SECTION 502: DRILLED SHAFTS
502.1 Description
This Work consists of construc ting drilled shafts. Drilled sha ft construction, with or without under-reamed bottoms (“be ll bottoms”), includes excavat ion, bottom hole cleaning, reinforcing steel placement and concrete.
502.1.1 Work Experience
The Contractor shall demonstrate to the State Geotechnical Eng ineer that the Contractor is able to perform the Work in accordance with the Contract. T he Contractor shall provide evidence of two (2) Projects within two (2) years of the Bid da te involving drilled shaft construction for the conditions expected and use a Superintende nt with experience from one
1.of those Projects who will provide all oversight responsibi lity of all aspects of drilled shaft construction covered in Secti on 502, “Drilled Shafts.” The Con tractor shall provide the latest NMDOT drilled shaft inspection fo rm of each drilled shaft eleme nt signed by the Drilled Shaft Superintendent indicating drilled s haft construction completed in accordance with Section 502, “Drilled Shaft” requirements.
502.1.2 Geotechnical Data Information
P r o j e c t Foundation and/or Geotechnical Reports include subsurface c onditions present at the time of field investigation. The Contractor shall use this information to anticipate conditions that include but are not limited to subsurface water , obstructions, soil stability, and presence of rock. If Foundation and/or Geotechnical Report information is unavai lable, the Contactor shall assume the Casing Construction Method and/or the Slurry Displac ement Construction Method referenced in 502.3.4, “Construction Preparations.”
502.1.3 Submittals
The Contractor shall submit construction and field designs to t he Project Manager for review and approval by the State Geotechnical Engineer. 30 Day s shall be allowed for submittal review, 14 additional Days shall be allowed for resub mittal review.
502.2 Materials
502.2.1 General
The Contractor shall provide Materials in accordance with Table 502.2.1:1, “Applicable Drilled Shaft Standards.” Table 502.2.1:1 Applicable Drilled Shaft Standards Material description Standard Portland cement concrete, Class G Section 510, “Portland Cement Concrete” Reinforcing steel cage Section 540, “Steel Structures” Reinforcing steel HP pile ASTM A 572, Grade 50 Steel pipe (longitudinal or continuous spiral welded) piles and columns ASTM A 252, Grade 3
502.2.2 1 Concrete
For Class G concrete requirements see Section 509, “Portland Ce ment Concrete Mix Designs.”
502.2.2 2 Temporary Casings
The Contractor shall provide temporary steel casings with an in side diameter equal to or greater than the shaft size in accordance with the Contract. T he Contractor shall ensure the casings are smooth, clean, watertight, and of ample strength to withstand both handling and driving stresses, pressures o f concrete, and the surrounding so ils.
502.2.2 3 Permanent Casings
The Contractor shall provide permanent casing with a wall thick ness that is at least the thickness specified for the shaf t construction. The Contractor shall provide a greater wall thickness if necessary to withstand handling and installation s tresses. The casing dimensions are subject to the American Pipe Institute tolerances applicabl e to regular steel pipe. If approved by the Project Manager, the Contractor may use casings larger than specified, at no additional cost to the Department.
502.3 Construction Requirements
502.3.1 Pre-Drilled Shaft Conference
The Project Manager will hold a Pre-Drilled Shaft Conference at least seven (7) Days before the anticipated drilling begi ns to review the Specificat ion requirements and discuss the Contractor’s preparations. The recommended conference agenda is available from the State G eotechnical Engineer.
502.3.2 Equipment
502.3.2 1 Excavation and Drilling Equipment
The Contractor shall use excavation and drilling Equipment that can excavate a hole of the specified diameter 20% deeper than what is shown in the Con tract. The Contractor shall use excavation Equipment that can complete a flat shaft bottom. The Contractor shall ensure that the cutting edges are normal to the vertical axis of the E quipment within a tolerance of 0.25 inch per foot of diameter. The Contractor shall ensure th at under-reaming tools do not allow the base diameter to exceed three (3) times the specified shaft diameter. The State Geotechnical Engineer may approve a change in other under-reami ng Plan dimensions to accommodate the Equipment. When the State Geotechnical Enginee r requires over-reaming of the shaft sidewall, the Contractor shall use an over-reaming bucket, grooving tool, or other approved Equipment. The Contractor shall use an over-reaming t ool that over sizes the shaft diameter from 0.5 inch to three (3) inches. If the Contractor cannot drill the Material with conventional earth augers, the C ontractor shall use special dri lling Equipment, such as core barrels, rock tools and other Equipment, as necessary. Blastin g is not allowed.
