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6- Selected Case Studies The ten projects (nine mined tunnels and one shaft) presented in this section were selected because they represent problems or situations which the subcommittee feels it will be instructive to explore in de- tail. The case studies of the mined tunnel projects were chosen to match as many of the following criter ia as possible: Taken together, the projects should represent the widest possible range of basic problems encountered, as reflected under that subheading in the project abstract. (In fact, most of the selected cases will illustrate two or three major problem groups and twice as many subgroups.) The nine cases should represent at least several different tunnel purposes, such as water conveyance, power generation, rapid transit, etc. Each case must be based on a thoroughly researched study proj- ect. This eliminated, for example, those projects for which a follow-up interview with the owner was not carried out. ~ Each case must be based on a study project for which all con- struction has been completed. Each case must be based on a study project for which all lit- igation (if any) has been resolved. At least one of the cases should be based on a project with no significant construction problems and no subsurface-related cost over r uns . Although all of the 84 mined tunnel projects illustrated some prob- lem 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. Thus, it might appear that those six were singled out for particular criticism, but that would be a misconception. It is purely coincidence, and not perceived flaws in philosophy of design or site investigation, that caused the selected case studies to represent so few of the owners or agencies. In any case, limiting the number of projects selected for special examination necessarily restricted the set of owners and agen- cies . For the shaft case study, the choice was much more severely limited because only three deep shaft projects were studied. The subcommittee 46

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decided to use the Waste Isolation Pilot Plant (WIPP) project because it is comparable to the type of undertaking contemplated in the construc- tion of waste repositories requiring a number of deep shafts for access to chambers designed for storage of radioactive and other hazardous sub- stances. Neither the Loon Lake pens tack 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. There- fore, the WIPP project was selected as best meeting the criterion of ap- plicability to user needs. It should be noted that the costs presented in the case studies are as taken from bid tabulations and pay vouchers. The dollars represent values for the years in which they were obligated or paid, with no esca- lation factors applied . 47

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CASE STUDY NO. 1 Name of Project: MBTA Red Line Extension, Porter Square Station Purpose: Passenger station for subway system Location: Massachusetts (Cambridge) Construction Period: March 1980--June 1981 Site Investigation Period: 1976--1978 Size: Trainroom 490 ft long; 45 ft 7 in. high by 70 ft 6 in. wide. Crossover 68 ft long; 37 ft 1 in. high by 44 ft 2 in. wide. Project Cost: Estimated $36,969,138 Bid $43, 887, 900 As Completed $44,877,854 (includes all extra payments) Mined Tunnel Construction Cost: Estimated $13,035,444 Bid $21,045,650 General Contract Mods -$701,598 Subsurface Related Overruns $0 As Completed $20,344,052 Subsurface Investigation Cost: $2,000,000 {plus or minus) Summary of Site Geology: Predominantly fresh to slightly weathered, bedded argillite with a slight dip, and overlain by thin glacial till, marine clay, outwash sands, and miscellaneous surf icial till. Minor in- truded dikes of basalt and andesite. RQDs indicate generally fair to excellent quality, but two faults were identified in addition to fre- quent shears perpendicular to the station axis. Unconfined compressive strengths were 9,740 to 45,500 psi for argillite and 15,900 to 24,800 psi for igneous rocks. Joints and fractures, a source of stored water, were mostly tight but areas adjacent to intrus ive dikes likely to be more pervious. Depth of overburden ranged from 64 to 82 ft above tunnel crown (30 to 47 ft of rock cover above crown). Static water table at 15 to 20 ft below surface; no water inflow predicted. Design Criteria: Maximum total load of 8,800 psf for final lining; concentrated rock loads of 1,200 to 3,500 psf also used for other geome- tries. Water level at E1. 123 (60 ft above crown in trainroom and 48 ft above crown in crossover chamber). Contract Provisions: Type: Unit price per cubic yard of excavation and per unit of lining components (support steel and shotcrete). 48

