Micropiles

Section 569. - MICROPILES

Description

569.01 This work consists of furnishing all necessary materials, services, supervision, labor, and equipment to install and test micropiles (piles).

Material

569.02 Conform to the following Subsections:

Water 725.01(a)

Admixtures 711.03

Hydraulic cement 701.01(a)

Grout 725.22(e or f)

Welding 551.09(a)

Lean Concrete 614

Construction Requirements

569.03 Qualifications. The Contractor or subcontractor must demonstrate satisfactory completion of at least 5 permanent micropile projects of similar size and scope during the past 5 years, and demonstrate experience with micropile testing. Submit a brief description of each project including the owning agency’s name, contact person, current telephone number, and load test reports.

Provide an engineer, on-site supervisors, and drill operators with experience installing permanent micropiles on at least 5 projects over the past 5 years. At least 30 days before starting micropile work, identify the engineer, on-site supervisors, and drill operators assigned to the project and submit a summary of their individual experiences.

569.04 Submittals. A pre-construction meeting will be held by the CO prior to the start of micropile installation to clarify construction requirements, coordinate the construction schedule and activities, and identify contractual relationships and delineation of responsibilities amongst the Contractor and the Subcontractors.

At least 20 days prior to construction, submit the following to the CO for review and allow 10 days for response:

(a) Proposed micropile construction schedule and sequence. Schedule pile installation to avoid interconnection or damage to piles in which grout has not achieved final set.

(b) Drawings for micropile installation showing:

(1) Plan and elevation views

(2) Micropile number, location and pattern

(3) Micropile design load

(4) Type and size of permanent casing

(5) Type and size of reinforcing steel

(6) Type and dimensions of structural steel plates

(7) Minimum total bond length

(8) Total micropile length

(9) Micropile top attachment

(10) Micropile cut-off elevation

(11) Quantities summary

(c) Description of the proposed equipment suitable for drilling, hole cleaning/prep, and grouting procedures in the ground conditions expected to be encountered. Review geotechnical and environmental site conditions prior to selecting the appropriate equipment. Demonstrate an understanding of the subsurface conditions at the site and reference subsurface data provided in the contract test hole boring logs prepared for this project. Indicate how minimal disturbance to the construction site or any overlying or adjacent structure or service will be achieved.

(d) Details of methods used to ensure borehole stability during excavation and grout placement. Include a review of the drilling and installation method’s suitability to the anticipated site and subsurface conditions. In case of borehole failure, provide methods of stabilizing the borehole that do not affect the required micropile capacity.

(e) Proposed method(s) for constructing and load testing the micropiles. Provide the micropile verification load testing proposal in conformance with ASTM D-1143 and ASTM D-3689, and indicate the minimum following information:

(1) Drawings and details describing the load test method(s) and equipment.

(2) Calibration reports for hydraulic jacks, pressure gauges and master pressure gauges. An independent testing laboratory must have conducted the tests within 6 months of the date submitted.

(a) Type and accuracy of apparatus for load measurement,

(b) Type and accuracy of apparatus for applying load,

(c) Type and apparatus for measuring pile deformation and displacement,

(3) Type and capacity of reaction load system, including sealed design drawings, supporting calculations for all structural components of the micropile load test apparatus.

(f) Grout mix designs, including details of all materials to be incorporated and the procedure for mixing and placing the grout. Include certified test results verifying the acceptability of the proposed mix designs whereby 4-inch diameter by 8-inch long cylinders are made and standard cured in accordance with AASHTO T23 and tested at 7 and 28 days in accordance with AASHTO T22.

569.05 Micropile Installation. Before drilling holes for constructing production micropiles, demonstrate the proposed methods and equipment are adequate and the grout-to-ground bond value used is accurate by installing pre-production micropile(s) for verification load test(s). Verification and production micropiles shall be installed according to the following:

(a) Drilling. Drill holes according to submitted and reviewed installation plan. Upon drilling completion remove drill cuttings and/or other loose debris from the bottom of the hole. The borehole must be open to the defined nominal diameter, full length, prior to placing reinforcement elements and grout. Develop methods of stabilizing borehole that do not have a deleterious effect on the geotechnical bond development of the grout.

If, during installation of a pile, an obstruction is encountered that prevents the practical advancement of the pile, abandon the hole and fill with lean concrete. Drill a new hole at a location to be determined by the CO; however, it must be acknowledged that in certain structures, relocation options may be severely limited, and further attempts at the original location with different methods may be required.

(b) Pipe Casing and Reinforcing Bar Placement and Splicing. Provide permanent steel casing and reinforcing steel bars meeting material requirements as shown on the plans. Install the central reinforcement steel with centralizers into the stabilized drill holes to meet the minimum clearance as shown on the plans and according to Section 554. Fabricate centralizers from any material, except wood, that is not deleterious to the reinforcement steel or casing.

Secure lengths of casing and reinforcing bars to be spliced in proper alignment and in a manner to avoid eccentricity or angle between the axes of the two lengths to be spliced. Locate threaded pipe casing joints at least two casing diameters (OD) from a splice in any reinforcing bar. When multiple bars are used, stagger bar splices at least one foot. Construct all pile splices to develop the required design strength of the pile section. Welding, except as shown on plans, is not permitted without

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