502.3.2 2 Slurry Equipment
The Contractor shall use desanding Equipment to keep the slurry sand content to less Section 502: Drilled Shafts Page 281 than eight percent (8%) by volume for mineral slurry and less t han one percent (1%) by volume for polymer slurry. This is required during shaft excav ation to maintain mix consistency of the slurry in the shaft. The Contractor shall u se slurry tanks for slurry circulation, storage, and treatment. The Contractor shall not use excavated slurry pits in place of slurry tanks without the wr itten permission of the Project M anager. The Contractor shall use a slurry-sampling tool to conduct the slurry control tests in a ccordance with Section 502.3.4.1.3.3, “Slurry Control Tests.” The Contractor shall use a slurry sampler capable of sampling slurry from the bottom of the hole and with drawing the sample without loss or contamination of sample fluid.
502.3.2 3 Concrete Placement Equipment
Depending on the type of shaft construction method, the Contrac tor shall place the concrete in the excavated shaft with a rigid tremie pipe, a con crete pump line, or a drop chute.
502.3.2 3.1 Tremies
The Contractor shall use a rigid tremie pipe that can deposit c oncrete at the shaft bottom. The Contractor shall not use a tremie with aluminum parts that will have contact with the concrete. The Contractor shall ensure the inside diameter is a t least ten (10) inches. The Contractor shall ensure the tremie’s inside and outside surface s are clean and smooth. The Contractor shall ensure that the tremie is watertight. In slur ry displacement shafts, the Contractor shall use a plug initially placed at the top of the tremie to separate the concrete from the displacement fluid until the concrete is flowing throu gh the orifice. The Contractor shall ensure that plugs left in the shaft concrete are made of Material approved by the Project Manager. The Contractor shall construct the discharge end of t he tremie to permit the free radial flow of concrete dur ing placement operations.
502.3.2 3.2 Concrete Pumps and Lines
The Contractor shall use watertight pump lines with a diameter of at least five (5) inches. The Contractor shall use schedule-40 steel pipe or heavier. Th e Contractor shall use plugs in accordance with Section 502.3.2.3.1, “Tremies.”
502.3.2 3.3 Drop Chutes
The Contractor shall use rigid-pipe drop chutes that are either one (1) piece or sectional. The Contractor shall ensure they can be added and removed from a metal hopper. The Contractor shall not use flexible trunk line hose.
502.3.3 Submittals
The Contractor shall provide the required drilled shaft submitt als to the Project Manager for the State Geotechnical E ngineer’s review and approval. The C o n t r a c t o r m a y u s e documented Work experience (per S ection 502.3.3.1, “Work Experi ence”) and proposed construction procedure submittals (per Section 502.3.3.2, “Prop osed Construction Procedure”) approved on previous Department Pr ojects of similar size, diffi culty, and geology, in lieu of the detailed submittal requirements listed below. Administrative approvals are s ubject to field verification of p erformance.
502.3.3 1 Work Experience
The Contractor shall submit documentation verifying the require d Work experience in accordance with Section 502.1.1, “Work Experience.” The Contra ctor shall include the names Section 502: Drilled Shafts Page 282 and phone numbers of references that can verify successful comp letion of the listed Projects.
502.3.3 2 Proposed Construction Procedure
At least 30 Days before the drill ed shaft Work begins, the Cont ractor shall submit a complete written proposal of the construction procedure. The f ollowing information is required: 1. Superintendent name and experience record; 2. List of proposed Equipment including: cranes, drills, auger s, bailing buckets, final cleaning Equipment, desanding Equipm ent, slurry pumps, core sam pling Equipment, tremies or concre te pumps, casing, etc.; 3. Description of constr uction operation sequence; 4. Description of shaft excavation methods; 5. Details of mixing, circulating, and slurry desanding methods ; 6. Manufacturer and type of apparatus for testing slurry; 7. Description of methods for cl eaning the shaft excavation; 8. Description of methods for dewatering shaft excavation; 9. Description of methods for managing caving or unstable zones within the shaft excavation; 10. Details for placing reinfo rcement including support and cen tralization methods; and 11. Details for placing concre te including operational procedur es for free fall, tremie or pumping methods.
