The single most important consideration associated with installing an aerial tramway or ski lift is the lift line survey or ground profile over which it is to operate. An approximate or preliminary profile will adequately serve planning needs; an accurate design profile is absolutely essential for design, construction, and eventual operation.
(Note: In this paper, the term “profile” relates to ground surface information and should not be confused with the term “lift profile” frequently used in the aerial tramway and ski lift industry to designate a document showing ground line, lift structures, wire rope location or working points, and related lift information. The references regarding Forest Service requirements for ski lift profiles are, of course, applicable only to installations on land under Forest Service administration, but the information they surface may be equally beneficial to installations on state or private land. The referenced documents are available through Forest Service Regional and Forest offices.)
Preliminary Profile
Many factors must be considered in selecting the location of a new aerial tramway or ski lift facility. The ANSI Standard B77.1-1976 lists several under Section 2.1.2; Forest Service Manual (FSM) Section 7321.41 lists others. No other single consideration is more important than the profile. Forest Service form 7300-4 (6/73), Request for General Location Approval of an Aerial Passenger Tramway, lists specific requirements for the preliminary profile required at this stage of planning and approval. The profile scale, accuracy, and related data are established. A flagged compass line, made without tree clearing, may be run between terminals for field considerations; if topographic maps are inadequate or questionable, a rough profile using clinometer and tape may be necessary.
The profile and its related plan view, keyed to an accurate topographic map, are essential to planning and are a pre-requisite of general location approval. Emphasis might well be added in regard to the terminal locations. This consideration is paramount for the lift in question and for its relationship to other facilities, natural features, and operational considerations in the area. Once established, the terminal area locations should be well marked or identified, and the location held strictly as lift plans progress and construction is started.
Design Profile
An accurate lift line survey or ground profile is absolutely essential for design and construction of an aerial tramway or ski lift facility. This profile and associated plan view information may well be at issue in meeting requirements of state codes and the national standard; ANSI B77.1-1976, Section 2.1.2 Location, and Section 2.1.2.1.1 Ski Track Gradient, are examples. FSM 7321.41(2) and Form 7300-5 (6/73), Request for Design and Construction Approval of an Aerial Passenger Tramway, establish requirements for this profile and certification of its validity.
The design profile should be made immediately (field survery conditions permitting) following conclusive determination of the lift line and terminal locations. This is essential in order that it be available for lift bidding and, particularly, design work which may precede the ground again being available for accurate survey. The ground should, preferably, be free of snow; it must be suitable for staking and the establishing of identifiable monuments (stakes, spikes, rebar). The profile must be prepared either by qualified survey personnel, whose work will be acceptable to and certified valid by the engineer responsible for lift design, or it must be prepared by a licensed engineer or land surveyor. The profile must be sufficiently marked and documented so that the line and stationing can be re-established for construction purposes. It must extend to a well-established benchmark in an area unlikely to be disturbed by construction and at least 100 feet beyond the terminal structures contemplated. The survey should reflect an accuracy of 1:5,000 for monuments and closures; centerline field shots 1:3,000; and cross slopes 1:100. When snow depth is critical to lift design, as with surface lifts and aerial lifts in deep snow areas, the profile must show maximum expected snow depths along the line; this information is obtained most expediently by winter snow depth surveys along a previously established lift line.
The plan view of the profiled line must indicate as a minimum:
- Two-foot contour intervals for terrain extending 100 feet in any direction from the center of lift bull wheel locations in both terminal areas and any intermediate loading or unloading area.
- An indication of magnitude and direction of any cross slope along the line exceeding 10%.
- Steams, cliffs, or natural features occurring along the line.
- Road, ski trail, pipeline, powerline, or other manmade features crossing or occurring along the line.
- Other information pertinent to lift design including true or magnetic bearing of the lift line.
The profile should be platted to a scale of 1 inch = 40 feet horizontal and vertical.
The design profile must be available to the “qualified design engineer” (FSM 7321.2) for use in preparing documents for the initial Request for Design and Construction Approval of an Aerial Passenger Tramway (FSM 7321.41) and Form 7300-5 (6/73). No review of the design for tower line sheave pressures, drive horsepower requirements, or other design conformity with applicable codes or standards will be made for a submittal using other than a valid Design Profile.
The emphasis placed upon having available and using a valid design profile suggests the intent that the location of lift terminals and towers for construction purposes will follow precisely that indicated in the drawings submitted for approval. The infrequent instance where field conditions or others force a relocation of structures must be seriously considered. The necessity for change may originate with the engineer responsible for construction (FSM 7321.2), but specifics for a change of location must be made by the engineer responsible for design. The change must be made of record by resubmittal of drawings to support relocation of structures, foundation changes, and recalculation of line reactions on all tower or terminal structures affected by the change. The “qualified construction engineer” is responsible for assuring that “as built” drawings and the corrected lift profile accurately reflect the final location and details of ground line, foundations, and structures. These final or “as built” drawings must have been prepared and made available to authorities having jurisdiction prior to postconstruction inspection and load testing a new, relocated, or remodeled facility. The absolute minimizing of tower relocation and, particularly, terminal relocation during construction is fully intended.
The above requirements for both preliminary and design profiles suggest the importance of preparing them well in advance of their being needed for approval purposes, design, or construction. New development and existing areas contemplating expansion should, if possible, have profiles prepared during the summer months one year before actual construction is begun. Clearing a minimal line of sight for survey should be permitted, but excessive cutting along a survey line before approval should be rigidly controlled. Preparing profiles well in advance of their actual need is expedient and in the best interest of all parties concerned: The area owner (permittee), the lift designer, the lift constructor, and authorities having jurisdiction.
