Good one GeoEnvGuy - I guess the Reeve didn't know about offshore drilling platforms and that oil companies wouldn't spend hundreds of millions of dollars without knowing what their oil producing platform was to sit on.
It would be interesting to know more details about the alignment of the pipeline - will it be a long pipeline or relatively short (say 100 m). 4 m deep seems like it would be a very small lake. A barge would be expensive and the OP might not even be able to get a barge to the lake. All the pictures of platforms for offshore are of the "huge" variety. In Indonesia many years ago - we drilled off the coast in the Java Sea - water level about 4 to 6 m. Primitive platforms were made by the drilling contractor by driving poles into the sea bottom - then putting on a wood deck. Using a small diamond rig that could be disassembled, they would manhandle it onto the platform - about 3 m above water level - and then carry out the investigation - as noted, by putting casing to the sea bottom. It worked very well - and given the nature of the project, this might be cheaper than going for a Mercedes. The OP said that they cannot/will not do CPT; yes, it would be nice but the OP has constraints. We do not know the nature of the soil beneath the lake bottom - possible some loon schiesse, maybe not. If it were I, once the platform was in place and given the equipment with which he is to use in the investigation, I would consider driving a Canadian dynamic cone (50 mm cone at 60deg apex on the end of an A-rod driving with the 62.4 kg hammer (140#) dropping 750 mm (30"). This would give the OP a quick understanding of what the OP is dealing with - substantial soft material? Shallow - say 1 m of soft material? etc. This would help him, too, decide what the OP should anticipate using in his "retrieval" methods - SPT, thin-walled tubes, vane testing, etc.
Years ago (1978), I was involved in a CP railroad siding widening up near Estaire Ontario (south of Sudbury). We knew the site was peat underlain by competent material. We had a drill rig with us which moving along the track for probing at, say 50 to 75 m - would involve a lot of moving time and then, too, we had to worry about the existing track being used by trains. We would have to move the drill rig off the hole when a train was coming. I decided to take a split spoon and rods and "hand push" the spoon into the peat until I hit something "hard". This worked very well in that I was able to determine how thick the peat was at many locations (not good for extending the width of the rail embankment and also, with the split spoon at the end I was able to get a sample of the upper few inches of the competent material - to keep in mind that a number of boreholes were to also to be drilled. It seems that ASTM a few years late put out a "standard" on this. I did something similar in north New Jersey from a boat on a local pond that was to be filled in as part of a new building complex.
The OP could also use a small rowboat and probe the lake bottom to determine how much "mud" - or better, loon scheisse was a the lake bottom. Of course, knowing the thickness of incompetent material is very important in the installation of the pipeline.
Sometimes we do not have the money to do a "perfect" job - this is where thinking comes into play 0- to figure out what can be done with what one has.
My view on this post for what it is worth.
