British Columbia Mine Reclamation Symposia

Erosion control on a steep slope pipeline crossing of the Sikanni Chief River, northern British Columbia Bowes, A. G. 1988

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th  Proceedings of the 12 Annual British Columbia Mine Reclamation Symposium in Vernon, BC, 1988. The Technical and Research Committee on Reclamation  113  EROSION CONTROL ON A STEEP SLOPE PIPELINE CROSSING OF THE SIKANNI CHIEF RIVER NORTHERN BRITISH COLUMBIA  A.G. BOWES, A.Sc.T. SENIOR SUPERVISOR, PIPELINE PROJECTS  WESTCOAST ENERGY INC. 1333 WEST GEORGIA STREET VANCOUVER, BRITISH COLUMBIA V6E 3K9  th  Proceedings of the 12 Annual British Columbia Mine Reclamation Symposium in Vernon, BC, 1988. The Technical and Research Committee on Reclamation  114  WESTCOAST REPLACED THE  30” NATURAL GAS PIPELINE ACROSS THE SIKANNI  CHIEF RIVER IN NORTHERN BRITISH COLUMBIA DURING THE SUMMER AND  1987. THE RUGGED TERRAIN AT THE SITE REQUIRED THAT SOME UNUSUAL TECHNIQUES BE USED TO INSTALL THE PIPE, AND TO GROOM AND SEED THE RIGHT-OF-WAY FOLLOWING PIPE INSTALLATION TO ENSURE EARLY FALL OF  THAT THE PIPELINE WOULD REMAIN SECURE AND THE STEEP SLOPE WOULD NOT ERODE. THE SIKANNI CHIEF RIVER, A TRIBUTARY OF THE LIARD SYSTEM, FLOWS THROUGH A DEEP VALLEY CUT INTO HORIZONTALLY-BEDDED SHALES AND SANDSTONES TYPICAL OF THAT PORTION OF BRITISH COLUMBIA. FOR LONG STRETCHES OF THE RIVER , THE NATURAL RIVER BANK HAS SLOPES IN  45°; THERE ARE NO CROSSING SITES AVAILABLE THAT OFFER GENTLER APPROACH SLOPES. THE EXISTING FORT NELSON PIPELINE ON THE EXCESS OF  NORTH SLOPE OF THE SLKANNI CHIEF RLVER CROSSING LIES IN AN OPEN  (45°) SLOPE. IN THE 23 YEARS THAT THIS PIPELINE HAS BEEN IN SERVICE, EROSION HAS WEAKENED THE GROUND SUPPORT OF THIS PIPE SECTION. THE PURPOSE OF THE PROJECT WAS TO RELOCATE THE CROSSING OF THE SLKANNI CHIEF RLVER- TO A POINT TRENCH BECAUSE OF THE STEEP  UPSTREAM WHERE A LESS PRECARIOUS AND STABLE SLOPE HAS BEEN LOCATED AND THEREBY PROVIDE GREATER PROTECTION TO THE PIPELINE. IN  1987 THE DECISION WAS MADE TO CONSTRUCT A MORE STABLE REPLACEMENT PIPELINE AT A POINT UPSTREAM FROM THE ORIGINAL CROSSING.  th  Proceedings of the 12 Annual British Columbia Mine Reclamation Symposium in Vernon, BC, 1988. The Technical and Research Committee on Reclamation  115  FOLLOWING THE ISSUANCE OF DETAILED DRAWINGS AND SPECIFICATIONS, THE GENERAL CONTRACT WAS AWARDED TO MAJESTIC CONTRACTORS LTD. OF EDMONTON . WESTCOAST INSPECTION STAFF WERE PRESENT ON SITE THROUGHOUT THE PROJECT.  THE CONTRACTOR BEGAN MOBILIZATION IN MID-JULY COMPLETED THE PROJECT BY OCTOBER  1987.  1987  CONSTRUCTION WITHIN THE  RIVER CHANNEL ITSELF WAS CONFINED TO THE PERIOD JULY  15 WHITEFISH). SEPTEMBER  AND HAD  BECAUSE OF FISHERIES CONCERNS  (DOLLY  15  TO  VARDEN AND  SOME CLEARING OF THE RIGHT-OF-WAY ON THE NORTHERN PLATEAU SECTION REQUIRED THE CLOSE LIAISON OF THE CONTRACTOR WITH PROVINCIAL FORESTRY OFFICIALS. ACCESS TO THE SITE WAS AVAILABLE ONLY ON THE NORTH SIDE OF THE RIVER. HELICOPTERS WERE FREQUENTLY USED TO TRANSPORT WORKERS TO AND FROM THE WORK SITE LARGELY BECAUSE WET WEATHER CONDITIONS MADE THE ROADS IMPASSABLE THROUGHOUT MUCH OF THE WORK PERIOD.  