filler and 10% Yssel lake sand, and reinforcement of cocos 

 matting with o 015 m gauge sprayed with a binder before use. 



The methods described above for construction, at the site 

 or elsewhere, transportation and placing of asphalt mattresses 

 can only be used in quiet water, whereas the slabs must be of 

 restricted size -when floating cranes or drums are being used» 

 For some time therefore attempts have been made to find a method 

 to transport and sink asphalt-mattresses, similar to the one 

 which can be used with fascine mattresses , Also, if an asphalt 

 mattress of any size could be kept afloat with inexpensive 

 means and could be towed through a medium swell, the skilled 

 fascine mattress workers could be used to assist in the difficult 

 handling and placing of the mattresses, which would be of great 

 value e In the system of W c J e van der Oord this can be achieved 

 by providing the asphalt mattress with a temporary flexible rim 

 of some impermeable material, thus forming a vessel of sufficient 

 buoyancy „ 



A mattress of asphalt mortar was constructed for the piers 

 at Hook of Holland according to this system The mixture con- 

 tained 20% asphaltic bitumen 60 /70, 10$ filler and 10% dune sand« 

 The slab, 7e5 x 3 x 07 m, was reinforced with cocos matting 

 of Oo015 m gauge and three towing cables of wire rope„ The 

 slab was constructed on a horizontal wooden floor which was built 

 at a small beach along the New Waterway near Hook of Holland, 

 at 0„80 m below the high water level (Figure 18) The slab 

 floated as soon as the water reached 0.20 m above the floor and 

 was towed out on the river e The asphalt slab and rim followed 

 the wave movement easily (Figure 19 ) e Presently the slab was 

 towed back and anchored above the floor after which water was 

 admitted through the tube in the centre and the slab was sunk 

 for the time being to await transport to its final destinations 



Although dependent on the most suitable construction method, 

 it is to be expected that the cost of such a mattress will be 

 considerably less than the cost of a fascine mattress with dumped 

 stone o 



The advantage of an asphalt mattress over a fascine mattress 

 is that in sea water the former will nut be attacked by the ship 

 worm (teredo navaiis)^ Experience will show whether the asphalt 

 mattress will stand up under current and wave action and whether 

 it is suitable for the protection of steep and uneven submarine 

 slopes c. 



Reinforc ement of _Beach Groins and Ha rbour Dams 



One of the great difficulties met in the construction of 

 beach groins and harbour dams, is tha removal of damped stone 

 and set stone by wave action „ This is true particularly near 

 deep water ? where the effect of a heavy ground swell may be 