502.3.4 Construction Preparations
502.3.4 1 Site and Subsurface Conditions
The Department’s test results and rock core samples are availab le for examination upon request.
502.3.4 2 Protection of Existing Structures
If specified in the Contract, the Contractor shall submit a pre ventative-measures Plan to the Project Manager, at least 14 Da ys before the construction o f the shaft.
502.3.4 3 Site Preparation
If footings are present, the Contractor shall excavate to the f ootings' bottom elevation before beginning shaft construction, unless the Contract or Pro ject Manager allows otherwise. If the Contractor drills shafts in conjunction with placing Emb ankment, the Contractor shall drill the shafts after placing the fill , unless the Contract or Proje ct Manager allows otherwise.
502.3.4 4 Proof Drilled Shafts
The Contractor shall construct a proof drilled shaft, when spec ified in the Contract, at the location shown in the Plans. The Contractor shall construct th e shaft after the State Geotechnical Engineer approves the Equipment and methods. If s pecified in the Contract, the Contractor shall load test the proof shaft in accordance with t he Contract and Section 504, “Load Testing of Bearing Piles.” The Contractor shall drill th e shaft to the maximum depth of any production shaft unless otherwise shown in the Contract. I f specified in the Contract, the Contractor shall under-ream the proof shaft to establish the fe asibility of under-reaming in a specific soil strata or rock. The Contractor shall fill the pr oof shaft with concrete in the same Section 502: Drilled Shafts Page 283 way as the production shafts. I f the methods and Equipment pro duce inadequate results as determined in 502.3.8, ”Acceptance,” the Project Manager will r equire the Contractor to demonstrate Acceptable results with another proof shaft. Once the proof shaft is approved, the Contractor shall construct production shafts using the same means and methods. The Contractor shall not change the means or methods without writte n approval from the State Geotechnical Engineer. The Contractor shall cut off the proof shafts five (5) ft below finished grade and leave in place. The Contractor shall restore the pro of shaft sites to their original condition.
502.3.5 Construction of Drilled Shafts
502.3.5 1 Construction Methods
502.3.5 1.1 Dry Construction Method
The dry method consists of the following: 1. Drilling the shaft; 2. Removing accumulated water and loose Material from the excav ation; 3. Testing and approving bottom hole conditions by Project Mana ger; 4. Placing the reinforcing cage; and 5. Concreting the shaft. The State Geotechnical Engineer will approve the dry constructi on method in accordance with the Proposed Construction Procedure submittal when the fol lowing occurs: 1. The shaft accumulates less than 12 inches of water above the base over a one
1.hr period without pumping; 2. The shaft remains stable without caving, sloughing or swelli ng over a four
4.hr period immediately following excavation; 3. The Contractor can remove loose Material and water before in spection and concrete placement; and 4. Use of low strength grout collars to stabilize running sands or unstable zones within the drilled shaft excavation. The Contractor’s Proposed Constr uction Procedure submittal shal l include the use of the slurry-displacement construction method or the casing construct ion method for shafts that do not meet these requirements.
502.3.5 1.2 Casing Construction Method
The Contractor shall use the casing construction method when ca lled for in the Contract or where the dry construction method is inadequate. If necessa ry, the Contractor shall use the casing method combined with the sl urry displacement or dry cons truction method. The Contractor shall place the casing by twisting, driving, or vibr ating into the ground before cleaning it out, unless the Contract requires the Contractor to place the casing in a predrilled hole. If the Contractor elects to use casings or shafts larger than those specified, the Contractor shall provide the concrete necessary to fill the add itional volume, at no additional cost to the Department.
