Canal Failure - a Case Study in Forensic Civil Engineering

CANAL FAILURE: A CASE STUDY I N FORENSIC CIVIL ENGINEERING A. M. Shingarey Chief Consulting Engineer, Geotech Services, Nagpur Introduction: Right Bank Canal (RBC) of a Major Irrigation Project at Gosikhurd in Vidarbha region (Maharashtra), has failed at many locations. The job of consultancy for detecting causes of the failure & offering solutions for rehabilitation was awarded to the author. In projects such as these, technical failures have severe economic, social, environmental and legal repercussions, as was largely testified during the site visits. Thus it becomes imperative to study these cases in the light of Forensic Civil Engineering.

Project Details: A major dam is constructed for irrigation purpose, on the river Wainganga at Gosikhurd in Dist. Bhandara (Maharashtra). Major features of the project are as under: 1. Dam Max. height in the river gorge

: 22.55 m

2. Dead storage in the dam

: 405 Mm at 50 years silting

3. Live storage

: 740 Mm at 50 years silting

3

3

4. Canal bed level at the dam

: RL 235.00

5. Year of the canal excavation

: 1997 to- 2007

6. Year of the canal lining

: 2007 to 2009

7. Year of the retaining wall const. At KM 21

: 2009

Salient Features of the canal structure: Main right bank canal of the Gosikhurd dam is 103 km in length. Bed width is 18.10 m up to Km 37 & reduces to 10.10 m after Km 37 with constant canal depth of 5.3 m. Side slopes of section are in 1:1.5, and are provided with concrete lining up to 5.3m depth. Berm, 3 to 5 m wide is provided at some locations, at 5.3 m height. Muroom (granular soil) 0.75 to 1m thick, is laid below concrete lining as CNS (Cohesive Non Swelling) material. Depending on the topographical features, at many locations, canal section is in total cutting, at chain-age Km 21, where failure has occurred, canal was in 14 m below GL in cutting.

Geology of the Region: The area, through which RBC passes, is mainly covered with highly weathered Gneiss with a few patches of Lateritic soil. Due to a difference in degree of weathering, soil stratification shows layered zones. Intermediate bands with a high percentage of sand/silt have separated clay layers, making them vulnerable to saturation & development of pore pressure. Laterite is coarse grained (GW-GM) with silt/clay. It is mainly available in top layers with varying thickness.

Canal Section & General Soil Stratification: At RD- 20910: The top, thin layer of about 0.5 to 1 m is whitish soft soil. Granular soil (GW-GM) is present up to 4 m, followed by a layer of sandy silt. Thereafter a layer of clayey soil is sandwiched between clayey gravel & sandy silt. Yellowish clay is observed from 8 m onwards. Continuity of this layer is assumed, since no detailed soil investigation data was available from previous reports.

Canal Slope Failure: During the construction stage itself, rain cuts & partial failure of slopes were experienced. Retaining wall

was

constructed at vulnerable locations. Wall was 9 m thick at the

the bottom and 0.5 at the top with a 1:1.5 slope, matching with canal profile & was 6 m high. It was constructed in 20 m long sections with expansion joints. In the monsoon of 2010, a major failure of ACCE(I) Conference on Forensic Civil Engineering, Bangalore, Aug. 23-24,2013

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Canal Failure: A case study in Forensic Civil Engineering – Amol Shingarey

1m 3m

3m

1.5 m

1

1.5 m

1.5

2m

Concrete retaining Wall 6.25m including

5.3 m

Raft & PCC 18.1m

9m

Top white

granular soil

silty gravel

sandy soil

Yellowish Clay

Fig- 1 slopes occurred at Km-21 & Km-32, where retaining wall was constructed for protection. Four hundred meter section of the wall moved in curve shape inside the canal bed. Max movement was to the tune of 9 m. While from Km- 42.80 to 43.300, slopes have failed at many locations before construction of the proposed retaining wall.

Observations at the site: The canal site was visited on 22

nd

Feb.2011. Observations are as under:



Slope has failed from the base.



Width of the slope is much larger than length of the failed portion, which is not a usual slope failure.



