Kaikōura Earthquake Repair and Recovery Programme – South Bay Marina and Coast Guard Station

Introduction

This paper describes the damage that was caused to the South Bay Marina and Coast Guard Station by the 2016 Kaikōura earthquake, and, the associated impact on the local community and economy. An overview of the “fast track” design and construction process that was undertaken to complete the marina earthquake repair program is also provided.

Kaikōura is a small semi-rural community with a district population of 3,552. The local economy has a strong reliance on the marine environment as fishing and marine based tourism are the prime drivers. Figures published by the Ministry of Business, Employment and Innovation (MBIE) indicate the pre-earthquake total annual tourism spend in Kaikōura was $120 million while discussions with local fishing operators indicated the value of the annual fishing catch was between $25 and 30 million per season.

Reliance of the Kaikōura economy on tourism and fishing was borne out by the following 2015 Statistics New Zealand data:

Table 1: Summary of Kaikōura Employment by Sector

Marine based tourist activities are the main drawcard for tourists to Kaikōura. A study undertaken in 1998 indicated that the main motivations for visitors to Kaikōura were whale watching and dolphin swimming, with over 50% of overnight visitors participating in whale watching and over 30% in dolphin swimming.

South Bay is located on the southern side of the Kaikōura Peninsula, approximately 2.7 km due south of the Kaikōura Village centre. The South Bay Marina is an important part of the Kaikōura community and economy as it is the departure point for most of the local marine tourism operations (including Whale Watch Kaikōura, Dolphin Encounters and Seal Swim) and is the base of operations for almost all of the commercial fishing fleet. This infrastructure is also crucial to the regional recreational boating community and is the site of the safest public launching ramp and the South Bay Coast Guard station.

Figure 1: Location of the South Bay Marina and Coast Guard Station, Kaikōura.

Photograph 1: South Bay Marina and Coast Guard Station. This photograph was taken on 25 November 2016, within approximately 30 minutes of high tide.

Figure 1 shows the location of Kaikōura Village, the South Bay Marina and the South Bay Coast Guard Station.

The MW7.8 Kaikōura Earthquake of 14 November 2016 resulted in an average of 0.93m of tectonic uplift in the South Bay area. This had serious consequences for the Kaikōura coastline and the associated marine industry. In particular; many new navigation hazards were created and the depth of water associated with the existing marina facilities was significantly reduced.

Photograph 1 illustrates the significant tectonic uplift and change to the coastal environment that occurred as a result of the 2016 Kaikōura earthquake.

In the days immediately following the Kaikōura earthquake, Government New Zealand quickly identified the importance of the South Bay Marina and Coast Guard Station to the wider Kaikōura community and economy. As such, steps were taken to expedite construction to reinstate the preearthquake level of service of these facilities. As an interim measure, while the North Canterbury Transportation Infrastructure Recovery (NCTIR) Alliance was being finalised, Government New Zealand appointed Environment Canterbury (ECan) to co-ordinate a stakeholder group and construction of slipway and launching ramp emergency repair works commenced immediately prior to Christmas 2016.

NCTIR took over the management, design co-ordination and delivery of the marina and coast guard station earthquake repair program during February 2018. This phase of the repair works was the subject of a meticulously planned construction plan and program to ensure the fastest-possible high-quality project delivery was achieved. The repaired marina and Coast Guard facilities were officially opened on 14 November 2017, exactly one year after the Kaikōura earthquake event. As described below, this was an incredible outcome that exceeded stakeholder expectations and demonstrates the value and advantages that an alliance type delivery structure can achieve.

Geology

The South Bay area is predominantly underlain by Amuri Limestone. This group is described on published geologic maps³ as ‘Hard, siliceous, micritic limestone locally interbedded with siltstone, marl, sandstone, chert or green sand. Includes intrusive and extrusive igneous rocks of the Grasseed Volcanics member with dikes, flows, sills, pillow lavas and agglomerate of peridotite, gabbro, dolerite and basalt,’ from the Muzzle Group approximately 55 million years old.