502.3.5 1.2.1 Temporary Casing
The Department will consider subs urface casing to be temporary unless shown as permanent in the Contract. The Contractor shall remove the tem porary casing when placing Section 502: Drilled Shafts Page 284 concrete for the drilled shaft when the concrete is in a fluid state. If the Contractor removes a casing or replaces it with a longer or larger diameter casing t hrough caving soils, the Contractor shall stabilize the excavation with slurry before in stalling the new casing. Other methods to control the stability of an excavation require appro val of the State Geotechnical Engineer. Before withdrawing the casing, the Contractor shall ensure that the level of concrete in the casing is at least ten (10) ft above either the hydrostatic water level or the drilling fluid level, whichever is higher. The Contractor shal l maintain a concrete level in the casing as it is removed so that fluid trapped behind it is disp laced upward and discharged without contaminating or displaci ng the shaft concrete. Tempor ary casings that become bound or fouled during shaft cons truction, and cannot be practi cally removed, constitute a defect. The Contractor shall repair defective shafts in accord ance with 502.3.9, “Correction of Defective Drilled Shafts.”
502.3.5 1.2.2 Permanent Casing
The Contractor shall make permanent casing continuous from top to bottom. The Contractor shall cut off the permanent casing at the prescribed elevation after installation. The Contractor shall complete the shaft by placing the reinforcing steel and concrete in the casing. If using temporary casings in conjunction with permanent casing s, the Contractor shall keep the temporary inner casing aligned with the permanent outer cas ing. The Contractor shall maintain a water-tight seal between the two (2) casings during excavation and concrete placement where an oversized hol e or temporary casing is approv ed by the Project Manager. When approved by the State Geotechnical Engineer to allow drill ing an oversize hole to aid in the placement of the permanent casing, the Contractor shall pos t grout the exterior annular space outside of the permanent cas ing, such that the direct con tact between casing and the surrounding soil/rock is created.
502.3.5 1.3 Slurry Displacement Construction Method
The Contractor shall use the slurry displacement method at site s where maintaining a dry excavation is not possible. The Contractor shall use a mineral or polymer slurry, or water to maintain stability around the hole's perimeter while advancing excavating, placing the reinforcing cage, and placing c oncrete. The Contractor shall d isplace the slurry during final cleaning of the excavation with a bailing bucket, air lift, or submersible pump. The Contractor shall place concrete with a tr emie or concrete pump beginning a t the shaft bottom. During construction, the Contractor shal l keep the slurry level in the shaft excavation high enough to prevent caving and at least fi ve (5) ft above the highest expec ted piezometric pressure head along the depth of the shaft. If not using permanent casings, the Contractor shall provide temporary surface casings to aid shaft alignment and to prevent sloughing, unless otherwise approved by the State Geotechnical Engineer. If the slurry con struction method does not produce the necessary results, the Contractor shall discontinue operations and make corrective modifications to the procedures and Equipment.
502.3.5 1.3.1 Polymer Slurry Requirements
The Contractor shall use polymer slurry that will stabilize the hole and inhibit the influx of ground water. Table 502.3.4.1.3.1:1, “Polymer Slurry Requireme nts, Emulsified or Dry partially hydrolyzed polyacrylamide (PHPA) Polymer,” lists Acce ptable ranges of values for slurry viscosity and gel. Table 502.3.5.1.3.1:1 Polymer Slurry Requirements, Emulsified or Dry PHPA Polymer (at time of introduction or before concreting) Test Method Density (pcf) 62.4 – 64.0 Density Balance Viscosity (seconds/quart) 50–120 Marsh Funnel pH 8–11.7 pH Paper Sand Content (% by volume) 0–1 API Method Note: Perform tests when the slurry temperature is above 40 °F. The Contractor shall premix the polymer slurry according to th e manufacturer’s directions. The Contractor shall prevent the slurry from losin g the required viscosity and gel characteristics in the shaft. The Contractor shall neutralize expended polymer slurry with b leach or in accordance with the manufacturer’s recomm endations and dispose of it in ac cordance with Section 107, “Legal Relations, Environmental Requirements, and Responsibilit y to the Public.”
