike finished top surface of concrete to true plane at required elevation.
3.3.4. Concrete placement in each secant pile shall be one continuous operation. If placing operations must be stopped, leave surface approximately level. If concrete has hardened, clean surface and slush with a 1-to-1 cement sand grout before placing operation is resumed. Concrete pours shall not begin within one hour of darkness. In the event that this type of continuous sequential operation cannot be performed, the Contractor shall submit, for approval by the Engineer, a method of securing the open excavation. The Contractor shall not leave excavations open overnight without receiving prior written approval from the Engineer.
3.3.5. When water is present, control water level to within 50 mm (2 in) of bottom of the secant pile by pumping. If impossible or impractical to control water, secure written permission from the Engineer to place concrete through water by means of a watertight tremie pipe.
A When placing concrete under water, discharge end of tremie shall be submerged in fresh concrete and shaft of tremie maintained full of concrete to a point above water level.
B Increase cement content of concrete required to be placed in water by one sack per cubic yard of concrete.
3.4. SECANT PILE RECORD
For each secant pile placed, and before superstructure framing is placed, submit to Engineer for approval a certified report recording following information prepared by Registered Professional Land Surveyor or Registered Civil Engineer.
3.4.1. Secant pile number, length, and bearing material.
3.4.2. Location.
3.4.3. Concrete and steel reinforcement properties.
3.4.4. Plumbness.
3.4.5. Dates.
A Excavation completed.
B Concrete placed.
3.4.6. Diameters.
A Top of shaft
B Bottom of shaft.
3.4.7. Elevations.
A Top of ground.
B Top of concrete.
C Top of rock.
D Bottom of secant pile.
3.5. CLEAN UP
3.5.1. All debris from excavation of objectionable material, obstructions, and any material not to remain as part of the construction are to be removed and disposed of by the Contractor in a legal manner at no additional cost to the Owner.
3.5.2. The site shall be cleaned at frequent intervals and no material shall be stored on the site in a manner that could obstruct the easy access of equipment and personnel.
