Introduction

Danielle Grant Kaipatiki Local Board Chair

Rawene Carpark Update

7th December 2017

Rawene Carpark Update

1. Overview - Dean Kimpton, Chief Operating Officer, Auckland Council

2. Update on stability of land in the car park and surrounding area - Ross Roberts,

Geotechnical & Geological Practice Lead, Auckland Council & Andrew Scoggins,

Chief Engineer, Auckland Transport

3. Update on safety/integrity of surrounding buildings - Ian McCormick, General

Manager Building Consents, Auckland Council, Steve Crawford Tonkin and Taylor

4. Next Steps - Dean Kimpton

1. Overview - Council and CCO Response

Watercare - wastewater and water asset assessment, repair and management

Healthy Waters - stormwater response and additional stormwater control

Building Control - identification and resolution of dangerous building structures

Infrastructure & Environmental Services - closed landfill management, geological and geotechnical advice, long term slip remediation

Auckland Transport - initial response management, temp stabilisation works, project management and communications support, parking, streetscape upgrade

2. Geology - History of the Site

Figure 1: Aerial photo November 1978

Historic aerial photographs have been assessed.

Aerial photos show filling operations occurring throughout the 1970’s and 1980’s period

From earlier photo images in the 1940’s-1950’s the original houses were located at the crest of the gully on natural ground.

It is inferred that the current buildings are located on natural ground.

2. History of Site

Figure 2: Aerial photo 1963

2. History of Site

Figure 3: Aerial photo 1991

2. History of Site

Figure 4: Aerial photo 2015/16

2. History of Site - ongoing monitoring

Figure 5: Monitoring photo 23/08/16 Monitoring photo 16/05/17 Monitoring Photo 30/08/17

2. History of Site - AMIS assessment

Figure 6: Aerial photo Council GIS 2015/16

Asset Management Intelligence Support (AMIS) - Community Facilities, Auckland Council completed a visual assessment on the cracked areas to the car park surface 30 August 2017.

Recommendations included;

• Engage a Geotechnical Engineer to study and investigate the stability of the slope.

• Improve surface stormwater and relocate cesspits.

• Engage a Structural Engineer to design a retaining wall.

2. History of Site - closing area of carpark

Figure 7: AMIS Assessment 30/08/17

AT engaged Opus on 14th

September 2017 to inspect the site and advise Council/AT on the risk posed to users of the carpark.

Site inspected 15th Sept with report 18th Sept recommending closing of carpark and further geotechnical testing.

Decision to close 19th and car park area closed 20th

September.

2. History of Site - Initial Slip

Figure 8: Initial landslide at the western end of Rawene Carpark, 09/10/17

The western end of Rawene Carpark dramatically failed on the afternoon of 9th October 2017 (Figure 8).

The mode of failure observed was a deep-seated mass-movement failure. After the initial failure, the material became a viscous liquid and flowed, suggesting the material was fully saturated.

2. History of Site - Initial Slip

Figure 9: Backwards regression of the initial landslide at the western end of Rawene Carpark,

looking east towards Rawene Road, 10/10/17

Further regression of the headscarp/top occurred over the night of the 9/10th October 2017 (Figure 9).

2. History of Site - Initial Slip

Figure 10: Initial landslide drone photo, 14/10/17

The slip resulted in a nominal 25m width by 50m length of carpark to be deposited downslope in a debris slide.

The total length of the slip is some 250m with a width ranging from 50m at the head/top to 15m at the toe/base.

2. History of Site - Instability

What initiated the instability has not been conclusively established, however the following areas are being investigated;

level of saturation of the fill

level of compaction of the fill

makeup of material in the fill

higher ground water level in the base of the gully from a natural spring outfall below the fill

stormwater outflow into the gully

water ingress at the top of the gully

2. Stabilisation Works

Figure 11: Jet grouting rig position on the footpath adjacent to the grassed area, 27/11/17

Testing completed after first slip - Inclinometers (measure movement), vibration monitoring, Piezometers (measure water), UAV surveys (3D imagery), visual monitoring, boreholes (material type and strength).