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Stipulations: Schedule and/or time of completion: Total contract to be completed by 9/11/82. Definition of delay and suspension of work. Liquidated damages: $2,500 per calendar day of delay. Payment: Monthly; 5% retainage (may be eliminated after 50% comple- tion). Construction method: Drill-and-blast (4-stage scheme, modifiable by contractor). Restrictions: Work not permitted on weekends or holidays without approval. Surface hauling not allowed between 11:00 p.m. and 7:00 a.m.; route and disposal site specified. Monitoring required for blasting. Strict noise level control. Disputes resolution: Decision by owner's engineer. If agreement is reached, contractor reimbursed at cost plus 1%, 6%, or 10%, as determined by engineer. Recourse is appeal to director of con- struction, then a review board, then litigation. Geotechnical data made part of contract documents: "Geotechnical Interpretive Report" (available for purchase), which included cross sections and test data. Boring logs and pilot tunnel maps included in contract drawings. Core samples available for inspection by ap- pointment. Disclaimers: None with respect to owner-furnished information on subsurface conditions. Changed-conditions clause: Yes Construction Method: Drill-and-blast, 3-stage excavation (top head- ing, intermediate heading, and lower bench). Primary support of steel ribs, rock bolts, and 3 stages of shotcrete. Permanent support the same as primary support plus 4th stage of shotcrete (minimum total thickness of 15 ink. Conditions Encountered: Relatively good conditions, essentially as predicted and perhaps slightly better. The contract was modified to permit the contractor to change from a 4-stage to a 3-stage excavation scheme. Groundwater inflow of 42 gpm for two months, until underground reservoir drained. Problems Encountered: Construction: None of major consequence. There was a delay of perhaps three weeks when a fault was encountered in the portal. (This was early in the learning curve of perfecting the support system.) Operations and Maintenance: Groundwater flowing through the bed rock has sufficient concentration of CaCO3 to be considered cal- careous. There is evidence that the carbonates may be precipitating in open air, enough to begin clogging drainage systems over a period 49

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r lad of time . At this wr iting, it is not known how ser ious the problem may become. (The problem is well documented on several sections of the Washington Metro system.) Resolution of Assertions Re Subsurface Changes: No assertions were made with respect to subsurface changes. Analysis/Opinion: When planning for the Porter Square site investiga- tion was begun, just after the mid 1970s, there had been no previous ex- perience with design and construction of a large shallow chamber in the argillites around Boston. The INMATE system in Washington, D.C. , had been providing a record of experience since the late 1960s, but those shallow chambers were constructed in schists and gneisses of a complete- ly different geological regime. The MBTA geotechnical engineer appar- ently dec ided that a very great deal of information about the rock in his local area would have to be developed before attempting such excava- tions and therefore took a very conservative approach to the site inves- tigation. The resulting body of knowledge was quite impressive and was undoubtedly a major factor in the absence of cost overruns in the mined opening. Because the investigation seems to have been extremely suc- cessful in achieving its primary purpose, cost effectiveness is the only aspect of the program that is legitimately open to debate. Shallow rock chambers are generally regarded as some of the more critical of the civil engineering projects because of the excavation spans involved, the probability of closely spaced discontinuities (and perhaps intense weathering) so near the bed rock surface, and the general looseness of rock blocks because gravity induced stresses are too low to keep them pressed firmly together. An absolute minimum site investigation for such construction would certainly include a generous number of boreholes with rock coring, lab testing to determine strength, hardness, etc., and borehole water level and permeability tests. 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. Perhaps in addition to or as a substitute for some of the above, one might consider pumping tests, blast vibration tests, or the construction of a test shaft. The interesting thing about the Porter Square investigation is that it encompassed all of the above techniques of rock and soil exploration. Although some of the tabulated costs are estimates or bid prices rather than final recorded figures, it appears that the total amount spent for the complete program was in the neighborhood of $2 million. With the final cost of the mined station chamber being about $20.3 million, a best guess is that the owner's exploration costs were about 9.8 percent of the construction costs {ignoring the fact that exploration dollars had a mid-to-late 1970s value while construction dollars had an early 1980s value). Still another way of looking at the matter is to note that the owner originally estimated the cost of the mined opening at slightly more than $13 million. Hence, exploration costs were perhaps 15.3 percent of the presumed construction costs (again ignoring the ef- fects of inflation). 50

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It is logical to ask if the scope of the site investigation could not have been reduced without detracting too much from the data base de- veloped for designers and bidders. Because the pilot tunnel {excavation bid price of $1,683,800) took the lion's share of the exploration bud- get, a closer look at its cost effectiveness seems warranted. Sized at 12 ft by 12 ft. this opening certainly did its job of providing an op- portunity for measuring water infiltration, confirming rock joint pat- terns and conditions, and demonstrating how certain joint sets would control overbreak. It also was instrumental in locating two small faults and two minor igneous dikes that had been missed by core bor- ings. However, water infiltration had already been measured with accu- racy in an inspection shaft (excavation bid price of $69,070) that was 36 in. in diameter and 111.5 ft deep. Assuming the pilot tunnel was truly needed to confirm the other geologic features, it could have been done just as easily in a smaller tunnel, perhaps 6 ft wide by 8 ft high. The smaller s ize surely would have cut the cost of the opening and would not have provided so much opportunity for the rock in the crown to loosen pr for to opening up the full station chamber. The argument that only a large pilot tunnel easily permits the early installation of rock dowels for station excavation support may be a case of circular reason- ing because too large an opening can be the very cause for needing such dowels in the first place. Indeed, a small construction problem did de- velop at Porter Square because blasting for the pilot tunnel damaged the integrity of the rock enough to require shotcreting of the pilot tunnel roof ahead of the advancing station chamber top heading in order to keep down overbreak. One may say that this is all quibbling and the only impor tent fact is that the pilot tunnel (in conjunction with the other elements of the s ite investigation) obviously reassured bidders about conditions, mini- mized construction problems, and eliminated cost overruns, thereby pay- ing for itself in the long run. The only easy way to make a tentative judgment on this is to look at the construction costs, whi ch 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 Modif ications -701, 598 +989, 954 Geology Related Claims 0 $20,344,052 o $44,877,854 It is true that if one compares the low bid amount with the final cost figures, there were no geology related overruns in the station chamber. There was even an apparent savings, the exact reason for which was never made clear to the subcommittee interviewer. However, the bot- tom line is that the low bid and the final costs came in at approxi- mately $7 million more than the owner had expected to pay. In a compet- itive situation, the question to be asked is whether less subsurface information from a less expensive exploration program would have raised the bid price by any substantial percentage of the $2 million (plus or minus) that was spent. This leads to the question of whether a less in- formed contractor might have encountered enough construction surprises to raise the ultimate cost to any great degree. There is no way to pro- 51

