Shinan-Ui OW · Early Refusal Mitigation Measures
Pin Pile Refusal Contingency Scenarios and Decision Taking Process — Guidelines for offshore decision taking shall the Pin Pile refusal occur.
MEMO
Rev. A — 2026-03-25
PRELIMINARY — UNCHECKED
Contents
Introduction & Purpose
This Memo outlines initial guidelines regarding the Pin Pile refusal scenario during the Shinan-Ui Pin Piles installation campaign, describing checks required during preparation and at the moment of the occurrence of the refusal event during offshore execution.
It provides an initial basis for offshore decision taking process shall the Pin Pile refusal occur and an overall sequence of events to be used as reference by the HESI T&I and Construction teams for preparation of further and more detailed Contingency procedures.
Refusal Definition
- During Vibrodriving: penetration rate (advancement / unit time) is below the refusal criteria
- During Impact driving: number of blows per unit penetration exceeds the refusal criteria
Configuration of the Ongoing Installation Operation
The following conditions are assumed to be in place at the time of the refusal event:
1Pile Installation Frame (PIF) has been deployed to the seabed and levelled
2PIF survey activities performed — all parameters within required tolerances
3Installation Vessel (floating crane HLV) positioned at location via 8-anchor point arrangement
4Transportation Vessel with 4x Pin Piles moored alongside HLV
5Pin Pile upended via Vibrohammer, positioned and stabbed into PIF sleeve
6Hammering commenced — Vibrohammer for initial penetration, then Impact Hammer to target
Decision Flowchart — From Refusal to Scenario
Starting from Pin Pile Refusal during Impact Driving, the following checks determine which post-refusal scenario (A, B, C or D) applies:
Fig 1 — Flowchart from Pile Refusal Event to PIF / Piles abandonment or retrieval Scenarios
CHECK 1 — Can Vibrohammer be reinstalled onto the refused pile?
- Define elevation of Pin Pile top (in air / splash zone / underwater)
- Define weather window requirements and check forecast
- Check Vibrohammer guides/clamps suitability for pile top location
- Check visibility and conditions for stabbing/clamping operations
YES → ACTIVITY 1
NO → ACTIVITY 4 (go to Scenario A)
ACTIVITY 1 — Remove Impact Hammer, reinstall Vibrohammer
Lift-off Impact Hammer → Hook-up Vibrohammer to HLV crane → Set-down onto refused pile → Engage clamps
CHECK 2 — Can pile be extracted and set-down back onto transport vessel?
- Check Vibrohammer + clamps capacity vs pile weight + soil resistance
- Check HLV crane capacity for extraction
- Check PIF sleeve allows extraction without clashes
- Check reconnection of tailing tool, down-ending feasibility
- Check grillage suitability for set-down (impact loads, dimensions)
YES → ACTIVITY 2 (extract pile)
NO → CHECK 3
CHECK 3 — Is the Pin Pile self-stable without PIF sleeve and HLV crane?
- Perform desk study for theoretical self-stability penetration
- Collect actual driving data and recalibrate
- Define environmental criteria for verification
YES → CHECK 4
NO → SCENARIO A
CHECK 4 — Were other Pin Piles driven to target / self-stability before the refusal?
YES → CHECK 5
NO → SCENARIO D
CHECK 5 — Can PIF be removed while self-stable piles remain in sleeves?
- Check weather window for removal operations
- Check self-stable piles strength against PIF removal loading
- Check refused pile strength against PIF removal loading
- Check PIF structural integrity during removal
YES → SCENARIO C
NO → SCENARIO B
Post-Refusal Scenarios (A – D)
SCENARIO A
Temporary abandonment of PIF with self & non-self-stable piles
- Lift-off Impact Hammer, bring to HLV deck
- Disconnect all PIF–HLV connections
- Secure line extremities to PIF / marker buoys
- Retrieve 8 anchors and sail away
SCENARIO B
Temporary abandonment of PIF and piles (self-stable only)
- Same as Scenario A
- Preceded by removal of non-self-stable piles from PIF
SCENARIO C
PIF removal, with temporary abandonment of self-supporting piles
- Lift-off Impact Hammer to HLV deck
- Hook-up PIF lifting slings to HLV crane
- Lift PIF maintaining horizontal position and orientation
- Set-down PIF on HLV deck
- Mark self-supporting pile locations with buoys
- Retrieve anchors and sail away
SCENARIO D
PIF removal — no piles abandoned on seabed
- Same activities as Scenario C
- No need to mark positions with buoys
Post-Refusal Risk Evaluation (CHECK 6)
Fig 2 — Flowchart for Post-Refusal Scenario Risk Evaluation and Contingency Definition
CHECK 6: For which duration / foreseeable weather is the asset on the seabed (PIF and/or Piles) deemed stable and free of damage risk?
- Collect and analyze all as-installed and as-refused data
- Define weather limitations for stability
- Analyze metocean data and estimate risk of exceedance
- Continuously monitor weather forecasts
VERY HIGH RISK
Critical impact on project. Select contingency that can be applied immediately.
HIGH RISK
Critical impact. Select contingency applicable in 3–4 weeks.
LOW RISK
Apply contingency within 1–2 months.
NO RISK
Select contingency in line with project requirements (schedule, cost).
Proposed Contingencies
Contingency-Scenario Applicability Summary
| Contingency | Scenario A | Scenario B | Scenario C | Scenario D | Urgency |
|---|---|---|---|---|---|
| 1. Drive-Drill-Drive (HLV+JUV) | ✓ | ✓ | ✓ | ✓ | Immediate |
| 2. Higher Capacity Hammer | ✓ | ✓ | ✓ | ✓ | Weeks |
| 3. Higher Capacity Vibrohammer | ✓ | ✓ | — | — | Weeks |
| 4. DDD from JUV Only | ✓ | ✓ | ✓ | ✓ | Months |
| 5. Micrositing | — | ✓ | ✓ | ✓ | Weeks–Months |
| 6. Abandon + Spare WTG | ✓ | ✓ | ✓ | ✓ | Months |
Based on: HESI Memo — Pin Pile Refusal Contingency Scenarios and Decision Taking Process · Rev. A · 2026-03-25
PRELIMINARY — UNCHECKED · Content subject to further verification and update
PRELIMINARY — UNCHECKED · Content subject to further verification and update