roadway and parking area lighting systems; a water supply system, including a storage tank and 4-inch water supply line; and an electrical supply system from the Glen Canyon Switchyard.

256. CONTRACT ADMINISTRATION. The visitor center complex was constructed under specifications No. DC-6274 by Allen M. Campbell Co., General Contractors, Inc., of Tyler, Tex. A significant portion of the speciality work was performed by 12 subcontractors.

Although the contract was awarded on June 30, 1965, and notice to proceed was received by the contractor on July 12, the contractor was not able to start work until August 16 because of the statewide strike of operating engineers which prevented initiation of construction work at the site. A later findings of fact established that this delay was excusable from computation of allowed contract time.

A. CONSTRUCTION

257. FOUNDATION PREPARATION. Overburden was stripped from the general area. Drilling for excavation of the basement of the building was completed and the basement was blasted and excavated. During removal of the blasted basement rock, fill was placed and compacted in the parking areas and drilling and blasting was completed on miscellaneous features, such as sidewalks and the water tank at the base of "Beehive" rock. Excavation of foundations for major walls outside the building and major trenching was then completed using conventional methods and equipment. Concrete from the old high-line tail tower tracks had to be blasted and removed to construct the access road to the upper parking area, and high rock spots in the parking area were also drilled and blasted.

During the excavation of the trench for the 4-inch waterline, a previously covered portion of the old tail tower rail support concrete was found to be considerably thicker than had been anticipated. A rock knoll between U.S. Highway No. 89 and the ramp to visitor center parking area No. 3 also obstructed the view and created a traffic hazard. At another location, two catch basins and some exterior lighting standards were located such that the foundation excavation encountered other sections of the old tail tower support concrete. The excavation in these instances was performed as extra work by the contractor.

258. TUNNEL EXCAVATION. Rock bolts were placed at the portal of the tunnel between the dam and

the visitor center, and excavation of the tunnel was then performed, using conventional drilling and blasting methods. Owing to the relatively small size of the tunnel, a small rubber-tired conventional four-wheeled trailer was used as a drilling jumbo, which also served to carry tools and materials. On completion of the excavation in rock for the basement of the building, a pilot hole for the elevator shaft was driven from the top and was holed through satisfactorily. Line drilling and excavation of the elevator shaft to the A-line was then performed. The elevator pit was then excavated and tights were removed in the tunnel, shaft, and basement. Excavated material from the tunnel and elevator shaft was wasted into the reservoir from the top of the dam.

The mining work was performed by a subcontractor, the Mile Hi Drilling Co. As a general rule 35 holes, each 8 feet in depth on 2-foot centers, were drilled to excavate the 7- by 9-foot tunnel, using a 3-hole burn or burden breaker in a triangular pattern. Each round was loaded with 295 sticks of 35 percent powder. Knock-off bits were used on two jackhammers to drill the powder holes. As a general rule, the tunnel was driven on swing shift, sometimes making two rounds per shift and averaging about 7 feet per round. A hydraulic front-end loader was used to bring out the excavated material. To provide clearance for the loader at the points of intersection, the inside corners of the tunnel were removed resulting in considerable overbreak. As excavation progressed, rock bolts were placed in the roof as a safety measure. The drilling crew consisted of a foreman and two miners who loaded, blasted, and installed rock bolts.

The contractor placed considerably more roof bolts than had been normally anticipated from previous experience in Navajo sandstone. This condition was primarily due to the contractor's conservative attitude towards safety in the softer formations at the upper part of the canyon wall. No particular difficulties were experienced in blasting the tunnel, and overbreak was maintained within reasonable limits.

Drilling of the 5-inch drain hole for the elevator pit was initially abandoned at a depth of about 28 feet due to difficulties in drifting. A new 3-inch pilot hole was drilled through to the canyon which was then reamed to a diameter of 5 inches by pulling the bit from the canyon to the pit with a modified wagon drill.

259. FOUNDATION EXCAVATION. No unusual difficulties were experienced in the rock excavation or earthwork construction for the visitor center. Following rock excavation and general grading, trenching for the various utility lines was completed

and the pipes were laid. This included the water supply piping, the corrugated metal pipe surface drainage. system, electrical power supply duct bank and manholes from the switchyard, and buried area lighting conduits. The manholes for the surface drainage were precast concrete. In addition, a buried control cable and water supply piping were installed for an automatic sprinkling system for certain areas on the visitor center grounds to be landscaped by others under a future contract.

260. CONCRETE PLACEMENT. Concrete placements began with the placing of sections of the concrete integral retaining wall and sidewalk, parapet wall sequences and manhole invert slabs. On December 30, 1965, a fire gutted the batching plant owned by the concrete supplier. Replacement equipment and materials were ordered promptly, repairs were made, and the plant returned to full operation on January 10, 1966. Concrete was placed by conventional methods, including the use of wooden forms and snap-tie fasteners, generally following a logical sequence of construction. Foundations and basement walls were placed, followed shortly by the basement floors. The first floor was not placed until all of the basement Iwalls had been completed. With placement of the elevator machinery room roof, concrete placements were completed in August 1966. Except for those locations directly accessible to a transa-mix truck, the concrete was placed with a mobile crane using a bucket with a rubber tremie. Figure 295 shows the status of the work as of May 24, 1966.

Subsequent to completion of the of the concrete construction in the building proper and the completion

Figure 295.-Aerial view looking east over visitor center construction. P557-420-12274, May 24, 1966.

of trenching excavation, embankment was placed about the various major concrete structures and utilities, and the gravel underbed for the paved areas adjacent to the building were completed. Construction of the miscellaneous concrete structures took place over a period of about 1 year, progress being generally slow.