502.3.5 1.3.2 Mineral Slurry Requirements
The Contractor shall use attapulgite, in lieu of bentonite, whe re saline or chemically contaminated groundwater occurs. The Contractor shall use mine ral slurry with a grain size that remains in suspension and has sufficient viscosity and gel characteristics to transport excavated Material to the screening system. The Contractor sha ll provide mineral slurry in accordance with Table 502.3.5.1.3.2:1, “Mineral Slurry Requirem ents, Sodium Bentonite or Attapulgite in Fresh Water.” Table 502.3.5.1.3.2:1 Mineral Slurry Requirements, Sodium Bentonite or Attapulgite in Fresh Water Property (units) At time of slurry introduction In hole at time of concreting Test method Density (pcf) N/A 64.0 – 75.0 Density Balance Viscosity (seconds/quart) 28–45 N/A Marsh Cone PH 8–10 8–10 pH paper Sand Content N/A 0–4 API Method Note: Perform tests when the slurry temperature is above 40 °F. The Contractor shall premix the slurry according to the manufac turer’s directions. The Contractor shall prevent the slurry from “setting up” in the sh aft. The Contractor shall dispose of the slurry offsite in accordance with Section 107.14.8, “Dis posal of Other Materials and Debris.”
502.3.5 1.3.3 Slurry Control Tests
The Contractor shall perform control tests on the mineral slurr y to determine density, viscosity, pH, and sand content. The Contractor shall not plac e concrete unless the Project Manager has approved the bottom hole test results and after tes t results show Acceptable values. The Contractor shall provide test reports to the Proje ct Manager upon completion of each drilled shaft.
502.3.5 1.3.3.1 Pre-entry Tests
The Contractor shall perform tests to determine viscosity and p H before pumping the slurry into the excavation. The Contractor shall take at least two (2) sets of tests during the first eight (8) h of slurry processing. The Contractor shall d ecrease the testing frequency to one (1) set every eight (8) hours when the results are consiste nt.
502.3.5 1.3.3.2 Bottom Hole Tests
The Contractor shall test slurry samples taken from the shaft b ase before placing concrete in any shaft excavation. The Contractor shall test un til samples produce Acceptable values for density, pH, and sand content.
502.3.5 2 Shaft Excavation
The Contractor shall extend drilled shaft tip elevations when t he State Geotechnical Engineer determines that the Material encountered during excava tion is unsuitable. The Contractor shall dispose of Materials from the shaft excavation as directed by the Project Manager. When using vibrating casing, the Contractor shall not place adj acent casings or excavate shafts until 48 h after pour completion of an adjacent shaft, o r when concrete from the adjacent shaft pour breaks at leas t 2,000 psi, whichever comes first. This requirement applies to excavating any shaft within fo ur (4) shaft diameters measure d center to center.
502.3.5 2.1 Under-ream and Over-ream
The Contractor shall use sidewall over-reaming when the State G eotechnical Engineer determines the sidewall has: softened due to excavation methods ; swelled due to concrete placement Delays; or, degraded because of slurry cake build-up. The State Geotechnical Engineer will direct the thickne ss and elevation of sidewall ov er-reaming.
502.3.5 2.2 Obstructions
The Contractor shall remove surface and subsurface obstructions that are anticipated in the Contract. Obstructions may include manmade Materials, such as old concrete foundations, or natural Materials, such as boulders or nested c obble zones. When unanticipated obstructions are encountered, the Contractor shal l notify the Project Manager as shown in Section 502.4.3, “Unanticipated Obstruction Removal.” 502.3.5.2.3 Soil Samples and Rock Cores The Contractor shall take soil samples or rock cores at the loc ations shown in the Contract or as directed by the State Geotechnical Engineer to d etermine the character of Material directly below the botto m shaft elevation. The Contra ctor shall perform soil borings before excavating the shafts. The Contractor shall perform roc k cores before excavating the shaft from the bottom of an ex ploration hole at no additional c ost to the Department. The Contractor shall extract and ship the core samples in accordanc e with the Department’s Manual of Highway Structure Foundation Investigation and Subsurface Exploration . Unless otherwise specified in the Contract, the Contractor shall begin bore holes or rock cores at the top of the rock socket elevation to at least ten (10) ft below the bottom of the drilled shaft excavation. The Contractor shall record the rock quality desig nation, percent recovery, joint orientation and infilling, and joint water from the rock cores extracted. After exploration, the Contractor shall fill the core holes with grout, slurry, or mor tar having a minimum compressive strength of 3,000 psi at 28 Days. The Contractor shall deliver the geologist’s field log cards to the Project Manager after completing the logs. The Department will not require the Section 502: Drilled Shafts Page 287 Contractor’s geotechnical consultant to perform Laboratory test ing on soil samples or rock cores unless specifically specified in the Contract. The State Geotechnical Engineer will notify the Contractor of the final required shaft depth after receivin g the geologist’s field log sheets and the lab testing results. This notification may take as lon g as 48 h from the time the State Geotechnical Engineer receives t he field log sheets or the soil and rock samples test results.
