Submitted by: Chaz Weaver, P.E. VDOT and Jim Sheahan, P.E. HDR Engineering, Inc

1. Research Needs Statement Installation of Micropile Foundations in Karst Topography Submitted by:Chaz Weaver, P.E. VDOT and Jim Sheahan, P.E. HDR Engineering, Inc

2. General Background • FHWA-NHI-05-039 (December,2005) “Micropile Design and Construction”; • AASHTO LRFD Bridge Design Specifications 5th Edition, 2010, Section 10.9; • et al (ISM and other resources)

3. Possible Applications of Micropiles • Restricted Access/Headroom or A Remote Area; • Support System Close to Existing Structure; • Supplemental Support For An Existing Structure (e.g. Settlement Control); • Difficult Ground Conditions (e.g., karst, mines, boulders, uncontrolled fill); • Risk of Liquefaction From Pile Driving; • Need To Minimize Vibration And/Or Noise; • Need To Reduce Or Eliminate Spoil At Hazardous Or Contaminated Sites • As Alternate Deep Foundation Type, Especially Where Piles Penetrate Rock; • Where Spread Footings Are Feasible but There Is Potential For Erosion or Scour

5. Drilled Shafts/Micropiles [Bond Zone] [Bond Zone]

7. Duplex Casing and Roller Bit Rotary Eccentric Percussive Duplex

8. Micropile Design • Per AASHTO Section 10.9 • Special Features for Karst • Case through voids and check for buckling • Anticipate Variability and Adjust, if needed • -Room for additional piles in the pattern, if necessary • Design for Redundancy, and Adjust, if needed • - Resistance Factor <AASHTO = 0.70

9. QA/QC >>Pre-Construction • Contractor and Employee qualifications; • Performance Criteria (location, orientation, size, cross section, capacity); • Equipment List; • Installation Plan; • Grout Mix Design; • Load Test Procedures including calibration information; • Materials Disposal Plan; • Remedial Action Plan for Problems • Pre-Construction Meeting to Review Subsurface Conditions/Procedures/Installation Plan/etc.

10. QA – During Construction Contractor Set Up Drilling Reinforcement Grouting Post Installation

11. Submissions Required • Installation Records for each micropileinstalled: • (Minimum Information) • -drilling log with penetration rates (length/minute) • -materials encountered • -final tip elevation • -total micropile length • -description of unusual behavior/conditions • -grout quantity pumped • -pile materials and dimensions • -compliance with tolerances

16. Load Testing and QC Methods • Load Testing (Axial Compression) • Static (ASTM) • Dynamic (Statnamic, GRLApple, et al) • QC Field Test Methods • Downhole Camera • Pile Integrity Testing (PIT)

17. VIRGINA DEPARTMENT OF TRANSPORTATION SPECIAL PROVISION FOR MICROPILES (IN KARST) I. DESCRIPTION This work shall consist of all materials, equipment, services, labor and supervision, transportation and supervision, and manufacturing techniques required to perform all operations for the installation and testing of cement grouted micropiles and pile-top attachments in accordance with the Specifications, this Special Provision and plan details. This work also includes the installation of 16-inch OD casing and grouting of micropiles within the casing at abutments in accordance with plans details. The successful Specialty Foundation Micropile Contractor, from here forth called the Specialty Contractor, shall install a micropile system that will provide the load capacities/nominal resistances and allowable deflections indicated herein. The micropile load capacities/nominal resistances and deflections shall be verified by testing as required and specified herein. The Specialty Contractor may offer an alternate micropile design with a different interior casing OD of no less than 7 inches and no greater than 10 inches and/or reinforcement scheme but cannot reduce the number of micropiles or reduce the bond zone length, and must meet the load test requirements for load capacity/nominal resistance and deflection. Structural computations showing that the alternate micropile design meets or exceed the structural capacity/resistances of the design in the project plans shall be provided to the Engineer.

18. II. QUALIFICATIONS OF SPECIALTY CONTRACTOR The Contractor shall employ the services of a Specialty Contractor for this work. The Specialty Contractor shall have at least 5 years of continuous recent experience in all aspects of micropile design and construction, and shall furnish all necessary plant, materials, skilled labor, and supervision to carry out the contract. Due to the difficulty associated with installing micropiles in karstic conditions indicated by available site information, the Specialty Contractor shall have the following minimum experience over the past five years installing micropiles in karstic conditions using rotary percussive eccentric duplex drilling methods: I nstalled5,000 LF of micropiles Completed 5 projects Installed at least 500 micropiles The Specialty Contractor shall provide the VDOT with details of the above, utilizing micropiles of similar design and capacity/resistance as this project, including client contact information. The Specialty Contractor shall assign an Engineer to supervise the work with experience on at least 3 projects having similar scope to this project in the past 5 years, including at least 2 projects having karstic conditions. Consultants or manufacturer’s representatives cannot be used to satisfy this requirement. The on-site superintendent or foreman and the drill rig operators shall have successfully completed at least 3 micropile projects in the past 5 years in karstic terrain and with micropiles having a capacity/resistance equal or greater than those on the project. The Specialty Contractor shall not subcontract the whole or any part of this contract without the express permission in writing of the Engineer.

