Mind that gap

Hanging out over a massive sink hole, this hotel come cantilevered viewing platform clings to its mountain ridge through strategic, environment friendly engineering feats

The hotel is literally built up amongst the

A 34m cantilever over a world heritage sinkhole

The cantilevered structures rely largely on horizontal stresses

Skyboat's front cantilever under construction.

The cantilevered viewing platform's balustrades form part of

The contemporary interiors include the building's structural elements

The sculptural hotel seen from below at night.

A local celebration of the gravity defying tourist

The hotel's design touches lightly on the earth

Engineered by structural consultants XinY

From the structural consultants:

Located on a dramatic world heritage site – the Dashiwei Tiankeng Sinkhole in the Karst area in Le Ye County, Guang Xi Province – Skyboat is a two-storey building consisting of hotel rooms at the ground floor, a café at the first floor and a roof viewing platform with a 10m-by-12.5m walk-on glass floor.

The rich and unique karst area offers an incredible view of the nature, but also presented a poor/ challenging construction environment – being constrained and unstable, with a seismic intensity rating of 7.

The hotel/spectacular viewing platform sits on a mountain ridge at an altitude of about 1450m and extends over the lip of the massive (and slightly terrifying) Dashiwei Tiankeng sinkhole which has a vertical depth of 613m.

The transparent viewing platform, made of reinforced glass supported by a U-shaped steel structure, is 80ms long and 10m wide.

Skyboat’s project engineers and architects worked closely together to find innovative structural solutions to minimise the project's impact on the environment, to improve the stability of the site and to achieve the elegant cantilever structure required.

The resulting building comprises a construction area of 495m² and cantilevers out by 34m and 22m respectively at its ends while the total steel weight used in construction was 438 tonnes.

Extreme conditions

Washed by powerful underground rivers for thousands of years, the spectacular 613m-deep sinkhole overlooked by the hotel has sheer walls on all sides.

However, the top of the sinkhole is extremely narrow and can only accommodate a small passageway.

Skyboat spans this passageway and cantilevers out to each side of the mountain ridge.

A giant tumbler toy?

Following the loose principle of bottom-heavy tumbler toys, the architects and engineers lowered the structure’s centre of gravity and utilise the minimum area (10m by 30m) to self-balance/anchor the building.

As the structure was to cantilever over the vertiginous sinkhole, the construction method required a careful design solution.

To complicate things, there is an existing crack – 10cm wide and several 100m long, depth unknown – at the top of the ridge.

This was another instability factor to consider in the challenge to improve the stability of the site.

Engineering creativity and innovation

Together with grouting the existing crack, the design features several key struts at each end of the building, inclining out towards the ridge.

These horizontal component forces provide the required strengthening structural forces to the ridge – thus improving the overall stability of the site.

To avoid potential load-bearing vertical forces destroying the mountain, a massive rock load under the shadow of the building and with the same weight as the base structure was removed.

Having the front balustrades as part of the truss structure enabled the architects and engineers to create the front cantilever as thinly and lightly as possible.

Increasing the key strut lengths, also allowed for the double duty of pre-cambering the front cantilever structure.

This engineering move also provides stability for and protects the structure’s glazing.

Sustainability – touching lightly on the land

There are only five supports on the building, minimising damage to local vegetation.

In addition, to protect the local plants and rivers, hanging temporary framework structures were used during the construction stage and the structural members were installed in sections.

Due to its minimal interface with the local environment, this project has received a Sustainability certificate and awards from local government and sustainability organisations.

Structural artistry

The structural system and component arrangements are adapted to the building’s force distribution and perfectly aligned with the elegant architectural geometry.