This concerns a new build in a gap site, surrounded by 1970s houses with basements; none of these had pile foundations or similar.
The soil expert for the building company (developer) has now completed their work and presents the following results.
According to the soil report:
During the ground investigation, a highly organic layer of floodplain clay and mud with very low load-bearing capacity was found between 0.90 - 2.80 m (3.0 - 9.2 ft) below ground level. Because of these soils being prone to settlement, additional measures are necessary for the foundation (such as pile foundations with bored piles or deep foundations with concrete shaft rings).
Ground/stratified water: Water strike at 2.70 - 2.80 m (8.9 - 9.2 ft) below ground level, measured after drilling completion at 1.60 - 1.70 m (5.2 - 5.6 ft) below ground level (pressurized). Groundwater is possible in sandy and gravelly layers depending on precipitation.
Groundwater level (GWL): 0.40 m (1.3 ft) below ground level [-0.78 m relative].
Seepage water: After heavy rainfall events, full saturation of soil pores up to ground level is possible (pore water saturation), resulting in puddle formation.
Soil profile:
1. From surface to 0.30 m (1.0 ft) below ground level: Topsoil, sand, silty - weakly silty, slightly humic.
Consistency/structure: loose to partly medium dense. Color: dark brown - brown-grey - dark grey - brown.
2. From 0.30 m to 0.90 - 1.00 m (3.0 ft) below ground level: Cover sediments, sand, strongly silty - silty.
3. From 0.90 - 1.00 m to 2.70 - 2.80 m (3.0 - 9.2 ft) below ground level: Floodplain clay/mud, silt, sandy - slightly sandy, slightly clayey, organic.
General characteristics: Layers 2 and 3 are highly organic (decomposed wood and plant remains with musty odor).
4. From 2.80 m to 5.00 m (9.2 - 16.4 ft) below ground level: Fluviatile sediments, sand, weakly silty, weakly gravelly, in core sample 1 from 4.60 m (15.1 ft).
General characteristics: Sand, strongly silty.
Question: Pile foundations would not only be costly but also much more complex due to pressure probing (15 m to 20 m [49 - 66 ft]), aerial survey proving freedom from utility lines and unexploded ordnance, monitoring, etc. Is there an alternative solution here?
Thank you in advance!
The soil expert for the building company (developer) has now completed their work and presents the following results.
According to the soil report:
During the ground investigation, a highly organic layer of floodplain clay and mud with very low load-bearing capacity was found between 0.90 - 2.80 m (3.0 - 9.2 ft) below ground level. Because of these soils being prone to settlement, additional measures are necessary for the foundation (such as pile foundations with bored piles or deep foundations with concrete shaft rings).
Ground/stratified water: Water strike at 2.70 - 2.80 m (8.9 - 9.2 ft) below ground level, measured after drilling completion at 1.60 - 1.70 m (5.2 - 5.6 ft) below ground level (pressurized). Groundwater is possible in sandy and gravelly layers depending on precipitation.
Groundwater level (GWL): 0.40 m (1.3 ft) below ground level [-0.78 m relative].
Seepage water: After heavy rainfall events, full saturation of soil pores up to ground level is possible (pore water saturation), resulting in puddle formation.
Soil profile:
1. From surface to 0.30 m (1.0 ft) below ground level: Topsoil, sand, silty - weakly silty, slightly humic.
Consistency/structure: loose to partly medium dense. Color: dark brown - brown-grey - dark grey - brown.
2. From 0.30 m to 0.90 - 1.00 m (3.0 ft) below ground level: Cover sediments, sand, strongly silty - silty.
3. From 0.90 - 1.00 m to 2.70 - 2.80 m (3.0 - 9.2 ft) below ground level: Floodplain clay/mud, silt, sandy - slightly sandy, slightly clayey, organic.
General characteristics: Layers 2 and 3 are highly organic (decomposed wood and plant remains with musty odor).
4. From 2.80 m to 5.00 m (9.2 - 16.4 ft) below ground level: Fluviatile sediments, sand, weakly silty, weakly gravelly, in core sample 1 from 4.60 m (15.1 ft).
General characteristics: Sand, strongly silty.
Question: Pile foundations would not only be costly but also much more complex due to pressure probing (15 m to 20 m [49 - 66 ft]), aerial survey proving freedom from utility lines and unexploded ordnance, monitoring, etc. Is there an alternative solution here?
Thank you in advance!
@11ant
Because of the basement, the neighbors have their foundations below the non-load-bearing layer.
A full soil replacement could be an alternative. Cheaper? Well, not really.
This plot is meant for a house with a basement. If you don’t want that, don’t buy it.
Disposal of the slurry could also incur additional costs. But now at least you know why there was a gap for 50 years.
Because of the basement, the neighbors have their foundations below the non-load-bearing layer.
A full soil replacement could be an alternative. Cheaper? Well, not really.
This plot is meant for a house with a basement. If you don’t want that, don’t buy it.
Disposal of the slurry could also incur additional costs. But now at least you know why there was a gap for 50 years.
@lisaa11
You won’t have any other option than to get offers and cost estimates for all the different options... pile foundation, well foundation, soil replacement, basement...
We built our foundation using 16 concrete ring sections of 1.00 meter (3.3 feet) each, with a depth of 4.00 to 4.50 meters (13 to 15 feet)...
...at our neighbor’s house with a basement, we carried out a soil replacement directly underneath... it was a bit cheaper but, of course, primarily faster.
If you want to know more about this, just let me know. However, I work for a construction company, so our planning and execution regarding costs are naturally quite different.
Good luck!
You won’t have any other option than to get offers and cost estimates for all the different options... pile foundation, well foundation, soil replacement, basement...
We built our foundation using 16 concrete ring sections of 1.00 meter (3.3 feet) each, with a depth of 4.00 to 4.50 meters (13 to 15 feet)...
...at our neighbor’s house with a basement, we carried out a soil replacement directly underneath... it was a bit cheaper but, of course, primarily faster.
If you want to know more about this, just let me know. However, I work for a construction company, so our planning and execution regarding costs are naturally quite different.
Good luck!
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