As a pre-cursor to the publication “The Design of steep grassed waterways” a field trial was undertaken. This involved the construction of a series of trapezoidal channels down the 1 in 2 slopes of an abandoned reservoir. A water supplying flume was connected to the head of each channel, through which water was discharged at variable flow rates.

The trial was successful in benchmarking the capabilities of various armouring systems, as well as identifying the characteristic performance of grass itself under high flow conditions.

From the data provided, it was possible to identify GRASSCRETE as being able to exceed the 8 metres per second limit of the trial, without structural damage. This compared to lesser flow rates achieved by geotextiles and hand laid pre-cast block systems

A trapezoidal storage channel with concrete dry weather channel and revetments laid with Grasscrete.

Part of the preliminary works to the new Priory Business Park involved creating a flood alleviation scheme to the River Great Ouse. At this location the river was particularly prone to flooding the low lying site.

The works involved constructing a gabion weir to the dyke wall of the river with a 19 metre wide trapezoidal channel taken from and returning to the river. The first 150 metres of the channel had the revetments armoured by insitu Grasscrete in the GC2 (150m thick) type.

The specification called for Grasscrete to be laid via a geotextile directly on to a trimmed earth sub-grade. As the works were undertaken during summer months construction access was gained along the invert of the channel itself which enabled most of the area to be cast direct from the truck mixer. Other more inaccessible areas utilised a concrete pump for pouring.

Upon completion, the Grasscrete was seeded with a wild flora mix indigenous to the existing site and is now barely detectable as a hard lined flood channel.

An increasing environmental awareness and a need to upgrade ailing masonry revetments spawned this successful application for GRASSCRETE.

In a continuous cycle of operations, pre-cast masonry block slope and invert protection has been replaced using the GRASSCRETE case-on-site process. This has enabled the works to be fully reinstated with a system that improves the environmental balance, as well as providing the hydrostatic venting characteristics that have made this system so successful in water engineering projects.

Project Description and Brief

Embankments

Fairlop Sailing Park near Ilford had, in 1982, developed signs of erosion at various points to the embankment slopes. The lake was conceived from former gravel workings and the existing natural material retained for the slopes had a low scour resistance. Wavewash created by prevailing winds across the lake had scoured the higher risk areas of the embankments.

A system of surfacing was, therefore, required which could maintain the appearance of natural grass slopes yet achieve the scour resistance of say solid concrete together with a slip resistant surface for mooring sailing craft.

Project Specification

The erosion of the lakes had become concentrated along three separate stretches of embankment which had failed to resist the hydraulic loading created by the cross lake swirl.

The need, therefore, was to provide a continuous system of stabilisation without the risk of weak spots which would be the focal point of the erosive forces and yet retain the natural grassland environment of the lake.

The system adopted was the Grasscrete GC3 (76mm thick) insitu revetment surfacing. This system is continually reinforced by steel fabric with concrete poured on to plastic formers providing a structural carpet of grass and concrete. To enable work to commence on the revetments, the level of water in the lake was lowered to below the base level of the new surfacing.

The existing grass and topsoil coverings were removed from embankments and the exposed sub-grade regulated to form an even profile of between 1:2½ and 1:4 gradients. To prevent backwash erosion at the base of the surfacing a toe beam was excavated to provide an insitu concrete beam 250mm wide x 400mm deep. Further regulation of the embankment was provided by a sand blind 10-20mm thick. This and the sub-grade below were then protected by geotextile membrane.

The Grasscrete GC3 system was laid with the base abutting the edge of the toe beam, a further sacrificial covering of sand was spread over the Terram layer to prevent damage upon burning out the plastic former tops. After completion of the burning out operations, the pockets formed in the Grasscrete were filled with friable topsoil. A moisture tolerant grass seed type was selected for use. The presence of wild white clover in the mix provided a carpet of cover with early resistance to wear.

The new Grasscrete surface was now able to provide an ideal mooring point for the boats from the lakes sailing club, the pockets of the Grasscrete enabling mooring pins to be driven into the embankment and the fully enclosed concrete surround to each pocket allowed safe walking along the revetment.

In 1983 Grass Concrete Limited were contacted by Architects Peter Dann & Partners with a new 140 car parking space requirement for students.

A site had been identified as an island formed from natural meander in the River Great Ouse with an access connection to be made via a bridge to the main campus area. The nature of the site made it an ideal venue for organised canoeing with good all round visibility along the river. The isolated nature of the site did, however, pose a few design headaches.

