The Canterbury Earthquake Sequence (CES) of 2010-2011 produced large seismic moments up to Mw 7.1. These large, near-to-surface (<15 km) ruptures triggered >6,000 rockfall boulders on the Port Hills of Christchurch, many of which impacted houses and affected the livelihoods of people within the impacted area. From these disastrous and unpredicted natural events a need arose to be able to assess the areas affected by rockfall events in the future, where it is known that a rockfall is possible from a specific source outcrop but the potential boulder runout and dynamics are not understood. The distribution of rockfall deposits is largely constrained by the physical properties and processes of the boulder and its motion such as block density, shape and size, block velocity, bounce height, impact and rebound angle, as well as the properties of the substrate. Numerical rockfall models go some way to accounting for all the complex factors in an algorithm, commonly parameterised in a user interface where site-specific effects can be calibrated. Calibration of these algorithms requires thorough field checks and often experimental practises. The purpose of this project, which began immediately following the most destructive rupture of the CES (February 22, 2011), is to collate data to characterise boulder falls, and to use this information, supplemented by a set of anthropogenic boulder fall data, to perform an in-depth calibration of the three-dimensional numerical rockfall model RAMMS::Rockfall. The thesis covers the following topics: • Use of field data to calibrate RAMMS. Boulder impact trails in the loess-colluvium soils at Rapaki Bay have been used to estimate ranges of boulder velocities and bounce heights. RAMMS results replicate field data closely; it is concluded that the model is appropriate for analysing the earthquake-triggered boulder trails at Rapaki Bay, and that it can be usefully applied to rockfall trajectory and hazard assessment at this and similar sites elsewhere. • Detailed analysis of dynamic rockfall processes, interpreted from recorded boulder rolling experiments, and compared to RAMMS simulated results at the same site. Recorded rotational and translational velocities of a particular boulder show that the boulder behaves logically and dynamically on impact with different substrate types. Simulations show that seasonal changes in soil moisture alter rockfall dynamics and runout predictions within RAMMS, and adjustments are made to the calibration to reflect this; suggesting that in hazard analysis a rockfall model should be calibrated to dry rather than wet soil conditions to anticipate the most serious outcome. • Verifying the model calibration for a separate site on the Port Hills. The results of the RAMMS simulations show the effectiveness of calibration against a real data set, as well as the effectiveness of vegetation as a rockfall barrier/retardant. The results of simulations are compared using hazard maps, where the maximum runouts match well the mapped CES fallen boulder maximum runouts. The results of the simulations in terms of frequency distribution of deposit locations on the slope are also compared with those of the CES data, using the shadow angle tool to apportion slope zones. These results also replicate real field data well. Results show that a maximum runout envelope can be mapped, as well as frequency distribution of deposited boulders for hazard (and thus risk) analysis purposes. The accuracy of the rockfall runout envelope and frequency distribution can be improved by comprehensive vegetation and substrate mapping. The topics above define the scope of the project, limiting the focus to rockfall processes on the Port Hills, and implications for model calibration for the wider scientific community. The results provide a useful rockfall analysis methodology with a defensible and replicable calibration process, that has the potential to be applied to other lithologies and substrates. Its applications include a method of analysis for the selection and positioning of rockfall countermeasure design; site safety assessment for scaling and demolition works; and risk analysis and land planning for future construction in Christchurch.

This report to RCP Ltd and University of Canterbury summarises the findings of a 5 month secondment to the CERA Port Hills Land Clearance Team. Improvement strategies were initiated and observed. The Port Hills Land Clearance Programme is the undertaking of the demolition of all built structures from the Crown’s compulsory acquired 714 residential red zoned properties. These properties are zoned red due to an elevated life risk as a result of geotechnical land uncertainty following the 2011 Canterbury Earthquakes.

