ᐅ Foundation Recommendation after Demolition of a Semi-Detached House from 1880
Created on: 10 Nov 2021 10:16
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projektlandlieP
projektlandlie10 Nov 2021 10:16Hello everyone!
I would appreciate your assessment of the following topic:
---- Situation ----
Purchased a semi-detached house from the family. Built in 1880. Located in a rural area. Founded on natural rock stones. No concrete slab foundation. The semi-detached house is planned to be demolished and replaced with a new building without a basement (timber frame construction, clad with brick facing as required by the building authority) on the same footprint. Not wider, longer, or taller (requirements from the building authority, rural area!). Living area after reconstruction: 126 sqm (1357 sq ft), 1.5 stories.
--- Soil Report ---
2. Subsoil
The subsoil was investigated by four dynamic core borings (BS1 to BS4) down to a depth of 5.0 m (16 ft) below the ground surface (GOK). The locations of the boreholes can be found in the site plan; the results are illustrated in the bore profiles (Appendix 2).
The starting heights of the borings range between -1.81 m (-6 ft) and -0.59 m (-2 ft) relative to the reference point (HFP = manhole cover at the position indicated on the site plan).
The results show that up to depths of 3.2 m (10.5 ft) below ground surface (BS1), 2.6 m (8.5 ft) (BS2), 0.2 m (0.7 ft) (BS3), and 0.6 m (2 ft) (BS4), there are humus-rich topsoils, fill soils, and softened clay soils.
Beneath these layers are glacial tills (boulder clay, glacial marl) and, locally, medium-dense sands. The tills are classified according to consistency as “soft-plastic” (BS4: 2.4–2.8 m (8–9 ft) depth), “soft to stiff” (BS3: 2.2–3.6 m (7–12 ft); BS4: 1.2–1.8 m (4–6 ft)), and “stiff-plastic” (BS1: 3.2–5.0 m (10.5–16 ft); BS2: 2.6–5.0 m (8.5–16 ft); BS3: 3.6–5.0 m (12–16 ft); BS4: 1.8–2.4 m (6–8 ft) and 2.8–5.0 m (9–16 ft)).
3. Groundwater
After completion of the investigations, groundwater levels were measured between 1.14 m (3.7 ft) and 2.28 m (7.5 ft) below ground surface. These are shallow groundwater levels subject to seasonal and weather-related fluctuations.
4. Soil Assessment / Foundation
The near-surface soil layers in the area of the planned building constitute ground with a high potential for settlement, so deep foundation on small piles is recommended.
Load-bearing soils (glacial marl with at least stiff-plastic consistency) appropriate for deep foundation are available from depths of HFP -4.8 m (-16 ft) (BS1), HFP -4.5 m (-15 ft) (BS2), HFP -4.4 m (-14.5 ft) (BS3), and HFP -3.4 m (-11 ft) (BS4). The piles must be embedded depending on the required load and considering negative skin friction at least 3 m (10 ft) into the load-bearing subsoil.
For protection of the base slab against soil moisture and hydrostatic pressure, the DIN 18533-1: 2017-07 standard must be followed. Without drainage, a design water level at ground surface (top of terrain) must be assumed.
In the transition area between the neighboring semi-detached house and the planned new building, the guidelines of DIN 4123 for building stabilization must be followed.
Excavation work can be performed with open water control. Proper drainage of surface water must be ensured.
--- Uncertainty ---
The structural engineer (not the engineer for our new building) who is responsible for certifying the “structural stability of the remaining semi-detached house” required by the building authority for the demolition is now questioning the planned pile foundation. Quote: "This house has stood on natural rock stones since 1880 and has settled. If a strip foundation is installed in the same location, that might be sufficient, and an expensive pile foundation may not be necessary. This should at least be examined, especially since the new building will be a lighter timber frame house with brick facing."
What do you think about this? Thank you very much for your feedback.
-The Projekt Landliebe-
I would appreciate your assessment of the following topic:
---- Situation ----
Purchased a semi-detached house from the family. Built in 1880. Located in a rural area. Founded on natural rock stones. No concrete slab foundation. The semi-detached house is planned to be demolished and replaced with a new building without a basement (timber frame construction, clad with brick facing as required by the building authority) on the same footprint. Not wider, longer, or taller (requirements from the building authority, rural area!). Living area after reconstruction: 126 sqm (1357 sq ft), 1.5 stories.
--- Soil Report ---
2. Subsoil
The subsoil was investigated by four dynamic core borings (BS1 to BS4) down to a depth of 5.0 m (16 ft) below the ground surface (GOK). The locations of the boreholes can be found in the site plan; the results are illustrated in the bore profiles (Appendix 2).