502.3.5 2.4 Shaft Excavation Inspection
The Contractor shall measure the final shaft depths. The Contr actor shall ensure that at least 50% of each shaft base has less than one (1.0) inch of se diment when placing the concrete. The Contractor shall ensure that the sediment depth or debris at any place on the shaft base does not exceed 1.5 inc hes. For dry shafts, the Con tractor shall ensure that the water depth does not exceed three (3) inches before pouring con crete. The Contractor shall inspect slurry displacement sha fts using the methods that the S tate Geotechnical Engineer deems appropriate. The Contractor shall receive approval of bo ttom hole conditions from the Project Manager prior to cont inuing with the Work.
502.3.5 2.4.1 Inspection Procedures
The Project Manager will notify the Contractor which procedures will be used fo r the shaft inspections. The Contractor s hall supply Equipment and labor f or inspection of the shaft. Inspection procedures may include: 1. Inserting a casing in the shaft excavation temporarily for a lignment, cleanliness, and dimension checks; 2. Inserting a rigid rod assembly with several 90° offsets equa l to the shaft diameter; 3. Using Department video Equipment; or 4. Using a weighted tape and eval uation of results of desanding and density tests for slurry displacement excavations.
502.3.5 2.4.2 Remedial Work for Substandard Excavation
If the State Geotechnical Engineer determines that a shaft exca vation is substandard, the Contractor shall develop, propose, and implement corrective mea sures. Corrective measures may include: 1. Over drilling to a larger diameter to permit reinforcing ste el placement with the required minimum cover; 2. Over-reaming sidewalls of the shaft; 3. Increasing steel reinforce ment bar number and size; or 4. Enlarging the under-ream within allowed tolerance.
502.3.5 3 Reinforcing Steel Unit Placement
The reinforcing steel unit cons ists of longitudinal bars and ci rcular ties or a Structural Steel shape. The Contractor shall place the structural shape o r the reinforcing steel cage as a unit immediately after the Proj ect Manager approves the shaft e xcavation and before placing concrete. The Contractor shall tie and support the reinforcing steel unit in the shaft so that it remains within allowable tolerances given in Section 502.3.6, “ Location and Alignment Tolerances.” The Contractor shall use concrete spacers or othe r approved non-corrosive spacing devices at sufficient i ntervals, near the bottom and at maximum intervals of ten (10) ft up the shaft, to ensure concentri c spacing for the entire reinf orcement unit length. The Contractor shall use spacers equal in quality and durability to the concrete specified for the shaft. The Contractor shall inspect the bottom of the shaft im mediately before placing of the Section 502: Drilled Shafts Page 288 cage to ensure that there is no sloughing. The Contractor shall check the top elevation of the reinforceme nt unit before and after placing the concrete. If the re inforcement unit is not maintai ned within the specified tolerances, the Contractor shall make corrections. The Contrac tor shall not construct additional shafts before modifyin g the reinforcement unit suppo rt to the satisfaction of the Project Manager. The Contractor shall maintain the reinforceme nt unit at the proper elevation and orientation with an approved support mechanism at the groun d surface. The Contractor shall place shaft concrete immedi ately after installing the cag e. If more than 24 h elapses between the placement of the cage and concrete placement, the C ontractor shall remove the cage and inspect the shaft for sloughing or other damage.
502.3.5 4 Concrete Placement
The Contractor shall place conc rete in accordance with Section 511, “Concrete Structures.” The Contractor shall place concrete as soon as po ssible after placing reinforcing steel. The Contractor shall ensure that the time from when the concret e is batched at the plant to placement does not exceed two (2) h. The Project Manager ma y approve a longer time period if the concrete mixture r emains workable and plastic. T he Contractor shall use admixtures for the job conditions so the concrete remains in a workable plastic state through the approved placement limit.
