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6. Selected Case Studies
Pages 46-90

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From page 46...
... Although all of the 84 mined tunnel projects illustrated some problem or feature that might deserve discussion, the 9 cases selected best met the widest range of stated criteria. The projects represent only 6 of the 28 owners or agencies who provided information for the study.
From page 47...
... Neither the Loon Lake penstock shaft nor the Brunswick No. 3 mine shaft could yield the maximum amount of information to the parties involved in the planning for deep underground storage, because of their different needs and opportunities for subsurface investigations.
From page 48...
... Project Cost& Estimated $36,969,138 Bid $43,887,900 As Completed $44,877,854 (includes all extra payments) Mined Tunnel Construction Costs Estimated $13,035,444 Bid $21,045,650 General Contract Mods -$701,598 Subsurface Related Overruns $0 As Completed $20,344,052 Subsurface Investigation Costs $2,000,000 (plus or minus)
From page 49...
... . Primary support of steel ribs, rock bolts, and 3 stages of shotcrete.
From page 50...
... Prudence would dictate the use of a few oriented core holes to determine rock structure attitude and maybe some overcoring tests for quantifying and orienting locked-in stresses. It would not be unreasonable to consider a small pilot tunnel for detailed mapping and later access by bidders.
From page 51...
... obviously reassured bidders about conditions, minimized construction problems, and eliminated cost overruns, thereby paying for itself in the long run. The only easy way to make a tentative judgment on this is to look at the construction costs, which break down as follows: Mined Tunnel Total Contract Engineer's Estimate $13,035,444 $36,969,138 Low Bid 21,045,650 43,887,900 Contract Modifications -701,598 +989,954 Geology Related Claims 0 0 $20,344,052 $44,877,854 It is true that i f one compares the low bid amount with the final cost figures, there were no geology related overruns in the station chamber.
From page 52...
... • No amount of money spent on exploration can remove all construction uncertainty, so the owner and the geotechnical engineer must draw the line at some point. This project may be an exaaple of one where a line was drawn slightly beyond the bounds of cost effectiveness.
From page 53...
... Mined Tunnel Construction Costa Estimated $18,230,267 Bid $15,649,372 General Contract Mods $99,788 Subsurface Related overruns $9,217,999 As Completed $24,967,159 Subsurface Investigation Costa $98,150 pre-bid Summary of Site Geologya Recent alluvium and man-made fill overlying Pleistocene terrace deposits (fine and coarse grained sediments) overlying decomposed rock and schistose gneiss bed rock.
From page 54...
... De cision can be appealed within 30 days to owner's board of direc tors; board decision final unless question is one of law that results in litigation. Geotechnical data made part of contract documents& Boring logs (bound directly into the contract documents)
From page 55...
... In rock, blockiness and overbreak resulted in the use of steel ribs rather than the design support system of rock bolts and shotcrete. Operations and Maintenance& At present, problems caused by ground conditions are minimal.
From page 56...
... Analysis/Opinion& WMATA's C-4 contract provides examples of two caapletely different kinds of subsurface problema that led to complications during construction. The first, caused by a higher rock line than the contractor apparently had a right to expect, is extremely common wherever a mined tunnel impinges on top of bed rock.
From page 57...
... In the early 1970s, WHATA made its interpretive •subsurface investigation reports• available for reading by bidders, but disclaimed any responsibility for conclusions drawn therefrom. In spite of this disclaimer, the C-4 contractor did depend on the reports in putting together a bid and at least had access to an accurate assessment of actual ground conditions.
From page 58...
... Had there been such a report in the C-4 contract documents, it seeiiB likely that much misunderstanding and litigation would have been avoided. Aside from high rock and general rock conditions, a third and very minor C-4 problem is worth mentioning because it is symptomatic of the kind of occurrence that has proven more significant on other projects.
From page 59...
... Project Costa Estimated $49,587,227 Bid $42,266,620 As Completed $48,555,357 (includes all extra payments) Mined Tunnel Construction Costa Estimated $31,831,000 Bid $18,226,940 General Contract Mods $86,204 Subsurface Related overruns $4,718,311 As COmpleted $23,031,455 Subsurface Investigation Costa $49,775 pre-bid S...ary of Site Geology& Stiff to hard Cretaceous plastic clays and sandy clays and compact to very compact silty sands, with many intermixing& and interlayering& of the three basic strata.
From page 60...
... De cision can be appealed within 30 days to owner's board of direc tors~ board decision final unless question is one of law. Geotechnical data aade part of contract docuaentaa Boring logs (bound directly into the contract drawings)
From page 61...
