The objectives of this research were to make accurate measurements of thermal diffusivity at normal and elevated temperatures on eight well-characterized rocks and to investigate the effects of water saturation and heating upon thermal diffusivity. The eight rock types studied were Barre Granite, Dresser Basalt, St. Cloud Granodiorite, Westerly Granite, Berea Sandstone, Holston Marble, Salem Limestone, and Sioux Quartzite. A summary geologic description and chemical analysis of each rock type is included. The thermal diffusivity measurements were made at one atmosphere pressure using the laser flash method. In the natural, air-dried state at 300 K the values of diffusivity ranged from about 0.280 cm2 sec−1 for the quartzite to 0.0114 cm2 sec−1 for the limestone. Thermal diffusivity varies inversely with temperature and at 800 K the value is 50 to 75% lower than at room temperature. At room temperature, rocks saturated with water increase in diffusivity as much as 24 percent. Several qualitative trends were observed relating the thermal diffusivity of rock to its composition, texture and structure.
The year was particularly eventful in terms of the recognition of improved technologies impinging on the duties of the Engineering Geologist. National economies were strained to the limit under the pressure of the new world terrorist attacks and burgeoning populations. much of which stemmed from escapes from oppressive national regimes to the free world. The impacts of terrorism range from increased danger and costs of field work, to special design considerations and postponed and delayed project work.On the positive side, continued progress has been made in the means of recognition and professional development of our practitioners and in the general call for their work. Competent engineering geologists are in consistent demand, but the working conditions are not improved. A general deterioration of university funding, aggravated by bureaucratic excesses among administrators, have tended to make life miserable for dedicated faculty and a general move is afoot to cut back on the number of funded geology departments in North America and Europe. This situation has also been worsened by the general withdrawal of the mineral industries and by retraction of the petroleum companies from all but their most favored campuses.
On 13 May 1995 a strong earthquake of Ms=6.6 struck the cities of Kozani and Grevena in northwestern Greece. This region is characterized by low seismicity. In the same area, three hydroelectric dams have been operating for the last 30 years. One of them, the Polyphyto dam, is located only 40 km from the epicenter of the 13 May earthquake.In the present work all available seismological aspects of the main event, such as focal properties and source parameters together with foreshock and aftershock characteristics of the earthquake sequence are considered in order to examine whether the water level changes behind the Polyphyto dam induced the unusual seismic activity in this area. Thus, a detailed examination of the seismic activity is made and this is compared to the seismotectonic regime of the region and the reservoir loading from 1976 to 1995. The results show that there is no obvious correlation between seasonal or sharp fluctuations in the water level and the seismicity of the region (except once during 1989). Moreover, comparison with other previous cases of induced seismicity in Greece and in other countries shows no similarities to the Kozani–Grevena earthquake sequence.It is concluded that the Kozani–Grevena earthquake is therefore an event in the framework of the regional seismicity rather than an event triggered by the impounding of the Polyphyto artificial Lake.
The effects of the Catalan earthquake of February 2, 1428, between 8 h and 9 h local time, have been studied by reevaluating the information gathered by Fontseré and Iglesies (1971). MSK-intensities have been assigned to 45 localities to obtain an isoseismal map. A maximum intensity of IX has been deduced. The most probable location is the area around the village of Queralps (42.4° N 2.2° E) at a depth of about 8 km. The attenuation seems to be similar to that found for earthquakes in Central Europe, which considerably differs from that in southern Spain.
Strong motion records from the South Hyogo earthquake of January 17, 1995, are overviewed. The discussion is focused on (1) the characteristic of near field records including the predominant direction of motion versus the fault strike and their spectral characteristic, and (2) the orientation error of seismometers and ground motion amplification at borehole array stations. Two numerical techniques for seismic response analysis of ground are applied for the array stations. The one is the frequency-dependent equi-linearized technique for the frequency domain analysis, and the other is the effective stress-based liquefaction analysis method. The numerical calculations are compared with the records at four borehole array stations.
Landslides are common natural hazards in the seismically active North Anatolian Fault Zone of Turkey. Although seismic activity, heavy rainfall, channel incisions, and anthropogenic effects are commonly the main triggers of landslides, on March 17, 2005, a catastrophic large landslide in Sivas, northeastern of Turkey, the Kuzulu landslide, was triggered by snowmelt without any other precursor. The initial failure of the Kuzulu landslide was rotational. Following the rotational failure, the earth material in the zone of accumulation exhibited an extremely rapid flow caused by steep gradient and high water content. The Agnus Creek valley, where Kuzulu village is located, was filled by the earth-flow material and a landslide dam was formed on the upper part of Agnus Creek. The distance from the toe of the rotational failure down to the toe of the earth flow measured more than 1800 m, with about 12.5 million m3 of displaced earth material. The velocity of the Kuzulu landslide was extremely fast, approximately 6 m/s. The main purposes of this study are to describe the mechanism and the factors conditioning the Kuzulu landslide, to present its environmental impacts, and to produce landslide-susceptibility maps of the Kuzulu landslide area and its near vicinity. For this purpose, a detailed landslide inventory map was prepared and geology, slope, aspect, elevation, topographic-wetness index and stream-power index were considered as conditioning factors. During the susceptibility analyses, the conditional probability approach was used and a landslide-susceptibility map was produced. The landslide-susceptibility map will help decision makers in site selection and the site-planning process. The map may also be accepted as a basis for landslide risk-management studies to be applied in the study area.
The goal of this paper is to present especially the source and the type of liquefaction-related failures of those buildings which satisfied the structural codes of buildings and practices but experienced settlement, tilting and overturning in Adapazari during the Turkey earthquake of August 17, 1999. In this context, the Adapazari region is first evaluated in terms of geological setting, tectonics, seismicity and liquefaction susceptibility based on in situ and laboratory test data. In addition, the number of stories, types of buildings and their related failures have been mapped accordingly. Furthermore, laboratory model tests are conducted to enforce and/or confirm the type of building's failures with particular reference to their geometrical shape and the number of stories assuming that the models representing buildings satisfy the structural codes of buildings and practices.
One of the most significant effects of the 17 January, 1994 Northridge, California earthquake (M=6.7) was the triggering of thousands of landslides over a broad area. Some of these landslides damaged and destroyed homes and other structures, blocked roads, disrupted pipelines, and caused other serious damage. Analysis of the distribution and characteristics of these landslides is important in understanding what areas may be susceptible to landsliding in future earthquakes. We analyzed the frequency, distribution, and geometries of triggered landslides in the Santa Susana 7.5′ quadrangle, an area of intense seismic landslide activity near the earthquake epicenter. Landslides occurred primarily in young (Late Miocene through Pleistocene) uncemented or very weakly cemented sediment that has been repeatedly folded, faulted, and uplifted in the past 1.5 million years. The most common types of landslide triggered by the earthquake were highly disrupted, shallow falls and slides of rock and debris. Far less numerous were deeper, more coherent slumps and block slides, primarily occurring in more cohesive or competent materials. The landslides in the Santa Susana quadrangle were divided into two samples: single landslides (1502) and landslide complexes (60), which involved multiple coalescing failures of surficial material. We described landslide morphologies by computing simple morphometric parameters (area, length, width, aspect ratio, slope angle). To quantify and rank the relative susceptibility of each geologic unit to seismic landsliding, we calculated two indices: (1) the susceptibility index, which is the ratio (given as a percentage) of the area covered by landslide sources within a geologic unit to the total outcrop area of that unit; and (2) the frequency index [given in landslides per square kilometer (ls/km2)], which is the total number of landslides within each geologic unit divided by the outcrop area of that unit. Susceptibility categories include very high (>2.5% landslide area or >30 ls/km2), high (1.0–2.5% landslide area or 10–30 ls/km2), moderate (0.5–1.0% landslide area or 3–10 ls/km2), and low (<0.5% landslide area and <3 ls/km2).
