Debris Fall Research Articles

Investigating the Application of Smart Materials for Enhanced Maintenance of Rubber Expansion Joints in Bridge Expansion Joint Systems

In South Korea, the public infrastructure encompasses 172,111 facilities, with bridges accounting for a significant segment (totaling 34,199). These bridges undergo expansion due to traffic, vehicular loads, and temperature fluctuations. Expansion joint devices are installed to maintain vehicle stability and driving performance across expansion gaps. While these devices effectively ensure vehicular stability and performance, they do not address issues such as leakage and debris fall; therefore, rubber expansion joints should be installed. However, these rubber joints are prone to damage from various factors, resulting in secondary issues such as girder corrosion and accidents under bridges. Because of these inherent vulnerabilities, these joints require frequent replacements, making continuous bridge maintenance challenging. Therefore, this study explores the development of novel expansion joints using superelastic shape memory alloys to overcome the limitations of traditional rubber expansion joints. A comparative finite element analysis was conducted on the developed superelastic shape memory alloy and traditional rubber expansion joints. This study also assessed the long-term usability of these novel joints, particularly their ability to revert to their original shape post load removal. This research presents a promising alternative to conventional expansion joints and holds potential implications for enhancing the durability and safety of bridge infrastructure.

On the Size of the Safety Area around the Launch Trajectory of a Rocket

The safety zone around the flight path of a rocket is determined by the fall of debris in the case of an accidental explosion or commanded termination. The trajectory of a tumbling body in a vertical plane is determined by specifying the velocity, flight path angle and angle of attack as functions of time. This involves the lift, drag and pitching moment coefficients as functions of the angle of attack over a full circle—0 to 360 degrees—to account for the tumbling motion. The problem is reduced to a third-order non-linear differential equation for the angle of attack by using the approximation of free fall coordinates. The analytical and numerical solutions show that two types of tumbling fall are possible, one with rotation and the other with oscillation. The tumbling trajectories are plotted and discussed for a variety of initial conditions, mass and aerodynamic properties of the tumbling body.

Seismic and energy upgrading of existing buildings—full‐scale testing of retrofitted masonry‐infilled RC frames

AbstractTaking into consideration the seismic vulnerability and the poor energy performance of the European building stock, and the increasing socio‐economic and environmental need for integrating seismic upgrading with energy efficiency improvement, an experimental study involving the lateral load testing of full‐scale one‐story one‐bay masonry infilled RC frames and load‐bearing masonry walls was carried out in the framework of the SupERB research project aiming to investigate the efficiency of integrated seismic and energy upgrading systems. The integrated approach is based on the use of textile reinforced mortar (TRM) overlays combined either with traditional thermal insulation (extruded polystyrene, XPS) or with thermally efficient mortar incorporating phase change material (PCMs). The proposed integrated approach can be applied on the exterior face of the structure, so as to facilitate its application in real structures in the easiest possible way and with minimum disturbance to the inhabitants of the buildings. In this paper, only the structural performance of masonry‐infilled RC frames retrofitted with the proposed integrated approach is presented, while the energy benefits will be presented in a separate paper. Thus, in this paper, the structural performance of an integrated seismic and energy upgrading approach was assessed through five full‐scale one‐story one‐bay masonry infilled RC frames that were retrofitted with different schemes of TRM combined with thermal insulation materials subjected to in‐plane displacement‐controlled cyclic loading. The following parameters were investigated experimentally: the number of TRM overlays (one or two layers of TRM combined with thermal insulation), the use of thermally efficient PCM‐enhanced TRM layer in contrast to the use of conventional XPS insulation, and different retrofitting configurations (placement of the TRM in a sandwich form over and/or under the novel or the traditional insulation). From the results obtained in this study, it can be concluded that all energy and seismic upgrading systems examined have a positive impact on the response of the structural system to cyclic loading, with the ones with two layers of TRM having a better performance compared to the ones with one layer of TRM and all of them a better performance than the control specimen. The use of two layers of TRM cancels the drawback of infilled frames, which at very small drifts they reach their maximum capacity and after that they rapidly fall to the capacity of the bare frame, providing capacities above 80% of their peak capacity for drifts up to 2%. In all the tests the TRM whether it was combined with XPS or included PCMs contributed to a better distribution of the cracks in the infill and delayed premature brittle failures. The presence of the TRM had also the advantage that it remained intact throughout the tests preventing the fall of debris out of the plane of the infilled frame, both in the retrofitted and unretrofitted sides.

