WASTE LAND RECLAMATION BASIC INFORMATION

Green-Field † land not previously built upon. Usually part of the `green†belt' surrounding urban areas, designated inappropriate for development in order to preserve the countryside. Limited development for agricultural purposes only may be permitted on `green-belt' land.

Brown-Field † derelict land formerly a developed site and usually associated with previous construction of industrial buildings. UK government has set an objective to build 60% of the 4 million new homes required by 2016 on these sites.

Site Survey † essential that a geo†technical survey is undertaken to determine whether contaminants are in the soil and ground water. Of particular concern are: acids, salts, heavy metals, cyanides and coal tars, in addition to organic materials which decompose to form the highly explosive gas, methane.

Analysis of the soil will determine a `trigger threshold value', above which it will be declared sensitive to the end user. For example, a domestic garden or children's play area will have a low value relative to land designated for a commercial car park.

Site Preparation † when building on sites previously infilled with uncontaminated material, a reinforced raft type foundation may be adequate for light structures. Larger buildings will justify soil consolidation and compaction processes to improve the bearing capacity. Remedial measures for subsoils containing chemicals or other contaminants are varied.

Legislation † the Environment Protection Act of 1990 attempted to enforce responsibility on local authorities to compile a register of all potentially contaminated land. This proved unrealistic and too costly due to inherent complexities.

Since then, requirements under the Environment Act 1995, the Pollution Prevention and Control Act 1999, the PPC Regulations 2000 and the subsequent DCLG Planning Policy Statement (PPS 23, 2004): Planning and Pollution Control (Annex 2: Development on land affected by contamination), have made this more of a planning issue. It has become the responsibility of developers to conduct site investigations and to present details of proposed remedial measures as part of their planning application.

CAISSON STRUCTURES BASIC INFORMATION AND TUTORIALS

Caissons are box-like structures which are similar in concept to cofferdams but they usually form an integral part of the finished structure. They can be economically constructed and installed in water or soil where the depth exceeds 18„000.

There are 4 basic types of caisson namely:

1 . Box Caissons

2. Open Caissons

3. Monolithic Caissons

4. Pneumatic Caissons

The first three(3) used in water, usually of precast concrete and used in water being towed or floated into position and sunk. The last one is for land caissons of the open type and constructed in-situ.

Pneumatic Caissons ~ these are sometimes called compressed air caissons and are similar in concept to open caissons. They can be used in difficult subsoil conditions below water level and have a pressurised lower working chamber to provide a safe dry working area.

Pneumatic caissons can be made of concrete whereby they sink under their own weight or they can be constructed from steel with hollow walls which can be filled with water to act as ballast. These caissons are usually designed to form part of the finished structure.