502.3.5 4.1 Concrete Placement by Free Fall
The Contractor may use free fall placement in a stable shaft wh ere the maximum water depth does not exceed three (3) inches. The Contractor shall e nsure that free fall-placed concrete falls directly to the base without contacting either t he rebar cage or hole sidewall. The Contractor shall use a hopper at the top of the shaft or a rigid pipe extension from the hopper. The Contractor shall ensure that free fall placement d oes not exceed 60 ft below the bottom of the hopper or the rigid pipe extension. The Contract or shall not use fre e fall in slurry displacement shafts. If the Project Manager determines that co ncrete cannot be placed using the free fall method, the Contractor shall use either a tremie or pump to accomplish the pour.
502.3.5 4.2 Concrete Placement with Tremie or by Pumping
The Contractor shall use rigid tremie pipe and/or concrete pump s for concrete placement in either dry or slurry displacement shafts. The Contractor sh all place plug within tremie or pump line to ensure concrete does not segregate prior to develo ping concrete pressure head within tremie or pump line and that plug does not discharge fro m tremie or pump line prior to concrete developing continuous flo w. The Contractor shall not begin underwater placement before placing the tremie or pump line within one (1) tremie or pump line diameter of the shaft base elevation. The Contractor shall remove plugs from the exc avation if the Project Manager does not specifically approve them to remain in the shaft. The Contractor shall keep the discharge end continually immersed at least five (5) ft in conc rete after starting the flow of concrete. The Contractor shall keep the concrete flow continuo us. The Contractor shall maintain the concrete in tremies or pump lines continuously at a positive pressure differential to prevent water or slurry intrusion into the shaft concrete. When lifting pump lines during concrete placement; the Contractor shall temporarily reduce the line pressure until the orifice has been repositioned at a higher l evel in the excavation. If at any time during the concrete pour, the orifice is removed from the fluid concrete column and discharges concrete above the rising concrete level, the Depa rtment will consider the shaft d efective. The Contractor may at its own risk and cost, remove the reinforcing cage and concrete to complete the necessary sidewall removal as directed by the State Geotechnical Engineer . The Department will base Section 502: Drilled Shafts Page 289 Final Acceptance in accordance wi th Section 502.3.8, “Acceptanc e.”
502.3.6 Location and Alignment Tolerances
The Contractor shall adhere to the following construction toler ances unless otherwise stated in the Contract: 1. Ensure the drilled shaft and t he concentric reinforcement st eel unit is within three
3.inches of the position show n on the Plans at the top of the shaft; 2. Do not vary the vertical alignment of a vertical drilled sha ft from the alignment show on the Plans by more than 1/4 inch per foot of depth. Do not v ary alignment of a battered drilled shaft by more than 0.5 inch per foot of depth from the specified batter; 3. Ensure that the top of the reinforcing steel unit is no more than six (6) inches above and no more than three (3) inches below the elevation show on t he Plans; and 4. Ensure that the top elevati on has a tolerance of plus one (+ 1) inch or minus three (−3) inches from the top of shaft elevation.
502.3.7 Load Testing
When the Contract includes load testing, the Contractor shall c omplete the testing before construction of production sha fts, unless otherwise approved by the State Geotechnical Engineer. The Contractor shall allow three (3) Working Days af ter the last load test is completed before receiving tip elevations of the production sha fts from the State Geotechnical Engineer and proceeding with the c onstruction of production sha fts. After testing is completed, the Contractor shall cut off the test shafts and rea ction shafts at an elevation of five
5.ft below the finished ground elevation.
502.3.8 Acceptance
502.3.8 1 Concrete Strength
The Department will Accept drilled shafts in accordance with Se ction 510.3.5, “Acceptance.” Loads may be placed on the drilled shafts once 75% of compressi ve strength has been met. In place concrete strength shall be determined in accorda nce with Section 510.3.5.2, “In- Place Concrete Strength Measurements.”
502.3.8 2 Location and Alignment Tolerances
The Department will Accept drilled shafts if the construction t olerances are satisfied in accordance with Section 502.3.6, “Location and Alignment Tolera nces.” If the shafts exceed the location or alignment tolerances, the Department will rejec t the shafts. If the State Geotechnical Engineer determines that the extent of overloading is not detrimental to the performance of the shaft, the Department will accept the shaft.
