Columnar Joints Research Articles

A Study on Evaluation of Slope Stability and Range of Rockfall Hazard of Daljeon-ri Columnar Joint in Pohang, Korea

In this study, we evaluated the slope stability of the Pohang Daljeon-ri columnar joint (Natural Monuments # 415) and calculated the maximum energy, jumping height and moving distance of rockfalls using a simulation. Based on the results, we established the range of rockfall risk. The slopes of the Pohang Daljeon-ri columnar joint have dip directions of 93.79°, 131.99°, 165.54° and 259.84° from left (SW) to right (NE). Furthermore, they have a fan-like shape. The Pohang Daljeon-ri columnar joints are divided into four sections depending on the dip direction. The measurement results of the discontinuous face show that zone 1 is 125, zone 2 is 261, zone 3 is 262, zone 4 is 43. The results of slope stability analyses for each section using a stereographic projection method correspond to the range of planar and toppling failure. Although it is difficult to diagnose the type of failure, risk evaluation of currently falling rocks requires further focus. The maximum movement distance of a rockfall in the simulation was approximately 66 m and the rockfall risk range was the entire area under slope. In addition, it is difficult to forecast where a rock will fall as it rolls in various directions due to topographic factors. Thus, the installation of measures to prevent falling is suggested to secure the stability based on the results of the rockfall simulations and its probabilistic analysis.

GEOHERITAGE PRELIMINARY EVALUATION AND ITS IM-PLICATION ON GEOTOURISM POTENTIAL IN WEST BAN-DUNG, BANDUNG, INDONESIA


 
 
 
 Geoheritage is a term of geological sites that fulfill certain values and criterias which can impact the local community. The unique tectono-volcanic History of Bandung has produced several impressive geodiversity. This research aims to evaluate six geological sites (Bugbrug Waterfall Lava Ramp, Cimahi Waterfall Columnar Joint, Panganten Waterfall Columnar Joint, gunung Batu Fault Scarp, Cihanjuang Ignimbrite, and Tangkuban Parahu Ratu Crater) which are potential as Geoheritage in West Bandung District, Bandung, West Java. Quantitative evaluation was done through several parameters which include values that are important for geoheritage such as: Intrinsic and Scientific Value, Education Value, Economic Value, Conservation Value, and Added Value. This evaluation method will produce scores that will further be analyzed through qualitative means by using SWOT (Strength, Weak-ness, Opportunity, and Weakness) method and its implication on geotourism potential. Quantitative analysis shows that Geodiver-sity of West Bandung shows a good potential as Geoheritage with the final score ranges between 50.83 – 74.17%. The SWOT analysis was applied through strengths of geoheritage potential in this area, especially from Scientific, Economic, and Aesthetic Parameters. The uniqueness of West Bandung Geoheritage Potetial is currently slightly diminished due to the lack of public educa-tion aspects, the lack of significant cultural and ecologic value in several sites.
 
 
 

Study on the mechanical behaviour of Columnar Jointed Rock Mass under uniaxial compression state

The columnar joint is a special type of primary joints which the cross sections are mostly quadrilateral, pentagonal and hexagonal. Intact rock mass is always cut by columnar joints into regular or irregular rock prisms, resulting in poor properties. With the expansion of large-scale engineering activities, a number of hydropower engineering such as Baihetan hydropower station, Xiluodu hydropower station and Ertan hydropower station, have encountered columnar jointed rock mass. The existence of columnar jointed rock mass poses a challenge to the design, construction and safe operation of these projects. To understand the mechanical behaviour of columnar jointed rock mass, uniaxial compression tests were carried out on artificial specimens made from rock-like materials. In the experiments, a self-designed pouring apparatus was used to prepare the columnar jointed rock-like specimens. Based on the experimental results of axial stress–axial strain curves, the strength and deformation of columnar jointed rock mass were investigated. The effect of columnar joint inclination angle on the mechanical behaviour of columnar jointed rock mass was analysed. It is found that the columnar jointed rock masses are characterized by significant anisotropy. The strength of columnar joint plays a significant role on the mechanical response of columnar jointed rock mass. The study Formatting the text

Design of the dome shape of complicated huge cylindrical surge chamber in Baihetan hydropower station