The starting heights of the borings range between -1.81 m (-6 ft) and -0.59 m (-2 ft) relative to the reference point (HFP = manhole cover at the position indicated on the site plan).
The results show that up to depths of 3.2 m (10.5 ft) below ground surface (BS1), 2.6 m (8.5 ft) (BS2), 0.2 m (0.7 ft) (BS3), and 0.6 m (2 ft) (BS4), there are humus-rich topsoils, fill soils, and softened clay soils.
Beneath these layers are glacial tills (boulder clay, glacial marl) and, locally, medium-dense sands. The tills are classified according to consistency as “soft-plastic” (BS4: 2.4–2.8 m (8–9 ft) depth), “soft to stiff” (BS3: 2.2–3.6 m (7–12 ft); BS4: 1.2–1.8 m (4–6 ft)), and “stiff-plastic” (BS1: 3.2–5.0 m (10.5–16 ft); BS2: 2.6–5.0 m (8.5–16 ft); BS3: 3.6–5.0 m (12–16 ft); BS4: 1.8–2.4 m (6–8 ft) and 2.8–5.0 m (9–16 ft)).
3. Groundwater
After completion of the investigations, groundwater levels were measured between 1.14 m (3.7 ft) and 2.28 m (7.5 ft) below ground surface. These are shallow groundwater levels subject to seasonal and weather-related fluctuations.
4. Soil Assessment / Foundation
The near-surface soil layers in the area of the planned building constitute ground with a high potential for settlement, so deep foundation on small piles is recommended.
Load-bearing soils (glacial marl with at least stiff-plastic consistency) appropriate for deep foundation are available from depths of HFP -4.8 m (-16 ft) (BS1), HFP -4.5 m (-15 ft) (BS2), HFP -4.4 m (-14.5 ft) (BS3), and HFP -3.4 m (-11 ft) (BS4). The piles must be embedded depending on the required load and considering negative skin friction at least 3 m (10 ft) into the load-bearing subsoil.
For protection of the base slab against soil moisture and hydrostatic pressure, the DIN 18533-1: 2017-07 standard must be followed. Without drainage, a design water level at ground surface (top of terrain) must be assumed.
In the transition area between the neighboring semi-detached house and the planned new building, the guidelines of DIN 4123 for building stabilization must be followed.
Excavation work can be performed with open water control. Proper drainage of surface water must be ensured.
--- Uncertainty ---
The structural engineer (not the engineer for our new building) who is responsible for certifying the “structural stability of the remaining semi-detached house” required by the building authority for the demolition is now questioning the planned pile foundation. Quote: "This house has stood on natural rock stones since 1880 and has settled. If a strip foundation is installed in the same location, that might be sufficient, and an expensive pile foundation may not be necessary. This should at least be examined, especially since the new building will be a lighter timber frame house with brick facing."
What do you think about this? Thank you very much for your feedback.
-The Projekt Landliebe-
H
hanghaus200010 Nov 2021 10:37The geotechnical engineer has given their recommendation. If a structural engineer disregards this advice, they are responsible for the consequences. You should ask the structural engineer (not the one from the house) if they can justify this safely. A deep foundation certainly also carries risks for the existing semi-detached house.
Have you removed the foundation of the old house? You should be able to use it for the new building with the same dimensions, right? This would not only be the best solution for the neighboring house.
The additional party wall to the neighbor will probably be the issue.
Have you removed the foundation of the old house? You should be able to use it for the new building with the same dimensions, right? This would not only be the best solution for the neighboring house.
The additional party wall to the neighbor will probably be the issue.
P
projektlandlie10 Nov 2021 10:43hanghaus2000 schrieb:
The soil expert has given their recommendation. If a structural engineer overrides this recommendation, they assume full responsibility. You should ask the structural engineer (not the one for the house) if they can justify it safely. Because a deep foundation certainly carries risks for the existing semi-detached house.
Have you demolished the foundation of the old house? You should be able to use it for the new build with the same dimensions, right? This would surely be the best solution not only for the neighboring house. That’s exactly how the structural engineer sees it. Possibly a foundation on the existing rock stones since the house will have the same dimensions. The general contractor has just started the calculations with him. I’m curious to see the outcome.
H
hanghaus200010 Nov 2021 10:54Unfortunately, your plan is not readable on Instagram. Please upload the plan here in JPG format.
Is a concrete slab on strip foundation planned?
Who will supply it? The timber house builder?
Is a concrete slab on strip foundation planned?
Who will supply it? The timber house builder?
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