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duce any adequate proof when speculating on "what might have been, n but cutting the cost of the site investigation in half would have netted the owner approximately $1 million in early money savings to balance against bidding contingencies and potential construction cost overruns. In developing subsurface information, one must always ask: "At what expenditure level do exploration costs begin to exceed potential construction savings?" No amount of money spent on exploration can re- move all construction uncertainty, so the owner and the geotechnica] engineer must draw the line at some point. This project may be an exam- ple of one where a line was drawn slightly beyond the bounds of cost ef- fectiveness. 52 l

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CASE STUDY NO. 2 Name of Project: W}1ATA Section C-4, Huntington Paiute (Contract lC0041) Purpose: Running tunnels for subway system Location: Washington, D.C. (northwest quadrant and under the Potomac River) Construction Period: November 1972--August 1973 (shield tunnels) Site Investigation Period: September 1966--August 1969 Size: Soft Ground 2,740 ft long; 20 ft 6 in. diameter. Mixed Face 1, 069 ft long; 19 ft 8 in. diameter. Rock 8,303 ft long; 19 ft 8 in. high by 19 ft 8 in. wide Project Cost: Estimated $26,930,647 Bid $23,397,053 As Completed $32,009,752 (includes all extra payments) Mined Tunnel Construction Cost: 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 Cost: $98,150 pre-bid Summary of Site Geology: Recent alluvium and man-made fill overlying Pleistocene terrace deposits (fine and coarse grained sediments) over- lying decomposed rock and schistose gneiss bed rock. Eastern portion of alignment in terrace sands and gravels with boulders near base of depos- it and layers of clayey silt and silty clay throughout the upper reaches. A relatively thin layer of saprolitic decomposed rock separates the ter- race deposits from the underlying bed rock. Most of tunnel beneath the Potomac River in quartz-mica schist-to-gneiss of the Wissahickon and Sykesville formations. Foliation not particularly pronounced but shear zones common. Rock quality highly variable, ranging from slightly to highly jointed, with talc coating on some joint surfaces. Slightly to highly weathered, with some weathering zones at depth beneath sound rock. Unconfined compressive strength varying between 560 psi (in weathered zones) and 15,860 psi. Overburden ranges from 12 to 80 ft above the crown; soil thickness ranges from 0 to 50 ft except much thicker (120 ft) in gorge on east side of the river. Median permeability was 4 x 105 in rock. Predicted water inflow of 7 gpm in rock. Design Criteria: Water pressure (range) from 8 ft below the tunnel crown to 65 ft above the crown. 53

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Contract Provisions: Type: Unit price per linear ft of tunnel excavation as follows: 2,740 ft earth tunnel; 1,069 ft mixed face; 8,303 ft rock. (Total tunnel excavation length = 12,112 ft along 6,056 ft of alignment.) Unit prices for support items: shotcrete (cubic yard), ribs (each), steel (round). Estimated quantity variation limits set at 15%, without contract price adjustment. Stipulations: Schedule and/or time of completion: 730 days to complete tunnels. (Contractor to submit schedule, which then became the contract time.) Definition of delay and suspension of work. Liquidated damages: $1,500 per day of delay. Payment: monthly; 10% retainage (after 50% completion, may be re- duced at contracting officer's option). Construction method: TBM or drill-and-blast for rock tunnel. Vari- ous liner options, including shotcrete, cast-in-place concrete, and liner plates. Also option for either steel ribs or shotcrete and ribs in rock tunnels. Restrictions: Three shifts to be maintained when using a shield. Blasting not allowed from 10:30 p.m. to 7:00 a.m. in Washington, D.C., or Virginia, but no restrictions in tunnels under the Po- tomac River. Hauling subject to local jurisdictions. Disputes resolution: Decision by owner's contracting officer. 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: Bor ing logs (bound directly into the contract documents). Core samples avail- able for inspection. (Subsurface investigation reports, including profiles and laboratory test data, available for inspection and copies could be obtained from the Ilational Technical Information Service.) Disclaimers: Yes; data presented for information only with dis- claimer on accuracy, interpretations, and conclusions in reports. Changed~conditions clause: Yes Construction Method: Drill-and-blast (boom mounted 4-drill jumbo) for rock tunnels and some mixed face. Shield in earth tunnels and some mixed face where rock was below springline. Primary support of steel sets, some shotcrete (initial portion of rock tunnels), and some spiring {soil roof of mixed-face tunnel). Final lining of reinforced concrete (12 in.~. Conditions Encountered: In soft ground and mixed face, essentially as predicted, except elevation of rock line higher than expected. Blocky conditions and excessive overbreak in rock, but this is a controversial 54

