Building with Earth: Design and Technology of a Sustainable Architecture

Normally, soil compaction tools of the type

used in road construction are unsuitable for

rammed earthwork, because their frequency

is too high and their lift too low. Tools which

only vibrate might be suitable for sandy

soils, but not for clayey ones.

The pneumatic rams shown in 5 .11are

extremely effective for rammed earthwork.

The Ram II G, produced by the firm Atlas-

Copco, is fairly suitable because a special

feature prevents its head rotating, thus

ensuring that square heads can also be

conveniently used. All the rams illustrated

require a pressure of 6 bar and an air flow

rate of 0.4 to 0.9 m^3 /min. Due to their high

costs and the infrastructure and energy

required to run them, these rams are used

only for larger building projects. An electrical

vibration ram has been developed at the

BRL and manufactured by the firm Heuser

(5 .12and 5 .13). Its engine has a frequency

of 1000 to 1200 cycles per minute. The

most important part of this vibrating ram is

its specially shaped base, which allows the

apparatus to move within the formwork by

itself while compacting the earth. It can

compact loose soil in layers 7 cm thick.

Method of construction

In nearly all traditional rammed earth tech-

niques, the formwork is removed and

re-erected horizontally step by step. This

means that earth is rammed in layers from

50 to 80 cm high, forming courses of that

height before the formwork is moved.

When one course is complete, the next

course that is rammed is moister than the

one already in place, which is partially dried

out. Therefore, there is a higher shrinkage in

the upper course than in the lower, leading

to horizontal shrinkage cracks at the joint

(5 .14). This can be dangerous, since capillary

water can enter this joint and remain, caus-

ing swelling and disintegration. As can be

seen in the same figure, vertical cracks can

also occur in such walls.

With the French pisétechnique, this problem

was solved by using a layer of lime mortar

above each course before laying a new one.

A lime mortar cures over several weeks and

remains plastic until the loam has stopped

shrinking; sometimes even the side joint

between sections of the course is made

with mortar at an incline (5 .16).

Another method to avoiding horizontal

shrinkage cracks is to ram in a way that the

wall is produced vertically. This is described

in greater detail below.

Shaping of openings

The formwork can be dismantled immedi-

ately after ramming is completed. At the

same time, this rammed earth can be

shaped easily by scraping, cutting, scooping

or scratching. Normally, inserts are left in

the formwork to create openings. However,

with rammed earth, the opening can be

cut with much less effort with a knife or a

barbed wire used as a saw. This technique

also allows shaping of jambs and sills, as

shown in 5 .15. It should be mentioned that

at this stage rammed earth has already

achieved sufficient strength to grip nails

(they can be driven into the wall without

making a guiding hole with a drill).

55 Rammed earthworks

5 .16

5 .12 5 .14

5 .11

5 .15

5.9Electrical ram
(Wacker)
5 .10Pneumatic ram,
Australia
5 .11Pneumatic rams
(Atlas-Copco)
5 .12Vibrating ram
(Heuser)
5 .13Vibrating ram
(Heuser)
5 .14Shrinkage cracks
in a rammed earth
wall, Ecuador
5 .15Slicing rammed
earth directly after the
formwork is disman-
tled
5 .16The French pisé
technique