DTU Technical Release Series
Experimental Rammed Earth Tanks - Instructions for
(based on the construction of an
experimental rammed earth tank at Kyera Farm, Mbarara, Uganda)
Prepared by Dai Rees
Tools and equipment required
out the site and laying the base
the first section of wall
the first ring
The guidelines for manufacture given
below are based on an experimental tank built at Kyera Farm, Mbarara, Uganda
during June and July 2000. This type of tank is still at the experimental stage
and is NOT recommended for manufacture as yet. The tank described below failed
after being filled, but was due to a poor lining, which was the result of bad
|Tank internal diameter
|Tank external diameter
||approximately 6 cubic metres|
||100mm stone with 50mm concrete or 50mm
compacted stabilised soil, 2.8m diameter|
||Stabilised soil, 0.2m thickness|
||barbed wire hoops at 50-60mm spacing in rammed
||10% clay, 15 30% silt, 50 70% sand, 10
20% gravel, 4% cement stabilisation|
||plastic or cement render lining (latter
||by gravity or by siphonic tap (latter described
||DTU thin-shell ferrocement cover with extended
Section A quadrant of rammed earth wall (see Figure 1)
Lift One complete ring or 4 sections
Pour Earth is poured to a depth of 100mm before being rammed. This is
known as a pour
1 a Section of rammed earth tank wall
Tools and equipment required
Shuttering and tie rods (see Figure 1 and Figure 4 details for manufacture
available upon request)
Rammers (both flat and V) (see Figure 5)
Spirit level (600mm)
Spades or shovels (2)
Soil preparation equipment
Find suitable soil field and lab tests are required to confirm suitable
soils and some modification of the soil may be needed
Transport soil to site. It is good to find soil as close to the site as
Prepare the soil using suitable equipment (e.g. hammers, groundnut mill,
sieves or mechanised equipment). The soil needs to be made fine enough to allow
2 A groundnut sheller fitted with 4mm sieve being used to break down soil
ready for mixing
Calculate the amount of soil required for one section using the following
Volume, V = o (ro2
ri2) x h/4
Weight , W = Volume x Material density
where, o = 3.142
ro = outer radius of tank
rI = inner radius of tank
h = height of one liftTake material
density to be 2000kg/m3, where actual figures are not
Mix soil in the correct proportions if soil modification is needed (in the
case of the Mbarara tank we used 80% anthill soil, 16% coarse murram [and 4%
cement]). Mix enough for one section at a time and then add cement to enough
soil for one pour at a time.
When ready to pour, add the cement to give a 4% stabilisation and mix the
soil thoroughly and add enough water to satisfy the drop test.
The soil should be kept dry if not used and soil that has had cement added
should be discarded if not used.
3 Mix soils together and then add cement and water only enough for one pour at
Marking out the site and laying the base
Find a suitable location for the tank enough space and close enough to the
Level the ground to provide a circular area whose radius is at least 0.5m
greater than the tank (external) radius
Where the ground is soft, a stone base of 150mm deep is required whose
surface is 50mm below the normal ground level (NGL). The diameter of the stone
foundation and base is 2.5m.
The type of base used depends on whether a plastic or render liner will be
Ensure that there is sufficient clear area around the base to place the
- Where a plastic liner is used, the remaining 50mm is filled with
stabilised soil and rammed to provide a firm base for the tank.
- Where a render lining is used, the base is constructed using a concrete of
mix 4:2:1 to a depth of 50mm.
Ramming the first section of wall
Mark out the inner and outer wall radii, using chalk or a nail scratch mark.
Place the shuttering such that it sits in the correct position, straddling
the inner and outer marks
4 Showing the shuttering located over the marked radii with end stops and tie
rods in place, ready for the soil to be poured.
5 Rammers or tamps used for compacting the soil. The V tamp is used to
create the shear bond between pours.
Ensure that the end stops are in place and that the tie rods are in place
but not fully tight (Figure 4)
Level the mould both vertically and horizontally while tightening the tie
rods fully. Check well on all faces for level and plumb
Pour the mixed soil between the shuttering to a depth of 100mm. This can be
made easier by marking 100mm onto a stick and using this as a guide.
The soil is then rammed lightly using the flat rammer (Figure 5). The
ramming pattern should be kept even to ensure uniform compaction.
The soil is then rammed again more firmly until there is a solid feel.
Again the ramming pattern should be kept uniform.
The rammed pour is then finished with the V rammer. This aids bonding
between the rammed pours and helps prevent shear (Figure 5).