... The boring logs, which are presumably mostly factual, were bound into the contract drawings and the bidders were responsible for the information contained therein. However, the subsurface investigation reports contained much interpretive data for which the owner did not wish to be held completely responsible.
From page 62...
... Although one might quarrel with the lack of pWilping tests, the fact is that the owner's geotechnical engineer was able to use the available data to describe the wet, single-size sand lenses that would be difficult to dewater because of the intervening clay layers. Had the contractor relied on that information -- which he might have done if the subsurface investigation reports were considered full-fledged contract documents -- he might have based his bid on more stringent dewatering and/ or a better breasting system, thereby avoiding some very costly delays from bogged down shields.
From page 63...
... Possibly more important than the above changes in site investigation techniques is WMATA's relatively recent decision to upgrade the subsurface investigation reports from their status of information documents to full-fledged contract documents. Of course, the change came about because of many episodes of litigation on many projects, but the G-2 case history of flowing sand is a perfect example of why such a 63
From page 64...
... The decision to upgrade the statue of the reports may make the owner more certainly liable for mistakes in interpretive information. However, it should also create much more consistency in the assumptions made by bidders and · will definitely curtail much timeconsuming argwaent over whether a contractor ia to rely on all of the information provided.
From page 65...
... Mined Tunnel Construction Costa Estimated $5,834,261 (excluding profit) Bid $7,246,650 Extra Support Contract Mods $1,279,674 Subsurface Related OVerruns $0 As Completed $8,526,324 Subeurface Investigation Costa $1,452,026 pre-bid (excluding professional services)
From page 66...
... Changed-conditions clauaea Yes Construction Methoch Top heading and bench and drill-and-blast, with drilling jumbo, wheel muckers, rebar jumbo, and lining form. Primary support of steel sets, rock bolts, shotcrete, and concrete wall plate.
From page 67...
... tunnel had a geophysical study, thorough surface mapping, 54 boreholes of various types, and a pilot tunnel with a geologic report on the pilot tunnel. With this information, the contractor was prepared for any conditions and was able to complete on time and with no claims for differing site conditions.
From page 68...
... Project Coati Estimated $53,804,499 Bid $58,256,638 As Completed $65,613,963 Mined Tunnel Construction Costa Estimated $49,627,190 Bid $47,268,690 General Contract Mods $1,000,367 Subsurface Related overruns $5,441,077 As Completed $53,710,134 Subsurface Investigation Coat1 $1,238,000 estimated pre-bid SUIIIIIary of Site Geologya Volcanic flows in mass landscape of the Buckskin Mountains are dominated by andesite interlayered with tuff and agglomerate, which have been intruded by andesite dikes and laccoliths. The andesite is hard, dense, and blocky; it is situated in rather flatlying flows and ranges from 10 to 100 ft thick.
From page 69...
... Further appeal to Board of Contract Appeals, Department of the Interior. Geotechnical data ude part of contract docu.ntaa Preconstruc tion geologic report; surface geologic map, profile, and boring logs included in contract drawings.
From page 70...
... It is quite possible that a mechanical rock core log (i.e., discontinuity spacing determination, piece counts, etc.) of the drill holes could have provided a forewarning of thia loose joint problem.
From page 71...
... The preconstruction geologic study missed locating two fault zones encountered during excavation. 'l'he boring logs gave no indication of open joints or blocky rock conditions.
From page 72...
... Project Costa Estimated $35,494,430 Bid $34,681,703 As Completed $34,611,894 estimated Mined Tunnel Construction Costa Estimated $32,951,695 Bid $27,908,413 Subsurface Related Underruns $1,737,425 Subsurface Related overruns $1,380,086 As Completed $27,551,074 Subsurface Investigation eo.ta Not available Suaary of Site Geologya Alternating strata of limestone, sandstone, siltstone, and shale, dipping at 18 degrees in a regional hOIDOCline. Bedding ranging from thin to thick, with some of the lilllestone being massive.
From page 73...
... Primary support of steel ribs and rock bolts. Permanent support of unreinforced cast-in-place concrete (16 in.)
From page 74...
... Rather, its success can be attributed to the following: • The contractor developed efficient means of handling difficult ground conditions such as heavy water inflows, squeeze, and extensive overbreak/fallout. • Some problems were less severe than possible (e.g., geologic conditions were present for potentially even greater water inflows)
From page 75...
