Method Statement for Installation of Micropiles

Method Statement for Installation of Micropiles 

• To stabilize the sides of the borehole, a rotary drilling device drills a borehole with the appropriate diameter of 150 to 300 mm.
• It is vital to have a liner that extends to the hard rock or strata. Pipeliners made of M.S. or HDP are employed. However, MS liners are preferred.
• As pile reinforcement, a cage made of tor steel and a collection of rebars with large diameters is offered.
• A rich grout made of cement and fine sand with a water-cement ratio of 0.5 is used to grout the pile, and after 28 days it must have a minimum compressive strength of 480 kg/cm2. The bore could also be filled with coarse aggregate to a specific height of around 1 m and then filled with cement grout, among other alternative appropriate methods.
• The piles are adequately inserted into the hard rock or strata required to generate the capacity, which is mostly caused by friction in the socket.

What is a micropile?

A micropile is a small-diameter (commonly less than 300 mm), drilled, and grouted replacement pile that is typically reinforced and can either withstand axial or lateral loads or both of these.

What we mean here by the term “replacement” pile is the installation by removal and replacement of material contrary to the replacement of existing material.
A micropile is constructed by drilling a borehole, placing reinforcement, and grouting the hole.

Based on the definition as described in the principal guides and specifications written about the micropile, here are the various meanings which hold a number of similarities as such:

• FHWA-RD-96-016 (Drilled and Grouted Micropiles: State of Practice Review – Volume 1)
  “A small diameter (less than 300mm [less than 250mm in France]), replacement, drilled pile composed of placed or injected grout, and having some form of steel reinforcement to resist a high proportion of the design load.”
• FHWA-SA-97-070 (Micropile Design and Construction Guidelines – Implementation Manual)
  “A micropile is a small-diameter (typically less than 300mm), drilled and grouted replacement pile that is typically reinforced.”
• Deep Foundations Institute (DFI) Guide Specification
  “A small diameter, bored, cast-in-place pile, in which most of the applied load is resisted by the steel reinforcement.”
• FHWA-NHI-05-039 NHI Course No. 132078 (Micropile Design and Construction – Reference Manual)
  “A micropile is a small-diameter (typically less than 300mm (12 inches)), drilled and grouted non-displacement pile that is typically reinforced.”
• AASHTO LRFD Design Specification
  “A small-diameter (typically less than 300mm (12 in.)), drilled and grouted non-displacement pile that is typically reinforced.”
• AASHTO LRFD Construction Specification (latest draft)
  “The term “micropiles” as used in this section means a small (4″ to 12″) diameter bored, cast-in-place composite pile, in which the applied loads are resisted by steel reinforcement, cement grout, and frictional grout-to-ground bond.”
• 2006 International Building Code
  “Micropiles are 12-inch (305mm) or less bored, grouted-in-place piles incorporating steel pipe (casing) and/or steel reinforcement.”

Presented here is a sample method statement that can be modified and associated in the preparation of a method statement as part of Quality Assurance documentation in a civil construction project.

Method Statement of Micropile Installation

See also the Method Statement for Bored Piles here.

TABLE OF CONTENTS

I. Description of Works
1. Introduction
2. Definitions
3. Reference
4. Responsibilities
5. Interfacing with Other Operations
6. Duration, Phasing with the Subcontractors
7. List of Subcontractors

II. Resources
1. Plant and Equipment
2. WorkForce
3. Light Tools

III. Materials

IV. Site Planning
a. Preparation
b. Site Clearance
c. Traffic Management
d. Pre-construction Safety Meetings

V. Methodology
V.1 Working Platform
V.2 Construction Sequence
V.2.1 Drilling of Boreholes
V.2.2 Rebar Installation
V.2.3 Application/Injection of Grout
V.2.4 Sequence of Micropile Drilling/Installation
V.2.5 Protection of Micropile Heads
V.3 Micropiling Records, Drilling, Testing & Tensioning

VI. Risk Assessment

VII. Permit and Licensing Requirements

VIII. Drawings, Diagrams, Maps, and Survey Data

IX. Pre-Start Safety Briefing Arrangements
1. Protective and Safety Equipment
2. Information to Personnel
3. Special Safety Requirements
4. Emergency Procedures
5. Emergency Contact Numbers

