DIAGNOSTIC ANALYSIS OF DISTRESSED HYDRAULIC STRUCTURES: CASE STUDIES OF GUJARAT, INDIA

VIVEK P. KAPADIA

GOVERNMENT OF GUJARAT

2Backtracking from Symptoms to Causation

Forensic Analysis

Cause

CASE STUDY – 1 NARMADA MAIN CANAL

DESIGN FEATURES OF MAIN CANAL

• LARGEST IN THE WORLD HAVING CARRYING CAPACITY OF 1133 CUBIC METER PER SECOND AT THE OFF-TAKE POINT.

• AT CH. 195 KM BANK HEIGHT ABOVE THE GROUND LEVEL IS 12.5 M

• CANAL BED IS 70 M WIDE AND THE FULL SUPPLY DEPTH (FSD) IS 7.0 M

• DESIGNED DISCHARGE IS 825 M3/S

• CANAL SIDE SLOPES ARE 2 (H) : 1 (V)

4

DIAGNOSIS OF THE PROBLEM

BOILING

DIAGNOSIS OF THE PROBLEM

• BOILING AT SOME DISTANCE FROM THE TOE OF THE CANAL EMBANKMENT

• SUBSURFACE FLOW DUE TO FAVORABLE HYDRAULIC GRADIENT - COULD NOT BE ATTRIBUTED TO THE CANAL FLOW AS THE CANAL WAS LINED AND THE BED BANKING WAS MORE THAN 3.5 METER

• SHALLOW LIVE AQUIFER - CUT DUE TO CONSTRUCTION OF THE CANAL SIPHON IN THE DOWNSTREAM

DIAGNOSIS OF THE PROBLEM

BOILING

SHALLOW AQUIFER

DIAGNOSIS OF THE PROBLEM

• SEEPAGE ABOVE TOE - EITHER PHREATIC LINE DEVELOPED WITHIN THE CANAL EMBANKMENT OR CAPILLARY ACTION DEVELOPED NEAR THE TOE FROM WITHIN THE GROUND ITSELF OR BOTH TOGETHER

• LOAM TYPE OF SOIL - GENERALLY ERODIBLE AND PHREATIC LINE OR CAPILLARY ACTION COULD BE EASILY DEVELOPED DUE TO HIGH PERMEABILITY WHEN THE COMPACTION IS NOT SUFFICIENT

• DEEP RAIN-CUTS ON THE OUTER SIDE OF THE CANAL EMBANKMENTS WERE ALSO OBSERVED WHICH ALSO SUGGESTED ERODIBLE SOIL

UNFOLDMENT OF SOLUTION OF THE PROBLEM• EXIT TO THE SUBSURFACE FLOW BY PROVIDING A LATERAL DRAIN -

ESTABLISH A STEADY STATE OF THE SOIL BENEATH THE CANAL EMBANKMENT SO THAT CRUMBLING OF THE FOUNDATION RESULTING IN TO FAILURE OF THE EMBANKMENT COULD BE AVOIDED

• ALSO TO STOP THE CAPILLARY ACTION OF WATER IN TO THE CANAL EMBANKMENT NEAR THE TOE IF ANY

• LATERAL DRAIN - A COLLECTING DRAIN WAS EXTENDED TO A FAR SITUATED POND FOR THE DISPOSAL

• AIMED AT RELEASING THE WATER ACCUMULATED IN LARGE QUANTITY WITHIN THE SOIL BENEATH THE CANAL EMBANKMENT

UNFOLDMENT OF SOLUTION OF THE PROBLEM

BOILING

SHALLOW AQUIFER

UNFOLDMENT OF SOLUTION OF THE PROBLEM• OBSERVATION FOR SOME DAYS - BOILING PHENOMENON ALMOST DISAPPEARED -

SEEPAGE REDUCED BUT NOT COMPLETELY STOPPED WHICH SUGGESTED THAT THE PHREATIC LINE HAD ESTABLISHED WITHIN THE EMBANKMENT

• ADDITIONAL BERM OF 5 METER WIDTH AND 5 METER HEIGHT

• JUTE TEXTILE BAGS WERE SPECIALLY DESIGNED IN THE FORM OF LONG ROLLS - FILLED UP WITH CEMENT SOIL IN 1:9 RATIO AND NAILED ON THE OUTER SLOPE OF THE CANAL EMBANKMENT

• AVOIDING ROLLING DOWN OF THE JUTE ROLLS, AN ANTI-EROSION SURFACE ON THE OUTER SLOPE OF THE EMBANKMENT AND TO ADD EXTRA BURDEN TO PROVIDE MORE STABILITY

