Cutter Suction Dredger Abnormal Conditions Identification and Treatment | Dredging Fault Solutions

Cutter Suction Dredger: Identification and Treatment of Abnormal Conditions

During engineering construction, various abnormal conditions often occur and require shutdown for handling. Correct judgment and proper handling can reduce invalid downtime and increase the effective dredging time of construction vessels.

The following are common abnormal conditions and corresponding treatment measures:

I. Suction Port Blockage

Cause analysis: Excessive debris and oversized materials in the construction area exceed the cutter inlet size.
Identification method: Suction pressure (vacuum) rises, discharge pressure drops; low concentration under a certain vacuum degree.

Combined with site conditions:

1. Blocked by stones, wooden piles, debris;
2. Cutter head covered by soil collapse;
3. Cutter suction port clogged by sticky clay lumps.
Treatment and prevention:
1. Lift the cutter above water and manually remove debris at the cutter platform, then dispose of debris properly;
2. In rocky areas with frequent blockages, lift the cutter off the seabed, stop the pump, and flush the suction port with backpressure water; use manual cleaning if ineffective;
3. For bottom-layer excavation, deepen in place and push large stones/obstacles into pits with the cutter; conduct diving salvage if necessary;
4. Push debris out of the construction area when excavating boundaries.

Prevention:
1. Maximize suction port grid spacing while keeping it smaller than the impeller passage minimum size;
2. Install stone guards and stone shifting rings in the cutter chamber;
3. Pre-excavate the upper layer with a grab dredger in debris-heavy areas;
4. Increase cutter speed, reduce slice thickness and cutting layer for stiff clay; excavate thick soil in layers.

II. Cutter Head Blocked by Hard Sticky Clay

Cause analysis: High viscosity of dredged soil adhering to the cutter opening.
Identification method: Excavation in high-plasticity clay zones; suction vacuum rises, discharge pressure drops, cutter pressure fluctuates.
Treatment and prevention:
1. Lift the cutter bridge to idle the cutter above the seabed;
2. Lift the bridge for manual cleaning.

Prevention:
1. Increase cutter speed and reduce traveling speed;
2. Reduce cutting layer thickness and use clay-specific cutters.

III. Cutter Collides with Underwater Obstacles

Cause analysis: Presence of underwater obstacles.
Identification method: Sudden rise in cutter oil pressure, impact noise, and vessel vibration.
Treatment and prevention:
1. Stop cutter rotation and transverse swing, lift the cutter bridge, and inspect for damage;
2. Probe obstacles gently (or dive inspection); report with coordinates if unmanageable.

Prevention:
1. Pre-survey the construction area, record obstacle coordinates, and salvage known obstacles;
2. Operate cautiously in complex zones with slow cutter speed and transverse movement.

IV. Transverse Mooring Anchor Cannot Be Retrieved

Cause analysis: Insufficient winch capacity; deep penetration or high soil viscosity; wrong anchor lifting angle.
Identification method: Overload of anchor winch oil pressure; anchor embedded in silt or silty sand.
Treatment and prevention:
1. Use a larger anchor boat;
2. Lock the winch and utilize tide buoyancy;
3. Retrieve via transverse cable with slow winching, monitoring current and position to avoid cable derailment.

V. Discharge Pipeline Blockage

Cause analysis: Low flow velocity causing sedimentation; high soil viscosity; large particle size; pipeline bending or misalignment.
Identification method: Increased pump discharge pressure, decreased suction vacuum; reduced main engine load. Prone to blockage at pipe restrictions, submerged sections, culvert crossings, sharp bends, or when transporting large particles/clay at low velocity.
Treatment and prevention:
1. Stop transverse movement, lift the bridge or slow traversing, reduce discharge concentration, increase pump speed to maintain pressure;
2. Inspect pipelines to locate and assess blockage;
3. Disconnect and clean manually.

Prevention:
1. Maintain flow above critical velocity;
2. Keep pipelines straight with gentle slopes; avoid sharp bends in flexible pipes;
3. Regularly check restricted sections (diameter > grid spacing);
4. Control concentration for large particles/clay and avoid sudden pump shutdown.

VI. Dredge Pump Blockage

Cause analysis: Oversized dredged materials.
Identification method: Simultaneous drop in discharge and suction pressure; unstable pump operation, impact noise, shaft jumping, and elevated bearing temperature. Impeller inlet blocked by stones, wooden piles, etc.
Treatment and prevention:
1. Stop the pump and flush debris from the impeller with backpressure water;
2. Shut down, open the manhole, and remove foreign objects.

Prevention:
1. Install stone guards or suction grids (spacing slightly smaller than impeller passage);
2. Install a "general" shifter at the suction pipe bottom ~0.5m upstream of the pump.

VII. Water Pipeline Rupture

Cause analysis: Pipeline blockage, high discharge pressure, aging or insufficient wall thickness.
Identification method: Sudden drop in discharge pressure, increased flow rate, higher suction vacuum; increased main engine load and exhaust temperature. Rupture due to steel pipe wear or rubber pipe aging/wear/kinking.
Treatment and prevention:
1. Repair by welding or clamping;
2. Replace steel/rubber pipes.

Prevention:
1. Align pipelines to avoid sharp bends;
2. Inspect and rotate worn pipes;
3. Replace aged/damaged rubber hoses;
4. Reduce discharge pressure based on equipment capacity.

VIII. Steel Pile Cannot Be Lifted

Cause analysis: Damaged lifting system or insufficient power; deep penetration or sinking in silt/silty sand.
Identification method: Hydraulic pressure reaches rated value but the pile remains stationary.
Treatment and prevention:
1. Repeat lifting and clamping to prevent further sinking;
2. Lower the bridge, lift main/auxiliary piles to ballast the stern, then jack up the bridge.

Prevention:
1. Avoid free-falling piles;
2. Lift piles regularly to prevent deep sinking;
3. Limit penetration depth for positioning in soft silt.

IX. Cutter Ladder Cannot Be Lifted

Cause analysis: Damaged lifting system or insufficient power; ladder/cutter buried by soil collapse during trenching or high-face excavation.
Identification method: Excessive or overloaded transverse/hoisting oil pressure; bridge immovable.
Treatment and prevention:
1. Stop traversing, increase cutter speed to dredge surrounding soil if not buried;
2. Pull the vessel backward with the carriage while slowly hoisting the bridge, then clear soil after exposure;
3. Lift steel piles or adjust hoisting cables according to tide level if stuck during ebb.
Prevention:
1. Excavate in layers to avoid excessive height difference;
2. Combine trenching with side excavation to prevent overburden and excessive bridge penetration.