Field observations at the South Bay Marina indicated that the bedding was the dominant defect in the rock mass at this site. The bedding layers were very thin and moderately inclined, dipping unfavourably towards the mooring basin, due to folding in historic seismic events (refer to Figure 4). The rock joints were very widely spaced and sub-vertically inclined towards the north-west.

¹ 2013 Census, Statistics New Zealand
² Summertime Visitors to Kaikōura: Characteristics, Attractions and Activities, Simmons, D.G et al. 1998. Lincoln University.
³ Rattenbury, M.S.; Townsend, D.; Johnston, M.R. (compilers) 2006: Geology of the Kaikōura area: scale 1:250,000 geological map. Lower Hutt: GNS Science. Institute of Geological & Nuclear Sciences 1:250,000 geological map 13. 70 p. + 1 folded

Earthquake damage and consequential effects

Somewhat surprisingly, considering the magnitude and duration of earthquake shaking experienced at the site, no significant structural damage was apparent to the Coast Guard and marina infrastructure after the magnitude 7.8 earthquake. However, the tectonic uplift of the South Bay area due to the earthquake created many new navigation hazards and the depth of water associated with the marina facilities was significantly reduced.

The reduced water depth adversely affected use of the marina approach channel, the mooring basin and all three of the local launching ramps: the Coast Guard slipway, the marina launching ramp and the Kaikōura Boating Club launching ramp (refer to Photograph 1).

Post-earthquake, most commercial vessels could only use the marina launching ramp during a 2 to 4 hour window over high tide and this placed severe restrictions on their operations. The limited tidal windows also had a brutal impact on tour operations, that were the subject of additional constraints such as DOC marine mammal permits or regulations on deployment times of fishing gear. The extremely narrow operational window prevented the ability to provide a good quality tourism experience at regular and convenient times during daylight hours. Preliminary estimates indicated that, prior to completion of the marina earthquake repair works, the tour operators could only provide between 10 and 20% of the pre-earthquake tour capacity.

After the Kaikōura earthquake the Coast Guard slipway was subject to water depth issues an hour either side of low tide, in particular during times of bad weather or heavy seas. In the low-tide situation the Coast Guard vessel had to be transported by road to the adjacent marina launching ramp resulting in a minimum 20 minute delay to emergency response.

As the nearest alternative Coast Guard stations are located in Picton to the north and in Lyttelton to the south, both at least 6 hours sailing time from Kaikōura in fair weather, it was imperative that the South Bay Coast Guard facilities were made fully operational as quickly as possible.

Figure 2: Overview of the works that were completed at the South Bay Marina site as part of the NCTIR program.

Overview of the permanent repair works program

The works required to reinstate the pre-earthquake functionality of the Coast Guard and South Bay Marina facilities predominantly comprised excavation of the seabed to correct and compensate for the tectonic uplift rather than the specific repair of structural damage to the harbour facilities. This included excavation of the approach channels and mooring basin.

The marina excavation and dredging works had a significant adverse impact on the existing seawall, jetty and mooring pile structures as it undermined their foundations. The launching ramps also needed to be extended as, post-earthquake, the bottom of the ramp was too high relative to the low to mid-tide sea level. In total, approximately 14,500 cubic metres of seabed material was excavated from the marina approach channel and mooring basin as part of the NCTIR earthquake repair program. Most of this excavated material, which generally a combination of silt, sand, gravel and cobble sized material derived from the limestone bedrock, was used to construct temporary working platforms prior to being placed in an approved, environmentally appropriate offshore disposal area.

Figure 3: Typical cross-section through the Whale Watch Kaikōura berthing area.

Figure 2 provides an overview of the earthquake repair works program that was constructed under NCTIR.

