Micropiles

In this presentation i have gone through about various prospects and challenges that have been faced at the time of installation,its types,method of installation &its application.

1. MICROPILES- PROSPECTS & CHALLENGES SUBMITTED BY SUMIT RAWAT CIVIL ENGINEERING 4 TH YEAR 1202700048

2. CONTENT INTRODUCTION HISTORICAL BACKGROUND CLASSIFICATIONS CONSTRUCTION SQUENCES USING CASING ADVANTAGES DISAVANTAGES APPLICATION CHALLENGES CONCLUSION REFRENCES

3. INTRODUCTION A micropile is a small-diameter (typically less than 300 mm), drilled and grouted replacement pile that is typically ( up to 20% As/Ac) reinforced . A micropile is constructed by drilling a borehole, placing reinforcement, and grouting the hole. Micropiles can withstand axial and/or lateral loads.

4. HISTORICAL BACKGROUND The use of micropiles has grown significantly since their conception in the 195Os, 1952 - First introduced in Italy for foundation restoration (underpinning) of WWII damaged buildings 1960’s – Widely used in Europe for underpinning old sensitive structures mid 70’s – First introduced in USA (New York &Boston) 1980’s – Being introduced in East Asia

5. CLASSIFICATIONS Based on Design Application Based on Grouting method

6. Based on Design Application CASE 1 :- micropile elements ,which are loaded directly and where the pile reinforcement resists the majority of the applied load. CASE 2 :- micropile elements circumscribes and internally reinforces the soil to make a reinforced soil composite that resists the applied load.

7. Figure 1 - 1. CASE 1 Micropiles (Directly Loaded)

8. Figure2-2.CASE 2 Micropiles -Reticulated Pile Network with Reinforced Soil Mass Loaded or Engaged

9. Figure 3 - 1. CASE 1 Micropile Arrangements

10. Figure 4 -2. CASE 2 Micropile Arrangements

11. Based on Grouting method The method of grouting is generally the most sensitive construction control over grout/ground bond capacity . Grout-to-grout capacity varies with the grouting method . Type A: Gravity Grout Type B: Pressure through Casing Type C: Single Global Post Grout Type D: Multiple Repeatable Post Grout

12. Type A: Here the grout is placed under gravity head only using sand-cement motors or neat cement . TypeB : In this type neat cement grout is placed into the hole as the temporary steel casing iswith drawn . Injection pressures varies from 0.5to 1.0 MPa . The pressure is limited to avoid fracturing of the surrounding ground.

13. Type C: This is done in two step process: As of Type A Prior to hardening of the primary grout, similar groutis injected one time via a sleeve grout pipe at pressure of at least 1.0MPa . Type D: This is done in two step process of grouting similar to Type C with modifications to step 2 where the pressure is injected at a pressure of 2.0 to 8.0MPa :

14. Figure 5: Based on method of grouting

15. CONSTRUCTION SEQUENCES Installation process in accordance with the requirements of NBN EN1536:1999 Positioning and drilling of the first section of the drill casing (recoverable steel casing as temporary support during the boring process ). While drilling, the drill casing – inside equipped with a drilling head fixed on a rod - is oscillated into the soil. (back and forth movement / twisting in place ).

16. 3 . As the drilling process progresses, soil is removed from the borehole by the excavating and additional sections of casing are jointed (added) to protect the soil from collapsing into the borehole during drilling.. 5 . After reaching the design depth, clean-up of the borehole front, removal drilling tool, drilling fluid (water) pumped out from the bore Formation of the pile : insertion and lowering of the reinforcement cage, pouring of the concrete   6.  During the continuous concreting process, the temporary casing elements are progressively withdrawn whereby the concrete forms the pile shaft.

17. Figure 6:Micropile construction squence’s using casing

18. Figure 7: M icropile construction squences using casing

19. CHALLENGES COST SLOW & TIME CONSUMING RISKS

20. COST RM $150–350 /meter Price Depends on : Reinforcement Type Volume (φ) of hole Grouting Method (any post grouting) Location - Accessibility Length/Quantity of piles High Steel (up to 20% As/Ac) High Labour Cost – Low Prod Grout (NS) (+admixture) expensive Fabricate cage in-situ compared tomass production for precast RC pile Specialist technology expensive Few players in the market

21. SLOW & TIME COSUMING Although Drilling rate alone is high (e.g. up to 1’/min DTH thru granite) Adding/Dismantling of Rods manually Installation/Extract of casing time-consuming Manual in-situ fabrication of cage on-site Fixing of couplers, spacers, welding take time Manual mixing of cement grout High rig breakdown (mostly hydraulic) Estimation of soil / selection of drill bit difficult – slow down during drilling Figure 8

22. Risks Figure 9: Damage to public properties While maneuvering / setting up/ drilling . Figure 10:Damage to own equipment: Rod shears off &drop into hole .Rod/DTH gets stuck in-hole.

23. ADVANTAGES Micropiles are often used to underpin the existing structure where need of minimal vibration or noise is of prime importance. Micropiles can be easily laid where low head room is a constraint . Micropiles can be easily installed at any angle below the horizontal using the same equipment used for ground anchors and grouting projects . Do not require large access road or drilling platforms

24. Figure 11: Applications

25. APPLICATIONS Supporting New Loads in Congested Areas. Seismic Retrofit. Arresting Structural Settlement. Resisting Uplift/Dynamic Loads. Underpinning. Excavation Support in Confined Areas.

26. CONCLUSION Use of Micro piles is versatile in situ ground improvement technique and has been used very effectively in many stability problems. API pile system provides good compression performance in terms of lateral stability and vertical movements. Tension piles can be economically reinforced by a bars system. Micropile can be costly option to support lateral load and bending movement.

27. REFERENCE Armour, T, groneck , P, keeley , J and sharma , s. (2000). Micropile design and construction guidance implementation manual . US department and federal highway administration, FHWA-SA-97-070.

28. THANK YOU