Cut off from the rest of the campus by the river, a temporary bridge structure would be required to cater for the loading of construction traffic. A permanent structure of limited load capability would eventually provide traffic movement on to the island.

Converting a natural landscape into 140 car parking spaces would ordinarily call for a significant increase in demand on the surface water drainage network if a sealed paving layer were to be used. The isolated nature of the site meant, however, that pipe work could not be brought back to the campus infrastructure. A solution to this was the adoption of a porous surfacing system, which would enable filtration both naturally to water table and also via land drains into the river.

Given the long narrow profile of the island, good parking management would be essential in order to maintain maximum use. The ability to delineate individual parking bays was, therefore, an essential requirement.

The third factor was the aesthetic impact on the site of mass parking. It was thought desirable that the appearance of the area should maintain the overall aspect of a natural landscape.

The ideal solution to these criteria was found with GRASSCRETE, the unique cast on site paving featuring steel reinforcing mesh within the cellular concrete structure, which therefore resists differential settlement in heavily trafficked areas.

With a drainage capability approaching 90% that of normal grassland, the paving layer was able to accept surface water without the need for a piped system.

Though providing an overall grassed environment, Grasscrete’s network of soil pockets are continuously surrounded by concrete ribs. Further delineation was provided by casting integral solid concrete strips across each bay at 2.40 metre centres. This involved the simple omission of a 200mm module strip from the plastic void formers.

Instead of concrete bollards, tree planting was used to provide further subtle definition and to give height to an otherwise linear perspective of the site. This was easily achieved by forming planters within the Grasscrete.

Actual construction commenced in December 1983 and after a break for adverse weather conditions completion was achieved in March the following year with the occupation taking place almost immediately.

If repeat business is a good sign of customer satisfaction, then this University Project in Spain must provide a good testimonial. From 1996 to 2003 five phases of construction have taken place using GRASSCRETE for parking areas.

With the self-draining design that GRASSCRETE provides, there is no need for an underlying drainage system. The finished levels can also be laid without the normal drainage falls associated with sealed surfacing system.

Such advantages mean that laid areas can be easily extended or phased without the need to undertake infrastructure work for the whole site at the onset.

For this particular project, the open nature of the site means that access may be required for a wide range of vehicles including coaches. To cater for this need, GRASSCRETE GC2 150mm thick has been used throughout, when combined with 8mm diameter mesh reinforcement this permits use by 30 tonne vehicles.

All phases have been constructed with plastic formers sourced in the UK, via our Spanish Agents. The lightweight nature of the formers means that transport costs are low, infact, much lower than would be for locally produced pre-cast blocks.

The low lying fenlands of England’s East Anglia is never the easiest place to construct large parking areas using traditional positively drained paving systems. Position a car park in a flood plain and it could be viewed as a problem of nightmarish proportions.

St Ives is a town with a parking problem – congestion in the market square has resulted in a traffic scheme that denies access into the central core, making out of town parking a necessity. The owners of the Dolphin Hotel close to the core, saw a means of gaining significant financial assistance in their desire to extend and develop the hotel. They had the land to provide both free parking for the hotel and paid parking for town visitors. The difficulty was that the area lies in a flood plain well below the adjacent road level making a positive draining system a non-starter.

An answer to the problem was found by using the GRASSCRETE GC3, 76mm deep, cast on site paving system substituting normal soil and grass infill with a 20-5mm gravel. The surface is designed to be self-draining without generally the need for pipework. In this installation, GRASSCRETE provides for the re-charge of both rain and flood impounding as well as enabling the natural rise and fall of near ground level water table levels.

The success of a product is often judged by repeat business and in this respect it is interesting to note that a recent extension to the car park has now more than doubled its size, again without the need for a drainage infrastructure.

Above and overleaf
The construction of the car park coincided with the development of a new wing to the hotel. A Barriered access from New Bridge Street enables charges to be made for parking on the area, which is usually fully occupied during business hours. The success of this has led to a recent extension to double the parking area.

Project Description and Brief

The Isle of Sheppey is a major centre for storage and pre-delivery inspection of imported vehicles. Much of the island is, however, low lying marsh or scrub which has in recent years been reclaimed by vehicle storage companies.

Storage areas have generally been constructed of compacted shale, minestone, slag or stone. On such a scale, however, little can be done to lower the natural ground water level. After rain, the areas drain slowly and continuous vehicle movement can, therefore, turn the adopted surfacing into expanses of mud and water. In dry spells, the mud then becomes dust forming a cycle of problems for the user.

