Mike Turner Applied Geotechnical Engineering Micropiles – UK Trends Mike Turner Applied Geotechnical Engineering

Increasing load capacity 1970s & 80s : 200-300 kN (compression) [500 kN achievable] End 1980s : 500-600 kN common End 1990s : 1000-2000 kN

Diameters are also increasing 500kN : 125-160mm 1000kN : 190mm (typical) 2000kN: 240mm - For rock-socketed micropiles

Increasing load and diameter

Diameters are also increasing for micropiles in soils Because small rigs are more powerful 450mm diameter piles not uncommon with Klemm and Hutte-type rigs Blurring divisions between ‘piles’ and ‘micropiles’

Contiguous micropiled retaining walls Increasing use, for: Restricted sites: basements and city-centre redevelopments Using 140-220mm thick-walled steel tubes Supported by ground anchors or props

Long slender micropiles High slenderness ratios (length to diameter) 100:1 not uncommon 200:1 installed and load-tested 33 metres long

Long slender micropiles – working load and slenderness ratio

Long slender micropiles – typical working loads and pile lengths

Driven pipe piles G-piles in Sweden (& Northern Europe?) Dywidag-Systems just introduced systen into UK Driven ductile cast-iron pipe piles (Type TRM): 500-1100kN capacity 119-170mm OD

Chance-type piles Mechanical auger piles, based upon the Chance design Very useful on railway infrastructure and mobile phone tower installations ‘Screwfast’ piles

Ischebeck-type piles ‘Self-drilling’ piles and nails Paul Woodfield has more details

Dynamic load testing As an addition to static load testing Mike Turner has more details