Retaining Wall

[Flyboy]

Hi all,
Was after some help with a retaining wall we're building. We're using concrete blocks (not exactly sure what they're called) that Concrite make up from their left over concrete. They are 1200x600x600 and weigh about 1 tonne. The wall has to go on a river front, about 800mm high, and the land slopes back from it about 1:3.

Have been to the structural engineer, and he's specified that the design of the wall has to be roughly as per the attachment. My 2 concerns with this are:

1. The wall has the 1200 length of the block at 90 degrees to the river, not parallel as you would, say, in a normal brick wall. This greatly increases the number of blocks required and not sure if the council will allow us to excavate that far back.
2. If we could reduce the depth of the footing to around 400mm, that would allow us to only have 2 rows of blocks instead of 3, also reducing the number of blocks needed.

I think the engineer's main concern is that the tide will wash away the sand from underneath the wall, and that's why he has made the wall so 'hefty'. I was thinking, would a gravel footing under the wall reduce the amount of sand being eroded? If not, would some kind of barrier between the tide and the sand help. I have no idea about seawalls but was thinking if you could sink some FC sheeting into the sand in front of the wall this might stop the sand being washed away. Have to speak to the engineer on Monday, so any other ideas I can fire at him will be greatly appreciated.

Cheers

[Sturdee]

Have been to the structural engineer, and he's specified that the design of the wall has to be roughly as per the attachment.

By all means ask the engineer those questions and ask him to explain his reasons for the way he has calculated the wall to be built, but I presume that he has taken all those things into account when designing this wall.

He may well have taken a very conservative approach but he is certifying, and taking the responsibility, for the structural integrity of that wall.

Peter.

[Wood Butcher]

I'd go with Sturdee on this one. The engineer would not say to do what you have mentioned without a good reason. Remember that he is the professional with (hopefully) the right knowledge and experience. I you disregard his recommendations than you could end up regretting it down the track.
But.... by all means ask why he designed it like that and if you are still really against the idea get another opinion for an alternative design (if there is one!)

[Flyboy]

Thanks for the replies,

I guess my worry is that he is being overly conservative. We did have another engineer who was going to specify a wall basically as I have described, 2 rows of blocks, 400mm footings. Unfortunately, his customer service left a lot to be desired, spent 3 months chasing him about this and various other things and just gave up.

The other thing is that all of the neighbours have 'normal' type retaining walls - sandstone blocks, loc-a-blocks, even corrugated fibro. All of which I presume have also been certified by an engineer.

BTW, has anyone used these blocks before? If the engineer still isn't happy with my suggestions, was wondering if there was a way you could anchor the blocks to each other to strengthen the wall.

Cheers