Preliminary investigation of emerging suburban landsliding in Gisborne, New Zealand

Recently uplifted, soft Pleistocene sediments in northern New Zealand are particularly vulnerable to landsliding because they are often underlain by less permeable, clay-rich Neogene mudstone/siltstone rocks. Typically, instability is rainfall-induced, often due to a high intensity rainfall event from extra-tropical cyclones, following wetter months when antecedent soil moisture has increased. Using remote sensing, field surveys and laboratory testing, we report on some emerging slope instability hazards in the eastern suburbs of the coastal city of Gisborne, on the North Island. Retrogressive failure of the main landslide (at Wallis Road) is ongoing and has already led to the abandonment of one home, while an adjacent landslide (at Titirangi Drive) appears to be in an incipient phase of failure. The Wallis Road landslide has been particularly active from mid-2017, with slumping of the headscarp area transitioning to a constrained mudflow downslope, which then descends a cliff before terminating on the beach. In contrast, the incipient Titirangi Drive landslide at present displays much more subtle effects of deformation. While activity at both landslides appears to be linked to rainfall-induced increases in soil moisture, this is due to the effects of prolonged periods of rainfall rather than the passage of high intensity cyclonic storms.

A cluster-based multiparametric similarity test for the compartmentalization of crystalline rocks into structural domains

Usually, fracture sampling studies comprise the collection of several fracture samples, which involve many fracture clusters. Grouping fracture samples into structural domains is generally useful for geologists, hydrogeologists, and geomechanicians as a region of fractured rocks is subdivided into sub-regions with similar behavior in terms of their hydromechanical properties. One of the common methods used for grouping fracture samples into structural domains considers the fracture orientation of clusters and ignores several fracture parameters, such as fracture spacing, aperture, and persistence, which are important for fluid circulation in the rock mass.In this study, we proposed a new cluster-based similarity method that considered the orientation of clusters as well as clusters’ aperture, persistence, and fracture spacing. Field investigations were conducted in the Grenville geological province of the Canadian Shield in the Lanaudière region, Quebec, Canada, where fractures were sampled from 30 outcrops and four boreholes. The proposed method is more suitable than other methods, and has applications in hydrogeology, rock mechanics, and especially in studies of fluid circulation in the rock mass. In addition, a method for the compartmentalization of a given study area into structural domains by means of Voronoi diagrams was also proposed.

Some of the geological challenges and opportunities associated with the dynamics of the Cenozoic East African Rift System

The Cenozoic East African Rift System (EARS) is the largest continental rift valley system on Earth. Extending over a total distance of approximately 4,500 km, and with an average width of about 50 km, it is home to some of East Africa's largest urban populations and some of its most important transport, energy and water supply infrastructure. Rifting commenced during the Early Miocene and crustal extension has continued to the present day, posing seismic and volcanic hazards throughout its history of human occupation. Deep-seated landslides also present significant challenges for public safety, land management and infrastructure development on the flanks of rift margins. The rift floor itself poses a range of geohazards to community livelihood and engineering infrastructure, including ground fissuring and cavity collapse, flooding and sedimentation. On the positive side, the development of the EARS has created hydrocarbon and geothermal energy resources, and geomaterials for use as aggregates and cement substitutes in road and building construction. Optimising the use of these resources requires careful planning to ensure sustainability, while land use management and infrastructure development must take full consideration of the hazards posed by the ground and the fragility and dynamism of the human and physical environment.

The role of engineering geology in delivering the United Nations Sustainable Development Goals

Engineering Geology has an important role to play in sustainable development. This is due to the unique perspective that Engineering Geologists have of the interfaces between: science and engineering; the natural and built environments; the past, present and future. This paper examines the role of Engineering Geology in delivering the United Nations Sustainable Development Goals and demonstrates that there is a strong link between the knowledge, skills and activities of Engineering Geologists and the delivery of all 17 goals. The study includes a detailed evaluation of all 169 SDG targets and highlights the key impact areas where Engineering Geologists already contribute to sustainable development, as well as identifying opportunities for contributions to be strengthened. It is hoped that this paper will empower Engineering Geologists to confidently communicate the value of their role, act responsibly, and exert their influence to drive positive outcomes in terms of sustainable development in everything that they do.Thematic collection: This article is part of the Sustainability in Engineering Geology & Hydrogeology collection available at: https://www.lyellcollection.org/cc/sustainability-in-engineering-geology-and-hydrogeologySupplementary material:https://doi.org/10.6084/m9.figshare.c.5778817