Many large-scale landslides induced by earthquakes have been reported in loess soils. They often cause catastrophes because they travel long distances at high velocity. To clarify the mechanism of these landslides, field survey was performed on the landslides triggered by the Haiyuan Earthquake (China, 1920), and a series of ring shear tests was conducted on the loess soils collected from a landslide. The field surveys revealed that most of the loess landslides triggered by the Haiyuan Earthquake occurred on concave slopes gentler than 15° with long runout distance, showing very small equivalent friction angle. Cyclic ring shear tests on saturated specimens in the undrained condition showed that when cyclic shear stress was applied to a loose loess specimen, pore pressure was built-up gradually before the failure, and after that, large pore pressure was quickly generated due to the failure of loess soil structure. Meanwhile, to investigate the mechanism that produces the high mobility of loess landslides, ring shear tests were conducted on loess specimens with large shear displacement of up to several meters under the undrained condition, and it was found that the initial normal stress has no effects, and overconsolidation ratio has little if any effects, on the apparent friction angle in the steady state for loess soils. Results of tests on soils at different saturation degrees revealed that the reduction in shear strength results more likely from the generation of pore water pressure, not of pore air pressure.
Earthquake-triggered landslides are a major geological hazard in Central Asia. In July 1949, the M7.4 Khait earthquake triggered many hundreds of landslides in a mountainous region near the southern limit of the Tien Shan Mountains, central Tajikistan. These landslides involved widespread rock-slope failure as well as large numbers of flowslides in loess that mantles the steep slopes of the region. In the Yasman valley hundreds of loess landslides coalesced to form a massive loess flow (est. vol. 245 Mm3) that travelled up to 20 km on a slope of only 2°. In an adjacent valley, the Khait landslide involved transformation of an earthquake-triggered rockslide into a very rapid flow by the entrainment of saturated loess into its movement. It travelled 7.41 km over a vertical distance of 1421 m with an estimated average velocity of ~30 m/s. We estimate its volume as 75 Mm3, an order of magnitude less that previously published estimates. The Khait landslide was simulated using DAN. The number of casualties due to earthquake-triggered landslides in the epicentral region was considerable. Approximately 4000 people were killed in the Yasman valley loess flow as 20 villages (kishlaks) were overwhelmed. In the Khait landslide alone we estimate ca. 800 people lost their lives when the villages of Khait and Khisorak were overrun by rapidly moving debris. Our data indicates that a total of approximately 7200 people were killed by earthquake-triggered landslides in the epicentral region of the Khait earthquake and that, in terms of loss of life, the 1949 Yasman valley loess flow was one of the most destructive landslides in recent history.
The Baastad landslide occurred within a large area of marine clay deposits where the clay had been transformed into quick clay from leaching. The landscape in the area is highly dissected from stream erosion and numerous slope failures and slides. The slide scar covers about 80,000 m2 of farmland. Three buildings were destroyed in the slide.According to observations and investigations, the whole area slid out almost simultaneously, i.e., the slide was of the so-called flake type. For all known documented slides of this category, conventional stability analysis based on ultimate effective stress parameters φ′ and c′, give values of the factor of safety which are too high. It is an unsafe procedure. The behaviour of quick-clays has been studied extensively at the Norwegian Geotechnical Institute over the last 20 years. These studies show that the strength properties of these clays should be based on undrained shear strength values rather than the parameters φ′ and c′.Back calculations of the Baastad slide based on undrained shear strength values have been carried out and were in good agreement with the theoretical value of the factor of safety.
Liquefaction effects generated by the 1977 San Juan Province, Argentina, earthquake (Ms = 7.4) are described. The larger and more abundant effects were concentrated in the 60-km long band of the lowlands in the Valle del Bermejo and in an equally long band along the Rio San Juan in the Valle de Tulum. Fissures in the Valle del Bermejo were up to several hundred meters long and up to several meters wide. Sand deposits, from boils that erupted through the fissures, covered areas up to tens of square meters. Fissures generally parallelled nearby stream channels. Because the Valle del Bermejo is undeveloped, these large features caused no damage. Liquefaction in the Valle del Tulum caused important or unusual damage at several localities, including the following five sites: (1) At the Barrio Justo P. Castro, a subdivision of Caucete, liquefaction of subsurface sediments decoupled overlying, unliquefied stiff sediments, producing a form of ground failure called “ground oscillation”. The associated differential ground movements pulled apart houses and pavements in extension, while shearing curbs and buckling canal linings in compression at the same locality. (2) At the Escuela Normal, in Caucete, the roof of a 30-m long single-story classroom building shifted westward relative to the foundation. That displacement fractured and tilted columns supporting the roof. The foundation was fractured at several places, leaving open cracks, as wide as 15 mm. The cumulative width of the open cracks was 48 mm, an amount roughly equivalent to the 63 mm of offset between the roof and foundation at the east end of the building. The ground and foundation beneath the building extended (or spread) laterally opening cracks and lengthening the foundation while the roof remained in place. (3) The most spectacular damage to structures at the community of San Martin was the tilting of a 6-m high water tower and the toppling of a nearby pump house into a 1-m deep crater. Similarly, a small crater developed beneath a hand-pump in an open area and a large, 6-m diameter crater formed nearby. The following sequence of events created the craters and toppled the pump structures: During the earthquake, ground shaking generated excess pore pressures which were dissipated by upward flow of groundwater. Free drainage was restricted by an impermeable plastic-silt layer. Water apparently accumulated below the plastic-silt layer and then burst to the surface through several holes and cracks, including holes around well casings. (4) At the San Isidro winery, nine storage tanks tilted 2 to 5°. Five reinforced-concrete tanks were dismantled but four steel tanks were repaired by placing new footings and jacking the structures into an upright position. (5) At Escuela J.J. Pasos, differential settlement beneath building fractured several columns and walls. The largest settlements were about 60 mm and the maximum settlement of footings supporting columns was about 40 mm. In spite of the damage, the buildings were in no danger of collapse.
