Rock Structures
Rock revetments and structures have been used successfully in coastal, river and dam engineering for many years. By combining the strength of rock and the flexibility of mastic grout, an incredibly robust and versatile material is available to engineers when combating erosion and scour.
For new rock structures, a rock / mastic combination offers considerable benefits to both the engineer and the environment. For existing rock structures which no longer provide a satisfactory factor of safety against the design loads, mastic grout can be applied as a cost effective alternative to overlaying/replacing with new rock.
Environmental advantages of grouted rock
- A thinner rock / mastic layer means less material acquisition
- With less material to import road haulage is reduced
- Can use a lower grade rock so locally won materials more likely to be suitable
- Easily recycled mastic helps achieve sustainability targets
- Natural stone appearance retained by placing black grout around not over rock
- Asphalt blends with rock colour in time
- Smaller voids on surface makes for safer structures in areas of public access
Engineering advantages of grouted rock
- Security of structure increased by bound rather than individual elements
- Security of vulnerable sections of rock structure increased by local application
- Angle of designed slope can be increased when grout is added to rock
- Bituminous grout can be placed underwater
- A heat tolerance can be built into grout design appropriate for local climate
There are 4 different techniques for grouting as follows
Surface Grouting
When the existing revetment stone is barely adequate to resist hydraulic loads, applying a limited amount of grout over the whole surface will increase the security of the revetment. Approximately 30% voids in top half of stone layer are filled.
Pattern Grouting
Grout penetrates the full depth of the stone layer over 50-70% of the surface, increasing the effective weight of the stone by 5-7 times. It allows new designs with smaller rock in thinner layers, but is most useful for upgrading rock revetments which no longer satisfy the design load conditions. The construction creates a very strong grid of grouted stone, with voids in between to retain the necessary porosity.
Full Grouting
Fully grouted stone is a very robust material virtually unaffected by waves and currents. Used in locations where the integrity of the structure is crucial and access for maintenance is difficult. Placed as a layer it is flexible and will follow settlements for toe details.
Selective Grouting
Grouting the most vulnerable parts of a rock structure will give additional security to these areas. For example, the ends of breakwaters/groynes and the inter-tidal zone of revetments.
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