Comprehensive Notes on Earth Construction Systems

Earth construction is categorized into various structural systems according to the technique used:
- Prefabricated Molded (Prefabricado Moldeado): Includes systems like Adobe and BTC (Bloque de Tierra Comprimida / Compressed Earth Block).
- Rammed Earth (Apisonado): Specifically refers to the Tapial system.
- Modeled (Modelado): Includes Cob and Enfundada (wrapped/straw-heavy earth).
- Infill (Relleno): Includes Tierra Aligerada (lightweight earth) and its variations.
- Tiered/Lattice (Entramado): Systems like Entramado de Adobe (adobe frame).
- Woven/Basketry (Encestado): Includes traditional and prefabricated Quincha.
Structural groupings:
- Load-bearing Systems (Sistemas Portantes): Adobe, Tapial, Cob, and BTC.
- Framed Systems (Sistemas Entramados): Quincha (Traditional and Prefabricated), Tierra Aligerada, and Entramado de Adobe.
- Mixed Systems (Sistemas Mixtos): Combinations like Adobe-Quincha or the CET System (Coordinación Dimensional).

Definition: Adobe is soil molded into blocks that are air-dried.
Fabrication Process and Dimensions:
- Standard block size: $40 \times 20 \times 10\,cm$ .
- Requires soil sifting (tierra tamizada) and mixing with additives like cut straw (paja cortada) to control shrinkage and improve cohesion.
Foundation and Sub-structure (Cimiento):
- Cimiento Corrido: Cyclopean concrete with a ratio of $1:10$ (Cement:Hormigón) plus large stones (Piedra Grande).
- Sobrecimiento: Concrete with a ratio of $1:8$ (Cement:Hormigón) plus medium stones (Piedra Mediana), with a depth or height ( $h$ ) of approximately $30\,cm$ . The width typically matches the wall thickness ( $e = 2\,cm$ for rendering).
- Impermeabilization: Polished concrete finished for moisture protection.
Construction Details:
- Mortar (Mortero de Barro): Earth-based mortar used between blocks with a standard thickness of $e = 2\,cm$ .
- Wall Intersections (Encuentro de muros): Use of $\frac{3}{4}$ adobe blocks to ensure proper bond/interlock.
- Rendering (Tarrajeo) Layers:
  - First Layer (Tarrajeo 1º capa): A mix of $3$ parts sifted earth (tierra tamizada), $1$ part coarse sand (arena gruesa), and cut straw.
  - Second Layer (Tarrajeo 2º capa): A finer mix of $3$ parts sifted earth and $1.5$ parts fine sand (arena fina).

Definition: Rammed earth constructed by compacting moist soil within a formwork (tanda).
Construction Process:
- The wall is built in sections or lifts called "tandas."
- Dimensions: Each lift or tanda typically measures $0.60\,m$ in height and $0.60\,m$ in width.
- Base: Starts from the level of the natural terrain or exterior floor level, supported by a foundation (cimiento) and a false floor (falso piso).
- Passages (Pase de agujas): Holes left by the transverse tension rods (needles) used to hold the formwork together during ramming.

Cob (Tierra Modelada I): A monolithic system where the wall is hand-sculpted from a mixture of subsoil, water, and straw. It does not use blocks or formwork.
- The process involves building the foundation and then building the wall sequentially in layers.
Enfundada (Tierra Modelada II): Also known as "wrapped" earth. It often involves long straw fibers saturated with clay slip and wrapped or layered over a structure.
- Construction involves rich clay earth and extra-long straw (paja larga).

Material Preparation: Uses sifted earth in a humid state with a moisture content of $8\%$ to $10\%$ .
Equipment: The pressure required for block formation is achieved through different types of presses:
- Manual Press (e.g., Cinva-Ram type).
- Hydraulic Press.
- Mobile Industrial Press (AECT).
Finished Results: BTC walls can be left exposed or finished, as seen in the Yaqui Education Center example.

Tierra Aligerada (Lightweight Earth): Uses a structural frame (timber or cane) filled with a mixture of earth and high-volume organic fiber (usually straw).
- Structure: Timber framing (Tabiquería) or traditional cane structures (common in Colombia).
- In-situ Fill: The material is filled into the wall cavities or used for lightweight roof insulation (cubiertas).
Fardos de Paja (Straw Bale Construction):
- Relies on straw bales as the main infill material within a timber structure.
- Protection: The walls are covered with wire mesh (malla) and then rendered with a mud paste (empaste con barro).

Definition: A system of weaving or basketry (Encestado) using columns, canes (caña), and mud plaster.
Traditional Quincha: Uses whole or split cane woven between structural timber members.
Prefabricated Quincha: Uses standardized panels for faster assembly.
- Panel Structure: Frame (bastidor) of $1 \frac{1}{2}" \times 3"$ . Includes horizontal and diagonal bracing (arriostre horizontal and diagonal).
- Components: Columns approx. $6.5\,cm \times 6.5\,cm$ ( $5" \times 5"$ for larger frames). Split cane (caña) used as the membrane.
- Cimiento-Muro Details: Asphalt paint (pintura asfáltica) applied to protected wood, galvanized or black wire #8 used for binding, and gypsum plaster (revoque de yeso) of $1.5\,cm$ for final finish.

Description: A timber-framed house where adobe blocks serve as the infill material between posts and beams.
Construction Stages:
- Stage 1: Vertical structure: Columns ( $5" \times 5"$ ) and Sills (Rastrel $5" \times 2"$ ).
- Stage 2: Horizontal cross-members (Soleras) and secondary posts (Columnetas).
- Stage 3: Infilling with adobe blocks ( $7.5\,cm \times 30\,cm$ or $15\,cm \times 30\,cm$ ).
- Stage 4: Protective rendering (Tarrajeo).
Case Example: Casa Pinariega (Soria-España).

Adobe-Quincha Combination:
- Lower floor (Planta Baja): Constructed with heavy Adobe for structural stability and thermal mass.
- Upper floor (Planta Alta): Constructed with Quincha (lightweight timber/cane frame) to reduce weight and seismic risk.
- Connection (Encuentro): Use of L-joints where panels meet columns ( $3" \times 3"$ ) and top plates ( $1 \frac{1}{2}" \times 3"$ ).
Sistema CET (Coordinación Dimensional):
- Modulation: Based on a dimensional coordination system with a basic unit of one decimeter ( $1\,dm$ ).
- Shape and Resistance: Theoretical principles state that structures with specific shapes show more resistance than shapeless ones.
- Seismic Behavior:
  - Heavy structures (Adobe) generally experience more deformation during seismic events.
  - Light structures (Quincha/CET) experience less deformation.
- Equilibrium: The system considers the gravity line; a lower gravity line provides greater stability/equilibrium (mayor equilibrio).