In 1984 a mass of Quaternary pyroclastic rock (est. vol. 0.74×106m3) slid from the western flank of Mount Cayley volcano in southwest British Columbia. The disintegrating rock mass entrained a further 0.20×106 m3 and formed a rock avalanche that travelled a horizontal distance of 3.46 km from its source over a vertical elevation difference of 1.18 km, equivalent to a fahrböschung of 19°. From the superelevation of the debris trimline in the mid-path, it is estimated that velocities reached at least 42 m/s; in the upper part of its path velocities may have approached 70 m/s. The rock avalanche was partially transformed into a distal debris flow that travelled a further 2.6 km down Turbid Creek in a narrow channelised path to the Squamish River, temporarily blocking it. The motion of the rock avalanche, including the production of a distal debris flow, was successfully simulated using a dynamic analytical model. Both the results of this analysis and field evidence indicate that the rock avalanche did not come to a halt in the upper part of its path as suggested by Cruden and Lu (1992), but travelled to its distal limit in one uninterrupted movement. This finding has important implications for landslide hazard assessment at Mount Cayley and similar sites. The landslide is typical of those which occur on the steep slopes of dissected volcanoes and is one of seven high-velocity rock avalanches that have occurred in the Garibaldi Volcanic Belt of southwest British Columbia since 1855.
The Tschierva rock avalanche occurred on October 29, 1988 in the area of the Piz Morteratsch, Switzerland. Releasing a total volume of ~ 300,000 m3, the avalanche ran out over 1 km destroying a hiking trail before stopping on the Tschierva Glacier. We analyze the setting of this periglacial slope failure, combining geomechanical and cryosphere investigations to identify the primary factors contributing to the rock avalanche. An approach to slope stability assessment is presented that copes with existing data limitations in an inaccessible alpine terrain. Results from the analyses of morphology, geology, glaciation history, permafrost, hydrology, and meteorological data allowed preliminary inferences to be made regarding the influence of these factors on slope stability. Conceptual kinematic and numerical slope stability modeling critically analyzed the role of kinematic degrees of freedom, glacier retreat, and water infiltration from above the detachment zone. Results highlight the strong influence of discontinuity orientation with respect to the slope face, the role of a fault zone with increased joint density, and long-term progressive development of persistent discontinuities induced by glacier retreat and groundwater loading cycles in leading to the rock avalanche. The role of permafrost could not be clearly assessed, however observations and analyses indicate that permafrost had no dominant influence on the slope failure. Extraordinary precipitation prior to the event is suggested to have played a role in triggering the rock avalanche, especially in combination with observed superficial ice that could have sealed the rock face generating high water pressures. Our results emphasize the importance of analyzing multiple contributing factors when assessing alpine rock slope failures, with careful consideration of data limitations prevailing in such areas.
The 1989 Loma Prieta, California earthquake (moment magnitude, M=6.9) generated landslides throughout an area of about 15,000 km2 in central California. Most of these landslides occurred in an area of about 2000 km2 in the mountainous terrain around the epicenter, where they were mapped during field investigations immediately following the earthquake. The distribution of these landslides is investigated statistically, using regression and one-way analysis of variance (ANOVA) techniques to determine how the occurrence of landslides correlates with distance from the earthquake source, slope steepness, and rock type. The landslide concentration (defined as the number of landslide sources per unit area) has a strong inverse correlation with distance from the earthquake source and a strong positive correlation with slope steepness. The landslide concentration differs substantially among the various geologic units in the area. The differences correlate to some degree with differences in lithology and degree of induration, but this correlation is less clear, suggesting a more complex relationship between landslide occurrence and rock properties.
In 1992, a large magnitude earthquake (Ms = 7.3) hit the northern part of the Kyrgyz Tien Shan range where it triggered rockslides and many debris slides or flows. One of these mass movements occurred on the Chet–Korumdy ridge located in the Suusamyr Basin. It consists of a multi-rotational debris slump in its upper part that turned into a debris flow in its lower part. Involving arenitic material overlying silty clays, it has a volume of about 0.5 to 1.106 m3, a maximum thickness of 40 m and a run-out of 200 m. The field observations and measurements carried out on this slope suggest that local amplification effects could have contributed to the initiation of the seismic failure. To test this hypothesis in the lack of instrumental evidence of local ground-motion recordings, we conducted a sensitivity study of site effects based on a numerical analysis in the visco-elastic domain with a two-dimensional finite difference code. Varying the topography and the geology of the investigated slope, topographic site effects are found to be less important than geological site effects which are controlled by the contrast of impedance between the surface materials and the bedrock. The geometry of the low-velocity surface layer has also an influence on site effects, which is often difficult to be distinguished from pure topographic effects. Considering all modelling results, we conclude that site amplifications alone cannot have triggered the Suusamyr landslide during the 1992 earthquake. The static slope stability analyses done in previous studies revealed that the Suusamyr failure neither can have a purely static origin. Even if the water table is very high within the arenite layer, only a minor failure develops in the lower part of the slope. Therefore, we believe that the triggering of the Suusamyr landslide is a consequence of pore pressure build up in areas characterized by significant ground-motion amplifications.
The site amplification is estimated at five seismic stations of the Latur region using the horizontal to vertical spectral ratios of 33 aftershocks of the main Killari earthquake of September 29, 1993 (UTC). Spectral amplifications, ranging from a factor of 2–6 are found to vary with frequency at different places. Significant amplification is found at four sites within the Latur region, at Basavakalyan, Kasgi, Killari, and Mudgad Eakoji villages. Our results show a positive correlation between the site amplification and the damage pattern in area. The pattern and the nature of the site amplification estimated in the present study corroborates also with the analytical models and the borehole data indicating alternating layers of unconsolidated sediments and basaltic rocks.
Along the Rokko Mountains and Awaji Island, NE-SW to ENE-WSW oriented active faults exist in an en echelon arrangement. They constitute a portion of the Arima-Takatsuki tectonic line (ATTL) which extends from Kyoto, through Awaji Island, to the Median Tectonic Line. The ATTL is also correlated to lineaments linking the saddles and steep slopes of gravity (Bouguer) anomalies. The main shock of the 1995 magnitude 7.2 (M 7.2) Kobe earthquake was located at the mid-point of the ATTL. The main shock also created a 9-km long rupture on the ground surface along the NE-SW Nojima fault line in the northern part of Awaji Island. The earthquake aftershocks were distributed over a 40-km long zone along the central segment of the line. Surface ruptures and cracks accompanying the Kobe earthquake were scattered along a 40-km segment centrally located on the ATTL. Spatial correlation of the surface ruptures and aftershock distribution on the ATTL suggests that the Kobe earthquake was the result of a 40-km long rupture of the central segment of the ATTL.
Geomorphic effects observed in the Barranco (creek) de Arás basin are used to characterize the flood. Sediment features allow to qualify the flood as essentially a water flow. Using the critical section method, the peak flood discharge is estimated to be between 400 and 600 m3 s−1. Similar results were obtained using a paleohydraulic formula based on the size of the largest mobilized clasts. Using the rational method with available rainfall data, the discharge for a recurrence interval of 500 years is estimated to be between 150 and 200 m3 s−1. These results agree with predictions obtained using curves of peak discharge versus basin area based on regional data. Several trenches dug on the fan showed that the size of boulders mobilized by the event is larger that those left by previous floods at the same place. When the estimated peak flood discharge is related to the basin area, values between 20 and 30 m3 s−1 km−2 are obtained, demonstrating that the Barranco de Arás flood was most unusual.