Soil mass shows intermediate layers of coarse & fine grained soil. Cohesion of soil in dry conditions is very low, as lumps of soil were easily crushing under finger. Laterite had good dry strength.



Top layer of laterite has failed in big size blocks.



Retaining wall had moved max. 9 m in Canal bed.

“Under normal conditions , in slope failure , length of failed slope is always greater than width of

failure. But exception to normal failures is observed where layer of clay are separated by more permeable layers . Under these conditions slides caused by excess pore water pressure in sandy/silty layers, shows a very wide failure surface than length of slide.” ( Soil mechanics in engineering Practice

by Karl Terzhagi & Ralf Peck )

ACCE(I) Conference on Forensic Civil Engineering, Bangalore, Aug. 23-24,2013

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Canal Failure: A case study in Forensic Civil Engineering – Amol Shingarey

Thin layer of clay at bottom overlaid by Sandy soil, 6 m depth at CH.20900

Laboratory Test Results: Details

Test Results RD20900 LHS 6m Silty/Clayey Silty/clayey

Location Depth

RD20900 LHS 4m

Visual classification NMC

Sandy gravel

Gravel % Sand %

88.44 4.60

7.17 61.76

0.75 43.84

38.78 19.04

Silt/clay %

6.96

31.07

55.42

42.19

Liquid Limit % Plastic Limit % PI value % Triaxial Shear ckgf/sq.cm.  – deg. Permeability

48.31 24.51 23.80

37.12 26.00 11.12 C=0.120 ,  =28  -3 3.5x10 cm/sec

52.19 26.52 25.67 C=0.116,  =30.4 

58.62 25.61 31.01

c= 0, – 47

RD 20900 LHS 4.5 m

RD20900 LHS 8m Sandy gravel

In absence of the Piezometer data, i.e. hydraulic gradient at the time of failure & pore pressure developed cannot be known. As per the guide lines (word repeated) of “Guide lines for earthwork in Railway”, GE-G1, Geotechnical Engineering Directorate of Research & Design Standard Organization

of Railway, pore pressure parameter of 0.27 can be interpolated for a slope of 1:1.5 with full saturation. Phreatic line can also be given in computer software in place (stead) of pore pressure parameter. In the present situation, this line will pass along the retaining wall & then gradually meet ground line (shown dotted in fig.2). Trial 1: Analysis

is conducted without pore pressure to determine initial factor of safety (FOS) of slope, i.e. without retaining wall. FOS 1.22 shows a safe slope. But as per guide lines min. Factor of safety should be 1.4. Trial 2: Pore

pressure parameter of 0.27 reduces FOS to 0.91, i.e. slope will fail under the condition

of full saturation. Trial 3: Phreatic

line when given as shown in fig-2, FOS further reduces to 0.89.

Movement of Retaining Wall ACCE(I) Conference on Forensic Civil Engineering, Bangalore, Aug. 23-24,2013

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Canal Failure: A case study in Forensic Civil Engineering – Amol Shingarey

Under the condition of failure with FOS of 0.91, soil mass behind retaining wall looses entire shear strength and it will impose horizontal force on concrete Retaining wall. Net wt. of Active soil

= W (refer fig.2) = Total Weight of soil in slip circle – wt. of soil in RE wall area – Soil below RE wall. = 2416 kN - (1/2x9mx6m) x 19 – (4/3 x ½(9) x 1) x19 = 2416 – 513 – 114

W

= 1789 kN

If it is assumed that a) Horizontal force imposed by the slipping wedge on RE wall = Kh x W Where,

W

= is the weight of wedge in kN

Kh

= coff. Of horizontal earth pressure = (1- sin 22.5) / (1+ sin 22.50) = 0.38

Hence, Total horizontal force

= 1789 x 0.38 = 680 kN

b) Resisting force offered by retaining wall- R = wt. Of wall x TAN 22.5 Wt of wall

