Recently we undertook some stability analytics for a heavy crawler crane. The ground investigation indicated that the salient stratum was of a predominantly granular composition with some silt. We often see, through checking and review commissions, that engineers are inclined to err on the conservative side and assume effective cohesion of zero. Often, this will put marked constraints on the site activity.
Based on the soil descriptions and taking the ground investigation report at face value, one would have been forgiven for making the same assumption at the site in question. However, a quick spin around site showed that some excavations had already been undertaken, cut at 50°-60° and standing up to 5m for a substantial period. Based on this observation, we could take some effective cohesion into account.
The benefits of taking this cohesion into account for this particular project was that we could position the crane closer to the works meaning a larger (more expensive) crane wasn’t required. Additionally, the specification on the crane platform was relaxed resulting in cost saving on materials and preparation.
As our drawing and photograph adjacent show, the design is there for scrutiny. Fully exposed and nothing to hide!