Micropiles – UK Trends Mike Turner Applied Geotechnical Engineering

Increasing load capacity 1970s & 80s : kN (compression) 1970s & 80s : kN (compression) [500 kN achievable] [500 kN achievable] End 1980s : kN common End 1980s : kN common End 1990s : kN End 1990s : kN

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

Increasing load and diameter

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

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

Long slender micropiles High slenderness ratios (length to diameter) High slenderness ratios (length to diameter) 100:1 not uncommon 100:1 not uncommon 200:1 installed and load-tested 200:1 installed and load-tested 33 metres long 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?) G-piles in Sweden (& Northern Europe?) Dywidag-Systems just introduced systen into UK Dywidag-Systems just introduced systen into UK Driven ductile cast-iron pipe piles (Type TRM): kN capacity mm OD Driven ductile cast-iron pipe piles (Type TRM): kN capacity mm OD

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

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

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