Chickenhawk6451
Structural
- Mar 9, 2019
- 15
Hi everyone,
I've been practising for about 5 years now and have done my fair share of retaining walls and have come across something interesting. To be short, the site geology is rocky with 0.5 - 1m of residual soils over the top of the bedrock. In order to design the footing I've been snookered into a situation where I need to combine my footing slab and retaining wall for this site. This is mostly due to the practicality of excavating rock in order to do a more traditional "Offset T" style retaining wall.
My question is this; It is a reasonable assumption that an integrated slab-retaining wall system would act as 1 whole system and utilise all 3 stems of the slab in resistance against sliding from forces in the retaining wall?
My logic is that each individual stem would act as a shear-key to resist the forces developed by the active soil pressure behind the retaining wall. I would consider that each stem acts as a shear key because they are sufficiently far apart that the failure plane of the soil from each stem would not affect the failure plane of the adjacent ones.
However I also acknowledge that globalised failure plane of the soil may exist, extending under the first stem and skip past the other two, leaving only 1 stem resisting the soil pressure. In this situation the slab will slide as there is insufficient depth available to develop sliding resistance from the stems.
Soil is gravelly sand with traces of silt, bulk density = 18kN/m³ and internal friction coefficient of 30°
Any guidance you have would be appreciated, hoping to create an efficient design for the client as this is a residential job so really tight budgets for all involved.
Kind regards,
Chickenhawk
I've been practising for about 5 years now and have done my fair share of retaining walls and have come across something interesting. To be short, the site geology is rocky with 0.5 - 1m of residual soils over the top of the bedrock. In order to design the footing I've been snookered into a situation where I need to combine my footing slab and retaining wall for this site. This is mostly due to the practicality of excavating rock in order to do a more traditional "Offset T" style retaining wall.
My question is this; It is a reasonable assumption that an integrated slab-retaining wall system would act as 1 whole system and utilise all 3 stems of the slab in resistance against sliding from forces in the retaining wall?
My logic is that each individual stem would act as a shear-key to resist the forces developed by the active soil pressure behind the retaining wall. I would consider that each stem acts as a shear key because they are sufficiently far apart that the failure plane of the soil from each stem would not affect the failure plane of the adjacent ones.
However I also acknowledge that globalised failure plane of the soil may exist, extending under the first stem and skip past the other two, leaving only 1 stem resisting the soil pressure. In this situation the slab will slide as there is insufficient depth available to develop sliding resistance from the stems.
Soil is gravelly sand with traces of silt, bulk density = 18kN/m³ and internal friction coefficient of 30°
Any guidance you have would be appreciated, hoping to create an efficient design for the client as this is a residential job so really tight budgets for all involved.
Kind regards,
Chickenhawk