X. Supervision and Monitoring Arrangements

XI. Environment and Quality Issues
1. Precautionary Measure
2. Disposal Requirements
3. Inspection, Test, and Sampling
4. Quality Assurance Requirements Table

XII. Attachments
APPENDIX A: Micropile Records Sheets
APPENDIX B: Risk Assessment
APPENDIX C: Permit to Work
APPENDIX D: Inspection and Test Plan
APPENDIX E: Load Chart
APPENDIX F: Technical Data Sheet
APPENDIX G: Drawings
APPENDIX H: Organizational Chart

I. Description of Works

1. Introduction

The purpose of this method statement is to describe the method of installing micropiles as temporary tie-back supports for the temporary shoring. The shoring system designed and considered for the project is the contiguous pile wall wherein a series of piles are constructed. To provide lateral support, micropiles will be installed to reduce the bending moment on the contiguous piles.

In this Method Statement, we shall outline and describe, in a general way, the method of execution for the micro piling works. It is to be noted that this method statement is to be read in conjunction with the applicable specifications.

Note:
A. The construction of Contiguous Piles shall be done as per the approved Method Statement for the Construction of Bored Piles.

B. The construction/installation of Rock Bolts shall be done as per the approved Method Statement – Slope Protection Measures (Drop Chain Link, Rock Bolt, and Shotcrete).

2. Definitions
SE Site Engineer
QC Quality Control Engineer
SF Site Foreman
PM Project Manager
SA Site Agent representative from the Lab
HSE Manager Health, Safety & Environmental Manager
HSE Officer Health, Safety & Environmental Officer
GIS Geographical Information System
CEMP Construction Environmental Management Plan
QCP Quality Control Plan
HSE Plan Health, Safety, and Environment Plan
GWL Ground Water Level (meter)
NGL Natural Ground Level (meter)
Note: All dimensions are in mm unless specified.

3. Reference

ASTM D3689: Standard Test Method for Individual Piles Under Static Axial Tensile Load
BS EN 1536:2000 Execution of special geotechnical work- Bored Piles
MS- Construction of Bored Piles,
Micropile Specifications
MS- Slope Protection Measures (Drop Chain Link, Rock Bolting and Shotcrete),
Geotechnical Interpretative Report – All Site Investigation
Micropile System & Accessories for Shoring and Piling Works
Micropile System & Accessories for Shoring and Piling Works
uPVC/HDPE Sleeve for Micropile for Shoring and Piling Works
MS Sleeve (114 mm dia. OD, 6 mm thickness) for Micropile for Shoring and Piling Works
PVC Centralizer for Micropile System
Proposed Guide Wall Setting out and Details
Related Approved Shop Drawings

4. Responsibilities
1. Project Manager-Responsible for accomplishing the stated project objectives which include creating clear and attainable project objectives, building the project requirements, and managing the constraints of the project management triangle, which are cost, time, scope, and quality.

2. Superintendent-Organizes coordinates and supervises the work of the Foreman, Sub-Foreman, and/or craft employees on construction. Determines work priorities, schedules jobs, and operations, and coordinates work activities within the design area. Exercises control over the rate of construction progress in order to complete the construction project within time limits.

3. Site Engineer-Supervise operations in accordance with the approved Method Statement, shop drawings, specifications, material submittals, and schedules to achieve the acceptance of the project deliverables.

4. Site Supervisor-Supervise closely, the activities designated to them and ensure that all instructions and safety procedures are followed and strictly adhered to.
5. Site Foreman-To liaises with the Site Engineer and Supervisor for the work execution.

6. QA/QC Manager-Responsible for all aspects related to the Project’s Quality Assurance and Quality Control. QA Manager Prepares the detailed Project Quality Plan and ensures that it is understood, implemented, and maintained at all levels of the project organization.

QC Manager is in charge of the preparation of the Inspection and Test Plan (ITP) and liaising with Third Party Inspectors, Subcontractor Quality Personnel, and Independent Testing Laboratories for quality-related matters.

