張家界的武陵源風景區以其整齊排列的石英砂岩峰林而聞名於世，這在很大程度上要歸功於電影《阿凡達》。它被聯合國教科文組織列入《世界自然遺產名錄》，具有國家公園的地位。
這個位於湖南省的風景區，原為沖積土在海床中壓縮形成石英砂岩層。經過數百萬年的地質活動，岩層被提升到海平面以上的高度。
之後地表植被層開始被侵蝕產生裂縫，在天氣周期的循環中，內部結冰膨脹加深了裂縫。地面的流水夾帶着鬆散的石頭，造成廣泛的侵蝕，直至形成峽谷。這解釋了為什麼岩柱的高度大都接近。
這個國家地質公園最初修建了山路，但隨着遊客流量增加，導致道路擠塞，空氣污染和環境破壞的威脅也愈來愈大。
為了方便遊客在景區內觀光，電梯從路面一直延伸到峰頂，這些山峰的高度約為 300 米。
這座名為「百龍天梯」的電梯，由三部雙層設計的觀光電梯組成，以加強乘載量。每部觀光電梯可載客約50人，額定載重量為5000公斤。「百龍天梯」的垂直高度約為 320 米。
電梯下半部分在山體內的豎井中運行，上半部分則在貼山的鋼結構井架上運行，外面以玻璃覆蓋。遊客乘電梯登山，可以欣賞到令人嘆為觀止的景色。
這個設計盡量減輕了電梯組件的視覺衝擊，同時確保了電梯井架和機房基礎堅固。
電梯在1999年開工建造，2002年啟用。2015年進行了提速升級，約1分半鐘即可將乘客送到峰頂，大大提高了總載客能力，成為世界上最高的電梯系統之一。
三部電梯容許升降同時進行，保證了遊客出入園區的足夠載荷量，同時還提供了第三部備用電梯，以滿足日常維護和緊急維修的需要。
乘搭纜車和循原有的山路也可進入園區。作為替代方法，景區提供多種交通工具以滿足不同的需要。
最初，環保批評者指這套電梯系統破壞環境，破壞了砂岩峭壁的自然地貌，而且由於更容易進入園區，會吸引更多遊客，可能會給公園帶來不必要的環境負擔。
但當局認為事實恰恰相反。
首先，「百龍天梯」顯著減少了大量旅遊車運送遊客的需要，多輛旅遊車可能會導致嚴重的空氣污染。
更重要的是，更快的參觀時間，可以疏導每日巨大的客流量，大大減輕了對住宿和餐飲的需求，緩解對公園不斷增加的環境壓力。
再一次證明，好的工程設計可以在實用性和環境保護之間取得有效的平衡，達到讓大量遊客參觀的目的，同時盡量減少對環境的影響。
作者為資深工程師，以專家眼光評論出色的基建設施。
Going up in the world of carrying visitor load
Zhangjiajie National Park, with its neat array of quartz sandstone pillars, is a favorite tourist spot of international fame, thanks largely to the movie Avatar. It is a Unesco world heritage site and has national park status.
The scenic area in Hunan was originally alluvial soil, compressed in the ocean bed to form quartz sandstone. Through millions of years of the Earth’s movements it was raised to an elevation way above sea level.
Then erosion, started by vegetation on the surface, created cracks, which were aggravated by ice expansion inside them during weather cycles.
Loose stones carried by surface water caused widespread erosion until canyons were formed.
This explains why the pillars are generally of similar height.
At the early stage of this park mountain pass roads were built for access, but as tourist traffic has built up it resulted in route congestion with an increasing threat of air pollution and environmental damage.
To help visitors move around in the park elevators were built from road level to the top of pillars, which are at an elevation of about 300 meters.
The set of elevators, called the Bailong Elevators, consists of three double-deck lifts, each carrying about 50 passengers, with a rated capacity of 5,000 kilograms.
The total vertical lift is about 320 m.
The lower half of the shaft was built within a sandstone wall, with the upper half in a glass covering supported by a steel structure to offer breath-taking views as tourists rise.
This design minimizes the visual impact of the elevators assembly and ensures a solid foundation for the lift shafts and the machine room.
Construction started in 1999 and operation commenced in 2002.
It was upgraded in 2015 with a higher speed, delivering passengers to the top in about 1 minutes, greatly increasing the total carrying capacity and becoming one of the world’s tallest elevator systems.
The three sets of elevators ensure adequate capacity for tourists visiting and leaving the park, allowing for simultaneous up and down traffic while still providing a third lift for redundancy to meet the need for routine maintenance and emergency repairs.
The cable car system and the original mountain path road access provide alternative means to offer a variety of transport to satisfy different needs.
Environmental critics at first criticized this elevator system, claiming that it spoiled the environment with damage to the natural topography of the sandstone cliffs, and as the easier access could attract more tourists it could impose an unnecessary environmental load on the park.
But authorities believe the opposite is true.
First, the electric elevators significantly reduce the need for a large fleet of coaches to ferry tourists, which might cause excessive air pollution.
More importantly, the quicker travel time allows easy daily turnaround of tourists, significantly reducing the need for lodgings and food, eliminating the ever-increasing environmental demands on the park.
Once again, it demonstrates that good engineering can strike an effective balance between accessibility and environmental protection, achieving the purpose of allowing large numbers of tourists to visit while the minimizing environmental impact.
Veteran engineer Edmund Leung Kwong-ho casts an expert eye over standout infrastructure.
原刊於《英文虎報》，本社獲作者授權翻譯轉載。
