Micropile Drill Rig

Overview

A micropile drill rig installs small-diameter, high-capacity foundation piles in places where ordinary piling cannot go. A micropile is a slender drilled and grouted pile, usually 100 to 300 mm across, reinforced with a steel bar or steel casing, that carries large loads through its grout-to-ground bond rather than through a wide base. Because the rig is compact and the pile is small, micropiles are the standard fix for underpinning settling buildings, adding capacity inside existing structures, and founding in restricted or low-headroom sites where access rules everything.

The rig is a small, articulated drill plus a grout plant. The Base Carrier gets it into tight spaces, the Drill Mast aims it, the Rotary Head drills, the Casing and Drill Tooling bores and holds the hole, the Flushing System cleans it, and the Grout Plant forms the pile.

How a micropile is built

The rig drills a cased hole to depth, usually advancing temporary casing with the bit so the hole stays open in loose or caving soil. Once at depth and cleaned, the reinforcement, a high-strength steel bar or the casing itself, is placed and the hole is filled with neat cement grout. The grout bonds the reinforcement to the surrounding ground over the bond length, and that bond is where the pile gets its capacity. As the grout is placed, the temporary casing is withdrawn, leaving a grouted, reinforced column. A single 200 mm micropile can carry several hundred kilonewtons, and groups of them replace much larger bored or driven piles where those will not fit.

Capacity can be raised by pressure grouting: instead of letting grout settle under gravity, the Grout Pump injects it under pressure so it permeates and grips the surrounding soil more tightly, which sharply increases the bond in granular ground.

Restricted access carrier

The defining feature of a micropile rig is that it fits where other equipment cannot. The Base Carrier is narrow enough to pass through standard doorways, and its Expanding Track undercarriage retracts for access then widens for stability once in position. The Outrigger legs level the rig on uneven floors and slabs. For work inside occupied buildings the Power Unit is often electric rather than diesel, so the rig runs without exhaust in an enclosed space.

Mast for low headroom

The Drill Mast is built for cramped underpinning work. A Telescoping Section section lets the mast shorten to fit under a low ceiling, then extend to drill the full pile. The Positioning Boom reaches the mast to pile positions tight against walls and footings, and the Tilt Cylinder sets the angle for vertical or raked piles. The Rod Guide keeps the rod and casing aligned as they enter the ground.

Cased drilling

Micropiles are usually drilled cased so the hole cannot collapse before grouting. The Rotary Head turns both the inner Drill Rod and the outer Temporary Casing together. At the tip, a Pilot Bit leads through the soil while a Ring Bit on the Casing Shoe reams the hole to casing diameter, so the casing follows the bit down. This keeps caving soil out of the hole and gives clean, full-diameter grout cover. The Head Gearbox supplies the high torque needed to turn casing through dense ground, and the Feed System pushes the string down and pulls it back to add sections through the Rod Clamp.

Flushing and grouting

The Flushing System clears cuttings up the casing annulus with air from the Air Compressor or water from the Flush Water Pump, and a Dust Shroud at the collar keeps spoil contained in basement work. Before grouting, the hole is flushed clean so the grout bonds to fresh ground. The Grout Plant then takes over: the Colloidal Mixer makes the dense neat cement grout micropiles use, and the Grout Pump places it down the casing, under pressure where higher capacity is wanted. A Pressure Sensor tracks grout pressure and the Pile Logger logs the volume placed.

Control and records

The Operator Controls and Logger system suits the cramped working space. A Radio Remote radio remote lets the operator stand clear of the mast in a confined area, the Drill Controller balances feed, rotation and flush for clean cased drilling, and the Depth Sensor tracks depth. The Pile Logger saves depth, drilling rate and grout volume for every pile, which the engineer uses to confirm each micropile met its design.

Variants and use

Micropile rigs range from compact electric machines for indoor underpinning to larger tracked rigs for high-capacity piles in open sites. They are used to underpin and add capacity to existing foundations, to found new structures in difficult or restricted ground, to resist seismic and uplift loads, and to stabilize slopes and abutments. Their value is access and precision: where a wide pile or a big rig will not fit, a group of slender micropiles drilled by a small rig carries the same load.