Complex sentence: The southern piers on Inchgarvie are sited on solid rock with a slope of around 1 in 5, so the rock was prepared with concrete and sandbags to make a landing-spot for the caissons.
Split into simpler sentences: The southern piers on Inchgarvie are sited on solid rock with a slope of around 1 in 5. The rock was prepared with concrete and sandbags to make a landing-spot for the caissons.