= ½(6mx9m) x24 3

= 648 kN (concrete density assumed = 24kN/m ) = 648 x 0.41 = 265.7kN The above calculations show that the resisting force offered by concrete retaining wall, by virtue of its weight & base friction has been overcome by driving forces. The following analysis shows that driving forces can drag the wall to a considerable distance. Total Driving force - Total resisting force = Imbalanced force 680kN- 265 kN = 415 kN To dissipate the imbalanced force of 415kN, soil mass will move down. OR Alternatively RE wall can resist horizontal force of only 265 kN if the soil behind RE wall is assumed to create just this force to maintain equilibrium. Then active soil behind the wall should weigh = 265 /0.38 = 697kN 3

And the volume of this soil will be = 697/19 = 36m & Area of 1 m strip = 36m

2

Active Soil mass is assumed in the triangular shape with max height of 6m (ht.of RE wall). Other side of rt. angled triangle will be 12m., i.e. if the berm width is of 3 m at 6 m height then after the failure , soil mass is likely come to a rest after soil mass (it) has gained a shape of 6 m ht. up to 12 m length behind the wall. It means that the soil mass will have to move out 9 m plus 3 m existing berm, to accommodate this length. The wall at extreme position did move by this distance. As the sections of 20 m RE wall moved, it created gap for water & soil at liquid limit to flow out. This has resulted in dissipation in seepage pressure. Wall has shifted inside the canal depending on the volume slope failed behind it. 14 m

ACCE(I) Conference on Forensic Civil Engineering, Bangalore, Aug. 23-24,2013 10 m

Murum + white soil

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Canal Failure: A case study in Forensic Civil Engineering – Amol Shingarey

Remedial Measures: (a) At Km 21 & 31, development of pore pressure (& also seepage pressure) is the main cause of failure. To prevent this, effective drainage system is necessary. But water ingress from water bodies & pounding water during the monsoon is difficult to drain out at all locations; particularly when layers/lenses of pervious soil are present at random. Under this situation, it is more feasible to provide a ‘cut off’ on the back side of slope. This can be made available by ‘Curtain Wall of Clay’,

which will ensure complete prevention of water ingress from adjoining land. (Fig.4). This should be provided at all vulnerable locations. Thickness & depth of cut off will vary with site conditions.

(b) Drainage of the soil, when canal section is in cutting, should be achieved by installing horizontal auger drains. These should be terminated at sufficient distance away from the curtain wall. This system will need to be design as per site requirements.

(c) When canal section is in partial or total embankment, drain pipes be laid, surrounded by the filter. Size of the filter media will depend on mean particle size of soil. General guide line is that semi perforated pipes of 100 mm dia be laid in rows 1.5 m c/c. service road

1 8m 1.5

Cut Off in clay

Horizontal auger drains

Fig.4

(d) Muroom is used as CNS material for counteracting swell pressure of the embankment soil. But this material, though non-swelling, is not “cohesive” in nature. It cannot hold itself under saturation & is easily erodible. Instead of muroom, available clay in the area can be “stabilized” in the most

ACCE(I) Conference on Forensic Civil Engineering, Bangalore, Aug. 23-24,2013

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Canal Failure: A case study in Forensic Civil Engineering – Amol Shingarey

economical way by blending with fly ash. Differential Free Swell index of black cotton soil has been reduced from 66 to 20 % by fly ash, whereupon it can act as CNS material.

(e) Water entering from top surface, from adjoining areas & fields should be prevented by maintaining reverse slope on canal top.

To sum up, the main re asons of canal failure are: (1)Egress of excess water from the adjoining area: since the soil deposits contain bands of sandy soil (2) Inadequate drainage within the embankment body: Water accumulation in soil increases pore pressure & reduces it’s shear strength.

(3)CNS (Cohesive Non Swelling ) material laid under canal lining is actually granular & not cohesive , which on saturation slips by itself along the canal slope and is unable to prevent the lining from swell pressure exerted by embankment soil .

Remedial measures suggested for rehabilitation & to prevent further failures are (1) Cut off to prevent water egress from neighbouring fields (2) Horizontal effective drains within embankment to reduce pore pressure (3) Use of appropriate CNS material under canal lining to counteract swell pressure.

