Course 01: Soil, Relief, and Geological Nature in Architectural Design

Criteria for Soil Identification: Morphology and relief are identified as the primary and only criteria that allow for the identification of soil when it is hidden beneath vegetation (plantations) or existing infrastructure.
The Topographic Slope: This serves as an indexing tool for the definition of natural sites, such as mountains and hills.
Calculation of the Slope: The slope is defined as the mathematical ratio between the height (vertical drop or dénivelé) and the horizontal distance. It can be expressed as: $\text{Slope} = \frac{\text{Height (Dénivelé)}}{\text{Horizontal Distance}}$
Classification of Pente Types: Slopes are generally categorized into three distinct types based on their intensity:
- Gentle (Douce).
- Moderate (Modérée).
- Steep/Strong (Forte).

Role of Foundations: The fundamental purpose of foundations is to ensure the effective transmission of structural loads to the soil. This process is essential to guarantee both the stability and the safety of the construction.
Foundations Based on Soil Depth:
- Superficial Foundations (Fondations superficielles): Utilized when the "good soil" (load-bearing strata) is at a shallow depth of $\le 3\,meters$ . Examples include isolated footings (semelles isolées) or strip footings (semelles filantes).
- Semi-Deep Foundations (Fondations semi-profondes): These are employed in scenarios where superficial foundations are insufficient to reach stable ground. An example provided is concrete shafts or wells (puits en béton).
- Deep Foundations (Fondations profondes): Required when the load-bearing soil is located at a significant depth, specifically at distances $> 6\,meters$ . The primary example provided is the use of piles (pieux).
Special Cases in Foundation Engineering:
- Micropiles (Micropieux).
- Slurry walls (Parois moulées).
- Watertight screens/diaphragms (Écrans étanches).

Identified Risks: Building on slopes carries inherent geological and environmental hazards, including:
- Presence of clay, which leads to swelling (gonflement).
- Underground cavities.
- Rockfalls (Éboulements) and avalanches.
- Landslides (Glissements).
The Geotechnical Study: This study is considered essential for identifying the mechanical characteristics of the soil. The data gathered from this study is what dictates the specific type of foundation to be implemented.
Stabilization Techniques:
- Drainage Systems: Devices designed to evacuate runoff water and reduce water infiltration into the soil.
- Introduction of Resistant Elements: Structural interventions such as retaining walls (murs de soutènement), tie-backs/anchors (tirants/ancrages), or rows of piles.
- Earthworks (Terrassements): The modification of the site's topography to restore physical equilibrium.
Components of Earthworks (Terrassements):
- Excavation (Déblais): The process of removing soil to lower the ground level.
- Embankment/Fill (Remblais): The process of depositing soil to raise the ground level.

Role of Embankment (Talutage): The primary objectives are to prevent soil collapse (éboulement) and to eliminate the lateral pressure (poussée) exerted by the earth.
Classification of Slope Types (By Ratio and Stability):
- 1 pour 1 ( $100\%$ ): Used for unstable or crumbly (ébouleux) terrain.
- 3 pour 2 ( $65\%$ ): Subject to erosion risks; these slopes require revegetation (végétalisation).
- 2 pour 1 ( $50\%$ ): Suitable for soft/tender terrains that remain resistant and stable.
- 3 pour 1 ( $33\%$ ): Landscaped slopes that are compact and stable.
- 4 pour 1 ( $25\%$ ): Gently sloped ramps that are easily accessible.

Surface Protection: Methods used to stabilize surfaces include the revegetation of walls or the application of coverings made of stone or concrete.
Technical Solutions for Retaining Walls:
- Dry stone walls (Mur sec).
- Gabions (Gabion).
- Wooden logs (Rondins de bois).
- Riprap/Rock armour (Enrochements).
- Reinforced concrete (Béton armé).

Implantation in Overhang/Suspension (Sur Pilotis): The structure is detached from the ground using stilts. This method has a minimal environmental impact but often results in limited access.
Stepped Implantation (En Gradins/Paliers): The design follows the natural incline of the terrain in a cascade or staircase fashion, respecting the original natural terrain.
Embedded/Semi-Buried Implantation (Encastrée): This provides harmonious integration with the landscape and offers the benefit of natural thermal insulation.
Implantation by Land Displacement: The structure is placed flat on a leveled area created through massive earthworks. This is generally to be avoided as it significantly deforms the natural terrain. If used, the recommended guidelines suggest a balance of $50\%$ fill (remblais) and $50\%$ excavation (déblais).

Access to the Parcel: It is recommended to soften steep descents by designing curves or turns (virages). The location of the garage should be determined by the position of the access road, categorized as either upstream (amont) or downstream (aval).
Treatment of Pathways:
- Includes pedestrian paths, stairs, and plazas.
- Pathways should ideally be sinuous and narrow, with widths ranging between $1.5\,meters$ and $3\,meters$ .
- The use of stairs is mandatory if the slope exceeds $12\%$ .
Utility Networks (Réseaux Divers/VRD):
- Definition: The collective works required for site development, including water, gas, electricity, telecommunications, sanitation (sewage), and public lighting.
- Constraints on Slopes: Long-term profiles must be studied meticulously to respect specific flow velocity limits, particularly for sanitation/sewage systems.
- Water Supply: Identify the level and type of potable water service (fountains, wells, or networks) at the start of the project.
- Cable Networks: The general recommendation is to bury them. However, aerial solutions should be chosen if the soil is unstable (risk of landslide) or exceptionally rocky.

Required Site Knowledge: Architectural projects on slopes require understanding two key factors:
- Morphology (Relief): Identified via the degree of inclination/slope.
- Physical Consistency (Nature Géologique): This is imperative for determining the type and dimensions of the foundations.
Mandatory Preliminary Operations:
1. Calculation of the terrain slope.
2. Completion of a geotechnical soil study.
Specific Adjustments for Slopes:
- Execution of earthworks and stabilization for the creation of construction platforms.
- Strategic choice of implantation (pilotis, gradins, encastrée, or land displacement).
- Adaptation of pathways, access points, and various networks such as wastewater evacuation and electrical distribution.