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Title
Sand packed stone foundations in Kutch, Gujarat
Summary
Sand packed stone foundation is widely used in the region of Kutch with various types of masonry constructions. The local materials- just stone, sand and water; and their characteristic properties are utilised best in this construction. Many settlements in Kutch have difficult access and getting outside materials is not easy. Local artisans have developed this solution of packing the stones by using well graded sand to fill the joints in stead of cement mortar. Another advantage of not using cement mortar but only sand is that it can be managed even with saline water. The scarcity of fresh water does not affect this construction. As the foundations are within the ground in confined situation, sand filled stone joints remain safe but also provide required cushioning to absorb seismic shocks.
Location
Sand packed stone foundation is found in most parts of the Kutch region in Gujarat, though presently in rural areas this is followed most.
map 1. location of Kutch
Context
Kutch is an arid desert area in north western part of Gujarat.
Geography: Kutch, the second largest district in India1 is surrounded by the Gulf of Kutch and the Arabian Sea in south and west, while northern and eastern parts are surrounded by the Great and Small Rann (seasonal wetlands) of Kutch. Kutch or Kachchh, as it is in Gujarati, literally means something which intermittently becomes wet and dry. The same word is also used in the languages of Sanskrit origin for a tortoise and garments to be worn while having a bath. Large part of this district known as Rann of Kutch is shallow wet-land which submerges in water during the monsoon and becomes dry during other seasons.
Climate: Kutch has hot and dry climate with very little rains.
Summers- the cool wind in the evenings/night needs to be brought into the house from the south west; however the day sun/heat needs to be avoided from the south.
Winter- the sleeping room needs to be closed from the night cold of desert, but the day sun is welcome, though during most times it can be quite harsh.
Monsoon- rain is less but can come down in torrents and generally comes from the S-W direction.
Though the monsoon is very short, there are heavy showers of rains during the monsoon. Thus, for a short period of time, protection from rain is necessary. During the hot and dry summers, protection from heat is very essential as the temperature rises upto 45 degrees or more.
Natural Disasters: Most of the area of Kutch is highly vulnerable to many natural disasters. Below are some of the natural calamities that were registered in Kutch in the past:
Earthquakes - Whole of Kutch falls under Zone V of earthquake vulnerability. Observations suggest that it has a 50 year cycle with earthquakes ranging between 7 to 9 intensity on Richter scale. Last significant earthquake was observed on 26th January, 2001. after that also many minor earthquakes are observed in the region.
Fig 2: Gujarat Earthquake Hazard Map (Source: Vulnerability Atlas of India: Gujarat, 1997, BMTPC and MUD)
Cyclones – with 220km of coastline cyclonic winds are very common here. Winds upto 180-200 kmph are commonly observed. Last cyclone in July,1999 hit Abdasa in Kutch which recorded speed of 180kmph.
Fig 3: Gujarat Wind and Cyclone Hazard Map (Source: Vulnerability Atlas of India: Gujarat, 1997, BMTPC and MUD)
Floods - Banni region of Kutch has area of 4500 sqkm which has clayey soil. This flat region with elevations ranging from 7-14m above sea level observes periodic floods. Though monsoon is short and rain scarce, the wetlands are flooded regularly while the other part of the region faces frequent draughts and Kutch is famous for its scarsity of water.
Materials and Skill Availability: The terrain is formed of sedimentary limestone. Hence, well graded river sand is easily available in the region. Foundation would require large quantity of mortar. Traditionally the cement was not available and later, due to scarce economical resources cement was not used in vernacular construction for foundation.
Compact sandstone is also available in ample amount in the region, which is used as construction block for foundation.
Fresh water is a rare commodity in this region. However, for sand packed stone foundation, saline water is also useful. Also, in rural areas the construction of a house usually lasts over a few years. The rain water during monsoon helps the sand packed stone foundation.
Since stone is used in most traditional constructions for superstructure, good craftsmanship for stone masonry is well developed in this region.