Economic Impact: With the right bank canal, total area planned under irrigation is 78630 hectors. Canal excavation was done 10 years ago i.e. in 1997 & was lines with concrete from the year 2007 to 09. For the first 52 KM the canal is in cutting, i.e. flowing much below GL and adjoining fields cannot be irrigated by gravity. Percolation losses and evaporation losses increase the canal maintenance cost. Moreover, repairs of failures due to soil conditions & wrong CNS material used under the lining further add to the cost. As the area under command is much less than cost of irrigation, the Irrigation department thought of joining this canal to one of the old reservoirs as a feed canal and increase its command area by another 52,000 Ha. But for doing so, overflow section & some embankment portion of the old project is required to be increased in height. This work will add to the cost & is not yet commenced. Overflow section of this project is underlain by sandy soil. To restrict this seepage, again heavy treatment would be necessary escalating its cost even more. The total project cost in 1995 -96 was 155.05 Cr which is escalated (repeated- consider risen) to 6073 Cr up to 2012. White paper by State government on this issue, cited following reasons for cost escalation: 

Rise in schedule of rates

51 %



Land acquisition, rehabilitation, forest land

17.06 %



Change in the scope

3.86 %



Change in the design

5.33 %



Other Reasons

22.74 %

Even after spending this amount only 36894 ha of irrigation is created out of total 2,50,800 ha. By the year 2013, distribution system of 28,155 ha has been completed out of 1,90,00 ha. And filed channels for 11,801 ha are ready against a total of 2,00,000 ha . In short, the project is no more economically feasible.

Social Impact: Rehabilitation issue had gone out of hand because of a 25 years delay. The projectaffected persons (PAPs) were given compensation before 15 to 20 years. PAPs continued with their farming & stayed in their old house as usual because of delay. Land acquisition process was not done. And now when the dam work is complete and storage is required to be built, it cannot be ACCE(I) Conference on Forensic Civil Engineering, Bangalore, Aug. 23-24,2013

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Canal Failure: A case study in Forensic Civil Engineering – Amol Shingarey

done because of danger of land submergence, where PAP ’s are still living. Government plan for eviction of PAPs got stiff resistance. The reasons for such a resistance are multiple. Firstly, their money is exhausted. Secondly the prices have escalated. And most importantly, one family has grown into two or three or even four with the passage of time and each family now wants separate home. This has increased number of PAP’s and also the compensation amount. Now total 16,000 families are to be compensated for land acquired 4688 ha against 8228 ha to be required in rural area. And 1010 ha out of 1605 is in forest area. Recently Chief Minister announced a highest ever rehabilitation package of Rs 12000 Cr, which is in addition to project cost. Even after the compensation is paid, the PAP’s do not have their srcinal amount of land for cultivation, which was their major occupation. Moreover, at displaced locations, it will take time to set any small business and again will depend on market proximity, because population of the settlement colony may not be sufficient for all kinds of trades. Uncertainty has also affected their family life, particularly mental stress & marriages of youths. Low income & increase in debts has forced many farmers to commit suicide in last few years in this region.

Environmental Impact : Immediate effect of canal was observed on wild life , since this canal is virtually dividing forest in to two sides over a long distance of 50 Km. Particularly when the canal is in deep cutting & lined with concrete , the sloping surface become slippery and it is difficult for animals to cross canal even in dry season. (On many occasions field staffs have seen that even tiger has failed to cross the canal.) This type of block makes huge impact on seasonal migration of wild animals across the forest. It is surprising how government authorities gave a clearance for the canal, which under normal conditions even do not permit widening of existing roads in the forest. Second major aspect is drainage, both surface & subsoil. Canal has given a break to surface water flow during Monsoon, which will affect ground water table of areas adjacent to canal. As water flow is cut off on one side & stagnated on the other bank. Soil being stratified with sandy layers, subsoil water in the adjacent area will drain in to canal, lowering water table. Actually this seepage water is a major cause of canal failure. Draining out of water from subsoil is not favourable for paddy cultivation which needs water pounding over a long period.