... diameter. Project CO.ta Estimated $42,321,830 Bid $33,788,800 As Completed $48,316,215 Mined Tunnel Construction Coati Estimated $41,341,900 Bid $32,848,600 Extra Support Contract Mods $11,369,256 Subsurface Related Claims $2,500,000 As Completed $46,717,856 Subeurface Investigation Coati $2,000,000 estimated pre-bid S.-ary of Site Geology1 Mostly highly fractured, locally altered, strongly crushed and sheared Tejon Lookout granite with roof pendants of metalimestone and hornfels.
From page 76...
... There was general slow progress at 29 locations where faults, granu lar and clayey altered granitic materials, large water inflows, running ground, and heavy ground loads were encountered. OVerall conditions were so difficult that the contractor mobilized a shield and substituted steel rib and steel liner plate for the steel rib and rock bolt initial support called for in the contract documents.
From page 77...
... The general condition is sUllied up in the statement from the •as-built• geology report that faults were 11apped at an average spacing of ll ft along the entire tunnel length. The seriousness of the condition was highlighted early by the low bidder's opting for soft-ground shields and continuous steel liner plate in what was supposed to be a rock tunnel that could presumably be supported initially with steel ribs and rock bolts, according to the contract documents.
From page 78...
... He may have been very surprised later by the ultimate project cost because much of the money above and beyond the bid price went for an extensive number of unit priced steel ribs in addition to the agreed upon heavy steel liner plate. Nevertheless, the quick admission that previously presumed hard ground deserved some soft-ground treatment indicates that the owner had doubts about either his subsurface data or his interpretation of them.
From page 79...
... diameter. Project eo.ta Estimated $55,733,229 Bid $61,862,009 Mined Tunnel Construction Costa Estimated $50,242,060 Bid $52,283,285 General Contract Mods $ -80,168 Subsurface Related OVerruns $935,999 As COmpleted $53,139,116 Site Investigation eo.ta $74,000 pre-bid (post award costs not available)
From page 80...
... Primary support of heavy steel liner plate. Permanent support of cast-in-place concrete.
From page 81...
... The major probleiiS of a geologic nature that affected construction of the tunnel were as followss • An excessive number of large boulders, many more than indicated by the boring logs, and sometimes occurring as large pockets with little or no fines. In one 400-ft length of tunnel, 166 large boulders were encountered and mined through.
From page 82...
... tractors looking for work are notoriously (but not always wisely) optimistic about solving •field• problems.
From page 83...
... . Project Costa Estimated $20,592,461 Bid $18,366,780 As Completed $42,414,628 Mined Tunnel Construction eo.ta Estimated $7,166,097 Bid $5,990,163 General Contract Mods $998,977 Subsurface Related overruns $16,300,000 As Completed $23,289,140 Subsurface Investigation Costa Not available s.-ary of Site Geologya Generally fresh, hard and massive amphibolite with some granitic gneissic zones.
From page 84...
... Bncountereda Conatructiona Extensive overbreak during excavation of benches near where adjacent tunnels enter the powerhouse. This required large quantities of rock bolts, steel ribs, and concrete backfill for stabilization.
From page 85...
... Such zones did indeed occur, and the areas of poor rock caused severe shattering and over break in bench areas near intersections between the chamber and adjacent tunnels. The condition required unexpectedly large amounts of concrete backfill as well as additional rock bolts and steel sets for support of the excavation.
From page 86...
... Indications are that this step was not adequately pursued on the Edward Hyatt project, so there may have been a shortcc:aing in the final, interpretive stage, of the site investigation.
From page 87...
... diameter. Project COsta Estimated $10,207,109 Bid $10,361,071 As Completed $10,113,904 Mined Shaft Conatruction COsta Estimated $6,977,207 Bid $7,419,705 General Contract Mods $ -171,388 Subsurface Related OVerruns $0 As Completed $7,248,317 Subsurface Investigation COsta Not available S.-ary of Site Geology• overburden consisting of 10 to 40 ft of windblown sand (approximately 20 ft at shaft location)
From page 88...
... Cbanged-conclitiona clauaea Yes Construction Method: Downhole drilling using drill derrick and hoist with 12-ft diameter rolling cutterhead. Permanent support of steel liner in upper 850 ft1 no final lining at greater depths, but with rock bolts and wire mesh for support as required.
From page 89...
... It should be noted that the local geology and hydrology were well known to the construction manager; therefore, with the type of contract, full details including geotechnical data were not essential to the drilling subcontractor. The construction method was blind shaft rotary drilling with cuttings removal accomplished by a dual string circulation system.
From page 90...
... At the WIPP site, potassium ion was added to the drilling fluid to inhibit wetting of the shales, and the dual string technique minimized the exposure time. The project was completed ahead of schedule and under budget -- a tribute to good geotechnical data, good engineering, and good estimating.


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