7. QA/QC Engineer-Ensure the proper implementation of the Quality system and monitor the overall quality of the work is maintained. Conduct inspection and monitor tests. Determine and report any non-conformance and recommended corrective actions. Ensure that all personnel is aware of the quality requirement. Training of relevant personnel. Conduct surveillance and inspection duties at various stages to ensure compliance with QA/QC Plan.

8. HSE Manager-Health, safety, and environmental (HSE) managers generally plan, coordinate and implement issues and directives within the organization. They ensure safe environmental working conditions for all employees.

9. HSE Officer-Monitor and control all HSE matters related to project team members and contractors in ensuring that the Project is in compliance with the project requirement i.e. specification, safety code, and other policies/guidelines related to the project.

Participate in HSE Risk Assessment and hold the relevant meeting, and workshops internally and with related 3rd parties. Monitor and update the HSE risks register and ensure all mitigation plans are strictly adhered to throughout the project execution.

5. Interfacing with Other Operations
Excavation Works
Shoring Works
Concrete Works for Diagprahm Wall, Capping Beam, and Parapet Wall

6. Duration, Phasing with the Subcontractors
The duration of work is indeterminate but will not critically affect the progress of the project.

7. List of Subcontractors
Sub-Contractor:
xxxxxx

II. Resources
1. Plant and Equipment

2. WorkForce

3. Light Tools

III. Materials

Micropile System & Accessories for Shoring and Piling Works
Dywidag bar with 50 mm ø and locking nut
Micropile plate thickness 40 mm ø
Cement grout mixture (per batch):
2 bags cement = 100 kg
50 liters water = 50 kg
50 to 80 liters of sweet water depends on the ambient temperature
W/C ratio = 0.50
Design compressive strength of the grout at 28 days = 30 N/mm²
Water

This might interest you: Method Statement for Crosshole Sonic Logging for Bored Piles

IV. Site Planning

The duration of work shall be indeterminate but will not critically affect the progress of the project.

a. Preparation

Permits from the concerned authority shall be obtained prior to starting work at the site.

The contractor shall ensure that all gate passes, permits, tools, materials for safety precautions, manpower, and equipment are available before the commencement of work.

The Site Team shall make sure that access roads are always clear from any obstruction and that the site is always accessible.

Provision of access and egress such as ladders, steps, ramps, or other safe means of egress and be at a reasonable distance and must be extended at least 1.0 m above the ground.

b. Site Clearance

Before commencing the work, the area shall be cleared of all debris, materials, or other obstructions.

All concrete works such as the capping beams have been fully cured and approved in terms of compressive strength.

c. Traffic Management

The Site Team with the assistance of the Safety Officers shall coordinate logistics and materials movement through the site following the direction and road signs displayed on site. The required diversion routes shall be marked on drawings including the required traffic signs.

The Work Permits and Operator Certificates shall be compiled and filed for reference by authorized personnel.

d. Pre-construction Safety Meetings

The meeting shall be scheduled prior to the beginning of the work and before any subcontractor starts on the project.

General contractual safety, health, and environmental requirements.

Traffic safety will be discussed to emphasize these meetings.

Roles of the contractor, subcontractors, authorized representatives, and all project workers.

Accident reporting requirements.

Specific details of the work to be performed along with the use of personal protective equipment.

Emergency procedure.

V. Methodology – Installation of Micropiles

Micropiles shall be installed for the proposed shoring wall in order to reduce the bending moment and thereby reduce deflection on the wall top. Loads on each pile and their dimensioning are made as elaborated in the design.

Generally, the sequence of installation of micropiles involves the following activities:

Drilling of boreholes by rotary drilling (Klemm machine)

Supply and mixing of cement mortar

Installation of 50 mm ø Dywidag Bar

Grouting of drill holes

Testing of micropiles (1 preliminary test on non-working pile & 1 proof load test on
working piles)

V.1 Working Platform

Drilling of the micropiles will be carried out from the level approx. 500 mm- 800 mm below the face of the top level of the capping beam as per Approved shop drawings (refer to item I.3 Reference). The working platform shall be prepared to allow the unhampered and continuous movement of the Klemm/ drilling machines.

The working platform shall be maintained in a dry and stable condition.