Due to the presence of unfavourably orientated bedding plane defects (refer to Figure 3) and secondary joints in the basement rock, a risk was identified that blocks of rock or crushed zones could move or become unstable as a result of the seabed excavation works. This, in turn, had the potential to undermine and damage the existing breakwater and promenade structures. This risk was assessed to be highest during excavation construction and the Ultimate Limit State (ULS) seismic event scenarios. A combination of retaining walls, benching and reconfiguration of the marina layout was used in conjunction with a carefully designed staged construction sequence to mitigate these risks.

Some stakeholders used the earthquake repair program, and the presence of an unprecedented variety, size and number of construction resources in the Kaikōura region, as an opportunity to invest in upgrades and future proof their facilities. For example, Kaikōura District Council invested in a new tender jetty to allow cruise ship passengers to safely transfer from ship to shore, via tenders, in all tide conditions.

Whale Watch Kaikōura (WWK) also invested in the construction of a new vertical sea wall on the north-western side of their berthing area (refer to Figures 2 and 3). This enabled the length of vessel which could be accommodated in all of their berths to be increased from 18 m to 24 m. In conjunction with a staged replacement of their existing fleet, this enabled the total number of passengers that could be carried by WWK to be approximately doubled, in an environmentally sensitive manner.

Environment Canterbury invested in the installation of 6 new lighted navigation beacons. This significantly improved channel visibility and user safety at night and during times of poor weather conditions.

The type of repair work that was undertaken for the Coast Guard Station was similar to the adjacent marina site, but was significantly smaller in scale. In total, approximately 5,500 cubic meters of seabed material was excavated from the Coast Guard Station approach channel and turning basin as part of the NCTIR earthquake repair program.

Figure 4: Overview of the works that were completed at the South Bay Coast Guard Station site as part of the NCTIR program.

Figure 4 above provides an overview of the earthquake repair works program that was completed by NCTIR at the South Bay Coast Guard station site.

Overview of the emergency repair works program

Emergency repair works were undertaken by Downer Construction Ltd during December 2016 to improve the safety and functionality of the Coast Guard Station, marina and Kaikōura Boat Club (KBC) launching ramps over the 2016/2017 Christmas period. The scope of these works comprised:

• Partial excavation of the Coast Guard Channel.
• Placement of temporary hard fill at the end of the marina and KBC launching ramps (this enabled trailers to reverse further down the launching ramps), and,
• Excavation of a small basin in the seabed immediately in front of the marina launching ramp (this allowed a limited number of vessels to sit within the marina harbour while waiting to use the ramp at times of low tide).

During the 2016/2017 Christmas period the KBC allowed non-members with vessels that were less than 8m long to use their private launching facilities. This significantly reduced the demand and congestion at the marina launching ramp and reduced operation risks for the commercial and tourism vessels.

Environmental Management

An environmental management plan (EMP) was prepared and submitted for the project during December 2016, prior to commencing the physical construction works. This EMP was developed in accordance with the Contractor’s Environmental Policy and AS/NZS 4801:2001 – “Occupational Health & Safety Management Systems”.

The primary potential environmental risks which were identified at this stage of the project were:

• Discharge of seabed material to Kaikōura Harbour during channel excavations.
• Discharge of construction materials during reconstruction.
• Excessive disturbance to the coastal marine area.
• Spillage of hazardous substances.
• Construction noise and vibration.
• Fumes and smoke from machinery, and,
• Disturbance of archaeological remains.

All of the above issues had the potential to adversely impact the environment and wildlife, in particular:

• Penguins (which nested and moulted in the existing breakwater armour rock around the sites during November).
• Sea slugs (which were known to be present on the sea bed within the marina basin).
• Seals (which often rested on the breakwater rocks around the sites), and,
• Whales and dolphins (which were known to occasionally swim within a few hundred metres of the sites)

Several mitigation and control measures were identified and implemented to minimise or eliminate the potential adverse impact of the proposed works on the environment. In addition to the use of common techniques, such as the construction of bunds to control silt runoff, several less common measures were deployed such as:

• The University of Canterbury was engaged to relocate sea slugs and other fauna, as instructed by ECan, from the marina area in the week prior to commencing construction.
• Construction was programmed to minimise disturbance to Penguin nesting or moulting periods, and,
• NCTIR archaeologists assessed the footprint of the construction works and established exclusion zones which were clearly marked out on site. An On-Call Procedure (OCP) was established for notification of any suspected archaeological discoveries.

