iandig
Civil/Environmental
- Apr 10, 2003
- 212
Does anyone have any experience of 'attempting' to interpret data recorded during the formation of vibro-stone columns? I have received a large amount of data from the ground improvement contractor, which consists of the depth of penetration, along with pressure.
I am in the unenviable position where the ground improvment contractors site agent has said that the quality of the data is 'like a big DCP' and that 'there is a relationship between the pressure required and shear strength', but their own technical guys can only give a explaination of what the graph is showing and can't commit [understandably] to anything more. The Client is now expecting some form of qualative assessment, and even though we have explained at great length that this is very difficult to achieve and we don't currently have the comparative analysis data to form any kind of interpretation, we are doing whatever we can to aid the situation.
The reason for the desire to understand the data, is that the work is being completed on engineered fill, some of which has now been shown to be below the minimum requirement [post placement investigation], but its deposition within the fill is random i.e. poor fill placed discretely with no supervison or testing. There was no full-time supervision of the site works, and testing was only conducted when the earthworks contractor was 'ready' as it was only initially a general backfill operation and not covered by any specification until sometime after the infilling had already begun. Now the Client has signed up to provide a building over it within 6 months, without checking the ground conditions first. Foundation are to be founded on vibro-replacement stone columns, but nothing done yet for the floor slab. Maximum depth of the fill is circa 7m, which in turn overlies competent sandstone/ironstone. Fill is predominantly cohesive, and where tested acheived at least 95% of modified proctor [4.5kg rammer], less than 5% air voids and CBRs in excess of 5%. Where subsequent testing was done once the issue of the building was announced, shear stengths of less than 40 kN/m² were recorded at various depths, all below 3m from GL but pockets down to 6m. Distribution of the soft layers could be random, or could be continuous, just data so far is too limited. We have been reccomending CPT work to confirm ground conditions, but still waiting mobilisation of rig to site, which may turn up after the foundations for columns have been poured. Column loads have equated to allowable bearing pressure of 125kN/m², and floor slab has a design loading of 50 kN/m² [likley to be much lower than this, <10kN/m²]
Any help or advise would be greatly appreciated.
Many thanks
I am in the unenviable position where the ground improvment contractors site agent has said that the quality of the data is 'like a big DCP' and that 'there is a relationship between the pressure required and shear strength', but their own technical guys can only give a explaination of what the graph is showing and can't commit [understandably] to anything more. The Client is now expecting some form of qualative assessment, and even though we have explained at great length that this is very difficult to achieve and we don't currently have the comparative analysis data to form any kind of interpretation, we are doing whatever we can to aid the situation.
The reason for the desire to understand the data, is that the work is being completed on engineered fill, some of which has now been shown to be below the minimum requirement [post placement investigation], but its deposition within the fill is random i.e. poor fill placed discretely with no supervison or testing. There was no full-time supervision of the site works, and testing was only conducted when the earthworks contractor was 'ready' as it was only initially a general backfill operation and not covered by any specification until sometime after the infilling had already begun. Now the Client has signed up to provide a building over it within 6 months, without checking the ground conditions first. Foundation are to be founded on vibro-replacement stone columns, but nothing done yet for the floor slab. Maximum depth of the fill is circa 7m, which in turn overlies competent sandstone/ironstone. Fill is predominantly cohesive, and where tested acheived at least 95% of modified proctor [4.5kg rammer], less than 5% air voids and CBRs in excess of 5%. Where subsequent testing was done once the issue of the building was announced, shear stengths of less than 40 kN/m² were recorded at various depths, all below 3m from GL but pockets down to 6m. Distribution of the soft layers could be random, or could be continuous, just data so far is too limited. We have been reccomending CPT work to confirm ground conditions, but still waiting mobilisation of rig to site, which may turn up after the foundations for columns have been poured. Column loads have equated to allowable bearing pressure of 125kN/m², and floor slab has a design loading of 50 kN/m² [likley to be much lower than this, <10kN/m²]
Any help or advise would be greatly appreciated.
Many thanks