Micropiles: Applications, Advantages, and Installation Methods

What Is Micropile?

Micro-piles/ mini-piles/ pin-piles/ root-piles are high-strength, durable, small-diameter generally 6-12”(150-300mm) steel casing pile or rib or bar and stuffed with a high strength cement grout used to bore hole. The bearing stratum is logged throughout installation drilling to assure that bearing capability is adequate.

Since small piles are smaller in diameter they will be advanced through the bottom at a better speed and may break through materials with larger ease than a caisson casing or a driven pile. The micropiles will penetrate any obstructions which will typically cause premature refusal whereas putting in mistreatment typical spile strategies.

Grouting is achieved by tremie grouting, pressure grouting throughout casing retraction, and tremie-grouting with post-grouting. Post-grouting among the bond length will increase resistance forces with close soils, so achieving larger capability. Micropile capacities in way over four hundred kips (1,780 KN). Micropiles to depths surpassing two hundred feet (60 m).

Micropiles usually adopts pressure grouting, the pile and the soil around the pile can be closely combined, the virtual soil and bearing layer under the pile tip are cemented and reinforced, and pressure grouting can significantly improve the mechanical properties of the soil around the pile and increase the bearing capacity of a single pile.

Common Reasons to Use This Micropile

1. To give structural support
2. To underpin your foundation
3. To transfer hundreds
4. To enhance mass stability

Common Uses of Micropile

1. Provide structural support
2. Underpin foundations
3. Enhance mass stability
4. Transfer loads

Advantages of Micropiles:

1. The main advantage of a micropile is its ability to figure in terribly engorged and low height areas and on any soil surface regardless of its sort.
2. Fast ballroom dancing installation even in environmentally-challenging conditions. They’re little and comparatively lightweight. they’re comparatively cheap.
3. Simultaneous drilling and grouting allow low overhead, restricted access installation. Micropiles are typically preferred to “H” piles attributable to overhead physical constraints.
4. Improves the bottom (densification)
5. Offers higher skin friction
6. Total single corrosion protection intentionally
7. The restricted vibration and noise cause very little disturbance.
8. Piling rigs may be low-emission or perhaps electrically driven.
9. They can be put in on the point of existing walls with restricted headroom and engorged website conditions.
10. They have a high load capability and a capability to resist compressive, tensile, and lateral masses.
11. Micro-piles can penetrate any surface.

Disadvantages of Micropiles:

1. If there aren’t any obstacles they’re longer overwhelming than a driven pile
2. Valuable
3. Water infill is often a problem

Micropile Vs Typical Pile:

Micropiles are engaged in any difficult conditions involving soil and rock. Micropiles are custom and applied for tough terrains and applications. Micropiles are used for rehabilitation. Micropiles penetrate any surface and might be put in even though an existing foundation creating it one of the simplest doable solutions for foundation rehabilitation and strengthening works.

Small piles are used for slope stabilization, hill stabilization, and different soil improvement and any kind of ground improvement works. Micro piles are employed in areas wherever geological formation is high, urban backfills, areas having floating boulders or different tough terrains that can’t even be accessed with a traditional pile. Used extensively within the rehabilitation of monuments, recent structures, sinking structures, etc altogether components of the globe.

Micropiles for Foundation Stabilization:

Certain soil conditions will obstruct installation and even thwart the advancement of conventional underpinning solutions. When such conditions exist, trained and grouted micropiles provide an economical, deep foundation possibility capable of penetrating obstructions connected among competent bedrock.

In compression applications, capability is achieved through finish bearing and conjointly skin friction on the interface of the grout column and therefore the bedrock.In tension applications, solely the skin friction contributes to the micropile capability.

Drilling Ways Adopted for Small Piles:

The foremost common ways adopted for drilling are:

1. Percussive Drilling used with a driving point/drill at an all-time low of the permanent casing is outlined as displacement technique whereas once the air is employed as a flushing medium. It is outlined as a non-displacement technique.
2. Rotary drilling uses air or water as a flushing medium for removing the trained materials from the excavation. The air jet or water pumped up through the drilling system exit at the drilling bit finish flushing out the cuttings.

What Are the Everyday Applications for a Micropile?

Micro-pile systems are most popular to support and stabilize buildings, bridges, highways, towers and alternative unreal structures, either as new foundations or remedial construction. Morever, they are used for underpinning and shoring applications because of their high load capability and versatile installation techniques.

How Will the Micropile Installation Method Work?

The first and foremost affair anyone would like to attempt, is to dig a cavernous hole with a tiny diameter. Once, house has been secured for the pile, lower that into the outlet and apply force to secure the pile. Then fill the outlet with a concrete grout concoction to keep everything in situ.

How Are Micropiles Installed?

Drilled into bedrock, micro-piles are bond to the rock socket wall for conveying a load. The casings of the minipiles are advanced as piles are trained into bedrock. Drill rod is withdrawn and the steel casing remains. On reaching the saturation level the drilling bit is withdrawn with casing left within the bore-hole. A reinforcement load bar is lowered into the casing.

Assign reinforcement with centralizer within the borehole, along with tremie grout & cement water blend. Cementitious grout along with pressure is fed into the minipile casing and rock socket. After Tremie grouting, perform a pressure grouting through preinstalled grouting tubes. The casings for the mini piles are heaved up to a high of bedrock, which permits bonding to the bar. Excess steel is cut from the superior of minipiles.

Types of Micropile:

Piles are generally categorized into 2 types:-

1. Displacement Piles
2. Replacement Piles

#1. Displacement Piles

• Displacement piles are driven or vibrated into the bottom, there by displacing the adjacent soil sideways during the inauguration.

#2. Replacement Piles

• Replacement piles are constructed within a formerly drilled borehole, thus restoring the excavated ground.

Micropiles as Per Based on Design:

Based on Design Application mini piles are categorized into 2 cases:-

Case 1:

Micro-pile elements, which are stuffed directly & where the pile reinforcement withstands the bulk of the applied load.

Case 2:

Micro-pile elements circumscribe and internally reinforce the soil to create a reinforced soil composite that withstands the applied load.

Grouting Methods Adopted in Micro Piles:

Grouts utilized for micro-piling comprise a blend of sand, cement, and water. The micro piles are categorized into 4 types based on the stratagem of grouting.

Type A Micropiles: Gravity Grout:

1. They use tremie grouting and through gravity head.
2. The grouting is started from the substratum and follows an identical tremie grouting procedure followed in conventional piles.

Type B Micropiles: Pressure Through Casing:

1. After performing the initial tremie grouting, pressure grouting is finished concomitantly with the lifting of the casing from the bond zone through a pre-installed tube.
2. 2^nd stage of grouting serves in amplifying grout soil bonding.
3. Neat cement grout is placed in to the cavity as the provisional steel casing is withdrawn.
4. Injection pressures range from 0.5 to 1.0 MPa.

Type C Micropiles: Single Global Post Grout:

1. Pressure grouting is followed by tremie grouting.
2. Then, a global injection grouting is performed through a pre-installed sleeve port pipe.
3. Before hardening of the primary grout, similar grout is injected once via a sleeve grout pipe at a pressure of a nadir of 1.0MPa.

Type D Micropiles: Multiple Repeatable Post Grout:

1. This method is a twin of Type C.
2. Primary grout is done under pressure and after coagulation, secondary grout is finished through installed sleeve ports.

Micropiles Cost