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matter (conditions varying from poor to fairly good, and probably no worse than predicted by owner). Rock between tunnel crown and Potomac River bottom possibly sounder than expected; water pumped for the dura- tion of the project was on the order of 50 million gallons, only 10 per- cent of the specif fed allowance. Problems Encountered: Construction: In soft ground, runs into the heading caused ground settlements, including two surface slumps. In mixed face, a higher than anticipated rock line for part of the extent resulted in a change from shield excavation to heading and bench. In rock, blockiness and overbreak resulted in the use of steel r i bs rather than the des ign support system of rock bolts and shotcrete. Operations and Maintenance: At present, problems caused by ground conditions are minimal. Groundwater leakage is minor and there is hardly any buildup of the calcium carbonate precipitates that have plagued many other Metro rock tunnels. Drains were flushed perhaps 8 months ago (counting from January 1983) and still appear to be in decent condition. There is a bit of silt buildup in the drains at the low point of the tunnels; it is not known whether the silt originates in construction debris or in joint f illings in the surrounding rock. There was a short-term maintenance problem that stemmed from a man-made condition. Our ing construction, the tunnels penetrated soft ground saturated with a heavy, tar-like substance left from an old factory site. After tunnel completion the material continued to seep through the permanent concrete linings. Although not a fire hazard, it was messy and was carried by the drainage system to the pumping station beneath the Potomac River. When released into the river, the petrochemical was considered a minor environmental problem. The substance disappeared after a few years, pass ibly because the pocket was effectively drained. Resolution of Assertions Re Subsurface Changes: The contractor as- serted that he encountered higher rock than could be anticipated from the pre-bid data, primarily because the geologic profile contained a plotting error indicating a 1. 5-ft higher top by scaling than by written dimension. The contractor had scaled dimensions from the profile to prepare the excavation bid estimate and maintained that the error had increased his excavation costs by a factor of four. The owner's consul- tants contended that the plotting er ror was minimal, that all other drawings were accurate, and the written dimensions should have taken precedence. In addition, the geotechnical report indicated that varia- tions of 2 to 5 ft in rock elevation could normally be expected. A claim was filed but settled prior to hearing at a cost of $162,788 (part of a blanket settlement). The contractor asserted that steel ribs on 2-ft centers had been required due to blocky ground and safety of excavation and personnel, maintaining essentially that the design support system of rock bolts and shotcrete was faulty and not suff iciently conservative . The owner 55

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disagreed, indicating {1) that the contractor had never attempted to construct the tunnel as designed or as bid, (2) that numerous ribs in- stalled evidenced no blocking, no loading, and no deformation, and (3) that the design support system could have been used effectively. Claims pertaining to overrun in ribs were settled during performance for $2,503,815 by owner's final decision. Claims made by the contractor totaled $12,768,374. Some were set- tled by owner decision without litigation; others were filed before the Corps of Engineers Board of Contract Appeals but settled before an actu- al hearing. The final amount awarded to the contractor was $9,217,999. Analysis/Opinion: WMATA's C-4 contract provides examples of two com- pletely different kinds of subsurface problems 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. It was recognized that the tunnels would transition from soft ground to mixed face to rock, and the contractor laid plans to push with his shield to the point where the rising rock would force him to abandon this method. However, due to an owner plotting error on one contract drawing and some rather simplistic borehole-to-borehole rock line projections by the contractor, the top of rock rose to a higher than expected elevation in the soft ground tunnels and slowed progress considerably. Probably contributing to the problem was the somewhat less than desirable borehole coverage, with spacings on an average of perhaps 200 ft apart and staggered from one side of the alignment to another. WMATA's present practice in similar circumstances is to make borings or pairs of borings (one on each side of the align- ment) on 50- to 150-ft centers, coverage that is three to four times as tight as that provided on Section C-4. This constitutes acknowledgment of the fact that an owner can seldom go too far in determining the rock line when its presence is likely to affect a mined tunnel. In all fairness, however, it is difficult to say whether knowing the location of the top of rock with great precision would have made much difference in the ultimate cost of these particular tunnels. Sec- tion C-4 was not designed to skim the top of rock in order to avoid mixed face conditions; it hat to traverse those conditions in order to dive into rock, and a knowledge of their limits would not have lessened their extent or severity. The contractor made a high rock claim of $1,187,200 and ended up collecting $162,788 for it. A very precise knowledge of rock elevations would presumably have driven his bid up by a similar amount, and therefore it may be that the only money really "lost" was some relatively minor amount caused by the surprise factor and whatever the situation may have contributed to litigation expenses. By far the more serious of the C-4 problems was the one relating to rock conditions and how they affected tunnel support. The situation was quite complex, with many overlapping claims and counter claims which, had they been paid in full, would have netted the contractor extras worth +$12 million; however, they were finally settled for +$9 million. Though difficult to summarize without sacrificing accuracy, the basic problem appears to be that the contractor bid a construction option which he later decided was impossible to pursue. Passing up the chance to use a TOM, he chose drill-and-blast tunnels with a mostly rock bolt 56

