The micropile, also known as root pile, is a small diameter cast-in-situ bored pile formed by cement grout injection and subsequently equipped with lost, steel reinforcement element (bar, steel tube, H-type profile…). The boring is performed with compressed air or by means of a supporting drilling fluid (water, cement grout, bentonite).
Installation process in accordance with the requirements of the “NBN EN 14199 : Micro piles” standard
1. Placement of the first section of the steel drill casing equipped with the drill bit fixed on a rod. Start of the boring process under fluid flushed inside the drill casing.
2. Coupling of the additional casing segments and continued boring under supporting drilling fluid until the required depth has been reached
3. After reaching the design depth, replacement of the drilling fluid by the primary grout
Injection of cement grout under pressure. The micropile is formed by single stage grouting under the so-called “unitary and global” grouting under low pressure or I.G.U. mode (« Injection Globale et Unitaire ») or the micropile is formed by multi-step grouting under the so-called “repetitive and selective” grouting under high pressure or I.R.S. mode (“Injection Répétitive et Sélective”).
4. Completed micropile
• Vibration-free work in specific working conditions: restricted access or low headroom situations
• Foundations of new constructions, strengthening foundations of existing structures or underpinning works of building foundations.
• Drilling through obstacles
• Dealing with compression and / or tension loads at large angles (inclined loads: incline of > 20° to the vertical)
• Removal of excavated soil and drilling spoil from the job site is required
• A stable, dry and flat work platform is required
• Maximum of flexibility in use and restricted rig dimensions: execution with small to very small machines
• Execution with electrical machines possible (no emission of waste combustion gases).
• Diameter up to 250 mm (exceptionally 325 mm)
• The bearing capacity is derived exclusively from skin friction
• Allowable bearing capacity up to 1.000 kN
• Possibility to realize inclined micropiles
• Possibility to form a pile wall by means of single micropiles or tangent micropiles
• The load-bearing component allows for resisting tensile and/or compressive loads along its axis. The load to be accommodated / absorbed is transmitted to this component by means of a load-distributing device; e.g. a bearing plate with bearing and counter nuts.
• For drilled micropiles with casing, the embedded elements are placed inside the drilling tubes which are recovered afterwards (so-called ‘tube-tige’ method).