On 28 October 1996, a landslide occurred on the Huashiban slope near the Liangjiaren Hydropower Station. The landslide was caused by a failure mechanism induced by an earthquake (Mw 7.0) at Lijiang on 3 February 1996, after which a tensile fracture zone formed on the Huashiban slope. The subsequent impact of several small earthquakes on the slope increased the tension crack connectivity and the tensile strength gradually decreased. Severe rainfall in the rainy season between May and October, especially in July and August, decreased the shear strength of the bottom sliding surface, resulting in a landslide on the Huashiban slope on 28 October 1996. The stability of the Huashiban slope is important for plant site selection. If a further landslide occurs on the slope, the Liangjiaren Hydropower Station project will be critically affected, so analysis of the current slope stability is extremely important. At present, the Huashiban slope can be divided into five subzones: (1) a landslide deposit zone; (2) a landslide zone; (3) a tensile fracture zone; (4) a crescent-shaped zone; and (5) an upper slide zone. Using historic landslide data for 28 October 1996, retrospective analysis of the landslide process revealed shear strength parameters for the Huashiban slope. The cohesion strength is 0.024 MPa, the friction angle at the bottom sliding surface is 14°, and the tension crack connectivity is 50%. These parameters were used to compute the stability of the Huashiban slope. Under the same conditions, the stability of the whole slope is better than that of part of the slope, and the overall stability is dominated by the tensile fracture zone. Under earthquake and rainfall conditions, it is possible that failure will occur in the tensile fracture zone. Thus, the Huashiban slope should be reinforced for construction and operation of the Liangjiaren Hydropower Station.
From 1997 to 1999, a huge number of slides, often turning into extremely rapid debris-earth flows, repeatedly affected the late Quaternary volcaniclastic deposits mantling the carbonate slopes of Campania region, Italy. The Sorrento Peninsula was the epicentral district of the 1997 regional slope-instability crisis. Some hundred shallow mass movements took place during January 1997 in this area. These were the last episode of a long series of slope failure events dating back to mid-18th century. Results from geological and geomorphologic surveys are presented. Landslide mechanism and triggering factors are analysed for the most important mass movement, which occurred during the January 9–11, 1997, regional event. On January 10, 1997, at about 8:15 PM, a rainfall-induced debris slide-debris flow occurred at Pozzano (province of Naples), mainly affecting the 79 AD pyroclastic products. Following a J-path, the landslide destroyed a private house and invaded the State Road no. 145. This event resulted in four deaths, 22 persons injured and road closure for about 2 months. There was less than 200 mm of rainfall in the 72-h period prior to the landslide, although intense precipitation had occurred during a preceding 4-month period. However, the slope failure event was not preceded by an extreme short-term antecedent rainfall, as already noticed in previous landslides of this type in Campania. Finally, following a preliminary geotechnical characterization of volcaniclastic soils, a slope-stability back analysis was carried out, which adopted the classical infinite slope scheme. This analysis gave further evidence of the role played by pore pressure in reducing the overall shear strength of pyroclastic soils.
During the July 9, 1997 Cariaco earthquake, the small town of Cariaco (located 10 km SW from the epicenter) and Cumaná (capital of the State of Sucre, located about 80 km west from the epicenter) were the most affected towns. The damage in Cariaco was essentially restricted to one-century-old dwellings in the downtown area, but also three rather modern buildings collapsed. A maximum intensity of VIII (MMI) was determined for the epicentral area with a clear orientation of the major damage along the strike of the El Pilar fault in east–west direction. The induced effects associated with this event are dominated by liquefaction phenomena and lateral spreading on soft sedimentary lowlands (along the shoreline of the Cariaco Gulf and riverbeds), as well as sliding at unstable slopes. Site studies were carried out in Cariaco, involving the geotechnical analysis of boreholes, seismic refraction studies and microtremor measurements to determine the characteristics of the Quaternary sediment fill in the area. From seismic refraction surveys, an interface separating sediments with S-wave velocity lower than 700 m/s from stiffer ones was located at 60–90 m in depth in the southern part of Cariaco. Further north it is supposed to exceed 90 m. Predominant periods of soil, derived from microtremor observations in Cariaco, vary between 0.6 and 1.2 s. The high percentage of damage in the center of Cariaco can be attributed to the poor quality of the dwellings combined with the presence of thick, poorly consolidated soils, and, in some particular cases, to liquefaction phenomena.
A flank collapse occurred at the Casita volcano in Nicaragua on 30 October 1998 during Hurricane Mitch. The collapse transformed into a disastrous lahar that completely buried two small towns 6 km downstream (killing about 2500 people), destroyed small settlements and disrupted the Pan American Highway.Based on the knowledge acquired during previous investigations with additional unpublished field data and observations, this study provides a comprehensive review of all previous studies (published and unpublished) on the 1998 Casita lahar and new insights into the initial flank collapse and the current stability. The knowledge on pre- and post-failure geometry, geology, lithology, tectonics and stratigraphy of the scarp area is improved and a summary of available geotechnical data is provided. Lithological characteristics that were significant in the initial flank collapse and failure mechanism were identified. The location of the failure surface was more precisely defined and the number and sequence of stages in the initial failure presented in previous studies have been confirmed. Slope stability analyses were carried out using limit-equilibrium methods.Geological interpretations, analysis of digital elevation models and geotechnical back-analyses confirmed that the flank collapse took place in three stages involving both the northern and southern areas of the scarp and occurred continuously during a time interval of seconds to a few minutes. In the first stage, failure initiated in a highly fractured and altered volcanic breccia in the northern area of the scarp which released a volume of 260 000 m3. The flow that developed from this failure removed colluvium deposits at the toe of the slope in the southern part in not more than 40 s. This rapid removal of the colluvium triggered a second stage which comprised 640 000 m3 and consisted in the failure of the southern part of the scarp by the sliding of a fractured volcanic breccia over a unit of clay-rich pyroclastic deposits. The third and final stage consisted in a failure of the remaining breccia and the overlying fractured lavas in the northern area and involved a volume of 690 000 m3.The fact that future events can affect some remaining settlements and the segment of the Pan American Highway, between Chinandega and León, motivated an analysis of the stability of the remaining slope using parameters calibrated in the back-analyses of the 1998 flank failure. The results indicated that the remaining slope is stable as long as groundwater levels in the northern and southern area are deeper than 65 m and 90 m respectively (relative to the points of maximum elevation on the analysed section) and the colluvium deposits in the southern area are not removed from the toe of the slope.
