Micropiles are small-diameter (normally less than 300 mm) drilled and grouted friction pile that is usually reinforced (up to 20% AS/ AC), it can withstand axial and/or lateral loads. Micropiles are constructed by drilling the borehole, placing reinforcements, and grouting holes.
Here we will learn about micropiles, types of micropiles, advantages & disadvantages of micropiles.
Introduction to micropile:
A micropile is also known as a mini pile.
It is a drilled and grated non-displacement pile that is heavily reinforced and most of its weight is on high-capacity steel reinforcement.
Reinforcement and cement grout are the major components of the micropile.
Types of micropiles:
Classification based on the design application:
Case 1: Micropiles that are straight loaded, where the pile reinforcement resists many of the applied load.
Case 2: Micropiles elements restrict the internally reinforce the soil to a reinforced soil composite that prevents the applied load.
Classification based on the grating method:
Type A- Gravity grout:
Here grout is kept just below the head using sand-cement motors or clean cement.
Type B- Pressure through casings:
In this type, clear cement grout is kept within the gap as the short-lived steel casing is withdrawn.
Injection pressure varies from 0.5 to 1.0 MPa; stress is controlled to keep away from the fracture of the surrounding floor.
Type C- Single Global Post Grout:
This method is similar to gravity grout.
But before hardening the first grout, a sleeve is injected free of charge by a sleeve grout pipe at a stress of at least 1.0 MPa.
Type D- Multiple Repeatable Post Grout:
This course is similat type C with a 2.0 to 8.0-inch MPa pressure.
Method of Micropiles Installation:
1. Position and drilling of the first section of the drill casing.
2. While drilling, the drill casing is equipped with a drilling head fixed on a rod, oscillating in the soil.
3. As the drilling process progresses, the soil is removed from the borehole by the excavation method.
Additional sections of the casing are combined (jointed) to prevent the borehole from collapsing during drilling.
4. After reaching the design depth, the front of the borehole, drilling equipment, drilling fluid is removed from the bore by line action in the pile.
5. During the constant concreting process, the elements are gradually withdrawn, forming concrete piles.
Advantages of Micropiles:
- Micropiles are used to reduce the existing structure where the requirement of minimal vibration or noise is of major importance.
- They might be simply positioned where low headroom is difficult.
- Micro piles don’t require a big entry street or drilling platform.
- They might be simply installed at any angle horizontally using floor anchors and similar tools used for floor anchors and grouting project.
Disadvantages of Micropiles:
Higher cost as compared to other pilling systems.
micropiles vs helical piles:
|Helical piles is a solid square steel shaft, a round shaft open steel pile or a combination of both.
|Micropiles is a deep foundation constructed using high strength, small diameter steel casing, and negotiated bars.
|Helical piles, also known as helical piles or screw piles.
|Micropiles, also known as mini piles, pin piles, needle piles and root piles.
Use of micropiles:
1) Supporting new loads within the contested areas.
2) Seismic Retrofit.
3) To keep away from the structural settlement.
4) Resisting lift / dynamic load.
6) Excavation assists in confined areas.
Also read: Sheet Piles & Pile Caps
The use of micropiles is versatile in situ ground and has been very effectively in many stability problems, tension piles can be financially strengthened by the system once.
Micro piles might be a costly choice to support the lateral load and bending movement.