Setting out of piles to be carried out as per approved shop drawing.

V.2 Construction Sequence

V.2.1 Drilling of Boreholes

From the working platform level, the anchor drilling machines, KLEMM machine, and/or UBW drilling rig, will drill the micropile boreholes. All drilling works shall be performed from a dry and stable working platform and in a manner that affects adjacent structures, foundations, and services if any, shall be minimized.

The boreholes will be pre-cored through the capping beam with reservation pipe sleeves.

Where micro piles are to be drilled in the capping beam, sleeve pipes shall be pre-installed in the capping beam to the required inclination. The boom of the anchor drilling rig will be adjusted to the required inclination for the drilling process.

The drill bits are attached to the drill rods required for the drilling. Drilling will be supported by a water-flushing technique. In steps of 80 cm, the drilling rods will be extended until the length of the micropile is reached.

In the event that soil conditions as described in the borehole logs are differing from those encountered on site, the Engineer will be notified accordingly and adjustment of drilling tools and flushing technique as well as parameters of anchorage will be re-considered.

The process is to be understood that the first drilling rod is provided with teeth and a drill head for loosening the materials, while water is pumped simultaneously through the drilling rods for transportation of the loosened material. The loosened material, mixed with water, will flush out along the side of the rods at the cored location. A trench should be prepared to contain the drilling water.

V.2.2 Rebar Installation

When the required depth/length of micropile is reached, the KLEMM machine is de-coupled from the drilling rod. The Dywidag bars (with a plastic spacer to maintain the centricity) are then inserted into the rods over their full required length. Approx. 1.5-2.0m of the rebar is exposed outside the ground (projected/free length) for tensioning purposes.

V.2.3 Application/Injection of Grout

Grouting

When the anchor tendons are installed, again the KLEMM machine is coupled to the rods and a grout mixture (water-cement mix) is pumped via the rotary drive over the full length of the rods. While the grout is being pumped into the borehole, the drilling rods are also simultaneously being extracted in steps of 80 cm accordingly, the void around the anchor tendons is filled with grout.

V.2.4 Sequence of Micropile Drilling/Installation

The above steps are to be followed for all micropile’s taking into consideration that no drilling is to be done for 2 piles next to each other. Micropile drilling will be performed in a staggered way (i.e. installing one micropile and leaving the pile next to it then installation of the subsequent pile. The micropile in the middle between the 2 installed previously shall be drilled after a minimum of 24 hours).

V.2.5 Protection of Micropile Heads

After the testing of the reinforcing bar (for PTP only), the rebar will be cut and the head will be applied with grease for protection from the weather elements.

V.3 Micropiling Records, Drilling, Testing & Tensioning

The frequency of tests shall be in accordance with the requirements of IFC Drawings.
Drilling of Micropile shall be carried out as per approved shop drawings.

One preliminary test on the non-working pile (200% x Working Load)

One proof load test on the working pile (150% x Working Load)

Three grout cubes for each micropile will be tested for their compressive strength (1 for 7 days & 2 for 28 days)

Working Load = 297 KN (Type 17) and 418 KN (Type 18)

The Engineer shall be given at least 24 hrs’ notice before the installation of micropiles and tension test.

Tension Test Report

Tension test will be recorded every 1 minute, at 10%, 100%, 150% & 200% of the working load prior to off-loading (see Appendix E).
where: WL = Working Load

Micropile Data/Record
The following information shall be provided for each installed micropile:
1. Identification number
2. Drilling details
a. Date and time of drilling commencement and completion
b. Drilling equipment identification
c. Location, level, inclination, length, and diameter
3. Grouting
a. Date and time of grouting commencement and completed
4. Test loading
a. Date of tension test
b. Length of micropile
c. Working Load
d. Type and identification of loading equipment
e. The load applied during test loading and off-loading
The above-mentioned information will be recorded on the Bored Pile Record sheet as attached in Appendix A.