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Restrictions: Blasting subject to engineer's approval. Dewatering not allowed near anchorage of Brooklyn Bridge; elsewhere it was limited to a maximum 6-ft lowering of the water table. Disputes resolution: Decision, which is "final," by Commissioner of Water Resources. Appeal possible to commissioner; only other re- course is litigation in court. Geotechnical data made part of contract documents: Report of soil investigation for proposed tunnel section, dated June 1970. General profile included in soil investigation report. Disclaimers: Data furnished for information only and not a sub- stitute for personal investigation. Changed~conditions clause: Yes Construction Method: Full breasting, soft-ground shield with hydrau- lic excavator and using 18 psi compressed air. Primary support of heavy steel liner plate. Permanent support of cast-in-place concrete. Conditions Encountered: Essentially as predicted by owner informa- tion, except that boulders and timber obstructions were far more numer- ous. (The selected contractor, suspected this possibility during the bidding period because he performed his own subsurface investigation. ~ In addition, natural gas (methane) and man-made toxic wastes were en- countered. Problems Encountered: Construction: Running ground was severe enough to require full breasting in spite of the compressed-air operation. Air losses in many places and one fire. There were steering problems in the many tight curves. Methane gas ,a minor problem, but an encounter with toxic waste in both headings caused a 9-day shutdown. Shields were slowed by an almost continuous deposit of boulders in one 386-ft long section. Progress was slowed further by unexpected encounters with wood cribbing obstructions and timber piles of abandoned piers. Operations and Maintenance: No problems were identified. Resolution of Assertions RR Subsurface Changes: The contractor filed four claims for a total of $1,503,000. The claims covered extras for the toxic waste problem, the 386 ft of large boulders, the wood cribbing obstruction, and the timber pile obstruction. The owner accepted the contention that the conditions could not have been anticipated and reim- bursed the contractor by negotiating change orders amounting to $935,999. Analysis/Opinion: Many miles of sof t-ground interceptor sewer tunnels have been constructed by the owner, with substantially the same bidding format as the Red Hook tunnel . For this proj ect the owner provided "bar ing logs " and a "geolog ical report " which could be inspected or pur - chased by prospective bidders. 80

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The geologic report described the various soil strata identified in the boring logs, such as "fine sand-compact, till, possible boulders, etc.," with very little analysis or discussion of the effect of the varying geology on engineering and construction procedures and problems. It was not a "Geotechnical Engineering Report." The soils were, in general, reworked glacial soils and the project ran parallel and in close proximity to a terminal moraine. There is considerable information available on the local geology and history as well as on numerous construction projects in the area, including 10 sub- way tunnels which crossed the line of the sewer tunnel. None of this was discussed in the report and few conclusions were drawn or evalua- tions made. The soil samples available for inspection were about 10 years old and of little help to the bidders. The major problems of a geologic nature that affected construction of the tunnel were as follows: An excessive number of large boulders, many more than indi- cated 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. The largest boulder extended 13 ft along the axis of the tunnel. Rock filled timber cribs (some noted on the geology report). Pile foundations {not indicated on the borings). Toxic chemicals and gases (not indicated on the borings or the geology report). An area of very low cover under a heavily traveled industrial street, with major utilities and running sand. The construction problems encountered were severe, and delays were very costly as the tunnel was built in compressed air with six four-hour shifts per day. Fortunately, there was excellent cooperation with the owner and his contract manager, all with the attitude of how best to solve the problems and get the job done to the owner's specifications and requirements. Despite many substantial -disagreements in negotiating claims for changed conditions, all disputes were settled during the course of the work through negotiated change orders and no claims were f fled for liti- gation by the contractor. The major change orders relating to geolog- ical conditions totaled about $936,000 whereas the contractor had re- quested $1,503,000. (There was another major change order of $S74,000 relating to special requirements of the Transit Authority while mining adjacent to more than five pairs of subway tunnels, but this is not re- lated to the purpose of this analysis. ~ A more complete- "Geotechnical Engineering Repor t" would have pro- vided the contractors with more information for bidding purposes as well as for evaluating construction procedures. It might have predicted the incidence of boulders much more accurately (as a private report did). However, better data may or may not have resulted in a greater overall project cost to the owner; the size of the change orders were very nominal for the gravity of the problems, and in a competitive bid- ding situation the original bids might not have differed greatly. Con- 81