The Bovec basin, which is filled with glacial and fluvial sediments, has recently been struck by two strong earthquakes (1998 and 2004) which caused extensive damage (VII–VIII EMS-98). Strong site effects resulted in large variations in damage to buildings in the area, which could not be explained by the surface variations in Quaternary sediments. The microtremor horizontal-to-vertical-spectral ratio (HVRS) method was therefore applied to a 200 m dense grid of free-field measurements to assess the fundamental frequency of the sediments. Large variations in the sediment frequency (3–22 Hz) were obtained, with most of the observed values in the range 6–12 Hz. The observed frequencies cannot be related to the total thickness of Quaternary sediments (sand, gravel), but can be explained by the presence of conglomerate or lithified moraine at shallow depths. The results were compared also with the velocity structure derived from seismic refraction data. Microtremor measurements performed in several two and some three- and four-storey houses (masonry with RC floors), which prevail in the Bovec basin, have shown that the main building frequencies in the area are in the range 7–11 Hz. This indicates that damage to houses in both earthquakes in some parts of the basin was enhanced by site amplification and soil-structure resonance. Areas of possible soil-structure resonance were identified in the settlements Bovec–Brdo, Bovec–Mala vas, Čezsoča and Kal-Koritnica. Considerable changes in fundamental frequencies within short distances were established in the town of Bovec. Their values are as high as 22 Hz in the central part of the town, but diminish to 6–11 Hz in the adjacent Brdo and Mala vas districts. This is in agreement with the distribution of damage in both earthquakes, which was considerably higher in Brdo and Mala vas, although the houses in the central part of the town are older.
Heavy rainfall from 26 to 31 August 1998 triggered many landslides in Nishigo Village of southern Fukushima Prefecture, Japan. The Hiegaesi landslide, a long-runout landslide with travel angle of 11°, which occurred in loamy volcanic-ash/pumice layer and was deposited in a nearby rice paddy, was investigated. In an observation pit dug in the middle part of the landslide deposit, the sliding zone just above the deflected rice plants was observed, and it was confirmed that grain crushing occurred in the sliding zone. The triggering and sliding mechanisms of this landslide then were investigated by ring-shear tests in laboratory. For the triggering mechanism, one saturated naturally drained test (test A: torque-controlled test) and one saturated undrained test (test B: speed-controlled test) were conducted on the samples taken from the source area of the landslide. Even in the naturally drained test opening the upper drain valve of the shear box, a temporary liquefaction occurred. In the undrained test, excess pore-pressure was generated along with shearing, and “sliding-surface liquefaction” phenomenon was observed. The effective stress and shear resistance finally decreased to near zero. These results can explain the observed phenomenon of small friction resistance like a flow of liquid when the sliding mass slid out of the source area. For the sliding mechanism of the landslide in the rice paddy, saturated undrained test (test C: speed-controlled test) was performed on soil sample above the deflected rice plants. The apparent friction angle obtained in this test was 8°. In addition, the residual friction angle measured after test B and test C was the same value of 41°. Combining with the observation on the shear zone in the ring-shear box after test C, it is concluded that, during the sliding in rice paddy, the undrained shear strength of the soil layer itself mainly influenced the high mobility of the landslide, probably because the friction between rice plants and soils is greater than the undrained shear strength inside the soil mass.
Simple kinematic modeling of particle motion along a curved fault similar to the ruptured Chelungpu fault, Taiwan, indicates a unique spatial slip pattern. Specifically, we find that the large convergent slip on the curve is a result of the minimum deformation scenario of the fault geometry and regional northwestern movement of the Philippine Sea Plate (PSP). The modeled deformation regime portrays an accumulation of deformation in the curved region, which coincides very well with a long-term observed NW-SE-trending seismogenic zone in the central Taiwan. This consistence suggests that the Chelungpu fault is a preexisting curved fault. This is further evidenced by geological and geophysical observations. Because the spatial slip pattern is locally and regionally tectonically controlled, it indicates that the rupture behavior of the Chi-Chi earthquake is repeatable. Better knowledge of the fault geometry and the regional plate motion may help us to predict the possible spatial slip distribution of large earthquakes. This discovery is important for avoiding large buildings and constructions near predicted large slip regions.
In May of 1999, melting snow cover combined with heavy rainfalls in the northeastern part of Switzerland resulted in the occurrence of numerous shallow landslides. Many of these slides were located in the subalpine Molasse, a series of interbedded marls, conglomerates and sandstones. The subalpine Molasse is highly prone to such sliding activity given the dip of bedding, the surface topography and the weak nature of the marls that rapidly degrade when exposed to weathering. Historically, the subalpine Molasse has been the source of numerous slides of varying orders of magnitude and the surficial morphology is primarily dictated by previous rockslides, which periodically reactivate as secondary soil slips. Given the conditions contributing to the slope failure and the history of previous sliding, similar slides within the region are highly probable. This paper presents the findings from a detailed investigation of one such slide, the 1999 Rufi slide. Results from a detailed engineering geological investigation show that the initial rockslide failure plane predominantly developed and passed through the marl beds, as dictated by the penetration of the weathering front into the marls, and not along reactivated shears or the bedding plane contact between the marls and overlying conglomerates. Numerical modelling results based on a coupled hydromechanical distinct-element analysis were able to reproduce this mechanism by incorporating a progressive strength degradation procedure correlated to mapped weathering grades.
A disastrous earthquake rocked Taiwan on September 21, 1999, with magnitude ML=7.3 and an epicenter near the small town of Chi-Chi in central Taiwan. The Chi-Chi earthquake triggered landslide on the dip slope at the Chiufengershan. In this study, a review of the topography and geology of this area was followed by field investigations. Laboratory testing was applied to understand the geomaterial composing the slope. Then, based on a series of limit equilibrium analyses, the failure mechanism of this landslide and the risk of the residual slope were studied.According to the stability analyses, the pre-quake slope is quite stable, with factor of safety of 1.77 (dry) to 1.35 (full groundwater level); explaining why there is no written record of a landslide here for the past 100 years. In contrast, a back analysis shows that the Chi-Chi earthquake-induced dynamic loading is far more than the dip slope can sustain, due in part to the short distance to the epicenter. A Monte Carlo type probability analysis suggests that the residual slope is more dangerous than the pre-quake slope and needs more attention.
All professions began the countdown to the new world, considering the year 2000 to be the first year of the new millennium. Most of the actual impacts are already in place, including multinational businesses and the Euro as the first regional multinational currency. Most of the impacts have been harsh, and relief to individual consumers and professional people will be minor and felt mainly in enhanced ease of communication and media offerings. On the side of the conduct of the profession, the advantages will be far more narrow, as individual practitioners will be facing far stronger forms of competition for their services. Truly, the only way to survive will be for all of us to become more aware of the forces that impact engineering geology and the opportunities that engineering geologists have to provide their services, so basic to all forms of engineering, environmental protection and resource utilization.
Certain types of granite in mountainous areas are microscopically sheeted to a depth of 50 m due to unloading under the stress field that reflects slope morphology. Micro-sheets generally strike parallel to major slope surfaces and gently dip downslope, forming cataclinal overdip slopes. The cataclinal overdip slope accelerates creep movement of micro-sheeted granite, which in turn loosens and disintegrates granite via the widening or neoformation of cracks, probably in combination with stress release, temperature change, and changes in water content near the ground surface. The surface portion of micro-sheeted granite is thus loosened with a well-defined basal front, which finally slides in response to heavy rain. Innumerable landslides of this type occurred in Hiroshima Prefecture, western Japan, following the heavy rainstorm of 29 June 1999. Following such landslides, the weathering of micro-sheeted granite exposed on the landslide scar recommences, setting the stage for future landslide.