Sedimentological characteristics and their relationship with landsliding in the Bhilangana Basin, Garhwal Himalaya, India

Every year during the Indian Summer Monsoon, large landslides occur in the Lesser and the Greater Himalayan rock formations, triggered by intense rainfall episodes coupled with physiography and anthropogenic activities. The present study investigates the slope failure mechanism's relationship with slope material compositions. Hence, sediment samples of 25 landslides were collected along the road corridors. These samples were collected from the Lesser and Greater Himalayan ranges and rock formations. The sediment was collected from the active landslides to understand particle size, clay content, moisture content, mineral composition, crystallographic structures, and the influence of geomorphic processes on the landslide failure processes. The samples were analyzed using a sieve, X-ray Diffractometry (XRD), and Scanning electron microscopy (SEM) to accomplish the study's objectives. The analysis indicates that the Lesser Himalayan meta-sedimentary rock formations have a high composition of fine and medium-size particles, lesser quartz mineral compositions with calcite, and a highly crushed and fractured presence, conchoidal fractures types of morphological features. Micrographs obtained from the schist and phyllite rock of the Lesser Himalayan origin shows highly sheared and crushing, crystal overgrowth; and, in turn, have a higher susceptibility to landslides. The relationship between slope materials and instability has shown a definite pattern in the study area. The debris flow and slump have a comparatively higher percentage of clay and silt compared to debris fall, debris slide, and rockfall. The particle size composition of sediment collected from the slip zone is significantly related to the types of landslides. The present study is helpful in understanding the sediment composition and slope failure mechanism.

Long-term Studies of Annual Variation in Growth and Reproduction of the Understory Fern Steiropteris deltoidea in a Hurricane-prone Rainforest in Puerto Rico

Two long-term studies were conducted in a rainforest in Puerto Rico that included measurements of leaf and plant functional traits of the common fern species Steiropteris deltoidea. A Fern Demography study (1993-2009) compared annual variation and effects of a category 3 hurricane (Georges, 1998) on fertile and sterile leaf traits. A second long-term study (2003-2019), the Canopy Trimming Experiment, evaluated annual variation in growth and reproduction of S. deltoidea in response to two experimentally simulated and one category 4 hurricane (Maria, 2017). In the Fern Demography study, differences between fertile and sterile leaf production rates and plant leaf count of S. deltoidea were significant while leaf lengths and lifespans did not differ between leaf types. Fertile (but not sterile) leaf production increased three-fold after Hurricane Georges but declined 10-fold by the end of the study. Leaf lifespans of cohorts emerging before and in the three years after Hurricane Georges were significantly shortened by tree and debris fall. Elevated production of fertile leaves and increased plant leaf counts followed the two simulated hurricanes of the Canopy Trimming experiment and two natural hurricanes. Steiropteris deltoidea exhibits a level of interannual flexibility in some growth and reproductive traits in response to a changed understory environment that suggests it may be a good indicator species for evaluating microhabitat hurricane effects. Although S. deltoidea exhibited resilience, predicted increases in frequency and magnitude of hurricanes in response to climate change may test the limits of life history strategies of rainforest understory ferns.

Volcanic hazards assessment of Oldoinyo Lengai in a data scarcity context (Tanzania)

The objective of our study is to establish an assessment of four volcanic hazards in a country threatened by the eruption of the OlDoinyo Lengai volcano. The last major eruption dates back to 2007-2008 but stronger activity in 2019 has revived the memory of volcanic threats to the Maasai and Bantu communities and human activities (agro-pastoral and tourism). The methods chosen have had to be adapted to the scarce and incomplete data. The volcanic hazards and their probability of occurrence were analysed on the basis of data available in the scientific literature and were supplemented by two field missions combining geography and hydro-geomorphology. Our study enabled us to map the hazards of ash fall, lava flows, lahars and avalanches of debris. Each hazard was spatialised by being ascribed an intensity. They are sometimes synchronous with the eruption sometimes they occur several months or years after a volcanic eruption. The results are the first step towards developing a volcanic risk management strategy, especially for the pastoral communities living around Lengai and for the growing tourist activities in this area.

Seismic behaviour of brickwork chimneys in buildings

The construction of chimneys of solid bricks in buildings with sloped roofs was commonplace in Bulgaria for almost a century. The collapse of a chimney during an earthquake could potentially lead to damages greatly exceeding the loss of the chimney itself, e.g. partial damage to the roof tiling and leaks, as well as material damage, injury or loss of life due to debris fall. A FEM model was created, in which the storeys of the building are represented in a generalised way, while the chimney is modelled explicitly as a cantilever supported at roof level. The internal forces in chimneys with heights ranging from 0.5 m to 2.0 m, belonging to buildings with height ranging from two to seven storeys were computed. Acceleration records from real earthquakes acting at the base of the building with varying peak ground acceleration and predominant period were used for input loading. The maximum tensile stresses at the bed joints were computed and were compared to the typical tensile strength of the mortars used for chimney construction, to assess the possibility of collapse. A simple, low-tech method for upgrading of existing chimneys by applying a coat of cement-based plaster with embedded fiberglass mesh is proposed.

