Construction World December 2021

SPECIALIST CONTRACTORS OR SUPPLIERS

NORTHFIELDS BUSINESS PARK GROUND IMPROVEMENT

T he project i s located in Northfields Bus iness and Logi st ics Park , Durban North, on which numerous ‘mega’ warehouse structures are planned. The s i te compri ses large cut to fi l l earthworks plat forms which pose s igni ficant chal lenges for the foundat ion des ign, part icularly in areas where fi l ls in excess of 25 m are present . Instead of convent ional pi led foundat ions , Kel ler ’s foundat ion solut ion ut i l i ses stone columns to improve the ground to al low s imple shal low foundat ions to be used. For the various plat forms , over 3 500 no. 800 mm diameter stone columns wi th depths between 5 and 15 m were instal led. Stone columns proved to be a cost ef fect ive, envi ronmental ly f riendly solut ion for the development . Stone columns were instal led us ing the Kel ler Vibrocat . Gravel i s fed through a pipe to the bottom of the column and compacted by the Kel ler depth vibrator. The technique al lows gravel to be compacted ef ficient ly wi thout large consumpt ions of water. Stone columns wi th diameter up to 1 m and depths up to 18 m can be instal led us ing thi s technique. Af ter complet ion, the s i te i s clean wi th no obstruct ions (protruding rebar, concrete pi le) for the subsequent contractor. In addi t ion, the s i te i s immediately avai lable for the main contractor to commence subsequent civi l works . Kel ler invi ted consul t ing engineers to have fi rst- hand experience of the vibro stone column instal lat ion process . Since the solut ion i s relat ively new in South Af rica, i t i s important that these solut ion and ski l ls are transferred to local engineers for future appl icat ion. Stone columns were used to improve the exi st ing ground to al low shal low foundat ions to be used to support the warehouse structure. The ground i s des igned as a mass wi th improved shear strength and st i f fness propert ies . As the solut ion i s aimed to improve the ground as a mass , i t al lows des igners/contractors the flexibi l i ty to adjust pos i t ion, s i ze of foot ings eas i ly i f requi red. The use of stone columns s igni ficant ly reduces carbon emi ss ions for the project . Compared to

convent ional pi led foundat ions , stone columns use no cement , a primar y contributor to carbon emi ss ion in the construct ion industr y. The resul t i s emi ss ion of around 750 t CO 2 for the project , a reduct ion of around 80-90% compared to tradi t ional pi led foundat ions . Bes ides the program, cost and envi ronmental benefi ts , stone columns also provide s igni ficant heal th and safety advantages . The instal lat ion of stone columns does not requi re people working close to rigs , dramat ical ly reducing the probabi l i ty of accidents . The stone columns were completed over a period of around s ix months , around one thi rd of the t ime requi red to instal l pi le foundat ions , and around 40% of the cost . Al l work was carried out in accordance wi th Kel ler ’s ISO 9001:2015 accredi tat ion. Apart f rom the benefi ts on H&S ri sk , stone columns (and ground improvement in general ) are solut ions wi th low des ign and construct ion ri sk . Stone columns improve the propert ies of the soi l mass and hence smal l deviat ions f rom des ign requi rements would have l i tt le impact on the per formance of the ground improvement . The project was original ly des igned on pi led foundat ions , and subsequent ly revi sed to ground improvement wi th stone columns . The outcome i s a cost effective, environmentally friendly foundation solution completed in a significantly shorter program. 

PROJECT INFORMATION

• Company entering: Keller Geotechnics SA • Project start date: 24 November 2020 • Project end date: 27 September 2021 • Client: JT Ross Properties • Main Contractor: Keller & WBHO • Architect: Ries Shaw Architects • Principal Agent: JT Ross • Project Manager: Vigar & Associates

46 20 th Best Project Awards 2021