SHAFT SINKING BY GROUND FREEZING: ELY OUSE-ESSEX SCHEME

FOR THE SINKING OF SIX SHAFTS IN THE EAST ANGLIAN FENLANDS, GROUND FREEZING WAS ADOPTED AS THE SINGLE EXPENDIENT FOR TREATING A VARIED COMBINATION OF UNATTRACTIVE GROUND CONDITIONS. THE DECISION TO DO SO ON THE PERMANENT SHAFTS WAS TAKEN AT THE DESIGN STAGE AND THE METHOD WAS CHOSEN ALSO AT THE ALTERNATIVE WORKING SITES BY THE TENDERERS FOR THE SUBSEQUENT TUNNELLING CONTRACT. NOTWITHSTANDING SOME DIFFICULTIES, IT LED TO THE SATISFACTORY COMPLETION OF ALL THE SHAFTS. THEY WERE AN IMPORTANT FIRST STEP IN A SCHEME FOR THE BULK TRANSFER OF WATER, RIVER TO RIVER, FROM NORFOLK TO ESSEX. THAT SECTION OF THE TRANSMISSION LINK WHICH TRAVERSES THE FENS, BEING IN DIFFICULT COUNTRY FOR MAJOR PIPELINE WORK, LIES LESS EXPENSIVELY IN TUNNEL IN THE GAULT CLAY. THIS BED RUNS FROM ONE TO THREE HUNDRED FEET DEEP BELOW THE LOWER CHALKS AND UPPER GREENSAND WHICH ARE GENEROUS TO THE WATER SUPPLY UNDERTAKINGS OF THE REGION. THE CHALKS THEMSELVES ARE MASKED FOR THE MOST PART BY SUPERFICIAL DEPOSITS UP TO 50 FT THICK, CONSISTING OF PEAT, WHICH IS FARMED USING WIDE-TREAD TRACTORS, OR SANDS AND GRAVELS NORMALLY WORKED IN FLOODED PITS BY DRAGLINE EXCAVATORS. THE PAPER INDICATES SOME FACETS OF THE RELATION BETWEEN DESIGN REQUIREMENTS AND THE SPECIAL METHOD FOR CONSTRUCTION. THE EXECUTION OF THE WORKS IS DESCRIBED, TOGETHER WITH THE PROGRESS, AND CONSTRUCTION TECHNIQUES UNDER FREEZING CONDITIONS, INCLUDING THE SLIP-FORMING OF A NUMBER OF THE SHAFTS. THERE WERE A FEW GROUND FAILURES, NEVER IN A FROZEN SECTION, BUT WHICH COULD HAVE BEEN RELATED. THESE ARE CONSIDERED, TOGETHER WITH THEIR REMEDY AND THE STEPS TAKEN TO PREVENT THEIR RECURRENCE. INFORMATION CONCERNING GROUND HEAVE DUE TO FREEZING, A QUANTITATIVE ANALYSIS OF THE WORKS AND THEIR COST, AND A COMPREHENSIVE LIST OF SOME OF THE RELATED LITERATURE BY OTHERS CONCLUDES THE PAPER. /AUTHOR/