Baihetan hydropower station located at lower reaches of Jinsha River in China, the hydropower station is characterized by its large scale and complicated layout. Four cylindrical throttled surge chambers sit in each bank with their heights about 100 m, and the diameters 43 to 48 m. The surrounding rock of the dome is affected by high in-situ stress, interlayer dislocation zone and columnar joints. The geological conditions are extremely complex and the stability of the surrounding rock is prominent. The numerical simulation method is used to build the calculation model of the dome with different shapes, and the excavation response characteristics of the domes are compared to determine the optimal shape. Research results: (1) The domes of the 1#∼3#, 5#, 6# surge chamber are mainly affected by the initial in-situ stress and surrounding rock lithology. The semi-circular shape is beneficial to improve the smooth transition of surrounding rock stress at the crown and spandrel. (2) The interlayer dislocation zone C4 and C5 jointly affect the dome of the 7# surge chamber. The semi-circular scheme can be used to control the relaxation deformation of the surrounding rock. (3) The streamlined scheme of the 8# surge chamber can reduce the exposure range of columnar joints, reduce the risk of the impact of columnar joints, and improve the conditions of the dome.

Petrogenesis of Botorubuh igneous rocks at Gunungkidul: A preliminary study for paleomagmatism phenomenon in the southern beach of Yogyakarta - Indonesia

Botorubuh Beach is located at Southern Beach of Gunungkidul, in the Southern Mountain of Yogyakarta - Indonesia and is a promontory composed of Middle - Late Miocene igneous rock with a columnar jointing structure. This isolated igneous rock area is surrounded by limestone. Therefore, the regional geological map of Surakarta-Giritontro classifies this area as the Punung-Wonosari Formation which is dominated by limestone. Because of the geological phenomenon of the isolated igneous rock area, it is necessary to study the petrogenesis of the igneous rocks at the area. The petrogenesis research is based on a preliminary study of the petrographical and geochemical characteristics of this igneous rock samples. The petrographic identification of andesite samples shows porphyritic, trachytic, oscillatory zoning, and sieve textures. The results of geochemical analysis (major and trace elements) show that the rock samples are are classified to andesite rocks and calc-alkaline suites. These rocks are enriched in LILEs (Rb, Ba, K) and depleted in HFSEs (Nb, Ti, Ce). Additionally, REE shows a slight enrichment of light-REE and a slight negative anomaly of Eu. The patterns of the trace elements including REE show a typical pattern of calc alkaline arc. Petrographical and geochemical characteristics suggest evidence of magma differentiation process, that is by a mechanism of crystallization fractionation. The andesite was formed in relation to a Middle – Late Miocene paleomagmatism and the Late Miocene-Pliocene subduction zone.

The Kui boulder fields: Formation processes controlled by columnar joints of granodiorite

Boulder fields of granitic rocks have long been believed to be the result of subsurface spheroidal weathering and subsequent erosion of weathering products, such as saprolite, and the exhumation of corestones. However, the morphological characterization of boulder fields has not been sufficient to examine the details of their origin. We performed a 3-D morphological investigation of boulder fields using UAV and SfM for the Kui boulder field, Hiroshima, western Japan, and found that the boulder field consists of polygonal rock columns, as well as rounded corestones. Some of these rock columns had chamfering cracks making them primary corestones. An outcrop of the weathering profile near the boulder field showed that corestones covered by weathering rindlets were embedded in saprolite surrounded by a polygon that was inherited from the columnar joints. The saprolite was locally removed by subsurface erosion to leave openings, which eventually led to the collapse of the corestone framework. Thus, the columnar joints provided basic conditions for the boulder field formation.

Universal fluctuation of polygonal crack geometry in solidified lava.

Outcrops of columnar joints made of solidified lava flows are often covered by semiordered polygonal cracks. The polygon diameters are fairly uniform at each outcrop, but their shapes largely vary in the number of sides and internal angles. Herein, we unveil that the statistical variation in the polygon shape follows an extreme value distribution class: the Gumbel distribution. The Gumbel law was found to hold for different columnar joints, regardless of the locality, lithologic composition, and typical diameter. A common distribution for columnar joints implies a universal class that may integrate the polygonal crack networks observed on the surface of various fractured brittle materials.

Slope Stability Evaluation and Monitoring Plan of the Columnar Joints in Mudeungsan Mountain

Slope Stability Evaluation and Monitoring Plan of the Columnar Joints in Mudeungsan Mountain

Columnar jointing structures in lavas from the Nevado del Ruiz Volcanic Complex (Colombia): Facies, dimensions and geometry