The Jiufengershan rock avalanche was one of the largest and most damaging landslides triggered by the Chi-Chi earthquake (ML = 7.3, MW = 7.6) of 21 September 1999. The rock avalanche transported a mass of sedimentary rock 50 m thick and 1.5 km long, located on the western limb of the Taanshan syncline. The surface of rupture coincides with the bedding plane and dips moderately toward the Jiutsaihu valley.This paper is mainly devoted to the study of post-seismic surface processes that affected the sliding surface as well as the debris deposit, from September 1999 to February 2003. Large fractured blocks and a debris layer observed on the surface of rupture were subjected to mass wasting processes and denudation. The quantification of erosion was made using two different approaches.First, the subpixel correlation method was used to determine the horizontal displacement field from aerial photographs taken, respectively, 2 and 3.5 months after the earthquake. Displacements ranging from 1 to 6 m were observed around unstable blocks located at the western flank of the surface of rupture. Second, the co-seismic and post-seismic volume distributions in the sliding zone were determined from three digital elevation models, including a LiDAR image taken in 2002. Post-seismic erosion and deposition from September 1999 to April 2002 were mainly associated with mass wasting and denudation at the surface of rupture, deposition in small basins and lakes located in the debris deposit, and evacuation of materials from the debris deposit along natural and artificial drainage channels. The vertical compaction is 1% of the initial height of the deposit.
The 1999 Chi–Chi earthquake triggered the catastrophic Tsaoling landslide in central Taiwan. We mapped the landslide area and estimated the landslide volume, using a high-resolution digital elevation model from airborne LiDAR (Light Detection And Ranging), aerial photographs and topographic maps. The comparison between scar and deposit volumes, about 0.126 km3 and 0.150 km3 respectively, suggests a coseismic volume increase of 19% due to decompaction during landsliding. In July 2003, the scar and deposit volumes were about 0.125 km3 and 0.110 km3 respectively. These estimates suggest that 4 years after the event, the volume of landslide debris removed by river erosion was nearly 0.040 km3. These determinations are confirmed by direct comparison between the most accurate topographic models of the post-landslide period, indicating a very high erosion rate at the local scale (0.01 km3/year) for the deposit area of the landslide. Such a large value highlights the importance of landslide processes for erosion and long-term denudation in the Taiwan mountain belt.
From mid-October to 22 November 2000, the western Liguria Region of Italy experienced prolonged and intense rainfall, with cumulative values exceeding 1000 mm in 45 days. The severe rainfall sequence ended on November 23 with a high-intensity storm that dumped more than 180 mm of rain in 24 h. The high-intensity event caused flooding and triggered more than 1000 soils slips and debris flows and a few large, complex landslides. Slope failures caused three fatalities and severe damage to roads, private homes, and agriculture. Large (1:13,000) and very large (1:5000) scale colour aerial photographs were taken 45 days after the event over the areas most affected by the landslides. Through the interpretation of the 334 photographs covering an area of ∼500 km2, we prepared a landslide inventory map that shows 1204 landslides, for a total landslide area of 1.6 km2. We identified the rainfall conditions that triggered landslides in the Armea valley using cumulative- and continuous-rainfall data, combined with detailed information on the time of landslide occurrence. Landslide activity initiated 8 to 10 h after the beginning of the storm, and the most abundant activity occurred in response to rainfall intensities of 8 to 10 mm per hour. For the Ceriana Municipality, an area where the landslides were numerous in November 2000, we also collected information about a historical event that occurred on 8–11 December 1910 and triggered abundant landslides resulting in severe economic damage. A comparison of the damage caused by the historical and the recent landslide events indicated that damage caused by the 1910 historical event was more diffused but less costly than the damage caused by the 2000 event.
The Arequipa June 23, 2001, earthquake with a moment magnitude of Mw 8.4 struck southern Peru, northern Chile and western Bolivia. This shallow (29 km deep) interplate event, occurring in the coupled zone of the Nazca subduction next to the southeast of the subducting Nazca ridge, triggered very localized but widely outspread soil liquefaction. Although sand blows and lateral spreading of river banks and road bridge abutments were observed 390 km away from the epicenter in the southeast direction (nearing the town of Tacna, close to the Chile border), liquefaction features were only observed in major river valleys and delta and coastal plains in the meizoseismal area. This was strongly controlled by the aridity along the coastal strip of Southern Peru. From the sand blow distribution along the coastal area, a first relationship of isolated sand blow diameter versus epicentral distance for a single event is ever proposed. The most significant outcome from this liquefaction field reconnaissance is that energy propagation during the main June 23, 2001, event is further supported by the distribution and size of the isolated sand blows in the meizoseismal area. The sand blows are larger to the southeast of the epicenter than its northwestern equivalents. This can be stated in other words as well. The area affected by liquefaction to the northwest is less spread out than to the southeast. Implications of these results in future paleoliquefaction investigations for earthquake magnitude and epicentral determinations are extremely important. In cases of highly asymmetrical distribution of liquefaction features such as this one, where rupture propagation tends to be mono-directional, it can be reliably determined an epicentral distance (between earthquake and liquefaction evidence) and an earthquake magnitude only if the largest sand blow is found. Therefore, magnitude estimation using this uneven liquefaction occurrence will surely lead to underrating if only the shortest side of the meizoseismal area is unluckily studied, which can eventually be the only part exhibiting liquefaction evidence, depending on the earthquake location and the distribution of liquefaction-prone environments.
Fast-moving landslides are one of the most significant dangers deriving from slope instabilities. Landslides involving large volumes can develop in rock or debris avalanches with extreme mobility and enormous destructiveness. Nevertheless, a relevant number of casualties and damages derive from small, fast-moving landslides with flow-like behaviour.The Las Colinas landslide occurred at Santa Tecla (El Salvador, Central America) during a strong earthquake. It slid off the northern flank of the Bálsamo ridge, and resulted in almost 500 casualties and can be considered one of the most destructive landslides ever known. Earthquake shaking was amplified by the rock mass and the steep ridge topography.We collected original geological, geomorphological and geophysical data in the Cordillera del Bálsamo area. The involved materials, ranging from lapilli to tuff layers of different strength, have been mapped and characterized.Slope stability analyses have been performed both under static and dynamic conditions through limit equilibrium and finite element methods.Hazard zonation for this type of landslides requires the forecast of the movement velocity and final deposition area. We used a fully two-dimensional FEM model to simulate landslide spreading downslope. The developed code allows the use of different constitutive models and yield rules with the possibility to model and study internal deformation of the landslide mass, as well material entrainment and deposition.
Lahars are debris flows of volcanic origin, which can endanger or even destroy communities located near the flanks of volcanoes. Lahars are not always triggered by eruptions; they can form during heavy rainfall or after hydrothermal alteration and volcanic edifice collapse. Decision makers need lahar hazard maps to devise hazard prevention measures that will prevent casualties, so lahar modelling is an important tool for assessing flow behavior and determining inundation areas.The depth integrated numerical model used in this study is derived from the velocity–pressure of the Biot–Zienkiewicz model and was discretized using the smoothed particle hydrodynamics (SPH) method to simulate a lahar that occurred at Popocatépetl volcano in 2001. In order to investigate the convergence of the model, we used a range of different SPH mesh resolutions. Once the optimum mesh resolution was bounded, we analyzed the model's sensitivity to the initial lahar volume, the density of the geomaterial, and the rheological parameter of the Bingham fluid. The results show that the SPH depth integrated model produced a highly accurate simulation of the distribution and velocity of the 2001 lahar. The study also shows the effects of SPH mesh resolution and the relevant influence of rheological parameters.