A 2.3m length of barbed wire is cut and placed in the V trough. This should
give an overlap of 300mm at either end which is used for tying the wire to the
next length. The end of the wire is folded upward so that it can be pulled out
easily later (Figure 6).
6 shows the tails of the barbed wire that has been rammed into the earth wall.
These tails are tied to next piece of wire to form a continuous loop within the
A further 100mm is poured into the mould and rammed in the same way as
This is continued until the section is complete.
The tie rods are removed (they will be tight due to the compaction pressure)
and the shuttering moved very carefully away from the wall section.
7 The shuttering is removed to reveal the first completed section of rammed
the first ring
The shuttering is moved around and replaced in such a way that the part of
the shutting beyond the tie rod holes clamp lightly onto the finished section of
wall. The tie rods are butted against the end of the completed wall section. The
two end stops are both inserted in the open end.
The section is then rammed in the same way as the first section.
Barbed wire is tied to the tails as required and rammed into the wall, as
with the first section.
8 - The first ring is complete and the shuttering is lifted up to start the next
When the second section is complete, the third is rammed in the same way.
Finally the fourth section is rammed. The shuttering overlaps both the third
and the first sections now and no end stops are required.
Usually, it is possible to complete one ring per day. Cover each section
with polythene sheet, weighed down with stone, to prevent rapid moisture loss.
Remember that the cement has to be cured, just like concrete.
The subsequent lifts are rammed in the same way as the first.
The shuttering is now, however, clamped onto the previous lift and the tie
rods rest on top of the soil wall of the lower sections
The sections are built 45o out of phase with the section below
(as with brick wall building), to obtain a well-bonded structure.
Where the geometry of the tank is lost slightly and the shuttering no longer
fits properly (this sometimes happens due to poor levelling), the soil can be
cut away carefully with a machete.
9 The fifth lift is being rammed here and scaffolding is being used to allow
the workers easy access to the work
Scaffolding is used to access the work once it becomes difficult to do so
The overflow pipe is cut in during the last lift keep the pipe invert at
100mm below the top wall level. Give the pipe a slight gradient outward.
If a siphonic water extraction system is being used (see later), provision
should be made for a " pipe to be brought out at the top of the tank.
The tank should be cured for 2 weeks under plastic before the next stage.
The tank is rendered internally with a cement mortar. The mortar is a 1:4
mix with waterproofing agent. Two coats are applied, approximately 10mm each
Firstly the walls are cleaned to remove any loose material and then
scratched with a nail brush (or similar) to provide a key for the render. The
walls are damped before the render is applied to prevent the walls sucking the
moisture out of the render.
10 The tank is internally rendered with 1:4 mix sand cement mortar. Ensure a
good joint between the wall and the base as this can be a point of weakness
The waterproofing agent usually comes in powder form in 1kg bags. 1kg is
added for every 50kg of OPC.
Ensure a very good bond between the render and the floor of the tank and use
a good fillet to seal the joint well. This is a point of weakness.
For this tank, a thin-shell, ferrocement cover is used. The construction of
this cover is dealt with in another DTU Technical Paper. The cover is altered
slightly to give overhanging eaves, which help to protect the tank from rain.
When complete the cover is lifted into place by about 6 people and the joint
between the wall and cover rendered to make a good seal.
A basin is used as the cover hatch and this is also used a filter. The basin
is filled with coarse gravel and cloth is tied over the top, which prevents any
organic matter or larger debris from entering the tank.
11 Technical drawing of the RE tank
There are two methods described here for water extraction; one is the
siphonic system and the other the gravity system.
12 Showing the overflow and the overhanging eaves of the thin-shell,
The siphonic system is shown in Figure 11. It works as a simple siphon,
which once started, is controlled by the outlet tap. The floating off-take shown
in Figure 12 helps ensure that only the cleaner water at the surface is drawn
off first more detail of the floating off-take is given another DTU Technical
Paper titled A Manual for the Construction of Direct Action Handpumps for use
with Rainwater Harvesting Tanks. The benefit of the siphonic system is that the
tank wall need not be pierced.
The gravity system is the type more commonly fitted to rainwater tanks. This
type of system can also be used but then the outlet pipe needs to be
incorporated during the ramming of the first ring.
The tank can be finished externally using cement render if required. Figure
13 below shows a tank finished with rough cast (a cheap option) and fitted wiwth
a gravity water extraction system.
13 Showing the completed tank
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