UNFOLDMENT OF SOLUTION OF THE PROBLEM

CASE STUDY – 2 GORATHIYA DAM

INTRODUCTION

• SABARKANTHA DISTRICT I.E. IN NORTH GUJARAT IN INDIA - COMPLETED BEFORE 10 YEARS - RIVER MESHWO

• GROSS STORAGE CAPACITY - 146 MILLION CUBIC FEET

• CATCHMENT AREA IS 371 SQUARE KILOMETERS - DESIGNED FLOOD WITH 1 IN 50 YEAR FREQUENCY IS 3774 CUBIC METER PER SECOND

• LENGTH OF THE SPILLWAY SECTION IS 101.80 METER - CONCRETE GRAVITY DAM WITH PROVIDED 9 VERTICAL GATES - HYDRAULIC JUMP TYPE STILLING BASIN - UPSTREAM AND DOWNSTREAM KEYS WERE 3.5 METER DEEP

INTRODUCTION

• SIGNS OF DISTRESS IN ONLY 2 YEARS

• DOWNSTREAM GLACIS SLOPE 1:3 - TOE GOT DISINTEGRATED AND THE REINFORCEMENTS WERE PULLED OUT

• DOWNSTREAM APRON GOT DAMAGED BUT NOT IN THE ENTIRE LENGTH OF THE DAM, ONLY IN THE RIGHT HALF OF THE LENGTH I.E. RIVER’S HALF WIDTH

INTRODUCTION

PULLED OUT REINFORCEMENT

INTRODUCTION

PULLED OUT REINFORCEMENT AT TOE AND DAMAGED APRON

DIAGNOSTIC ANALYSIS

• GLACIS WITH 1:3 SLOPE WAS INSUFFICIENT TO AVOID CAVITY FORMATION - THERE SHOULD HAVE BEEN A MUCH FLATTER SLOPE OR AN OGEE

• SOME RECORD - ORIGINALLY A BASALT MINE AS THE RIVER WAS HAVING GOOD QUALITY BASALT IN ITS BED - FOR PREPARATION OF THE SITE, THE DESIGN INCLUDED LEAN CONCRETE FILLING WITH LARGE COARSE AGGREGATE I.E. PLUM CONCRETE IN THE PIT

• SOME OTHER RECORDS WITH GEOLOGICAL MAPPING SUGGESTED THAT THE MINE WAS ONLY IN THE RIGHT HALF WIDTH OF THE RIVER AND THE DEPTH WAS ABOUT 9 METER

DIAGNOSTIC ANALYSIS• LARGE COARSE AGGREGATES WERE IN PLACE - CEMENT AND SAND WERE IN LOOSE

FORM - WATER BENEATH THE APRON IN THE VOIDS - DAM WAS FULL UP TO CREST LEVEL - IT WAS THE WATER FROM THE RESERVOIR

• CONDITION WAS EXTREMELY DANGEROUS - SUBSURFACE FLOW COULD RESULT IN TO UNDERMINING THE FOUNDATION AND COLLAPSE OF THE CONCRETE DAM ITSELF.

• WHEN WATER WAS RELEASED, IMPACT OF THE WATER FALL WAS TAKEN UP BY THE APRON WHICH REQUIRED A SOLID FOUNDATION WHICH ACTUALLY WAS NOT THERE - CONCRETE APRON USED TO SETTLE - SAGGING RESULTING IN TO DAMAGE AT THE BOTTOM AND TOP – BOTTOM DAMAGE WAS NOT VISIBLE BUT THE TOP WAS

RESTORATION• PLUM CONCRETE REMOVED UP TO 1.5 METER DEPTH – RICH CEMENT SAND MIX 1:4

WITH POLYMER POURED TO PLUG VOIDS IN PLUM CONCRETE

• LAYER OF 1.5 METETR THICKNESS OF RICH CONCRETE

• ADDITIONAL PERIPHERAL KEY OF 5 METER – FOUNDATION OF ABUTMENT STRENGTHENED

• CASTING OF APRON – REINFORCEMENT MESH AT TOP WELDED WITH TOE REINFORCEMENT – SURFACE HARDENER TO PROVIDE IMPACT RESISTANT SURFACE – FILLET AT TOE

• DOWNSTREAM RIVER CHANNEL REGRADED

RESTORATION

RESTORATION

CONCLUSION

• PROBLEMS IN CIVIL ENGINEERING ARE VERY COMPLEX AND UNDERSTANDING THE REAL CAUSE OF THE PROBLEM IS THE MOST IMPORTANT ASPECT

• A SMALL ASPECT IGNORED AT THE CONSTRUCTION STAGE MAY LEAD TO DIFFICULT PROBLEMS

• EXPERIENCE AND INSIGHT NEEDED AS MOSTLY THE FINDINGS CAN BE REACHED BY WAY OF USING JUDGMENTAL AND INTUITIVE DECISIONS

CONCLUSION

• SOMETIME THE DIAGNOSIS IS REQUIRED TO BE DONE STAGE-WISE ALONG WITH STEP BY STEP IMPLEMENTATION OF SOLUTION

• SEVERAL ACTIVITIES TO BE EXECUTED WITH PROPER SEQUENCE AND PROPER MATERIALS

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