Housing/ Settlement Typology
The houses with sand packed stone foundation are found in most part of Kutch district. The house typology varies depending on local context and region. The houses having this foundation may be circular ‘bhunga’ construction or rectangular stone walled- mud mortar houses. Even today, it is estimated that almost 50% houses use this type of foundation in Kutch2.
Knowledge System/ Innovation
This type of foundation demonstrates most efficient use of materials- specially sand. The stone with its uneven surface, when used as foundation may leave big gaps. In normal stone construction with cement mortar, the mortar does not go inside the gaps between the stones. Due to these gaps the foundation becomes weak. Usually, to fill up these gaps, more water is added to mortar to make it more fluid so that it can reach into the gaps between uneven stones. Yet, it is also observed that the cement (being very fine) from the mortar is washed away and only the sand remains in the gaps.
In sand packed stone foundation, with the help of water the sand is pushed forcibly into the gaps between foundation stones. As the sand available here is well-graded, the gaps between the bigger particles of sand are filled up with smaller particles, not leaving much gap. This results in structurally stronger foundation. Hence, the sand packed foundation becomes very compact and dense. Another advantage of this method of construction is that the method does not require setting time or curing, which is crucial for cement/ lime based construction.
Disaster Resistance/ Structural System
This technique is used for foundation only. Foundation does not require any bond between construction units (bricks, stones, etc.) like the elements above the ground level (walls, roofs etc.) need. The sand filled in the gaps act as cushion between foundation layers and helps in absorbing the shock of earthquake waves3.
This practie is used in foundations only. It does not have much implication on other disasters in the region other than earthquake.
Though it is unsafe to leave the foundation exposed on any of the sides, since the sideways exposed/ open sand does not hold on the foundation stone units together.
Climate Response
There is not much impact of climate on foundations and hence it is not discussed.
Construction Methodology
The method for construction of sand filled stone masonry is simple and very close in its basics to the usual masonry with cement mortar foundations. It is described below.
1. Earth is excavated for the foundation. As in usual foundation, the depth of the foundation depends upon the soil type.
2. Approx. 2” of sand is laid before the stone lying. This levels the excavated surface and helps in creating a bed for the stones. Water is poured on sand so that the sand settles down and minute gaps are filled.
image 1. layer of sand acting as bed for foundation stones
3. First layer of stone is laid on the sand bed. The whole width of the excavation is covered with foundation.
image 2. first layer of stones for foundation
image 3. staggering joints and through stones at regular intervals
4. After the stones are laid, the sand is filled with the help of water such that all gaps get filled
image 4. compacting the foundation with sand and water
5. After the sand settles down the same process is repeated constructing the foundation layer-by-layer.
image 5. another layer of stones with staggered joints
6. The stone layers stop 6” before the earth level. Finally a layer of concrete covers the top of the foundation.
7. Normal masonry with stone, bricks or adobe units will start above the concrete layer.
Key Issues while construction and measures to be taken
1. All stones laid should be horizontally laid. Their height should be always lesser than their width.
2. The stone laid should be well balanced, resting on the layer of sand. Usually walking on them should indicate if any of them are not in balance.
3. Header stone should be laid at every 90-100 cm of length of the foundation.
image 6. placement of header stones
4. Overlapping of stone joints is a must. Therefore a trained mason is very necessary to carry out this construction.
5. Stones should not be placed such that it covers up empty space before sand has been filled up in the gaps of previous layer.
6. To avoid this, sand should be pushed in with water.
7. This process of sand filling should be done after laying each layer of stone.
8. Sand packed foundations should not be exposed and has to be fully covered within ground. To avoid the exposure, the concrete layer (ground beam) should come minimum at 6” below the ground line. If exposed, the sand comes out of the gaps, weakening the foundation.
Artisans
Masons in rural areas of Kutch, mostly elderly masons work with this technology. They are highly skilled in this method of construction.
Special Tools/ Equipments
Sand packed stone foundation construction requires usual stone masonry tools.