The year was marked by noteworthy advances in multinational consortia of commercial firms and of forward-looking universities. Again, the tenor of the practice of Engineering Geology has picked up. Not to be in the vanguard does indeed mean that one languishes in the dust raised by those on the move. Engineering geologists must understand an infinity of challenges stemming from land development, environmental protection and cleanup and resource development. This is a profession in which age can bring wisdom and increased competence.Most practitioners were busy in 2001; more than 80% of ASFE member companies report that business has increased or stayed the same for the past 6 months. Sixty percent of practitioners expect that their 2002 revenues will be stable or increase for Year 2002.
On June 8, 2002, the Pacific Northern Gas pipeline in the Zymoetz River valley was severed by a large debris flow. The event initiated as a rock avalanche in Glen Falls Creek, a tributary of the Zymoetz River. The rock avalanche involved 1 × 106 m3 of volcaniclastic bedrock, and travelled through a complex flow path, to finally deposit a large fan in the main Zymoetz River. Approximately half of the debris volume was deposited in the cirque basin at the head of the valley, with the rest deposited in the channel, and the fan.Examination of the initiation zone showed a very persistent, slightly curved, joint set that forms the main sliding surface for the failed block with a dip of 45°, and dip direction of 300°. A Geographic Information System (GIS) was used to examine the event and allowed for further interpretation of field data. Preliminary dynamic analysis indicates that the event reached velocities of up to 34 m/s.Comparison of the Zymoetz River rock avalanche (ZRRA) with other similar events from the literature indicates that it exhibited similar mobility and velocities. As evidenced from the literature, these long runout events can cause significant damage, and have the potential to be a very high risk as forestry and recreation activities spread further into remote areas.
The 2002 Avaj, Iran earthquake (Mw = 6.5) triggered many landslides over an area of about 3600 km2. In this paper, we describe a ground-based field study conducted during several days immediately after the earthquake, and pre and post-earthquake landslide inventory maps that were prepared. The landslides due to earthquake include 47 fall and topple zones, 9 slides, and 3 lateral spreads. The largest slide is a rockslide (150 × 100 m), which occurred southeast of the village of Changureh. The main results of this study are:•The density of earthquake triggered landslides decreases away from the fault zone in a manner that is asymmetric with respect to direction;•Although several slides and lateral spreads were seen, the most common types of triggered landslides are falls and topples;•The area throughout which landslides occurred, and maximum epicentral and fault zone distances of landslides, are comparable to similar data from other historical earthquakes;•Landslides mostly occurred in the most susceptible geologic units, in which there were many landslides before the earthquake;•New disrupted slides and falls generally occurred in ancient fall zones, but no information about reactivation of coherent slides is available.
A strong earthquake (Mw = 6.2) occurred offshore the island of Lefkada (or Lefkas) on August 14, 2003. The maximum intensity has been evaluated Io = VIII (EMS) at Lefkada municipality, while VI to VII+ intensities were evaluated at many other villages of the island. The offshore NNE–SSW oriented strike-slip right-lateral fault was activated by the main shock. This fault is the northern termination of the Cephalonia transform fault. The most characteristic macroseismic effects were extensive typical ground failures like rock falls, soil liquefactions, subsidence, densification, ground cracks and landslides. These macroseismic effects are remarkably similar to those reported from some historical Lefkada shocks, e.g. 1704, 1914 (Ms = 6.3) and 1948 (Ms = 6.5). Sand boils and ground fissures with ejection of mud were observed at the seaside of the town of Lefkada, and in the villages of Nydri and Vassiliki.In situ soil profiles are obtained based mainly on borings after the earthquake. Boreholes records with SPT values (standard penetration test) are obtained and the “simplified procedure” originally developed by Seed and Idriss was employed to evaluate the liquefaction resistance of soils. The results indicated that the silty sandy layer, which lies beneath the artificial fill in the coastal zone in Lefkada town, had liquefied during the 14 August Earthquake. An attempt was also made to establish a preliminary microzonation map for Lefkada town using the data from Liquefaction Potential Index analyses. Our map was validated by the occurrence of liquefaction phenomena inside the town.
The year began with additional evidence that global warming effects were bringing about unusual increases in free precipitation, as rain in greater amounts, but not as snow, in the mid latitudes of Europe and North America, setting new records for flooding. These effects surely will continue to magnify as practical concerns for Engineering Geologists, not the least of which will be slope instability. Worldwide, the profession appeared to be in a truly advanced state, as marked by a new high in indigenous practice, a broad base of authors in this journal, and of cooperation between practitioners of the various nations.
In this study, a complex landslide, which occurred on 17 March 2005 near Koyulhisar town of Sivas Province of Turkey, is presented. The landslide resulted in 15 deaths and the destruction of about thirty houses at Kuzulu village. The main aims of this study are to assess the landslide in terms of engineering geology and geotechnics, to back-analyze the landslide in the source area, and to estimate its motion and destructive forces on structures. Furthermore, the effect of a future earthquake on stability condition of the mobilized but not completely failed mass adjacent to the right flank of the landslide is also investigated. Field observations, eyewitnesses, geomechanical laboratory tests, interpretations on pre-event aerial photographs and analyses using different approaches have been fundamentals of this study. Site observations indicate that the initial landslide in the source area occurred in highly weathered volcanics along a failure surface passing through the volcanics and along the interface between the volcanics and underlying limestone. Then the movement transformed into an earth flow and moved down through a V-shaped channel in the underlying limestone about 2 km until it stopped at a small settlement, which is called Kuzulu. Site observations and back-analysis of the initial slide suggest that the most likely cause should be water pressure increase as it is the season of snow melting and thawing of the groundwater. Interpretations on pre-event aerial photographs and the information obtained from eyewitnesses indicated that slope movements in the study area, where old landslide topography is evident, were continuing for many years. The simulation of the landslide with consideration of Bingham type yielding criterion together with water pressure variation suggested that the maximum velocity of the earth flow was 14.4 m/s and 13.6 m/s when it reached Kuzulu. Furthermore, this evaluation showed that the earth flow reached Kuzulu after 300 s, which is consistent with the information obtained from local people. The impact of the earth flow on the structures could be about 170 kPa against which only reinforced concrete structures may resist. Dynamic analyses suggested that a future earthquake, which may occur in the region, may result in a complete failure of the unstable mass remaining at the source area.
