Micropile

Micro-piling is one of the efficient and cost effective ground improvement technique which can be use various condition. It can use to support foundation as well as soil retention.

1. Ground Improvement Techniques Micro Piling

2. History Micro-piles were conceived in Italy in the early 1950s, In response to the demand for innovative techniques for underpinning historic buildings and monuments that had sustained damage during World War II . It is used to support foundation to resist static and seismic loading conditions, and as in-situ reinforcements for slope and excavation stability.

3. Introduction A Micro pile have a small diameter, typically less than 300mm . It is a drilled and grouted non-displacement pile which is heavily reinforced and carries most of its loading on the high capacity steel reinforcement Reinforcement and cement grout are the major component of micro pile. It also known as mini pile.

4. Favorable use of Micropile Hard strata is available at higher depth Damaged structure Hilly area Uneven settlement Space is less Excavation support

5. Classification Based on Design Criteria/Application Based on Construction

6. Based on Design Criteria/Application Takes directly applied load Provide reinforcement to the soil to resist load.

7. Based on Construction type Type A: Gravity Grout Type B: Pressure through Casing Type C: Single Global Post Grout Type D: Multiple Repeatable Post Grout

8. Type A: Gravity Grout Gravity head only using sand-cement motors or neat cement Type B: Pressure through Casing Cement grout is placed into the hole as the temporary steel casing is with drawn. Injection pressures varies from 0.5 to 1.0 MPa. The pressure is limited to avoid fracturing of the surrounding ground. Type C: Single Global Post Grout This is done in two step process: As of Type A Prior to hardening of the primary grout, similar grouts injected one time via a sleeve grout pipe at pressure of at least 1.0MPa. Type D: Multiple Repeatable Post Grout This is done in two step process: As of Type A Prior to hardening of the primary grout, similar grouts injected one time via a sleeve grout pipe at pressure of at 2.0 to 8.0MPa

9. Construction of micro pile Following step are carried out for construction of micro pile. Drilling and/or installation of temporary casing Remove inner drilling bit rod. Placing reinforcement and grouting by tremie. Remove temporary casing, inject further grout under pressure. Complete pile (casing may be left in place of compressible stratum)

10. Application of micro pile For structure support New foundation Under pinning of existing foundation Seismic retrofitting of existing structure Scour protection Excavation support in confined area For situ reinforcement Slope stabilization Earth retention Ground strengthening and protection Settlement reduction

11. Advantages of micro pile It used to underpin the existing structure where need of minimum vibration. It can be easily laid where low head room is constraint. It can be installed at any angle . It offers practical and cost effective solution to costly alternative pile system . Not require large access road or drilling platforms .

12. Case Study KM 150.00 D-S-DBO Road The site at KM 150.00 is a deserted zone at elevation of 14500 feet with glacier valleys and during summer season glacier melts which increases the water level of Shyok River and damages the road which ultimately leads to difficulty in transportation. The site located along hilly terrain, a highly remote area where accessibility is very hard and climatic conditions are very harsh for humans . Government of India had tried various techniques for the foundation purpose of the bridge such as deep (well, pile, etc.) and shallow foundations (open cast foundation).  Well foundation is not suitable due to higher water level Due to requirement of mobilization of heavy machinery pile foundation is not feasible In case of shallow foundation the concrete is not setting due to the presence of high water table, dewatering is required continuously which is not considered to be a good option.

13. Site Location

14. Proposed Site Like this

15. Solution- ( Micro pile) The company Spar Geo planned to construct 42 micro-piles as a foundation each for 9 in river piers and 2 abutments . Each micro-pile will have 273 mm diameter socketed 21 meters into soil . Grouting will be carried out using cement (53 grade OPC) with addition of 1% special admixture of the total weight of cement to increase the strength of grout mix with the help of double packer for 1.5 m section which helps to maintain almost a uniform thickness of grout along the length. The pile testing will be conducted for vertical and lateral load up to two times of designed load as per IS: 2911 (part 4).

16. (http://www.spargrp.com/casestudy/micropile-foundation-at-150-00km-d-s-dbo-road/)

17. Inclined Piling

18. Pile Load Test

19. Preperd b : Thaiyam Sameer