Engineering design

The key elements of the earthquake repair design program comprised:

• Dredging and demolition works.
• Extension of the reinforced concrete Coast Guard and marina launching ramps.
• Construction of two new reinforced concrete cantilevered pole retaining walls to support the vertical edges of the basin dredging works.
• Supply and installation of 34 new mooring or gangway support piles.
• Supply and installation of four new floating gangway systems.
• Supply and installation of Six navigation beacons, and,
• Construction of two new jetties

Figures 2 and 4 show the location of the above works.

The design of the width and depth of the approach channels and basins were discussed and agreed with the key stakeholders and checked to ensure compliance with Australian Standard AS3962:2001. The mooring piles, jetties, retaining walls and navigation beacons were all designed to comply with the appropriate New Zealand standards and Harbour Master (ECan) requirements.

A considerable amount of effort was expended to optimise the WWK mooring basin layout, and; the final design of the two retaining walls. As a result of stakeholder engagement, WWK made a significant financial contribution which enabled the construction of both retaining walls.
The following options were considered for the Promenade and North-western retaining walls:

a) No retaining walls (provide a batter around the entire basin excavation perimeter).
b) Shotcrete facing with rock anchors.
c) Reinforced concrete “L- wall”.
d) Cast in-situ reinforced concrete cantilever walls, with or without tiebacks, and,
e) Pre-cast reinforced concrete pole walls with shotcrete, cast in-situ or precast panel lagging, and, with or without tiebacks.

Preliminary analysis, assessment and stakeholder engagement confirmed that the “no retaining wall” option was unacceptable as excavation was required immediately adjacent to the existing promenade or breakwater to enable the construction of a WWK berthing arrangement similar to the preearthquake situation.

Primarily due to the expected cost of the shotcrete and rock bolt solution, and potential maintenance and corrosion issues at the rock bolt heads, this option was judged to be technically and economically undesirable. Cost and constructability issues, in particular safety during construction and inadequate cut support during basin excavation, resulted in a cantilevered pole solution being strongly preferred over the L-wall options.

The cantilever pole wall solution had several key benefits over the other options, including cost, and could be constructed in such a way that it supported the existing promenade or breakwater structures before construction of the basin dredging works commenced. The use of precast poles was identified as the preferred design as it eliminated the durability and constructability concerns associated with the cast in-situ alternative. Discussions with the delivery team confirmed that this solution was likely to be the easiest and cheapest to construct. As such the “pre-cast reinforced concrete pole wall” option was collaboratively selected by the design and delivery team as the preferred retaining wall design.

Specialist finite element modelling (FEM) software was used to analyse and estimate the static and seismic soil and rock loads, deformations and structural demands which were associated with the precast reinforced concrete pole walls. At the location of the north-western retaining wall, the rock mass was observed to have bedding planes dipping at approximately 20° towards the basin excavation. Secondary rock Joints were also observed in the field to dip towards the north-west. Two failure block configurations were assessed to be the most critical kinematically-feasible failure mechanisms and were adopted as the ‘worst case’ design scenarios.

In total, three retaining wall height and embedment configurations were analysed and optimised during the detailed design process. Wall Type A had a maximum retained height of 3.0 m and an embedment of 3.0 m; Wall Type B had a retained height of 5.0 m and an embedment of 3.5 m; and, Wall Type C had a maximum retained height of 4.45 m and an embedment of 3.0 m. The apparent friction angle on the bedding plane was assessed to be 44° and a sensitivity analysis was also undertaken via a 2° reduction along the bedding plane.