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tractors looking for work are notoriously (but not always wisely) opti- mistic about solving ~field" problems. Sometimes they succeed and occasionally they do not. A difficult project like this could have be- come a catastrophe, greatly increasing the cost both to the contractor and the owner. It is neither fair to the contractor nor prudent for the owner not to provide all relevant information that can be obtained with- out excessive costs, including the geotechnical evaluation of the data as they impinge on design and construction of the project. 82 .

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CASE STUDY NO. 9 Name of Project: Edward Hyatt Powerhouse (formerly Oroville Power Plant) Purpose: Underground chamber for hydroelectric power production Location: California (on the Feather River, 5 miles northwest of Oroville) Construction Period: March 1964--June 1966 Site Investigation Period: December l9S9- - ctober 1962 Size: 550 ft long; 139 ft high by 71 ft wide (average). Project Cost: Estimated $20,592,461 Bid $18, 3 66, 7 80 As Completed $42, 414, 628 Mined Tunnel Construction Cost: 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 Cost: Not available Summary of Site Geology: Generally fresh, hard and massive amphibo- lite with some granitic gneissic zones. Three predominant joint sets with fractures, moderately to widely spaced. Many shear zones and schistose zones from 1 to 6 in. wide, containing crushed rock and clay gouge, dipping steeply and spaced 5 to 20 ft apart. Weathering along these zones, but not extending to powerhouse depth. Depth of overburden approximately 300 ft surface to crown. Water movement expected within fractures, joints, and weathered shear zones. Design Criteria: Modulus of deformation of rock mass = 1.5 x 106 psi; in situ rock stress determined to be isostatic at about 5,000 psi. Designed for relief of hydrostatic pressure (envelope grouting around the powerhouse with decreased injection pressures nearer the structure, combined with a system of gravity drains to relieve pressures on the structure). Contract Provisions: Type Unit price per cubic yd for excavation and concrete, per linear ft for rock bolts, and per pound for reinforcing steel. Estimated quantity variation limits not specified. 83

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Stipulations Schedule and/or time of completion: 1, 096 days for total contract. Def inition of delay and suspens ion of wor k. Liquidated damages: $1,000 to $3, 000 per day of delay and $100 per cubic yd for excavation outside the B line. Payment: Monthly; 10% retainage (optional after 50% completion). Construction method: Drill-and-blast; full face in three separate headings in upper portion and quarry method in lower portion. Restrictions: None Disputes resolution: Decision by owner's engineer. If the contrac- tor disagrees, he may file a notice of potential claim; the formal claim must be submitted within 60 days. The engineer decides all claims and his decision is final. The only further recourse may be litigation. Geotechnical data made part of contract documents: Project geol- ogy report available on request, including summary boring logs and mappings in exploration tunnels, but no interpretation. Core sam- ples available for inspection on application. Disclaimers: Owner completely disclaims responsibility for, and accuracy of, subsurface data. Changed-conditions clause: Yes Construction Method: Drill-and-blast using truck-mounted drill jumbos (two platforms with six drills on truck bodies). Primary support of rock bolts and shotcrete with wire mesh. Conditions Encountered: As predicted by owner information. Problems Encountered: Construction: 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. Rock movement in some areas and partial cave- ins of access tunnels. Operations and Maintenance: No problems identified. Resolution of Assertions Re Subsurface Changes: The contractor filed a $14,073,427 claim for the bench instability, contending that the com- plex design shapes were almost impossible to achieve in light of the ex- tensive network of shear and schistose zones. The owner denied the claim, maintaining that the joint patterns and frequency could be ob- served in the rock exposed in the powerhouse excavation and that the broken condition of the rock was due to poor blasting control and heavy blasting in adjacent tunnels. The owner forced the claim into litiga- tion. The Superior Court of California found in the contractor's favor within 6 months, but the $16,300,000 award (the amount claimed plus esca- lation and interest) was delayed by appeals until nine years after start of litigation. 84

