Clause 505 aggregate is a clean, free-draining crushed aggregate intended for use in drainage works, filter drains and associated trench construction in accordance with the requirements of TII Specification for Road Works, Series 500 – Drainage and Service Ducts.

Produced from high-quality crushed limestone, the material provides a durable, permeable aggregate layer that allows the efficient movement of water while providing stability and support within drainage installations.

Clause 505 specifically governs the backfilling of trenches and filter drains, so the exact material requirements can depend upon the particular application and the contract specification.

Product Breakdown

The important distinction is that “Clause 505” does not necessarily mean one universal stone size. The required grading/material depends upon how Clause 505 is being invoked in the particular drainage design.

For example, the Series 500 specification separately provides for various aggregate sizes in pipe bedding and surrounding applications, including 4/10, 6/14, 10/20 and 20/40 mm, depending upon pipe diameter and application. These aggregates are specified with reference to I.S. EN 13242.

So, commercially, I would avoid advertising Clause 505 as simply “20 mm clean stone” unless your Declaration of Performance/testing confirms that the particular Lavan product and grading is the material required by the relevant Clause 505 application.

Typical Uses

Clause 505-compliant aggregate/material can be associated with:

• Filter drains alongside roads and infrastructure

• Drainage trenches

• Highway and civil engineering drainage

• Backfilling around drainage installations

• Subsurface water management

• French-drain-type construction, where consistent with the project specification

• Infrastructure and road projects constructed to TII requirements

The objective is generally to provide a stable and appropriately permeable drainage medium rather than a densely compacted pavement material such as Clause 804.

Key Characteristics

A suitable Clause 505 drainage aggregate would generally be promoted on the basis of being:

Free draining – designed to permit water movement through the aggregate.

Clean graded aggregate – controlled grading and fines are important because excessive fines can reduce drainage performance.

Crushed limestone – in Lavan's case, giving a strong and durable natural aggregate.

Consistent grading – produced and tested to the relevant declared aggregate specification.

Suitable for civil engineering applications – particularly drainage and trench works where the contract calls for Series 500 materials.

I.S. EN 13242 aggregate – where applicable to the particular aggregate being supplied. The TII Series 500 specification references I.S. EN 13242 for aggregates used in these drainage applications.

Installation / Usage Guide

The actual installation should always follow the engineer's drawings, Appendix 5/1 requirements and the project specification. As a general guide, the drainage trench is excavated to the specified dimensions, any required geotextile is installed, the drainage pipe is positioned with the specified bedding/surround, and the appropriate drainage/filter aggregate is placed around and above the system.

The material should be placed so that it does not become contaminated with soil, clay or other fine material, because contamination can materially reduce permeability. Where a geotextile separator/filter is specified, it should be installed in accordance with the drainage design.

Most importantly, Clause 505 should not be treated as an installation design in itself. The project engineer's specification determines the drain dimensions, aggregate grading, pipe, geotextile, depth and other construction requirements.