The Kashmir Earthquake of the 8 October killed an estimated 87 350 people, 25 500 through co-seismic landslides. The largest landslide associated with the earthquake was the 68 × 106 m3 Hattian Bala rock avalanche that destroyed a village and killed around 1000 people. The deposit blocks the valley to a depth of 130 m impounding a lake that reached the dam-crest in April 2007. An outburst flood now threatens a major settlement 3 km downstream. A series of space images reveals landslide clusters in the rock avalanche source area prior to the earthquake. The images also reveal a large slow-moving landslide with its toe in the lake, failure of this landslide may induce dam failure through overtopping and scour. Eighty five landslides in the Hattian Bala catchment predate the shaking of 8 October 2005, a further 73 are co-seismic with the main shock, and 21 postdate it in the period up to October 2006. Landslide magnitude–frequency distribution plots derived from satellite images allow an assessment of the contribution of seismically triggered events as compared to background rates of activity.
The October 3, 2009 (01:16:00 UTC), Olancha M5.2 earthquake caused extensive liquefaction as well as permanent horizontal ground deformation within a 1.2 km2 area earthquake in Owens Valley in eastern California (USA). Such liquefaction is rarely observed during earthquakes of M ≤ 5.2. We conclude that subsurface conditions, not unusual ground motion, were the primary factors contributing to the liquefaction. The liquefaction occurred in very liquefiable sands at shallow depth (< 2 m) in an area where the water table was near the land surface. Our investigation is relevant to both geotechnical engineering and geology. The standard engineering method for assessing liquefaction potential, the Seed–Idriss simplified procedure, successfully predicted the liquefaction despite the small earthquake magnitude. The field observations of liquefaction effects highlight a need for caution by earthquake geologists when inferring prehistoric earthquake magnitudes from paleoliquefaction features because small magnitude events may cause such features.
This paper describes the results of research carried out during the past fifteen years on the quick clays of eastern Canada. The mineral composition and structure of these clays is similar to that of other glacial marine clays but they often exist with an unusually low salt content in the pore water. There is evidence of strong rigid bonds between particles of those deposits that are overconsolidated. The bonds are broken when the soil is loaded and this may lead to large volume changes or to exceptional loss of strength if drainage is not permitted. Some studies have been made on the physico-chemical characteristics of the soil and on its fabric but most of the research to date has involved laboratory and field observations of the response of the soil structure to stress changes. The important influence of rate of loading has revealed the need of careful interpretation of laboratory tests for field application.
Three-dimensional (3D) visualization of data is an essential step in the development of descriptive hydrologic and rock-mechanical models of fractured rock systems. Data includes geological properties, rock mechanical properties and hydraulic responses. The 3D visualization approach is applied to characterizing a hypothetical site for a high-level nuclear waste repository located at 500 m depth in granitoids of the trans-Scandinavian igneous belt (1.6–1.8 Ga old). The study is based on site-specific data at the Äspö Hard Rock Laboratory (HRL) on the southeastern coast of Sweden. The data are extensive and spatially complex and are based on surface information, as well as a large number of boreholes penetrating up to 1000 m. At this site, fractures and fracture zones control both groundwater flow and mechanical stability. Structures are found within a 2×2×1 km deep model block representing the site. 3D locations of fractures and fracture zones are hypothesized based on surface and subsurface geological and geophysical information, including borehole radar. This results in a 3D geological model structure of the site.
Gypsum dissolution can be the cause of damage associated with subsidence and collapse. In Paris, the authorities want to refine the current maps of the areas likely to be affected by ground movement due to gypsum dissolution in the Bartonian Saint Ouen Limestone and Beauchamp Sands, and in the Lutetian marl and limestone formation. The proposed method involves assessing separately the probabilities relative to factors that control the ground subsidence, i.e.: thickness of gypsum strata, sulphate-unsaturated water flows, groundwater level, thickness and nature of the overburden. The total susceptibility is represented in a map form by the product of these three values plotted on a grid map with a pixel size of 20 m. For this, we developed a multi-layer 3D geological model using the same 20 m mesh grid, integrating 21 lithostratigraphic units. The hazard prone areas were calculated by geostatistical methods from the archived descriptions of more than 3900 boreholes and from existing geological maps. At the same time, the analysis of some 300 piezometers made it possible to construct the High Water (HW) and Low Water (LW) levels of the groundwater likely to have an impact on the dissolution of the gypsum. The obtained results correlate satisfactorily with the Parisian authorities' field knowledge and to the location of the known events. The mapping also revealed some sensitive areas that had not been previously identified; these will be checked by drilling. The constructed geological model and the hydrogeological analysis have already been used for studying other phenomena (e.g. sand flow and clay creep).
In order to determine the most suitable location for a set of rock caverns, the fracturing of a rapakivi granite block is studied in three dimensions. Five vertical, 200 m deep boreholes (ø = 66mm) were drilled for this purpose.The selection of the geophysical measurements utilized for the fracture classification was based on the results of the previous geophysical investigations in the test holes.The connections between the boreholes are evaluated from dipmeter data, crossholeseismic data and from charged potential cross-correlation data. The hydraulic conductivities of fracture zones and rock-blocks between them and the fracture apertures are calculated from water-injection test data.
Physical modeling of excavation of a roadway tunnel in the geologically 45° inclined rock strata by using a newly developed physical modeling approach, the so-called “Physically Finite Elemental Slab Assemblage (PFESA)”, together with infrared (IR) thermography, were conducted for visualization and observation of the progressive development of the excavation damaged zone (EDZ). The excavation was schemed as two phases, i.e. phase 1: the full-face excavation and phase 2: the staged excavation. The experiment was performed under unbalanced confinement found in underground coal mining. The relative temperatures of the excavation zone were mapped by the IR camera, in real time and over the entire field, into thermography series which were processed using such procedures as statistics, noise removal and spectral-frequency analysis for image feature extraction. IRT, defined as the statistical mean of the thermography matrix, was used as a measure of rock responses, characterizing the full-face excavation and the staged excavation as a multi-linearity and nonlinearity processes respectively by its time-marching scheme. The temporal and spatial evolutions of the EDZ were described in detail by the denoised thermographies. Directional propagations of the excavation induced stress wave were characterized by the spectral-frequency analysis of the resultant thermographies.Highlights► A new physical modeling approach Physically Finite Elemental Slab Assemblage (PFESA) is presented. ► PFESA uses infrared (IR) thermography to study development of the excavation damaged zone (EDZ). ► Temperatures from excavation zone are mapped by a IR camera, in real time over the entire field. ► Induced stress waves were characterized by the spectral-frequency analysis of the thermographies.
Static and dynamic rock slope stability analyses were performed using a numerical discontinuum modelling technique for a 700-m high rock slope in western Norway. The rock slope has been investigated by the Geological Survey of Norway (NGU), which has been carrying out rock slide studies for the county Møre and Romsdal in western Norway. The purpose of numerical modelling was to estimate the volume of the rock mass that could potentially slide under static and dynamic forces. This estimation was required to assess the run-up heights (tsunami) in a fjord that could potentially be caused by the rockslide. Three cases have been simulated for predicting the behaviour of the rock slope. First, an initial static loading is applied in the numerical model to simulate the prevailing rock mass conditions at the site. Second, saturated and weathered joint conditions are modelled by reducing the residual friction angle along the discontinuities of the rock mass. In doing so, the model simulates the effect of degradation of discontinuities in the rock slope. Third, a dynamic loading, based on peak ground accelerations expected in the area, is applied to simulate dynamic earthquake conditions.