COSTAL EROSION PROTECTION AND INLET IMPROVEMENT

Reef Breakwater Construction at Ullal, Mangalore.

Need

Costruction of two offshore multipurpose artificial submered reefs to reduce coastal eroson at Ullal, Mangalore.

Challenge

Making the perfect base for the two (2) offshore reefs in necessary to increase the soil bearing capacity. Soil stabilization work below foundation of reef breakwater at depth of 15 to 21m below seabed was a challenge.

Solution

DDIL deployed Cutter suction dredgers for levelling followed by ground stabilization work. To stabilize the soil Geotextile and Geogrid were layed along with laying peripherally two rows of Gabion bags and tying them mutually adjacent and across the breakwater with Nylon ropes to arrest lateral movement of soft founding soil. Geotextile laying in off-shore project is first time in India.

Work Involves
  • Detailed hydrographic survey to ascertain actual sea bed and rock profiles in the dredging area using following equipments:
    • Single beam echosounder
    • Multi beam echosounder
    • Side Scan Sonar
    • Shallow Seismic Profiles
  • Removal of soft soil through TSHD and transported to offload at designated offshore disposal located 10NM form the dredging location.
  • Surveys conducted regularly at disposal area to confirm dumping done as per specifications of Employer.
  • Removal of rock embedded in the stiff clay using Grab Drdger and loaded in to the split bottom hopper barges. Tugs towed fully loaded hopper barges to the dumping location and offloaded at designated offshore dumping location. Rock boulders of bigger size (greater than 5 M3) also removed.
Result

DDIL completes project in compliance with high standards of safety.

Screenshots

Geotextile laying on off-shore(1st in India)

DDIL's Flat Top Stone Barge

Gabions with HDPE ropes

Placing of Gabion bags

Cross-section of offshore reef with tetrapods in the armour and stones in the crest




Cross Sectional view of Gabion with HDPE ropes




Top view of reef construction