AT A LOCATION UPSTREAM FROM THE ORIGINAL CROSSING, THE NEW PIPELINE RIGHT-OF-WAY WAS PREPARED BY REDUCING THE GRADE TO A  34°  SLOPE. THE WORK PROCEEDED FROM THE TOP OF THE SLOPE IN A SERIES OF BENCHES, THEN THE RIGHT-OF-WAY WAS GRADED BACK TO THE DESIRED ANGLE CUBIC  (AS  SHOWN IN THE RIVER CROSSING PROFILE). SOME  80 270  th  Proceedings of the 12 Annual British Columbia Mine Reclamation Symposium in Vernon, BC, 1988. The Technical and Research Committee on Reclamation  116  METRES OF ROCK AND OVERBURDEN WERE MOVED TO PREPARE THE RIGHT-OFWAY. THE SLOPE GRADE WAS APPROXIMATELY 70% RIPPABLE ROCK AND 30% REQUIRED BLASTING, HENCE THIS PART OF THE WORK WAS NOT UNDULY AFFECTED BY THE HEAVY RAINS. THE RIVER CROSSING SECTION WAS GRAVEL, AND SUPPORTED EQUIPMENT WITH NO PROBLEMS.  THE SOFT SHALE ROCK FACES ON EACH SIDE OF THE RIGHT-OF-WAY WERE A CONTINUING SAFETY PROBLEM THROUGHOUT THE PROJECT. INITIALLY THE CONTRACTOR USED A SIDE SLOPE CUT OF 70°, BUT ROCK FALLS OCCURRED FREQUENTLY, AND IT WAS NECESSARY TO GRADE BACK THE SLOPES TO AN ANGLE OF 50°± WHICH APPEARED TO BE THE ANGLE OF REPOSE. HEAVY RAINS DURING THE CONSTRUCTION PERIOD ADDED TO THE SLOPE INSTABILITY PROBLEMS. A CONSTANT PROGRAM OF SCALING WAS MAINTAINED TO ENSURE THE SAFETY OF WORKERS, AND NO INJURIES OCCURRED.  th  Proceedings of the 12 Annual British Columbia Mine Reclamation Symposium in Vernon, BC, 1988. The Technical and Research Committee on Reclamation  117  A TRENCH FOR THE PIPE WAS THEN EXCAVATED UP THE SLOPE; THE PIPE ON  "STOVE PIPE" METHOD. A BOTTOM SLED CONSISTING OF A SPLIT SLEEVE SUPPORT ON TWO 4" PIPE RUNNERS WAS ATTACHED TO EACH DOUBLE JOINT. A JOINTING STATION WAS SET UP AT THE TOP OF THE SLOPE AT WHICH WELDING, RADIOGRAPHY AND WRAPPING WAS COMPLETED BEFORE PIPE WAS SLID DOWN THE SLOPE. THE SLEDS WERE LEFT IN PLACE ON THE PIPE. THIS WAS THE FIRST TIME SUCH AN OPERATION HAS BEEN USED, AND IT WAS VERY SUCCESSFUL. THE EXTERNAL COATING OF THE PIPE CONSISTED OF FUSIONBONDED EPOXY WITH HAND-WRAPPING BEING DONE, USING POLYKEN TAPE. THE 30" O.D. X .433" W.T. PIPE USED ON THE NORTH SLOPE OF THE CROSSING WAS COATED WITH 1" OF CONCRETE. THE 30" O.D. X .362" W.T. PIPE USED ON THE RIVER SECTION WAS COATED WITH 5" OF CONCRETE. THE NORTH SLOPE WAS INSTALLED USING THE  TO CONSTRUCT THE RIVER SECTION, PIPE AND ALL OTHER MATERIALS WERE TAKEN DOWN THE STEEP SLOPE BY TRUCK. FOR THIS OPERATION, A PIPE TRUCK CARRYING THREE SECTIONS OF PIPE WAS CABLED TO A D9 TRACTOR AT THE TOP OF THE SLOPE, AND THE LOAD WAS THEN CAREFULLY LOWERED TO THE VALLEY BOTTOM. WINCHES AND SAFETY CABLES WERE ALSO USED BY INDIVIDUAL WORKERS TO ASCEND AND DESCEND THE SLOPES. ALL OTHER EQUIPMENT DESCENDED TO THE BOTTOM IN THIS MANNER. NO ACCIDENTS WERE RECORDED ON THE PROJECT.  AFTER THE PIPE WAS PLACED IM THE TRENCH , POLYURETHANE FOAM BREAKERS WERE CONSTRUCTED AT 20 METRE INTERVALS ACROSS THE TRENCH.  