ELEPHANT NIGHT TIME ACCOMMODATION
We plan to upgrade and substantially increase the size our night time enclosure. Due to Jabu's size and intelligence it needs to be very stout and as such will be very costly
Jabu has some very lovely ivory so we like to keep him and the girls safe, secure and close to us in an enclosure at night because even in Botswana, the elephant capital of the world, has increased poaching levels. During the day The Elephant Trio wonder freely, with a human guardian to keep them safe, in the bush and do all the things elephants naturally love to do.
Living With Elephants is based in a wildlife concession and the Botswana government discourages the erection of permanent structures and the use of concrete in such areas, this posed a special challenge for us when redesigning The Trios' enclosure. After very extensive consultation we came up with the following design for their 2.6 acres (i.e. 1 hec) new night accommodation.
For anyone interested in the details, outlined below is the proposed structural design of the elephant enclosure.
The enclosure will be 100m x 100m (328ft x 328ft).
To avoid having to cart 55 x 5 ton truck loads of concrete into the Delta, and to satisfy the authorities, we went in search of an alternative concrete free design that could hold a 7 ton elephant and came up with the following.
Posts will be placed 3m's (9.84ft) apart, with 3m's (9.84ft) above ground and 7m's (23ft) below the ground. 4 -5steel cables 16m in diameter energized with 10volts will be placed through the posts. A metal sleeve will be placed over the post and extended above and below the weak points or bendable areas of the pole 2m (6.56ft) above and below ground level. The inner pole will be filled with sand and extended above and below the weak points or bendable areas of the pole 2m (6.56ft) above and below ground level. The inner pole will be filled with sand and and the end cap screwed on which gives it impressive strength under pressure and avoids having to fill the post with concrete.
The contractor is a bridge builder and will sink the poles using the same method he uses to sink bridge-supporting pillars.
See below from the contractor:
The drilling rig that we plan to use is a commercial water drill rig that forms a pressurised water jet in a conical steel pipe. This water jet displaces material at the bottom end of the pipe as it
drills/moves down the shaft. Once the shaft has reached the required depth, the steel post is inserted into the sleeve before the sleeve is removed. Removing the sleeve collapses the surrounding sand onto the post thereby securing it firmly in place. This is a clean method that leaves no environmentally negative impacts during or after the project. A 5.5hp water pump is used during the drilling process.
The sand and clay that is displaced accumulates on the surface surrounding the drill site and this sand is then again collected and used to fill and secure the steel post that has been put in place. Once the post is filled and compacted with residual sand and clay an end cap is screwed over the top end of the steel post which gives the post a significant resistance toward circumferential and axial stress.
What we have now created is a closed-end thick-walled cylinder system in which the more pressure is placed on the system circumferentially and axially, the more pressure is produced by the closed system inside the cylinder giving it proportionately more strength. In essence, the more pressure you put on the cylinder, the stronger it becomes.
We are not too concernedhere with vertical pressure on the cylinder as we are in other applications such as bridges and building foundations. We are more concerned here with horizontal pressures or stress in the axial direction such as can be applied by a seven ton. elephant which can be expressed here as;
σa = (pi ri2 - po ro2 )/(ro2 - ri2)
σa = stress in axial direction (MPa)
pi = internal pressure in the tube or cylinder (MPa)
po = external pressure in the tube or cylinder (MPa)
ri = internal radius of tube or cylinder (mm)
ro = external radius of tube or cylinder (mm)
Given the specifications in the materials to be used and assuming that the internal pressure of the cylinder will be the same as the pressure outside the cylinder under no load and increase under load, we can therefore expect an individual post to withstand stress in an axial direction of around 9 tons per post or 29717593 Pa or N/M2 before stress point is reached.
This will therefore satisfy the stress requirements for the project.
In combination the posts will support each other further with an interlinked steel cable thereby increasing the individual strength of the posts and placing electrified strands along the posts will deter an elephant from being able to place substantial or prolonged pressure on any one post.