Temporary stabilisation technique of jet grouting chosen with 30 piles, 15m deep and 800mm in diameter.

2. Stabilisation Works

Figure 12: Location of jet grout piles are shown with “X”, orange highlight denotes completed pile

Temporary stabilisation successful from pile 1 to 22 with no new movement behind these piles

2. History of Site - Second Slip

Figure 13: Second landslide, drone photo, 29/11/17

On the evening of the 28th Nov 2017 a failure within the western gully with regression of 10m to 15m. This was a much larger distance than typical scarp regressions observed since the first slip and resulted in the loss of the jet grouting drill.

Again, the mode of failure observed was a deep-seated mass-movement failure. The material became a viscous liquid and flowed, the fill material exposed in the headscarp (top) appeared to be fully saturated.

2. History of Site - Initial Slip

Figure 13: Initial landslide drone photo, 14/10/17

2. History of Site - Initial Slip

Figure 13: Initial landslide drone photo, 14/10/17

2. Rawene Slip - Base

Figure 16: Base of Rawene Reserve Slip, 24/10/17

Watercare sewer half way down slip was damaged, a bypass is being pumped.

Healthy Waters project in Chelsea Estate.

Material found included small amounts of contamination, including tyres and possible asbestos.

2. History of Site - Second Slip

Figure 17: Second landslide drone photo, 29/11/17

2. History of Site - Second Slip

Figure 18: Drone Long section, 30/11/17

2. History of Site

Figure 26: UAV digital long section

2. History of Site

Figure 27: UAV digital long section

2. Mokoia Road Carpark - Cracks

Figure 28: Mokoia Road Carpark, NZH photo

An initial assessment has determined that the depression has been identified in imagery dating back from 2015 and the cracking today is consistent with heavy vehicle loading and unloading activities.

The ground conditions, geology and topography between the car park and the gully are completely different and Council are confident that there is no link between the two.

We are taking this case seriously and geotechnical specialists are investigating this further.

2. Slip Works – next steps

Slip stabilisation at headscarp/top (temporary works)• Further geotechnical testing (underway - site work to be completed in 1 week)• Early design works (underway) • Timing - following geotechnical testing timing can be confirmed

Slip Stabilisation at toe/base• Investigation works to commence before Christmas - helicopter required• Early works design once investigation is complete• Early works planned before this winter

Stormwater• Stormwater diversion works to remove water from entering top of slip

Water and wastewater• Continuation of pumping wastewater from damaged asset• Planning and design of options for temporary repairs• Continue investigations of water

3. Safety of Buildings - Process

Figure 29: Location of testing, second landslide, drone photo, 29/11/17

• Tonkin & Taylor used as specialist adviser in conjunction with Ross Roberts.

• Council and its specialist advisers agree that at the moment there is no active risk that requires evacuation of the buildings.

• Actively monitoring the site to detect any further settlement

• Buildings reviewed recently as part of seismic strengthening investigations.

• Council have engaged Tonkin and Taylor to complete additional testing shown above.

• This is underway and the site works will be completed by the end of next week.

• A Geophysics contractor will also be established.

4. Next Steps

• Ongoing monitoring

• Stormwater collection and diversion works

• Additional geotechnical testing to provide information for design and risk assessment

• Design and then construction of temporary stabilisation works

• Planning of longer term remediation works

• Communications - continue with email updates, direct communications with business/property owners, community meeting in new year, monthly Local Board updates

Lead Team

Project Manager / Geotechnical Lead - Ross Roberts (AC)

Chief Engineer - Sarah Sinclair (AC)

Chief Engineer - Andrew Scoggins (AT)

Communications - Nahri Salim (AT)

Parking - John Strawbridge (AT)

Transformation Project - Duncan Miller (AT)

Building Safety - Ian McCormick (AC)

Questions