During the colder winter months, the contractor kept the concrete curing temperatures above the minimum specification requirements through the use of plastic sheeting on wooden frames, warmed by space heaters. Construction of the electrical duct bank began during January 1966, and continued intermittently, with placement of concrete being completed during July and the backfill completed during August. Following completion of the tunnel invert concrete in May, no concrete was placed in the shaft or tunnel until September when the tunnel arch lining and elevator lobby arch concrete were placed. The tunnel entrance structure concrete was placed in October and November 1966. The tunnel entrance door installation and tunnel lighting installations were also completed at this time.

261. MISCELLANEOUS. The structural steel for the visitor center was delivered early in the project work and was stored at the site. After the concrete floors were placed and cured, the structural steel was quickly erected without experiencing any unusual difficulties. Terrazzo was placed in November and December 1966, except for the final fine grinding and sealing which was deferred until later. During placing of the terrazzo floors, a rainstorm washed white cement mortar over the nominal protective barriers provided and down over the canyon wall below the rotunda. The resulting white stains on the face of the canyon wall detracted from the appearance of the visitor center and it was necessary for the contractor to remove them. Installation of mechanical and electrical materials roughly followed the sequence of concrete and framing construction. Following discussions with the National Park Service, changes and additions were provided for the audiovisual system for the visitor center and numerous revisions were made in the finish requirements in the exhibit, information, and lounge areas on the main floor of the rotunda.

Numerous delays were experienced by by the contractor in obtaining precast concrete panels, primarily due to problems of the supplier. The problems were eventually resolved and the precast panels were delivered to the site. The rate of delivery was somewhat slow and other deficiencies were found in the panels upon delivery to the site. As a result,

some of the panels had to be returned for replacement. Delays in installation of the precast concrete panels were also reflected in a slower rate of progress for most of the finish work on the visitor center.

Installation of the buried portions of the 4-inch water supply line, including the fire hydrants, was completed early in 1966. Water supply and sanitary outfall pipes in the tunnel pipe chase were installed during the summer prior to completion of the tunnel arch lining and lobby arch. The water supply tank was completed early in the job so that it could be used for supply of construction water. The exterior surface of the water tank was initially painted an aluminum color in accordance with the specifications but was later repainted to blend with the surrounding sandstone. The VR3 (vinyl resin) paint on the interior of the tank proved to be defective at the welded seams. A reduction in contract price was made due to the expected shortened life of the paint.

On completion of the various excavation and placement of minor concrete foundations, placement of subgrades for the parking areas, roadways, curbs and gutters was performed as space became available. Owing to subsurface conditions, the retaining wall and the sidewalk at the toe of the sloped area between parking areas No. 2 and 3 were combined into a common section, which also affected the two stairways between these parking areas. Portions of the parking areas were used for storage of construction materials at different times. Grading of parking areas and roadway subgrades continued over several months.

262. ELEVATORS. Elevator rails and machinery room beams were delivered to the construction site in June 1966, prior to the arrival of the manufacturer's representatives on July 12. These elevators were furnished under invitation No. DS-6276 by Montgomery Elevator Co. Previous to work on the elevators, the machinery room beams were set to line and grade prior to placement of the machine room floor by the construction contractor. Installation of guide rails began in July and was complete in August. The two car frames were assembled in the elevator pit, electrical conduits for the shaft were installed, and hoist machinery and control panels were set in place. Following installation of the hoist cables, counterweights were installed to raise the car frame to the elevation 3210 landing for assembly of the elevator car. During October 1966, the west elevator car was assembled and placed in manual operation and the east car was assembled early in November. By the end of November, both elevators had been completed and the control wiring and device installation checkout were

satisfactorily made. Acceptance tests were satisfactorily completed during April of 1967. Ir general, the elevators were constructed using conventional installation methods and no unusual problems were experienced during this phase of construction. The hoist for elevator No. 1 did develop vibrations greater than normally expected. Representatives of the contractor returned to the project during June June 1967, and corrected an out-of-round brake drum.

263. PRECAST PANELS. Installation of the precast concrete panels for the building continued intermittently. Framing for the building interior and installation of associated conduit and metalwork continued when the panels were not available for installation. About 95 percent of the panels had been set in place by the end of March 1967. The south entrance precast column panels were rejected due to fabrication defects, and replacement panels were delivered and installed during May, which completed the panel installation. Calking of the panel joints began soon after completion of installation of the panels and was rapidly completed.

As soon as the last panels were in place, work began on installation of the building roof insulation and roofing, which was completed within about 1 month. Some difficulty was experienced with handling of adhesive, which was resolved when the critical limits of the temperature installation range were determined and the work schedule adjusted accordingly. Basically, roof surface temperatures of less than 95° F. were necessary at the surface of the black neoprene in order to effect adequate bond with the recommended adhesive. As soon as the building was closed in, work began on installation of the aluminum curtain walls, entrances, wallboard, insulation, and ceiling installations. Interior finish carpentry and electrical installations were followed by the installation of bat and rigid type insulation, gypsum wallboard, walnut paneling and other wall finishes.

264. FINISHING WORK. By the end of June 1967, finish grinding and sealing of terrazzo floor surfaces, installation of plumbing fixtures, and electrical fixtures, and finish painting of the building had been generally completed. Chain link fencing, aluminum handrails, and precast concrete benches were then installed. About a month after the terrazzo had been completed, a small crack appeared in a section of the terrazzo in the rotunda, showing some vertical displacement. Other cracks appeared during the next few weeks and a drummy area of about 1 square yard developed. The area was rebonded by drilling and