In 1980 we were contacted by A G Weeks and Partners of Maidstone, Consulting Engineers acting on behalf of Pre-Delivery Inspection Limited of Queenborough. They themselves had encountered this problem. Their process of de-waxing and rustproofing were hampered by the abrasive coatings thrown up from the storage areas.

Project Specification

A surfacing system was called for which would solve the above problems and be structurally sound so as to cater for the long term loadings of continuous vehicle use. The Planning Authorities had insisted that the surface water run-off should be no greater than the existing surface in order not to overtax the islands stream and culvert network.

A brief was discussed with both Consultant Engineer and the Plant Manager. As a result, a Grasscrete system was adapted to provide a low cost, self-draining dust free surface.

GRASSCRETE GC3, 76mm deep, continuously reinforced cellular concrete surface was laid by our Contracts Division on a 100mm thick prepared sub-base.

The normal soil and grass or gravel filling to the pockets of the system was in this case omitted, the resulting void enabling the previous rate of drainage to be maintained. Instead of flooding, however, any head of water is now restricted to the pockets of the new surface. The vehicles are, therefore, able to park on a consistent, clean, dry surface.

The system in this form has now been operating successfully since then and has proved to be a cost effective major benefit to its users.

BEFORE CONSTRUCTION
Cars parked on poorly draining minestone, influenced by the naturally high water table

AFTER CONSTRUCTION
The cellular surface without pocket infill allows ground water to rise and fall. The surface however remains clean and load supporting.

Project Description and Brief

The National Trust owned property, Nostell Priory, situated 7 miles from Wakefield, in the North of England, is like many other stately homes throughout the country today – it relies upon gate receipts and proceeds from functions to finance the maintenance of the buildings and its grounds and estates.

It had become apparent in recent years that the influx of cars for the many functions was creating a problem in itself. With a limited macadam area available for parking, the visitors were directed on to the grass verges adjacent to the approach road to the Priory. The combination of haphazard parking and poor natural drainage had conceived unsightly scars on the natural grassland with visitors having to tread through wheel ruts to attend restaurant functions. In order to overcome the problem by providing permanent hard standings, the Estate Manager was faced with a number of problems:

1. The verges formed part of the vista to the Grade 1 Listed Priory; therefore, any system of surfacing used must be able to blend with the surrounding landscape, particularly when not in use.
2. The vista itself is used for field events such as motor spectaculars and country fairs. There would be a likelihood therefore that the verges would be subjected to loadings considerably in excess of normal car weights.
3. The grasslands were open to grazing by the Estate sheep; therefore, any surface adopted must not be injurious to the animals.
4. In order to obtain full benefit from the new parking area, the required method of parking should be clearly shown.
5. The tar macadam entrance road was laid with falls away from the centre of the road; therefore, the verges would be subjected to surface water run-off. As no existing water drainage system was available, any new surfacing must have self-draining capabilities.
6. The car parking system should provide a cost-effective alternative to traditional macadam surfacing.

Project Specification

An area of 800 m² was excavated to reduce levels, including the removal of excessive undulation in the existing ground.

After laying the 150mm thick layer of blinded Clause 803 Type 1 sub-base, GRASSCRETE GC2 (150mm thick) insitu surfacing was laid. Utilising the ‘long strip’ pouring conditions, Grass Concrete’s operatives were able to carry out the 70 m³ pour in three days.

In order to denote the required parking bays, integral solid strips of concrete 200mm wide were incorporated at 2.40 metre intervals. After burning out of the former tops, soiling and seeding, the solid strips provided a clear definition whilst still maintaining the theme of natural grassed areas.

The car park now provided parking for 70 vehicles. The GRASSCRETE system provides a continuously linked concrete surface for ease of walking. When not in use, the area becomes grazing land for sheep that are equally ‘at home’ on the surface.

The A483 Gresford Bypass has been constructed alongside a fast flowing Tributary River, with a potential to swell, the river was particularly erosive at the bends along its route. At one such point. Much of the road bund had been washed away during havy flood to the extent thatpassing toe restraint was in danger of being lost.

To counteract that problem Grass Concrete was called in to assist with a suitable design for reinstatement works.

The lost earthwork was first replaced with local stone of a low fines content, formed to a gradient of 1 in 2.1/2. A toe beam was then constructed with a rip-rap, introduced at the low water mark to slow the rate of flow.

To the new formation, a geotextile was introduced and the stone infill blimded with sand ready to receive cast insitu GRASSCRETE GC1, a 100mm thick system with a flow rating of 6 metres per second.

Upon grass establishment the GRASSCRETE has fully reinstated the natural environment, at the same time together with a structure that enables the release of hydro static pressure