Asociados al Complejo Volcánico Nevado del Ruiz (CVNR) se encuentran varios flujos de lavas con estructuras de disyunción columnar formadas por el régimen físico de enfriamiento. Estos son de interés tanto para el campo de la volcanología como del geoturismo, especialmente para el Geoparque Volcán del Ruiz aspirante a reconocimiento UNESCO, dado que, no solo brindan información sobre los mecanismos de flujo y enfriamiento de las lavas, que a su vez tienen implicaciones en la permeabilidad aprovechable por los fluidos hidrotermales, sino que también hacen parte de los principales atractivos geoturísticos a nivel mundial. En este trabajo se caracterizan las facies de disyunción presentes en cuatro afloramientos ubicados en el flanco noreste del CVNR sobre la vía Manizales - Murillo. De cada afloramiento se realiza una descripción tanto de la morfología del emplazamiento, con base en la fotointerpretación y las observaciones de campo, como de los patrones poligonales, y se determinan las dimensiones de las columnas y sus rasgos menores identificables. Además, se caracterizan macroscópica y microscópicamente las muestras tomadas en cada afloramiento y se establecen sus características texturales y mineralógicas. Como resultado se confirma la composición predominantemente andesítica con presencia de fenocristales euhedrales de plagioclasas (andesina y oligoclasa) de hasta 4 mm y se determina que las columnas tienen dimensiones de 1,3 m de ancho y 3 m de alto en promedio, con estrías separadas por 12,6 cm en promedio aproximadamente y formas poligonales predominantemente de cuatro lados. A partir de los rasgos y características observados, se concluye que estas lavas tuvieron un proceso de enfriamiento rápido y complejo en el que se requirió una alta cantidad de energía, incluyendo disipación de calor y energía deformacional, y que además han sido afectadas por procesos meteorizantes y erosivos intensos.

Numerical investigation of the flow characteristics and permeability of 2D irregular columnar jointed rock masses

PurposeThe objective of this paper is to provide a better understanding of the effect of irregular columnar jointed structure on the permeability and flow characteristics of rock masses.Design/methodology/approachAn efficient numerical procedure is proposed to investigate the permeability and fluid flow in columnar jointed rock masses (CJRMs), of which the columnar jointed networks are generated by a modified constrained centroid Voronoi algorithm according to the field statistical results. The fractures are represented explicitly by using the lower-dimensional zero thickness elements. And the modeling scheme is validated by a benchmark test for flow in fractured porous media. The effective permeability and representative elementary volume (REV) size of CJRMs are estimated using finite element method (FEM). The influences of joint density and variation coefficient of columnar joint structure on the permeability of the rock mass are discussed.FindingsThe simulation results indicate that the permeability is scale-dependent and tends to be stable with increase of model size. The hydraulic REV size is determined as 3.5 m for CJRMs in the present study. Moreover, the joint density is a dominant factor affecting the permeability of CJRMs. The average permeability of columnar jointed structures increases linearly with the joint density under the same REV size, while the influence from the coefficient of variation can be neglected.Originality/valueThe present paper investigates the REV size of the CJRMs and the effect of joint parameters on the permeability. The proposed method and the results obtained are useful on understanding the hydraulic characteristic of the irregular CJRMs in engineering projects.

Geometric Attributes of Polygonal Crack Patterns in Columnar Joints

AbstractA well‐ordered polygonal crack pattern is frequently observed on the outcrop surface of columnar joints. The crack pattern's geometry and topology result from the volume contraction of solidified lava during thermal dissipation. In this study, we conducted field measurements of columnar joints at four different sites with various lithologies in Japan to understand the influence of geography and lithological character on their geometric characteristics. Drone‐aided photography and computer‐based image analysis enabled us to examine the constituent polygons' geometric attributes and their statistics with high accuracy. This methodology revealed a relationship between the geometry and topology of the polygonal crack patterns. Moreover, we established a positive correlation between the polygon area and the number of vertices of a polygon at each study site, irrespective of lithology, or geographic position. These results are consistent with previous investigational studies, in particular starch‐based analog experiments.

Experimental Study on the Strength Failure Characteristics of Columnar Jointed Rock Masses under Three-Dimensional Stress

In view of the typical anisotropy of columnar jointed basalt in the dam area of the Baihetan Hydropower Station on the Jinsha River in China, columnar jointed rock mass models with different column angles (α = 0°–90°) were constructed with similar materials, and three sets of intermittent joints are considered in the physical models. Uniaxial and equal-confining-pressure triaxial compression tests were carried out with a true triaxial testing machine, and the variations of the failure mechanisms, stress-strain relationships, and strength characteristics of the columnar jointed rock masses with the joint inclination angle were investigated under different stress conditions. The results revealed the following: 1) during triaxial compression, two types of stress-strain curves existed, namely the ideal plastic curve and the strain-hardening curve; 2) the strength and elastic modulus of the sample under uniaxial compression presented U-shaped curves with the variation of α. Moreover, the strength of the samples increased with the change of α under triaxial compression, and the elastic modulus Er increased significantly with the increase of the confining pressure. 3) There were four typical types of failure within the columnar joint samples under triaxial compression. In addition, the test data were used to verify that the Mogi strength criterion good applicability to the columnar jointed rock mass under three-dimensional stress. An empirical prediction model of the relationship between the elastic modulus and confining pressure of the columnar jointed rock mass was established, and its applicable conditions were analyzed. The empirical prediction model is verified by the test results of the columnar jointed rock mass, which indicates that the prediction model was in good agreement with the test data. Finally, the strength characteristics and failure modes of columnar jointed rock masses under different loading conditions were summarized.