Legal Issues:

Because of delay, price escalation & rehabilitation of PAP’s , Gosikhurd Irrigation

project has attracted many court cases. Many Public Interest Litigation (PIL) are filed by social groups & PAP’s themselves, major issues & demands are: 

CBI inquiry for corruption and misappropriation of funds.



Governments to recover losses caused to the public exchequer by erring officials of the State Government and also initiate criminal and departmental proceedings against them.



The petitions further prayed for blacklisting the contractors and recovering money paid to them for defective works and a direction to the Centre as well as the State Government to complete all projects in a time-bound manner



Within a span of seven months in the year 2009, the cost of 38 irrigation projects executed by Vidarbha Irrigation Development Corporation (VIDC) escalated by a whopping Rs 20,050.06 crore from the earlier Rs 6,672.27 crore, it alleges. (I) In one of the early PIL filed by “Gosikhurd Prakalpgrast” on 24 Nov 2004

“High Court

directed the State of Maharashtra to pay compensation to the persons possession of whose lands have been taken in connection with the execution of Gosikhurd” Project, and further ACCE(I) Conference on Forensic Civil Engineering, Bangalore, Aug. 23-24,2013

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Canal Failure: A case study in Forensic Civil Engineering – Amol Shingarey

directed that the lands in respect of which awards have been made but possession not taken, immediate steps be taken to take possession of the lands in question and to pay compensation within two weeks. Against this order state govt. has appealed in Supreme Court. (II) The first part of the report, submitted by Nandkumar Vadnere, retired Principal Secretary, Water Resources Department, in June 2010. ‘Vadnere Committee’ report highlighted gross irregularities in the Gosikhurd project, which is floundering in a maze of corruption and cost escalations. It reports : a.

Illegal hike in tender cost : The committee found that of the 195 major tenders (Rs. 1 crore and above) floated in the four financial years, 50 were allotted at five per cent below the srcinal estimated cost. Among the other 145 tenders, 18 pertained to roads and civic amenities. Of the 127 major tenders investigated, it was found that the cost of 37 major tenders was hiked as per government norms, while the estimated cost of the remaining 90 tenders was arbitrarily increased and done outside the purview of various rules and regulations.

b. Grant of Mobilization Advance: VIDC granted mobilisation advance at an interest rate calculated by adding 0.2 per cent to the prime lending rate of banks, documents scrutinised by the committee revealed. A total of Rs. 135.28 crore was paid as illegal mobilisation advance in the Gosikhurd project.

Conclusion: Most irrigation projects face similar problems: delay in land acquisition, inappropriate staging of the work, insensitive rehabilitation programs, and escalation of prices, technical failures owing to wrong designs or execution and unprecedented levels of corruption. But more often than not, a project failure is seen only in terms of its failure to create the required facility in the allotted time and cost. It is seldom assessed for its negative impacts on society and environment. The ‘so called’ clearances from forest and other departments turn out to be an eye wash; mere papers to

lubricate the project. Infrastructure is for the human beings and it can never be successful if interests of different groups of people are in conflict. An unthinking route of the canal through a forest can mercilessly divide it, affecting subtle aspects of ecology like migration of animals. Ruthless uprooting of the villages in order to make room for the project serves no benefit to the displaced residents, who have to start anew in their new, isolated habitats. An unsympathetic handling of resources can hamper natural systems like ground water table or loss of fertile soil cover, so crucial for agriculture. An irresponsible delay due to bureaucratic red-tape can lead to a loss of tremendous amount of taxpayers’ money. Time and money spent in solving litigations often goes to alarming

proportions; moreover such cases, which do not lead to a consensus, end in perpetrating loss of faith in the system. All these are failures of an enormous kind. If a detailed socio-economic-environmental feasibility report is prepared by a multidisciplinary panel of sociologist, environmentalists, economists and engineers, these negative effects can be envisaged and the proposal can then be suitably modified. More importantly, it should become a standard practice to assess a project on all these fronts and not merely in terms of the money lost or gained.

ACCE(I) Conference on Forensic Civil Engineering, Bangalore, Aug. 23-24,2013

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