The preferred wall layout was assessed to comprise 450 mm square piles at 1.3 m centres. The rock (and soil if present) between the poles was therefore assessed to be supported by arching effects between the poles.

In accordance with the requirements of NZS 3101-2006 Chapter 3, the walls were designated to be located within the tidal zone and were designed to have a minimum cover of 60 mm, a cement binder incorporating 8 % Amophous Silca (Microsilica, MS), a total binder of equal to or greater than 350 kg/m³, and a water to binder ratio of less than 0.45. The minimum specified compressive strength was 50 MPa.

The final retaining wall design incorporated a cast in-situ reinforced concrete capping beam running across the top of all the wall piles. The original pre-cast pile design specified starter bars projecting from the top of the piles. This detail was found to result in the starter bars being vulnerable to damage during pitching and installation of the piles, in particular when working adjacent to the existing promenade structure. To address this constructability issue, the starter bar detail was amended to comprise a Reid bar with coupler cast into the pile. Once the pile was cast in place threaded rods, which were designed to act as the starter bars, were screwed into the coupler as part of the capping beam construction sequence. A significant improvement in the speed and quality of construction was immediately observed after this amendment had been made, which more than off-set the additional cost associated with the Reid threaded inserts and rods.

The pile starter bars extended across the pile/capping beam joint. This joint was identified as being potentially vulnerable to corrosion, in particular due to its vicinity to the tidal and/or splash zones. To improve the level of corrosion protection at the joint location, Sikadur 32 Normal was applied to the top of the precast concrete piles. This product allows for wet concrete to be poured against the precast concrete and effectively form a wet joint and provide full cover to the starter bars.

Finally, the Promenade retaining wall design utilised a cast in-situ reinforced concrete lagging. The Delivery Team requested that the lagging for the north-western retaining wall be amended to a pre-cast panel system to better support the breakwater armour rock during excavation. This change in lagging system resulted in a different set of construction challenges, in particular around lagging installation, backfill placement and aesthetics if the wall piles are not installed to an extremely tight line, level and spacing. In hindsight, the designers believe that the cast in-situ lagging system resulted in less construction challenges, and, a slightly better final finish.

Photograph 2: South Bay Marina, March 2018. Construction of the temporary working platform is complete and excavation to deepen the marina approach channel is well advanced.

Construction

It was initially proposed that a temporary bund be constructed across the marina harbour entrance and the basin pumped dry to enable completion of the launching ramp, retaining wall and jetty construction. This would have resulted in the marina facility being completely closed to the public and commercial use for a period of between 7 and 9 months.

The stakeholder engagement process identified that the best overall solution, which resulted in the lowest adverse reputational, commercial and financial impact across all stakeholders, was to maintain at least partial access to the launching, mooring and berthing facilities during the construction works. As a result, the construction methodology and program were redesigned so that launching facilities were available at the marina and at least one berth was available for WWK operations at all times except for a period of four to six weeks at a time when the north western retaining wall was being constructed. The revised construction program had a total duration of 10 to 11 months.

Photograph 3: View showing the south-eastern temporary working platform. Note the barge-mounted excavator visible in the centre-top portion of this photograph.

In summary, the revised construction sequence and methodology comprised:

1.) Progressively excavate the Coast Guard station turning basin and approach channel.
2.) Progressively construct a temporary working platform adjacent to the Coast Guard approach channel using material excavated during Task 1 above.
3.) When the Coast Guard channel excavations were complete, remove the temporary working platform and relocate the excavated material to construct a temporary working platform adjacent to the marina approach channel (see Photograph 2 below).
4.) Complete all “land based” excavations for the marina approach channel. Use excavated material to improve the marina channel working platform, or, commence construction of a temporary access road and working platform for the Dolphin Encounter Jetty.

Photograph 4: Cruise Ship Tender Jetty construction. All construction for this and the Dolphin Encounter Jetty was completed within the temporary working platform.