Rock pillars shaped by columnar joints in granite at Mt. Mizugaki, Central Japan

AbstractRock pillars of granite form a special type of characteristic topography in granite, but their origin is not well understood, partly because their 3D morphology has never been well characterized. Rock pillars were investigated at Mt. Mizugaki, which is underlain by Neogene granite that intruded into the Cretaceous accretionary complex in central Japan. Three rock pillars and their surrounding areas were investigated in detail using unmanned aerial vehicle (UAV) images and structure from motion (SfM). The rock pillars were up to 70 m high and were shaped by columnar joints, which has hardly been reported before in granitic rocks. Columnar joints in granite are much larger than columnar joints in volcanic rocks. The columnar joints curved vertically, and some of them showed dipyramid shapes. The large size and curved morphology of the columnar joints may be the result of the slow cooling of the granite, compared to that of volcanic rocks. Thus, the columnar joints at Mt. Mizugaki made large, high rock pillars, which are not common in volcanic rocks.

Formation mechanism of hexagonal structure of basalt columnar joints based on Mechanics of Materials and infinitesimal method

The perfect hexagon showed by columnar jointed basalt gets great public appeal. However, the accurate illustration was not given. A new explanation, which has rigid calculation, is proposed here for their origin. With the cooling of basalt, the distribution of stress changes while the normal stress equal to the tensile strength of basalt. Using an equation as τ<em>_θ</em>=τ<em>_f</em>, where τ_θ is the force tangentially acting on the unit shear boundaries and τ<em>_f </em>represents the shear strength of basalt, to indicate the condition of the shear fracture. The result of numerical calculation shows that cleavages appear at angles of ±59.53° with the σ₁, which effectively illustrate why the columnar jointed occur in conjugate pairs with ~120° angle between cleavages. The angle depends on the internal friction angle, the cohesive force, the tensile strength and Poisson’s ratio of basalt. Other factors on the sides and diameter of columnar jointed, such as the velocity of cooling and components of magma, will be deeply researched in our future work.

고성 운봉산 암괴지형 분포와 형태적 특성

Unbongsan Mountain is a volcanic edifice with a unique landscape, which is located alone between granite mountains in Goseong-gun, Gangwon-do. The slopes of the mountain are partially covered with talus and block streams consisting of large basalt bouders. The geological features of this mountain have been investigated in detail. However, their overall distribution patterns and development processes are not well known. This study aims to classify these bouldery landforms through mapping the location of basalt blocks, the analysis of the morphological characteristics of the slope, and field surveys on the large boulders. The exposed boulders are concentrated in the western valleys of the mountains and are rarely found in the eastern slopes. Field data show that all the boulders are composed of basalt rocks with columnar joints, and that there is a long-axis isotropy related to the elevation and gradient of slope. In addition, the result of TPI and slope analysis for DEM indicate that block stream was mainly distributed along the valley, and the talus appeared in the steep ridge and the lower part of the cliffs. The slope classification indicates that flat mountain tops, basalt cliffs, talus, and block streams develop in sequence, as the distance from the center of the mountain increases. The bouldery landforms of Unbongsan Mountain illustrate the process of slope change that appears as a slope retreat in a volcanic edifice.

Rock Mass Classification for Columnar Jointed Basalt: A Case Study of Baihetan Hydropower Station

Rock mass classification is important in preliminary design of geotechnical engineering projects. Using the columnar jointed basalt at the foundation of Baihetan Hydropower Station as an example, this paper presents a classification scheme of the columnar jointed rock. Unlike many common rock masses, an obvious characteristic of columnar jointed rock is that it is discontinuous in geometry while continuous in mechanics. Due to the inapplicability of existing rock mass classification systems, a classification scheme, combined with rock mass integrity, weak plane tightness, and permeability, is proposed. The new classification system has five grades with quantitative factors, which takes into account the features of columnar joints. As an easy-to-use scheme and case study, it would be helpful as a reference in the rock mass classification of similar problems.