502.3.8 3 Shaft Integrity
If applicable, the Department will Accept shafts when the pile integrity testing reports verify the structural integrity of the piles. The Department m ay reject a shaft if integrity testing shows conclusive evidence that a defect exists in the shaft tha t may result in inadequate or unsafe performance under service loads. If the report is incon clusive, the State Geotechnical Engineer may require the Contractor to drill a core hole in the shaft. If the core hole confirms Section 502: Drilled Shafts Page 290 the defect, the Department will not pay the coring costs. If t he core hole does not find a defect, the Department will pay for coring costs, including pre ssure grouting.
502.3.9 Correction of Defective Drilled Shafts
If the Department determines that a shaft is unacceptable, the Contractor shall submit a Plan for remedial action to the Project Manager for approval. The Contractor shall provide calculations and Working Drawings, stamped by a New Mexico lice nsed professional Engineer for all foundation elements affected by the proposed correction s. The Contractor shall make corrections to drilled shafts at no additional cost to the Depa rtment.
502.4 Method of Measurement
502.4.1 Drilled Shafts
The Department will not measure additional shaft depth or addit ional shafts used due to defective procedures. The Department will only measur e the first proof shaft construc ted in place.
502.4.2 Soil Borings and Rock Cores
The Department will measure Soil Borings from the bottom of the exploration hole to existing grade. The Department will measure Rock Cores from the point at which rock cores are recovered to the bottom of the rock coring.
502.4.3 Unanticipated Obstruction Removal
The Department will measure and pay for obstruction removal onl y when it is not anticipated in the Contract Documents. The Department will measure an obstruction vertically beginning where it is encountered and ending where conventional d rilling Equipment adequately adv ances the hole. To qualify for Obstruction Removal measurement, the Contractor shall get t he State Geotechnical Engineer’s authorization and meet the following requirements: 1. Hole advancement requires spec ial procedures and tools, such as: chisels, boulder breakers, percussion hammers, core barrels, air tools, hand exc avation, temporary casing, or increasing hole diameter; or 2. The rate of auger advancement is decreased to where the dril ling rate through the obstruction is less than 50% of the drilling rate above the obs truction. Obstruction Removal cost will include Delay costs. The Departm ent will not allow additional Contract Time unless the Project Manager approves a detailed schedule analysis establishing the Critical Path of the additional time required to complete the Obstruction Removal. The Department will not measure Obstruction Removal outside the specified shaft diameter.
502.4.4 Certified Drilled Shaft Inspector
The Contractor shall provide a Certified Drilled Shaft Inspect or to oversee and inspect all aspects of the drilled shaft c onstruction and sign the NMDOT Dr illed Shaft Inspection Reports. The Contractor shall provide certification through NMDOT TTCP o r International Association Section 502: Drilled Shafts Page 291 of Foundation Drilling, also identified as ADSC.
502.5 Basis of Payment
Pay Item Pay Unit Drilled Shaft Foundation____Diameter Linear Foot Permanent Casing____Diameter Linear Foot Steel Shape Reinforcement Pound Soil Borings Linear Foot Rock Cores Linear Foot Obstruction Removal Linear Foot Steel Reinforcement in the drilled shaft is paid for under Sec tion 540, “Steel Reinforcement” except for overhead sign structures which are ad dressed in Section 701, “Traffic Signs and Sign Structures.”
502.5.1 Work Included in Payment
The following Work and items will be considered as included in the payment for the main item(s) and will not be measured or paid for separately: 1. Methods employed by the Contractor to maintain stability of the shaft, including the use of temporary casings, slurry assisted shaft excavation, or use of grout collars; 2. All Work associated with sidewall over-reaming; 3. Drilled shaft concrete required to fill shafts including ove rsized excavations, under- reams, and over-reams; 4. Excavation of anticipated Mate rials shown in the Contract of different densities and character, including employment of special tools and procedures necessary to accomplish the excavation through anticipated Materials; 5. Additional wall thickness required for handling and installa tion of casing; 6. The Equipment and labor require d for the shaft inspection pr ocedure; and 7. Certified Drilled Shaft Inspection. The Contractor shall dispose of Material in accordance with Sec tion 107, “Legal Relations, Environmental Requirements, and Responsibility to th e Public” unless otherwise specified in the Contract. The Contractor shall not dispose of Material within the Project limits without written approval from the Project Manager. Section 504: Load Testing Of Bearing Piles Page 292
Source: New Mexico Standard Specifications for Highway and Bridge Construction, 2019 Edition. Pages 0–0 of 974.