th  Proceedings of the 12 Annual British Columbia Mine Reclamation Symposium in Vernon, BC, 1988. The Technical and Research Committee on Reclamation  118  THE PRIMARY PURPOSE OF THE BREAKERS IS TO PREVENT WATER FROM FLOWING DOWNSLOPE ALONG THE PIPE AND ERODING THE PIPE SUPPORT. SECONDLY, THE BREAKERS ANCHOR THE PIPE TO THE HILLSIDE AND PREVENT LATERAL PIPE MOVEMENT. SPRAYED-IN-PLACE RIGID POLYURETHANE FOAM DITCH BREAKERS HAVE BEEN USED SUCCESSFULLY IN THE PIPELINE INDUSTRY FOR SEVERAL YEARS. THE TECHNIQUE IS PARTICULARLY VALUABLE FOR DIFFICULT SLOPES SUCH AS THE SIKANNI CHIEF RIVER CROSSING. IT IS ALSO USED AS ROCK SHIELD IN  ROCKY  TERRAIN.  THE  FOAM  ADHERES  TO  THE  PIPE  AND  HAS  EXCELLENT COMPRESSIVE STRENGTH TO SUPPORT THE PIPELINE. THE FOAM MATERIAL IS RESISTANT TO EROSION AND MOST CHEMICALS, AND DOES NOT DECOMPOSE WHEN BURIED IN THE SOIL. IT IS ALSO MORE ECONOMICAL AND CONVENIENT TO USE ON A STEEP SLOPE THAN THE CONVENTIONAL  METHOD  USING  SANDBAGS,  WHICH  IS  VERY  LABOUR-  INTENSIVE.  POLYURETHANE FOAM IS A MIXTURE OF TWO CHEMICALS: ISOCYANATE  100  901. WHEN MIXED AND SPRAYED, THE CHEMICALS EXPAND TO APPROXIMATELY 3 TIMES THEIR ORIGINAL VOLUME. THE FOAM IS APPLIED WITH SPRAY EQUIPMENT; ONE FOAM UNIT AND A TWO-MAN CREW IS ADEQUATE FOR A CONSTRUCTION PROJECT SUCH AS THIS . THE MATERIAL CAN BE PUMPED SOME DISTANCE FROM THE FOAM UNIT. FOR THE SLKANNI PROJECT, AND RESIN  ONE UNIT AT THE TOP OF THE SLOPE WAS ADEQUATE TO CONSTRUCT BREAKERS ALONG THE  380 M LONG HILLSIDE.  th  Proceedings of the 12 Annual British Columbia Mine Reclamation Symposium in Vernon, BC, 1988. The Technical and Research Committee on Reclamation  119  FOAM BREAKERS SHOULD BE INSTALLED BY EXPERIENCED CREWS USING SUITABLE PROTECTIVE CLOTHING AND EYE PROTECTION. IF  PROPERLY  HANDLED,  THE  MATERIALS  DO  NOT  PRESENT  A  SIGNIFICANT HEALTH HAZARD. THE FOAMING REACTION GENERATES CONSIDERABLE HEAT, AND CARE MUST BE TAKEN TO BUILD UP THE BREAKER GRADUALLY WITH THIN LAYERS OF FOAM TO PREVENT EXCESSIVE  HEAT  BUILDUP  AND  SUBSEQUENT  EXPLODING  OF  THE  BREAKER.  COST OF THE POLYURETHANE BREAKERS FOR THE SLKANNI RLVER PROJECT WERE AS FOLLOWS:  - A TOTAL OF 27 BREAKERS WERE INSTALLED - 383.2 CUBIC METRES OF FOAM MATERIAL WERE  UTILIZED  - COST PER CUBIC METRE OF FOAM = $255  - TOTAL - USING  = $97,716 = $306,500  COST OF FOAM BREAKERS SANDBAGS: THE COST  SAVING OF  $208,844.  THE SUBCONTRACTOR FOR THE FOAM INSTALLATION WAS PEDERO PLPE SUPPORT SYSTEMS LTD. OF EDMONTON. FOLLOWING INSTALLATION OF THE BREAKERS , THE PIPE TRENCH WAS BACK FILLED  AND THE ENTIRE RIGHT-OF-WAY GRADED AND CLEANED UP. SURFACE  BREAKERS, CONSISTING OF LOGS LINED WITH SANDBAGS, WERE ANCHORED TO  th  Proceedings of the 12 Annual British Columbia Mine Reclamation Symposium in Vernon, BC, 1988. The Technical and Research Committee on Reclamation  120  THE HILLSIDE WITH METAL RODS AND CONSTRUCTED AT AN ANGLE ACROSS THE SLOPE TO DEFLECT SURFACE RUNOFF TO THE LOW SIDE OF THE RIGHTOF-WAY.  THE AREA WAS HYDROSEEDED WITH GRASSES AND LEGUMES IN THE SPRING OF  1988. HYDROSEEDING WAS CARRIED OUT BY HELICOPTER, AN INFREQUENTLYUSED APPLICATION METHOD THAT WAS PARTICULARLY SUITED TO THE REMOTE SIKANNI RIVER SITE. THE TOTAL INSTALLATION COST OF THIS PROJECT WAS OR $941.55 PER FOOT.  $3,323,660  THE PROJECT WAS SUCCESSFUL DUE TO THE DETAILED GEOTECHNICAL WORK ON SITE PRIOR TO DESIGN, AND THE ADHERENCE TO DESIGN AND SPECIFICATIONS DURING INSTALLATION.  

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