Photograph 5: Promenade retaining wall construction. This wall design comprised precast reinforced concrete poles and cast in-situ infill panels. Its construction was completed within the temporary working platform.

5.) When the marina approach channel “land-based” excavations were complete, remove the temporary working platform and relocate such material to complete the temporary working platform for the Dolphin Encounter Jetty, the Cruise Ship Tender Jetty and the Promenade Retaining wall (see Photograph 3).
6.) Undertake additional “ship-based” dredging works for the approach channel and harbour basin using a barge-mounted excavator (see Photograph 3). Barge-mounted equipment was used for all areas where land-based excavators could not safely reach without the need to close the approach channel or launching ramp.
7.) Construction of temporary works platform from limestone material that was recycled from the channel deepening works. This enabled safe construction of the promenade retaining wall and Cruise Ship Tender Jetty. (Photo 3)
8.) Commence demolition and construction of the Dolphin Encounter Jetty and construction of the cruise ship jetty and promenade retaining wall structures (see Photographs 4 and 5). The pile construction for these structures was completed from the temporary working platform surface, with careful staging and shoring of future excavations to ensure the highest possible level of geotechnical stability and worker safety was maintained at all times.
9.) At a time that suited WWK operations, extend the temporary working platform within the marina across the full width of the WWK berthing area to enable construction of the north-western retaining wall to commence. During this phase of the construction WWK adopted an alternative, less efficient methodology to embark and disembark their passengers which made use of the launching ramp or the adjacent existing jetty.
10.) Commence and complete construction of the north-western retaining wall as quickly as possible.
11.) Install WWK berthing area mooring and gangway piles.
12.) Install WWK floating gangway system.
13.) Excavate and remove the temporary working platform for the north-western retaining wall, WWK berthing area and Dolphin Encounter Jetty. Simultaneously complete the final seabed excavation and dredging works in these areas. Transport spoil material from these temporary working platforms to the marina launching ramp and construct the temporary coffer bund (refer to Photograph 6).
14.) Complete construction of the promenade retaining wall. Remove temporary working platform and complete final seabed excavation and dredging works in this area. Transport all excavated material to the approved disposal area (two berths were made available for WWK to use upon completion of this task).
15.) Complete construction of the marina launching ramp extension. Remove the temporary coffer dam and complete final seabed excavation and dredging works in this area. Transport all excavated material to the approved disposal area.
16.) Disestablish from site and admire the final outcome (refer to Photograph 7). Note the north-western retaining wall is visible in the top-right corner of this photograph.

Conclusions

From a programming perspective, this was an extremely challenging project which required the highest levels of stakeholder engagement, responsiveness and collaboration from the Delivery and Design teams to ensure its success.

Stakeholder, environmental and Health and Safety requirements combined in a way that meant the Design Team had to be flexible, work extremely closely with the Delivery team, and, be willing to discuss and modify their designs, as appropriate, to ensure best-for-project outcomes were achieved. An example of this was the change to the retaining wall starter bar design to reduce the risk of reinforcing steel damage during pile installation and rework.

Photograph 6: South Bay Marina, 24 October 2017. Construction of the temporary coffer dam around the marina launching ramp is complete (top left-hand corner of photograph).

Photograph 7: Completed Whale Watch Kaikōura berthing area and north-western retaining wall. (Photograph taken at approximately high tide on 14 November 2017).

This project also reminded the authors that the best overall design and delivery program is not always the one which results in the quickest and cheapest construction. For this project the best construction methodology, sequence and program was one that enabled restricted use of the marina facilities by commercial stakeholders, thus allowing them to earn some income while the repair works were being constructed. In the case of this project, a relatively modest increase in construction cost enabled many millions of income to be earnt by the tourism and commercial fishery sectors while the repair works were being completed. Thi

Tags : #Dredging#Excavation#Kaikoura#Piles