3D stability analysis method for toppling failure on rock slopes

In this paper, an optimized solution method is proposed for the 3D stability analysis of rock slopes subject to toppling failure based on their geometric and mechanical properties. It was verified by a 3D block system that focused on the geometric properties of toppling slopes as a research object, considering the force and its action point on the interface of the block system as unknown variables, as well as introducing the definition of a safety factor considering both tension and shear strength reduction. The proposed method implied setting constraints, such as the balance equation corresponding to block force and moment, as well as non-violation of the yield criterion, considering the minimum value of the safety factor as the objective function. It was applied to the analysis of two typical 3D models simulating toppling failure on slopes. The example of a 3D spherical toppling slope was reconstructed and corroborated by calculations. The experimental results demonstrated that the proposed method could appropriately reflect the mechanical properties and stability behavior of a 3D toppling slope, thereby facilitating the analysis of the stability of 3D toppling rock slope model.

A sensitivity analysis of a single extraction well from deep geothermal aquifers in the Cheshire Basin, UK

Deep hot sedimentary aquifers (HSAs) are targeted for geothermal exploitation in the Cheshire Basin, UK. In this study, a single extraction well targeting the Collyhurst Sandstone Formation was modelled on MATLAB coupling heat and fluid flux. The Collyhurst Sandstone Formation in the Crewe area of the Cheshire Basin is expected to be found at a depth of 2.8 to 3.5 km, and was chosen as an area for geothermal exploration due to the high demand for energy.Model results suggest that low-enthalpy, deep geothermal systems with thick HSAs are affected by both geological and engineering parameters. The results of this study highlight that the thermal gradient, hydraulic conductivity, production rate, length and position of the well screen are the key parameters capable of affecting the success and viability of any single well scheme. Poor planning during exploration and development can hinder the productivity of any single well scheme and these parameters must be considered to fully understand the risk. Engineering parameters, such as the length of the well screen, can be used during well planning to mitigate geological risks in the aquifer, whilst the results presented can also be used as a guide for energy potential under varying conditions.

Application of geophysical and hydrogeological analyses to predict water and hydrocarbon entry to the T5 Tunnel, west Iran

The Garmsiri Project, including the 4.5 km long T5 Tunnel, is under construction in western Iran. The T5 tunnel passes through the NW-SE trending Emam Hasan Anticline (EHA), perpendicular to the fold axis. The fold is mainly composed of the marlstone and argillaceous limestone layers of Cretaceous to Miocene age, incorporating the Pabdeh-Gurpi Formation, karst limestone of the Asmari Formation, and marlstone and gypsum of the Gachsaran Formation. There was a risk of water entry into the tunnel since it was constructed below the regional groundwater table elevation. In addition the entry of hydrocarbons, in either liquid or vapour phase, to the tunnel was possible due to the presence of numerous active bitumen mines in the vicinity of the anticline. To predict the risk of water or hydrocarbon entry geological and hydrogeological analyses together with the Audio Magnetotelluric (AMT) method were applied. Based on the field works, resistivity and geological cross sections were provided along the tunnel path. Several boreholes were drilled along the tunnel route and watertable elevation, Rock Quality Designation (RQD) and permeability values were measured. To determine a broad range of features related to the anticline, 55 AMT stations were positioned along the tunnel route. Dimensionality analysis confirmed 2D dimensionality of the AMT transfer functions, which allowed to apply the 2D bimodal inversion using a non-linear conjugate gradient algorithm. Integration of the geological and hydrogeological data with the resistivity model resulted in a more detailed geological section along the tunnel, including watertable elevation and identification of highly conductive zones in which bitumen migrated. It was predicted that water entry would be observed through the Asmari Formation and also that elevated H2S concentrations would be encountered during drilling in the anomalous conductive zones. Monitoring results and field observations gained during the tunnel construction were compared by the predictions.