VI. Risk Assessment
Please refer to the attached document in Appendix B.

VII. Permit and Licensing Requirements
Refer to Appendix C for the Permit to Work.

VIII. Drawings, Diagrams, Maps, and Survey Data
Refer to Appendix G for Drawings.

IX. Pre-Start Safety Briefing Arrangements
Refer to Risk Assessment in Appendix B.
1. Protective and Safety Equipment
All workers involved shall be equipped with adequate PPE as stated below:
a. Safety Helmet with Company Logo
b. Safety Boots
c. High Visibility Vest
d. Safety Goggles
e. Hand Gloves
f. Coveralls
g. Safety Harness
2. Information to Personnel
a. Safety Induction
b. Job training
c. Superintendents’ Notices/Memos
d. Toolbox talks
e. START Card
3. Special Safety Requirements
a. All necessary personal/protective equipment (PPE), as well as a harness, be provided.
b. Banksman, wearing distinctive vests, shall be assigned to help operators maneuver their equipment.
c. The equipment operators shall possess the required licenses and certificates.
d. Generated dust shall be controlled by periodic water spraying.
e. The project safety officer is responsible along with the project zone site engineer for
ensuring that all operations are carried out with due regard to the safety of all
project personnel & property.
f. All working activity shall comply with Client Safety Procedure.
g. First Aid Material.
h. General management of protection/operation hazards is to be observed.
i. In case of working at night, please refer to Method Statement for Night Works

4. Emergency Contact Numbers

X. Supervision and Monitoring Arrangements

Construction Manager
He is in charge of all construction activities. Schedule the project in logical steps and budget the time required to meet deadlines. Inspect and review projects to monitor compliance with building and safety codes and other regulations.

Temporary Works Construction Manager
To support the project delivery teams, to support and lead the management and delivery of temporary works engineering whilst ensuring program, cost, quality, and safety objectives are achieved.

Site Engineer
The Site Engineer shall evaluate the number of materials consumed by each trade to be
compared to the planned quantity.

Site Foreman
A construction foreman is responsible for supervising the workers and also doing actual
construction work. The foreman monitors employees to ensure that the work is done
efficiently and within quality standards.

Chief Surveyor
A Chief Surveyor ensures that surveying data are collected and recorded accurately and that all company procedures are followed by crew members.

QA/QC Engineer
The QA/QC Engineer shall monitor whether the installation works are conforming to the
required quality otherwise he shall notify the Site Engineer should he find non-conformance to the ongoing activities. The Site Engineer shall immediately rectify the work to avoid receipt of NCR from the QA/QC Engineer.

HSE Engineer
The Safety Engineer shall be full-time at the site and shall frequently visit all the ongoing works at the site. All safety violations and on-conformance of the HSE Plan shall be registered and immediate action shall be done in coordination with the Site Engineer.

PMV Engineer
The PMV Engineer shall monitor the proper utilization of all equipment, types of machinery, vehicles, and plant on the site. Keep records of all equipment, types of machinery, vehicles, and plant as per Daily Checklist and prepares the schedule as well.

Environmental Manager
Prepares, reviews, and updates the CEMP. Ensures that the CEMP and project environmental procedures are implemented and maintained at the site and shall be communicated to the construction staff. Liaises with the Supervising Consultant, PM/CM, and Environmental Representatives to ensure variations to the scope or timing of the work that may impact the environment are discussed, and be the point of contact for all environmental issues and reporting.

Note: Site Engineers / HSE Staff shall have access on-site to each MS/RA. The consultant/inspector will monitor activities on-site based on the MS/RA.

XI. Environment and Quality Issues

1. Precautionary Measure
All precautionary measures shall be briefed to all workers prior to commencing the activity
2. Disposal Requirements
All waste shall be disposed of as per the Construction Environmental Management Plan and as per Government approved disposal areas.
3. Inspection, Test, and Sampling
Refer to Appendix D for Inspection and Test Plan.
4. Quality Assurance Requirements Table
Refer to Project Quality Plan
a. Project Specifications

XII. Attachments

1. Reference Documentation
Project Specifications

2. Appendices

Appendix A: Micropile Testing Records
Appendix B: Risk Assessment
Appendix C: Permit to Work
Appendix D: Inspection and Test Plan
Appendix E: Load Chart
Appendix F: Technical Data Sheet
Appendix G: Drawings
Appendix H: Organizational Chart

tag: Method Statement for Installation of Micropiles 

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