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Analysis/Opinion: For a project in which the awarded amount from changed-condition claims was equal to 272 percent of the bid amount, the Edward Hyatt Powerhouse location was unusually well explored. Although the cost of the subsurface investigation is not available, the scope of the program appears impressive considering the extent of boring and seismic work, the amount of field and laboratory testing, the footage of exploratory drifts, and the peg model which was constructed. The inves- tigation indicated that construction would be generally within fresh, hard and massive amphibolite with relatively small amounts of granitic and gneissic rock. However, shear zones and some schistose rock were also identified; it was predicted that between these two sources of in- competent materials there would be steeply dipping zones of crushed and/ or highly fractured rock every 15 to 20 ft along the chamber axis. Such zones did indeed occur, and the areas of poor rock caused se- vere shattering and overbreak 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. The contractor contended that the fractured and sheared condition of the rock at the foot of the powerhouse walls was inherently unstable and that the complex shapes re- quired in the large chamber were not possible to construct within the B Line. We must assume this contention to be factual because the courts eventually (after nine years) awarded the contractor the amount asked, plus considerable interest. The question then becomes: If the geologic site investigation was adequate to def ine ground conditions accurately, how did an almost un- constructible chamber configuration get into the contract documents? The answer would seem to be that the proper interpretation of geologic conditions as related to construction feasibility was not made by the geotechnical engineer or the designer. The effect of incompetent rock zones on the desired excavation outline apparently was not properly as- sessed dur ing the des ign s tage . A common tunnel design philosophy calls for the des igner to s ize and space the elements of permanent support under the assumption that all temporary and initial support and the maintenance of a proper excavation outline are strictly within the pur- view of the contractor. This philosophy prevents the owner from improp- erly taking too much responsibility for routine field situations and operations. It may also obscure the need for geotechnical specialists and designers to maintain construction-wise staffs to review the plans from that particular point of view. Such an approach can work well with small or uncomplicated open- ings, especially where the tunneling medium is well suited for under- ground construction. If that was the governing philosophy behind the Edward Hyatt design, it may have been inadequate because ground condi- tions were not ideal and the opening was neither small nor uncomplicated. Any powerhouse chamber is quite large, and the excavation shape and stress redistribution patterns are made complex by the intersecting tun- nels and the benches required for machinery emplacement. Planning for such a structure requires the designer to help ensure its ultimate in- tegrity by giving the greatest amount of thought to how the concept and the desired shape and dimensions can actually be executed in the field. This, in turn, requires that the designer and/or the geotechnical engi- 85

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neer (without usurping the contractor's final responsibility) review plans thoroughly for ~constructibility" in light of the geologic situa- tion and make changes where necessary. Indications are that this step was not adequately pursued on the Edward Hyatt project, so there may have been a shortcoming in the final, interpretive stage, of the site inves ligation. 86

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CASE STUDY NO. 10 Name of Project: Waste Isolation Pilot Plant Purpose: Exploratory access shaft to determine site suitability for storage of low-level nuclear waste. Location: New Mexico (approximately 30 miles east of Carlsbad) Construction Period: July 1981--December 1981 Site Investigation Period: 1974--1980 Size: 2, 242 ft deep; 11 ft 10 in. diameter. Project Cost : Es timated $10, 207 ,10 9 Bid $10, 3 61, 0 71 As Completed $10 ,113, 904 Mined Shaft Construction Cost: Estimated $6, 977, 207 Bid $7, 419, 7 05 General Contract Mods $ -171,388 Subsurface Related Overruns $0 As Completed $7,248,317 Subsurface Investigation Cost: Not available Summary of Site Geology: Overburden consisting of 10 to 40 ft of windblown sand (approximately 20 ft at shaft location) underlain by silt- stone. Siltstone interbedded with sandstone and muds tone (the Dewey Lake Red Beds) overlies an anhydrite section infer beaded with dolomite and muds tone which merges into the massive salt horizon {from a depth of 800 ft to greater than 2,400 ft). The salt horizon contains thin anhydrite interbeds and one zone enr iched in potass ium chlor ide . Design Criteria: Concrete key at 850-ft depth designed for lateral pressure of 75 percent of overburden weight; steel liner and key de- signed for hydrostatic head of 600 ft. Contract Provis ions: Type: Cost plus. (Drilling contract on "day work" basis. Stipulations: Schedule and/or time of completion: Unknown Definition of delay and suspens ion of wor k. Payment: Monthly; 10% retainage until 50% completion. Construction method: Blind hole drilling. Disputes resolution: Standard "General Conditions " for federal gov- ernment contract. 87