19. VII SUBMITTALS The Contractor shall prepare and submit to the Engineer, for review and completeness, the following information developed by the Specialty Contractor for construction of the micropiles: A. Detailed step-by-step description of the planned micropile construction procedure including personnel, testing, and equipment to assure quality control. Sufficient detail shall be provided to allow adequate documentation of construction and quality by the Engineer. Procedures shall include the installation of the 16-inch diameter OD upper casing at the abutments and micropile within the upper casing as indicated in the plans. B. Proposed start date, order of micropile materials, and order/schedule for installation. C. Information on headroom and space requirements for installation. D. Plan detailing how surface water, drill flush and excess grout will be controlled and disposed of. E. Certified mill test reports for reinforcing steel. The ultimate strength, yield strength, elongation and material properties composition shall be included. F. Proposed Grouting Plan including grout mix design, mix materials, batch design reports, methods to monitor and record grout depth, pressure and volume, grouting rate computations, estimated curing times to reach specified strength, and procedures to monitor grout quality including a grout sampling plan.

20. G. Detailed plans for micropile load testing (verification and proof tests) including drawings, details, structural computations, and apparatus to measure test loads as well as pile top movement. Submittals required for load tests shall be submitted within 24 hours of test completion. H. Calibration reports for each test jack, pressure gauge, and master gauge and related calibrated monitoring equipment. Calibrations shall have been performed within 60 calendar days of the date submitted. I. Installation records for each micropile installed. The records shall be submitted within 24 hours after installation is completed for each micropile. The records shall include the following minimum information: Micropile drilling logs indicating penetration rates (length minute) and materials encountered, final tip elevation, total micropile length, description of unusual installation behavior or conditions, grout quantity pumped, pile materials and dimensions, and compliance with tolerances. A pre-construction meeting shall be scheduled by the Engineer and held prior to the start of micropile construction. The Engineer, Contractor, Specialty Contractor, micropile designer, excavation contractor, and instrumentation specialist shall attend the meeting. The meeting shall be conducted to review and clarify planned micropile construction procedures, coordinate the construction schedule and activities, identify contractural relations, and delineate responsibilities. Items reviewed shall include at a minimum, excavation/shoring methods at piers, proposed construction methods at abutments,, anticipated subsurface conditions, micropile installation procedures and equipment, load testing, survey control, and site drainage control.

21. VIII PROCEDURES A. Installation The Specialty Contractor shall install the micropiles through the overburden soils and incompetent bedrock using rotary percussive eccentric duplex drilling methods with internal flush (Tubex drilling system).Advance the micropile through clay seams, voids and fractured rock to the required depth into sound and continuous rock as determined by the Engineer and based on drilling results and penetration rates obtained during installation of verification and proof test micropiles. The procedure will allow near intimate contact to be maintained between the drill casing and the borehole wall. The entire length of the micropile above the bond zone shall remain cased as the pile is advanced. No external grouting around the casing will be allowed. Upon completion of advancing the casing to the determined micropile tip elevation, the internal rods will be withdrawn and the pile will be filled internally with grout. The centralized reinforcing steel shall be placed prior to the grout achieving initial set. 1. The drilling equipment and methods must provide a cased borehole to the defined nominal diameter, full length, prior to placing grout and reinforcement. 2. Centralizers shall be provided on central reinforcement. The upper most centralizer shall be located no more than five feet from the top of the central reinforcement and additional centralizers shall be installed at intervals no more than 10 feet along the remaining length of the reinforcement. Centralizers shall permit the free flow of grout without misalignment of the reinforcement.

22. 3. The central reinforcement steel with centralizers shall be lowered into the stabilized drill holes to the required depth. Partially inserted reinforcing bars shall not be driven or forced into the hole. 4. The grout shall be injected beginning at the lower end of the drilled hole. The pipe casing shall be filled with the specified grout from bottom to top of micropile through a grout tremie tube, which is constantly below the level of the grout by at least 5 feet as it is extracted. 5. The Specialty Contractor shall check micropile top elevations and adjust all installed micropiles to the planned elevations. 6. Open hole drilling will not be allowed. Open hole drilling is defined as pre-drilling the hole and allowing the hole stand open and uncased until the structural casing is placed in the drill hole. 7. If a manmade obstruction is encountered during installation of a micropile that prevents the advancing of the hole, the hole shall be abandoned and filled with grout. A new pile shall be drilled at locations to be determined by the Engineer.

23. Research Proposal • Review available literature on the use of micropiles in karst and summarize design methods including consideration of variability and voids as well as specifications and procedures used to verify assumption during installation. • Review field documentation procedures including logging for drilling and documentation of grout volumes placed. • Review load testing procedures available and QC methods. • Develop specifications including QA/QC procedures for micropile construction on VDOT projects, particularly in karst topography. • Develop training program for design and construction staff that results in understanding of micropile design and construction QA/QC prodecures