This thesis aims to create a specific and robust geotechnical data set for the Lyttelton Volcanic Group, and investigate the effect of emplacement and post-emplacement mechanisms on geotechnical characteristics. The thesis provides an engineering geological model of a representative section of the Lyttelton Volcanic Complex, which, in conjunction with field observations, informed the subdivision of the main lithological groups into geotechnical sub-units. The sub-units account for the geological variations within the rock types of this study. Eighteen geotechnical sub-units were identified, sampled and characterised: 1trachytic dykes, 2trachytic domes, 3trachytic lava, 4brecciated basaltic ignimbrite, 5moderately welded basaltic ignimbrite, 6highly welded basaltic ignimbrite, 7red ash, 8crystal dominated tuff, 9lithic dominated tuff, 10rubbly basaltic breccia, 11unweathered basaltic lava, 12slightly to moderately weathered basaltic lava, 13highly to completely weathered basaltic lava, 14highly vesicular basaltic lava bomb, 15basaltic dyke, 16blocky basaltic lava, 17volcanogenic conglomerate and 18volcanogenic tuffaceous sandstone. Thirteen units were able geotechnically tested. Sample preparation and geotechnical testing followed ASTM and ISRM guidelines respectively. Geotechnical testing included: uniaxial compressive strength (σci), point load strength index (Is(50)), porosity (n), density (ρd), P and S wave velocities (Vp and Vs), slake durability (Id2), Young’s Modulus (E), Poisson’s Ratio (υ), shear modulus (G) and bulk modulus (K). The igneous lithologies included in this study have been characterised using the Detailed Engineering Geological Igneous Descriptive Scheme, developed purposely for the needs of the thesis. The results of laboratory testing showed many strong trends with geological characteristics and relationships between geotechnical parameters. Parameters such as porosity, density, P-wave velocities, Young’s Modulus and point load strength showed very strong correlations with uniaxial compressive strength. Variability in the physical and mechanical properties is attributed to the geological factors, which dictate the material behaviour. These include texture, grain size, composition, welding, lithification, flow banding, percentage and size of phenocrysts/clasts/lithics. Geological factors affecting geotechnical behaviour are a function of emplacement mechanism. Four distinct emplacement mechanisms were identified in this study: lava flows, pyroclastic density currents, intrusions (dykes) and airfall deposits. Typically, lava flows and intrusions have higher strength, durability, density and lower porosity than pyroclastics and airfall deposits. Importantly, the data illustrates a considerable variability in some geotechnical parameters within the same unit (e.g. 58-193 MPa strength variation in the unweathered basaltic lava). Variability within rocks with similar emplacement mechanisms is attributed to the effects of post-emplacement mechanisms and processes (e.g. weathering, alteration and micro/macro fracturing leading to lower strength). Evaluation of engineering geological and geotechnical parameters of rock and soil materials are required for engineering purposes, specifically when any form of design is required. This study has highlighted the importance and necessity to identify volcanic lithologies and features correctly as there are consequences for geotechnical behaviour, and that volcanic data from literature data should not be used without the correct degree of ground-truthing and geological context. Location-specific engineering geological data are necessary for the quantitation of variability in engineering geological characterisation for engineering geological models, designs and simulations in the Port Hills Volcanics.

Following the 22 February 2011, MW 6.2 earthquake located on a fault beneath the Port Hills of Christchurch, fissuring of up to several hundred metres in length was observed in the loess and loess-colluvium of foot-slope positions in north-facing valleys of the Port Hills. The fissuring was observed in all major valleys, occurred at similar low altitudes, showing a contour-parallel orientation and often accompanied by both lateral compression/extension features and spring formation in the valley floor below. Fissuring locations studied in depth included Bowenvale Valley, Hillsborough Valley, Huntlywood Terrace–Lucas Lane, Bridle Path Road, and Maffeys Road–La Costa Lane. Investigations into loess soil, its properties and mannerisms, as well as international examples of its failure were undertaken, including study of the Loess Plateau of China, the Teton Dam, and palaeo-fissuring on Banks Peninsula. These investigations lead to the conclusion that loess has the propensity to fail, often due to the infiltration of water, the presence of which can lead to its instantaneous disaggregation. Literature study and laboratory analysis of Port Hills loess concluded that is has the ability to be stable in steep, sub-vertical escarpments, and often has a sub-vertically jointed internal structure and has a peak shear strength when dry. Values for cohesion, c (kPa) and the internal friction angle, ϕ (degrees) of Port Hills loess were established. The c values for the 40 Rapaki Road, 3 Glenview Terrace loess samples were 13.4 kPa and 19.7 kPa, respectively. The corresponding ϕ values were thought unusually high, at 42.0° and 43.4°.The analysed loess behaved very plastically, with little or no peak strength visible in the plots as the test went almost directly to residual strength. A geophysics resistivity survey showed an area of low resistivity which likely corresponds to a zone of saturated clayey loess/loess colluvium, indicating a high water table in the area. This is consistent with the appearances of local springs which are located towards the northern end of each distinct section of fissure trace and chemical analysis shows that they are sourced from the Port Hills volcanics. Port Hills fissuring may be sub-divided into three categories, Category A, Category B, and Category C, each characterised by distinctive features of the fissures. Category A includes fissures which display evidence of, spring formation, tunnel-gullying, and lateral spreading-like behaviour or quasi-toppling. These fissures are several metres down-slope of the loess-bedrock interface, and are in valleys containing a loess-colluvium fill. Category B fissures are in wider valleys than those in Category A, and the valleys contain estuarine silty sediments which liquefied during the earthquake. Category C fissures occurred at higher elevations than the fissures in the preceding categories, being almost coincident with bedrock outcropping. It is believed that the mechanism responsible for causing the fissuring is a complex combination of three mechanisms: the trampoline effect, bedrock fracturing, and lateral spreading. These three mechanisms can be applied in varying degrees to each of the fissuring sites in categories A, B, and C, in order to provide explanation for the observations made at each. Toppling failure can describe the soil movement as a consequence of the a three causative mechanisms, and provides insight into the movement of the loess. Intra-loess water coursing and tunnel gullying is thought to have encouraged and exacerbated the fissuring, while not being the driving force per se. Incipient landsliding is considered to be the least likely of the possible fissuring interpretations.