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Geotechnical data made part of contract documents: Vertical sec- tion (composite of two borings) included in contract drawings. Core samples available for inspection. Disclaimers: None with respect to owner-furnished information on subsurface conditions. Changed~conditions clause: Yes Construction Method: Downhole drilling using drill derrick and hoist with 12-ft diameter rolling Butterhead. Permanent support of steel liner in upper 850 ft; no final lining at greater depths, but with rock bolts and wire mesh for support as required. Conditions Encountered: As predicted by owner information, but less convergence than expected in salt. Problems Encountered: Construction: None of any significance. Operations and Maintenance: No problems identified. Resolution of Assertions Re Subsurface Changes: No assertions made . Analysis/Opinion: The site investigation was carried out almost con- tinuously during 1974-1980 and covered an area of more than 100 sq miles before the final site was selected. The cost of this overall effort was very high--in aggregate more than the cost of the shaft itself. It is not possible to identify and separate those costs that are site specific to the shaft, but only a small percent of the investigation cost can be assigned to site description for design purposes. Two boreholes were drilled near the shaft site. Deliberately, drilling in the immediate area was held to a minimum so as to avoid possible communication path- ways into the repository area. Given that the project was conducted in a glare of publicity, much of it adverse to the concept of a low-level nuclear waste repository, it was essential that unforeseen problems or delays did not occur. 5 problem--particularly if unexpected--would have been used as "proof" of site unsuitability. Thus, the preconstruction geotechnical investiga- tions and design were of necessity over-conservative. It was a classic example of "belt and suspenders" design. The skeletal design criterion was to rapidly construct an access shaft, plus a ventilation/escape shaft. The access shaft would be used to excavate chambers in the salt, at the preselected repository horizon, in which to conduct various long-term tests. There were two major specific design criteria. One was that the Dewey Lake Red Beds could not be allowed to become water saturated; his- torically, if wet the beds would swell, spell, and cave. The other cri- terion was that the minor-flow fresh water aquifer could not be allowed to contact the salt; it would cut channels and could disrupt the shaft fittings in the unlined portion of the shaft {i.e., that portion in salt). 88

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Large diameter drilling was selected as the construction approach for several reasons: It was demonstrably much faster, and there was no risk to personnel from working in a shaft bottom (no one entered the shaft until it was completed). It was not subject to the delays and problems with water that have accompanied conventional shaft sinking in the area. It provided minimum disturbance to the salt, earl., no blast fractures, so that the necessary measurements of salt creep and long- term stability could be carried out in the shaft as well as in the chamber areas. The unlined ventilation/escape shaft could be quickly and economically "slashed" {enlarged) to a size suitable for long-term usage, should the test program demonstrate acceptability of the site for a re- pository. In the meantime, the small shaft, which was a safety-dictated necessity during the test program, could be constructed very rapidly and at much less cost than a conventional drill-and-blast shaft. The construction manager developed the contract specifications and, because the technique and methodology had been preestablished by the owner, opted for a "day-work" type subcontract for the drilling opera- tions. (Equipment and personnel operated on a fixed hourly rate, with the rate dependent on the type of work being performed.) The construc- tion manager estimated the number of hours required for each category of work, and the drilling contractors bid hourly rates for their rig, an- cillary equipment, and personnel based on their estimated quantities. The minimum size and capacities of the drill rig were specified in de- tail in the call for bids, and the drilling subcontractor's experience in similar work was also a bid appraisal consideration. The given geologic data consisted of a geologic column in the form of a strip log, with pertinent geologic and hydrologic comments in the margin. It should be noted that the local geology and hydrology were well known to the construction manager; therefore, with the type of con- tract, full details including geotechnical data were not essential to the drilling subcontractor. The construction method was blind shaft rotary drilling with cut- tings removal accomplished by a dual string circulation system. With this technique, a mix of high-pressure air and dr illing fluid is pumped down the annulus between two coaxial str ings of pipe (in this case 7 in. by 13 3/8 in.~. The mixture flows into a chamber in the bit body, through jet nozzles in the bottom of the bit, and returns to the surface via the 7 in. inner pipe, carrying with it the cuttings from the hole bottom. A "blanket" of fluid, 150 to 200 ft deep, in the shaft prevents the air-fluid mix from filling the shaft. The conditions encountered were precisely as anticipated; the for- mation changes were within inches of where shown on the strip log. Aside from minor operational problems with the dual-string system, the construction proceeded as planned and scheduled. This project is not a good example of severe construction problems, or of highly critical geologic-geotechnical features. However, it is a good example of how smoothly construction can proceed when the hazard 89

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areas are recognized in advance and appropr late plans made for over- coming them. On this project, the major hazard by far was the tendency of the Dewey Lake Red Beds to absorb water, swell, and slough. Much of the drilling in the area for oil wells has been plagued by this problem, and many holes have been delayed or lost. What is an irritation in an oil well can be a catastrophe in a large drilled shaft. If the shaft walls collapse atop a Trig hole" drilling assembly, the cost of the tools lost exceeds $500,000. In addition there is a delay of several months while new tools are procured. At the WIPP s i te, potassium ion was added to the drilling fluid to inhibit wetting of the shales, and the dual string technique minimized the exposure time. The proj ect was completed ahead of schedule and under budget--a tribute to good geotechnical data, good engineering, and good estimating. 90