a 25 m deep secant pile retaining shaft in sensitive clay
TRANSCRIPT
A 25 m Deep Secant Pile RetainingShaft in Sensitive Clay
Geotechnical Engineer Jørgen Johannessen, Norconsult ASNGM 2012, Copenhagen May 10th 2012
Sjakt 9 - Møtepunkt mellom jord og berg
Shaft S9
Kuba
Outlet tunnel at deepwater
Transportation by gravityfrom Kuba towardsBekkelaget; 5 km
Bekkelaget wastewatertreatment plant
Pipejacking……….Trenching………
Introduction
• Owner: City of Oslo, Water and Sewerage Works (VAV)• Costs and Project Duration
– Total costs 1.3 billion NOK (approx. 160 million EUR)– Planning started in 2005– Completion in 2014
• Norconsult's Role:– A large, and inter-disciplinary challenging project. – Design, all disciplines is being done by Norconsult AS:
Rock mechanicsCivil engineeringGeotechnical engineeringEnvironmental engineeringWater and wastewater engineering
Anleggsområdet
Rock tunnel towardsBekkelaget
Pipes arejacked/bored from Shaft S9
Sheet pile wall towardsMosseveien
Ground Conditions
Approx. 5 - 6 m of miscellanous fillmaterial on top of sensitive clay.
Undrained shear strength in theorder of 25-40 kPa.
Ground water assumed 2 - 4 m below ground surface.
Significant local variation in claysensitivity.
Secant pile wall details - plan view.
P
PS
S
S
Secant piles
Diameter 1080 mm, c/c 813 mm
33 primary piles 33 secondary piles
Lime-cement columns as ground stabilization
Sheet pile wall towards Mosseveien
Securing Mosseveien: 6 m long Sheet pile wall, anchored into theconcrete slab.
140 ton pile driver
Soft clay replaced bylight fill material in orderto maintain acceptablestability in the area.
Drilling Template to Assure AccurateInstallation of the Secant Piles.
”Barrel hoop” on the outsideof the template, in order to ensure contact between thepiles.
Cross sectionalview of the ”barrel hoop”
…Which later was replaced by a 70 tons backhoewith 20 m range
• Film av utgraving ved ca. 12 m dybde
18 m depth
A 9-tonner wasplaced at thecurrent level, causing significantloss of efficiency.
Lime columnswere so stiff at thebottom of the shaftthat they had to be chizzled.