Fracture evolution in oil-rich rhyolitic lavas of the Hailar Basin, northeastern China

Rhyolitic lavas can hold considerable oil exploration potential which is inferred to be controlled by fracture systems. The need for a better understanding of fracture properties and related petroleum systems for such rocks is the principal motivation of this study. We investigate the fracture evolution of this play type by an analysis of the Early Cretaceous oil-rich rhyolitic lava outcrops, located in the Hailar Basin, northeastern China, integrating multiscale fracture data from field investigation, optical microscopy, fluorescence imaging, and scanning electron microscopy. Six main types of volcanic-related and tectonism-induced fractures are identified. Aperture, spacing, and length of these fractures predominantly show power-law distributions, and in most cases, the dimension of these three parameters follows that columnar joints > platy cooling fractures ≈ tectonic fractures ≫ conjugate shear fractures ≫ perlitic fractures. In addition, the fracture orientation patterns are commonly predictable. Small fractures usually make significant porosity contribution and are excellent reservoir spaces, while large fractures control the permeability and act as channels. The early Early Cretaceous NW–SE extension (D2 of the five phases of basin deformation) dominated the fracture evolution of the lavas. Although the seal of the reservoir is probably not extensively damaged by the reactivation of fractures during the multistage deformation of the basin, the likelihood of reactivation of fracture sets C1, C3, and T1 needs to be carefully evaluated during the exploration and recovery, as the reactivation tendency factors (fa) of these sets are > 1 at a certain stage of deformation. We suggest that the observed patterns may be extrapolated to similar rhyolitic lavas in many parts of the world.

Volcanostratigraphy of Krakatoa Islands, South Lampung District, Lampung Province

The research area is within the territory of Nature Preserve and Marine Preserve region of Krakatoa Islands, South Lampung District, Lampung Province. The study aims to determine the surface geological, mapped on a scale of 1: 20,000, and to determine the geological history that forms the Krakatoa Islands. Volcanostratigraphy is made by combined from literature studied, shoreline analysis, petrographic analysis and field observation. From these results, it is poured into a map of geological outcrops, maps of volcanostratigraphy profiles, geological maps and geological sections. Volcanostratigraphy on the research area is divided into 30 rock units that consists of 22 lava, 8 pyroclastic and allvuial. Geological structure that developed in the research area in the form of secondary structure that is crater and caldera, and the primary structure that is sheeting joinnt, columnar joint, vesicular and autobreccia. New and detailed geological map of Krakatoa volcano is presented.

Despliegue de siltitas columnares en el borde nororiental del Rift de Asunción en la Ciudad de Limpio

Coincidente con una de las fracturas principales del rift de Asunción, se expone una pequeña elevación en forma de domo, constituida por siltitas columnares del tipo cerro Koĩ a orillas del valle del río Salado. Los prismas columnares denotan gran desarrollo de sus lados y dimensiones, en donde se presupone un cuerpo ígneo alcalino infrayacente (semejante a sus congéneres regionales) como el responsable del efecto térmico y contracción mecánica por pérdida de agua del material clástico, para el crecimiento y evolución del diaclasado columnar. Se comprueba una cantera abandonada con cierto grado depredación.

Delineation of Potential Groundwater Zones Using Shear Wave Velocity in Eastern Deccan Volcanic Province, India

A comprehensive study based on Multichannel Analysis of Surface Waves (MASW), a near-surface geophysical technique, was carried out for the first time in the Mandla Lobe of the Eastern Deccan Volcanic Province. The study was conducted to demarcate fractures, which are essential for finding potential groundwater zones in the hard rock region and for the delineation of shallow subsurface geological features in terms of shear wave velocity. The MASW surveys were carried out at different selected locations in the study area to delineate fractures in the basaltic terrain covered with thin weathering and alluvium cover. These basalts are mainly comprised of massive, vesicular and amygdaloidal varieties and interpreted as different basaltic flows of Mandla, Dhuma and Pipardahi formations. The shear wave velocity sections divulge the layered nature of the basalt sequences. In some of the massive flows, there are low-velocity vertical zones that can be deduced to be either vertical columnar joints or fracture zones, and the low-velocity weathered flows can be the good groundwater reservoirs. The shear wave velocities Vs obtained are in the range from 300 to 2500 m/s at different locations, and the thicknesses of flows are varied in the MASW sections. The obtained shear wave data are compared with the borehole data, and the results are well correlated. The study clearly differentiates the variations within basaltic formations, which are interpreted as potential groundwater zones.