Developing an in situ, hydromechanical coupling, true triaxial rock compression tester and investigating the deformation patterns of reservoir bank slopes

Interactions between water and rocks are the main factors affecting the deformation of rock masses on sloped banks by reservoir impoundment. The technology used in laboratory tests of water-rock interaction mechanisms cannot simulate the coupling of water, the rock structure and the initial stress environment. In this work, we develop an in situ hydromechanical true triaxial rock compression tester and apply it to investigate the coupling response of reservoir bank rocks to changing groundwater levels. The tester is composed of a sealed chamber, loader, reactor, and device for measuring deformation, which are all capable of withstanding high water pressures, and a high-precision servo controller. The maximum axial load, lateral load and water pressure are 12 000 kN, 3 000 kN and 3 MPa, respectively. The dimensions of the test specimens are 310 mm×310 mm×620 mm. The test specimens are grey-black basalts with well-developed cracks from the Xiluodu reservoir area. The results show that increasing water pressure promotes axial compression and lateral expansion, while decreasing water pressure causes axial expansion and lateral compression. A water pressure coefficient, K, is introduced as a measure of the hydromechanical coupling effect (expansion or compression) with changing groundwater level. A mechanical tester can be used to perform accurate field tests of the response of wet rocks to hydromechanical coupling. The test results provide new information about the deformation patterns of rock slopes in areas surrounding high dams and reservoirs.Thematic collection: This article is part of the Role of water in destabilizing slopes collection available at: https://www.lyellcollection.org/cc/Role-of-water-in-destabilizing-slopes

Baseline surface- and groundwater monitoring prior to an onshore shale gas operation in the Vale of Pickering, UK

A comprehensive programme of baseline groundwater hydrochemical monitoring has been carried out in connection with the proposed hydraulic fracturing of a 2 to 3 km deep Bowland Shale gas reservoir in borehole KM8 at Kirby Misperton, North Yorkshire, UK. The monitoring infrastructure encompassed: five on-site boreholes with hydraulically open intervals ranging from shallow weathered cover to a c. 200 m deep Corallian limestone aquifer, six off-site wells (hydraulically open in superficial materials and/or Kimmeridge Clay) and four surface water monitoring stations. Groundwater chemistry was high stratified with depth, ranging from slightly acidic, fresh, very hard Ca-HCO3-SO4 waters in shallow weathered cover, to brackish, calcium-depleted, highly alkaline waters in the Corallian aquifer. Dissolved methane was detected in most boreholes, with 10 µg/L being typical of shallow boreholes and around 50 mg/L in the Corallian. Low ethane concentrations and isotopic evidence suggest that the methane was predominantly microbial in origin (carboxylate fermentation at shallow depth, natural methanogenic CO2 reduction at greater depth). Elevated dissolved ethane (20-30 µg/L) was found in one well of intermediate depth, suggesting admixture of a possible thermogenic component, although this could be derived directly from the Kimmeridge Clay penetrated by the well.

Structural damage to carbonate pillar hazardous rock masses subject to long-term water level fluctuations in the Three Gorges reservoir area, China

Given the wide distribution of carbonate pillars in the Three Gorges reservoir area, there is a need to investigate the possible structural damage they experience from long-term water level fluctuations. This study analyzed the coupled effects of the improved time-dependent crack propagation pattern and failure modes of structural rock masses under stress-seepage using the Jianchuandong pillar hazardous rock mass (JCD) as a case study. A new crack simulation method based on FLAC3Dis proposed in which the interface element is immediately set on the surface of the yielding zone during the calculation step when a zone yields under tensile or shear stress. The two zones are directly separated during the tension or shearing of the bond at the contact surface. The JCD simulations illustrated that fractures and failure zones within the rock mass would propagate along the existing vertical cracks and extend to the base toe. The base rock mass would experience fracturing, finally leading to failure of the entire rock mass. The presented model provides sufficiently accurate predictions and is an optional method for analyzing time-dependent failure of pillar hazardous rock masses subject to water level fluctuations.Thematic collection: This article is part of the Role of water in destabilizing slopes collection available at: https://www.lyellcollection.org/cc/Role-of-water-in-destabilizing-slopes