Natural Calamities - Tsunami 2004 - Houses ReconstructionPolicy - Some suggestions

To

Dr. N. Lakshmanan,
Director, Structural Engineering Research Centre,
CSIR Campus, Taramani,
Chennai - 600 113.
E-mail : director@sercm.csir.res.in , director@sercm.org , and others


Sir,

Sub: Natural Calamities - Tsunami 2004 - Houses Reconstruction Guidelines - Housing Reconstruction Policy - Some suggestions submitted.

Ref: 1) Guidelines for Reconstruction of Houses Affected by Tsunami in Tamil Nadu issued by Revenue Administration, Disaster Management and Mitigation Department, Govt. of Tamil Nadu.

2) G.O. Ms. No.172 dt.30.03.2005 Revenue (NC III) Department.

I submit my views on the above subject for your kind consideration.

Ever since my voluntary retirement on 31.08.1984 after a 24-year service as Junior Engineer in Tamil Nadu P.W.D., I practice Civil Engineering. I am involved in design, planning, supervision and construction of buildings for the past 21 years. With a team from Gandhigram Rural Institute (Deemed University) led by Dr. T. Karunakaran, the Vice-Chancellor, I visited the tsunami affected areas in Kanyakumari, Nagappattinam and Cuddalore districts and Pondicheri. Positioning of buildings, layout, and structural design of the buildings are important aspects of the envisaged habitats. We therefore observed the behaviour pattern of sea during tsunami, vis-a-vis topography and other natural features, besides infrastructural influence and interference. We put forth our views and suggestions in the light of our inference. .

We attended the "Workshop on Habitat and Shelter for NGOs involved in reconstruction activities” held on 05.04.2005 at Nagappattinam Collectorate.

I. GUIDELINES

Siting of Buildings

1. I.B.1 Natural Shielding:

In Serudhur hamlet of Nagappattinam District casuarina trees had been cut and new saplings planted. The young saplings could not resist the waves. The destruction had been massive. If usufruct trees such as coconut, cashew, scented screw pine (thazhai) whose fragrant flower has good market had been planted, they could have mitigated the damages. Longstanding trees form reliable natural shield that is preferable to firewood or timber trees. .

2. I.B. 2. Construction on raised earthen mound is costly and hence undesirable. The structure has however to be founded only on firm natural ground. Such localities require deeper foundations and hence costly. Excavation in such soils, that has not consolidated would require costly timbering or shoring. Construction of stilts to bear the buildings is obviously a better alternative. The area between stilts can serve non-residential purposes. Nonetheless, it is presumed that the natural ground level is above H.T.L.

3. Planning aspects:

2. A.3. Tsunami had lesser effects at places, where the streets ran perpendicular to the coastline. Damages had been disasters where row of houses ran parallel to the sea shore because the sheets perpendicular to coast line increases the porosity of the building complex and mitigate the ferocity of the waves in contiast to the effects of storm Forming wide gardens between the coastline and the colony with densely planted trees such as coconut, arecanut and other palmaceous trees could be ideal as a fortress to protect the habitat against wind and tsunami.

4. Construction : Dwelling Units :

3.2.A.2 Foundation : It has been stated that "when there is risk of scouring due to storm surge minimum depth of foundation 1.5m below natural ground level may be provided in coastal regions. In other places it can be 1m"

There is no specific definition to ascertain whether a site falls in the coastal region or not. Hence, it is necessary to formulate and spell out a yardstick to this effect. It could be a predetermined distance from, and elevation above the coastline at H.T.L., together with soil specification.

5. Under 3.2A.6 stepped foundation has been recommended and non stepped foundation rejected. There are frequent instances when stepped foundation on firm soils like hard gravel have given rise to vertical cracks in the absence of belt beams.. Theoretically belt beams are not required in such soils. Minor unevenness in soil conditions disturb the foundation and causes such cracks.. However, old buildings imposing heavy load on the foundation on gravelly or even clayey soils without any offset below natural ground level stay strong. New constructions having foundation without offsets below ground level have also proved safe. This is due to the friction between the rough face of the foundation and the vertical faces of the foundation trench supplementing to the bearing capacity of the soil at the bottom. It rather compares better than pile foundation, because the pile foundation secures only the friction offered along its small circumferential area, while foundations without offsets have wider area of friction on either side. In the meantime, in case of piles the sharp point of piles acts against this frictional resistance by its wedging action.

Whereas in the case of a load bearing wall foundation without offsets, built butting against the sides of the foundation trench the frictional resistance is supplemented by the bearing power of the soil at the bottom of the foundation. In this way it is possible to gain as much strength as the area of the foundation walls go, and hence even economy in materials too is plausible. The exact value of the frictional resistance offered by different classes of soils to different types of construction like R.R. Masonry, C.R. Masonry, brickwork etc. is to be ascertained by necessary research processes.

