Different methods of earthen wall construction, its categories, material properties and tests, earthen construction for seismic prone areas are discussed.
Historically, earthen materials have been used for building construction and its utilization is still ongoing due to certain advantages such as low cost, aesthetics, heat insulation, and low energy utilization.
However, there are serious disadvantages pertain to earthen materials, for example, low resistance to water influences and low strength.
Fig.1: Wall Constructed from Earthen Material
Fig.2: Earthen Wall Construction
Following topics are covered for earthen wall construction:
- Material quality tests
- Earthen wall construction methods
- Recommendation for construction in seismic area
Material Quality Tests for Earthen Wall Construction
There are different tests which should be conducted to specify the suitability of the material. Dry strength test, fissuring control test, and strength test of adobe are the tests which are commonly used to determine earthen material properties. These tests are explained in the following sections:
Dry Strength Test on Earthen Material
Dry strength test procedure includes crushing of five or six balls with diameter of 20mm between thumb and forefinger after they have been created and dried for forty-eight hours.
The earthen balls are assumed to have sufficient clay content and accepted as construction material if they remain intact and does not suffer damages. Nonetheless, it is required to take necessary measures to control small fissures caused by drying process.
However, the soil need to be dismissed whey they break under dry strength test.
Fig.3: Dry Strength Test
Fissuring Control Test on Earthen Material
Fissuring control test is conducted on eight sandwich units made from mortar by using blending clay and coarse gain sand. The specified soil to coarse sand proportions ranges from 1:0 to 1:3.
The best proportion of soil to coarse sand would provide the desired strength acceptable for earthen construction. If the sandwich does not show obvious fissures during its opening after forty-eight hours, then it possesses the desired properties and hence is suitable as a construction material.
Strength Test of Block or Adobe
This test estimates the strength of earthen blocks qualitatively rather than quantitatively. The manufactured block, which is sun dried for four weeks, need to support weight of an individual without failure otherwise fibers materials and clay should be blended with the soil to increase the block strength to a desired value. This means the bock must carry the weight of the person without suffering damages.
Fig.4: Produced Adobe need to be Sun Dried for Four Weeks prior to Testing
Fig.5: Strength Test of Blocks of Adobe
Earthen Wall Construction Methods
There are different approaches are used for the construction of earthen walls which includes hand molded layer construction, adobe or block construction, pise or tapial construction and earthen construction with wood or crane structure. These techniques are discussed in the following sections:
Hand Molded Layer Construction of Earthen Wall
This type of earthen wall construction is considered to be the weakest technique because of the poor compaction obtained and low quantity of moisture applied to create hand molding. That is why the clay content cannot be activated either by compaction or moisture.
Moreover, it is highly likely that fissures are initiated to a certain degree even though the quantity of used moisture is considerably low. This need to be tackled by implementing necessary measures, for example, blending straw or coarse sand. It is required to use appropriate amount of coarse sand because too much sand leads to decrease in strength of the wall.
Finally, it is recommended to wet the contact area between first layer and the mud so as to prevent fissure. Figure-6 and Figure-7 shows hand molded earthen brick and wall construction respectively.
Fig.6: Hand Molded Earthen Brick Production
Fig.7: Hand Molded Layered Earthen Wall Construction
Adobe or Block Construction
The strongest blocks are produced from clay or plastics and they should be properly dried to prevent shrinkage. Test strength should be used to check the suitability of the applied soil. As far as fissures are concerned, it can be prevented by adding clay and sands or free the block from any restriction while the block is dried.
Moreover, it should be known that, the most significant factor that affect the wall strength is the joint between blocks after that the role of the block strength come into play.
Added to that, it is required to pay attention to the mud employed between joints. This is because the mud might lose moisture at it is in direct contact with the block and consequently small fissures would initiate which can decrease the bond between placed blocks. It is recommended to utilize the same material for both mud and block production.
Finally, there are certain measures that need to be considered during block construction, such as, placed courses must be level, vertical joints between two successive courses should be broken by and by overlap of block and filled with mud properly and right-angle joints between walls should be executed in a manner that prevents continuous vertical joints.
Fig.8: Earthen Block Wall Construction
Fig.9: Earthen Block House Construction
Pise or Tapial construction
Pise or tapial construction include the placement of forms and pouring moist soil forcefully into the forms and then consolidated to a desired degree. The strength of the pise or tapial construction is dependent on the achieved degree of compaction in addition to small quantity of moisture used.
Fig.10: Pise or Tapial Construction
If the used soil contains clay, then high strength wall can be achieved using through applying proper compaction and providing suitable amount of moisture.
Moreover, the risk of fissure development would arise if the amount of clay is high and moisture content is excessively low. So, this problem should be avoided by introducing sand.
Furthermore, the number of blows applied to compact the soil is based on the shape and weight of equipment used. High strength can be achieved by applying high compaction but this statement is valid to a certain limit which is when the soil does not adhere to the form while it is removed.
Lastly, it is advised to use compaction equipment with 8 to 10kg mass and apply 50 blows for each 1000cm2. Additionally, the thickness of compacted layer should be maximum 10cm and the height of each the bock commonly vary between 50 to 80cm. Water shall be introduced to sub joints at every 10cm to obtain a monolithic structure.
Fig.11: Pise or Tapial Construction
Earthen Construction with Wood or Cane Structure
In this construction technique, a structural framework which is composed of horizontal elements of wood or cane and vertical posts is built as may be seen in Figure-12.
After the installation of the structure, panels would be filled with cane (cane knitting in Figure-12) and then both sides would be covered with mud.
The desired behavior of earthen structure may not be achieved unless the required construction measures are accounted for adequately. For example, protective layers such as painting by coal tar should be applied for surface of cane or wood element especially when such elements are embedded in foundations and it is recommended to build foundation from stone, concrete or bricks placed with gypsum, cement or lime mortar.
Moreover, wood or cane mesh should be used as a panel filling material and the mud applied to the both sides of the panels should be composed of equal portion of straw and mud.
Furthermore, a placement of ring beam on prefabricated panels and houses continuous system is recommended to help evenly spread of roof loads and guaranteed integral response of the wall.
Finally, it is advised to apply mud to the panels surface after the installation of the ring beam and roof to prevent fissuring lead by nailing.
Fig.12: Earthen Wall Construction with Wood or Cane Structure
Recommendation for Earthen Wall Construction in Seismic Area
There are several recommendations regarding earthen wall construction in seismic prone areas. These considerations include the provision of vertical buttress wall, an intermediate strengthen member for long walls. The maximum height of the wall should not be higher than eight times thickness of the wall.
Moreover, it is advised to construct outside pilasters for the entire wall junctions and corners. This is because seismic stability of the wall and the entire building would be increased considerably.
Furthermore, the width of wall opening should not be wider than 1.2m and between this opening and outside corner must be at least 1.2m.
Total width of openings in a wall should not be more than one-third of entire wall length in size zone A, B, and C. Added to that, lintel embedment or bearing length on each side of openings in the wall should not be smaller than 50cm.
Finally, it is desired to taper hand constructed wall upward; maintaining at least 30cm width at the top of the wall and increase this wide gradually with a batter of 1:12 at the bottom of the wall.