Non-plastic soils, ie. soils without sufficient cohesive property like sand, loam, alluvial soil etc. have little frictional resistance. Stepped foundation with plinth beam could be the right choice in such cases.

1.3.2.A.8. The vertical reinforcement proposed in fig.13 is not safe against corrosion. A better alternative would be using 7-cm precast concrete square sections with 10mm bar at the centre to anchor one end on the ground beam and the other on plinth beam. Similarly, such sections should be anchored at the plinth beam and the lintel.

Paras 3.2.A.7 - 9 require clarity. Fig.13 displays a stepped brick foundation whereas para 3.2. A.&. details a R.C. column. It is confusing whether the R.C.C. band in the middle of the bottom is a belt running throughout the length or a square block at specific points.

The method recommended in para 3.3.A.10 (Fig.13) is difficult to execute in site, because it will interfere with the brickwork if filled for every layer of brickwork and the cover and compaction cannot be assured if done after several layers of brickwork. Hence, the precast block suggested will be best suited.

7. Quality Control

Normally, wet sand is available. Even when dry sand is available the labourers make it wet because dry sand spills over mortar pans or flows through baskets on their heads and shoulders. The practice is only to mention the ratio between cement or lime and sand in terms of dry sand. Usually when the work is done under the supervision of qualified engineers the contractor and engineer understand the issue of bulkage of sand and hence due allowance is made. However, owners of buildings, or supervisors not technically qualified seldom understand bulkage issue. Such people mistake any addition of sand as a pretext for misappropriation of cement. Inasmuch as tsunami reconstruction works will be under community supervision it would create unnecessary suspicion and strain the relationship between the community and builders. Hence the sand ratio should be spelled out explicitly for both dry and wet conditions, in layman’s language.

8.Mixing of Concrete : 4.B

In the method detailed in 4.B, it will require much more labour in hand mixing to get a satisfactory degree of mixing. Usually sand and cement is mixed first and then spread on the course aggregate. The latest method is spreading sand cement mix first and spreading the metal above it. This method facilitates easy penetration of the spade through the sand cement mix to reach the bottom. A satisfactory mixture is obtained with less labour.

II.House Reconstruction Policy

1) Para 3 says "government recognizes that the fishermen people have to remain close to the sea for their livelihood." In this regard we would like to point out that since tsunami, it is imperative that the fishermen shift sufficiently away from the reach of sea waters. The habitats that remained before tsunami (B.T.) could at the best be suitable only for the storage of implement, instruments, equipment etc. Now the people having clearly understood after tsunami (A.T.) that the old locations of habitats are unsafe for habitation, they will relent if we persuade and help the fishermen to adopt fishing techniques that are conducive to living a bit away from the coastline. Breakthroughs in fishing are many in recent times. To facilitate novel fishing techniques infrastructures such as tiny, mini, minor and major fishing harbours could be built at estuaries to suit new techniques. There must be provisions for dormitories and cloak rooms for fishermen and their implement, boat service yards, fish sorting and packing facilities, net and hook service yards, fish drying yards, net drying yards, cold storage, training centres for trades relating to fishing and navigation, canteen, recreation halls, medical centres, libraries and reading rooms, weather observatory, signal posts, disaster warning centre, disaster shelter etc. In addition, steps need be taken to retrain the present catamaran fishers to adopt sophisticated technology to the adept. A model plan and a paper on behaviour of tsunami and protective measures are appended.

If such an infrastructure proposal is announced and effectively communicated to the fishing people and timely steps taken to convince them of the accruing benefits they would readily agree to reside in habitats beyond 500 m from the coastline. We request the government to announce its infrastructure policy early. The success of the housing scheme depends entirely on the affected people understanding the infrastructure policy and recognising the benefits there on.

Also, we would like to point out that most of the tsunami affected people and eyewitnesses are still averse to live in the vicinity of the sea shore any more. This is more so in case of women and children who have undergone psychological trauma. Horrors still haunt them. If anybody chooses to live close to the sea it is all because of their economic compulsions, in the wake of lack of skill and opportunity for any alternative employment. Such an indirect compulsion drives them to despair and even thoughts of suicide lingers in the minds of a few. We must prevent such grim possibilities at any cost. We request the Government of Tamil Nadu to take suitable steps in the light of the above.

2) Para 6 (a) allows the fishermen to construct new houses of their own within 200 m limit from HTL without any restriction.. This will result in non fishing people encroaching the sea shore. We request that such clauses are revised so that habitats are formed only 500m away from the coastline at HTL and all other structures demolished when all people concerned are provided with houses 500m away from the coastline.