Fault‐controlled base‐of‐scarp deposits

AbstractThe term base‐of‐scarp is proposed for those submarine deposits controlled by a fault and physically disconnected from their more proximal counterpart located on the footwall, although genetically linked to it. These systems differ from conventional fault‐controlled deltas, such as shoal‐ and Gilbert‐type, because they are entirely subaqueous and lack equilibrium morphology—a steady state in which the system grows in size without altering its shape. We present field examples of fault‐controlled deposits from the Crati Basin and the Messina Strait (southern Italy) consisting of stratigraphic clastic wedges that thin towards and onlap onto the active margin with primary inclined bedding. Beds are composed of immature coarse‐grained gravels and sand, lack structures representative of wave‐action and reflect gravity‐driven processes such as debris flow, debris fall and high‐density turbidity currents. These deposits represent the unsteady‐state phase in which the system grows reducing its slope angle leading to conditions under which the unsteady state may eventually turn into a Gilbert‐type or shoal‐water system. A diagram for fault‐controlled base‐of‐scarp (B), Gilbert (G) and shoal‐water (S) deposits is presented, including their steady‐ and unsteady states, and the conceptual conditions under which a base‐of‐scarp system might evolve into Gilbert‐type or shoal‐water systems and vice versa.

Identification of Landslide Disaster Potential based on Weathering Grade of Rock in Parepare City South Sulawesi, Indonesia

The purpose of this research is to identify the potential of landslide disaster based on weathering grade of rocks from selected areas. There are three aspects of field observation method used in this research, consist of slope geometry, lithology, and weathering grade of rocks aspects. The result shows that the rocks on research area have been slightly to completely weathered, some areas have became residual soil and slope angles of the research area varieties from steep to very steep. With those condition of weathering and slope angle, the research area will be slightly to very susceptible to landslide. The landslide models or types that will occur are debris slide and debris fall.

Fragility Curves of the Urban Road Network Based on the Debris Distributions of Interfering Buildings

Fragility curves are essential tools to quantitatively assess the physical vulnerability of structures and infrastructures at risk for a given seismic hazard. They describe the probability of exceeding a given performance level under earthquake excitation, and are usually defined by a lognormal probability distribution function. Although debris from damaged buildings adjacent to road edges is the main cause of urban mobility disruption, studies on the fragility curves development for infrastructures subject to seismic actions focus on geotechnical effects, and do not analyze this type of road blockage. The article proposes an analytical procedure to construct fragility curves for urban road networks. It is based on the construction of debris graphs and the use of an appropriate fitting technique. For a given seismic intensity measure level, the developed fragility curves express the probability that the road is open or closed to the transit of emergency vehicles after debris fall. Therefore, the performance level is defined in terms of the width of the road pavement that remains free after the debris fall, or the width of the debris heap on the road pavement. Finally, the proposed framework is tested with real data of the main street in Amatrice, and the results are presented and discussed.

Propagation of the trajectories for reentry spherical debris including rotation, melting fragmentation and voxel method

It is estimated that more than 22.000 objects are in orbit around the Earth, with a total mass of 8.400.000 kg. These numbers consider only objects with dimensions above 10 cm and some non-operational, but still orbiting satellites without control (debris). The debris represent a hazard to operational satellites and aerospace operations due to the high probability of collisions. Due to the interaction of the debris with the atmosphere of the Earth and the solar activity, they began to lose energy and finally decay. During the de-orbit process, the debris fall into the Earth’s atmosphere at hypersonic speeds and these objects can break-up and/or be fragmented due to the aerodynamics, thermal and structural loads. It is important to obtain the trajectory and attitude of any fragment to determine the possible survival mass, impact area, hazard conditions and risks to the population, the air traffic control, and infrastructure. In this case, it is implemented a computational code to integrate the equations of motion to propagate the dynamics and kinematics of spherical debris or propellant tanks. It is also analyzed the results of trajectories with six degrees of freedom, atmospheric winds, and Magnus effect. A voxel method is implemented to analyze the tanks heat transfer, surface temperature and structures stress. To determine and observe the influence of the rotation and the Magnus force in six reentry spherical bodies, three materials are selected; aluminum alloy, due to its application in many aerospace structures; titanium and graphite epoxy I, due to their highest melting point and specific heat. Generally, these materials are used in tanks and rocket motors. More than 62 trajectories were simulated. The mathematical model and computational code were validated in three degrees of freedom. Results are compared with data from other computational tools available in the scientific literature. The results show a good approximation with reported cases of study. New results are generated in the simulations of rotational bodies, due to the influence of aerodynamic forces in the trajectory and the changes in the stagnation regions. Due to the implementation of wind and rotation of the debris, the fragments increased the survivability and the dispersion area.

Energy budget for a rock avalanche: fate of fracture-surface energy

A detailed energy budget of a rock avalanche at Lake Coleridge, New Zealand, included fragments as small as 70 nm in diameter in the debris particle-size distribution, and used ultrasonic disaggregation of agglomerates formed during emplacement of the deposit to properly sample the fine fragments created during the rock avalanche. Using the maximum likely value of potential energy released during the debris fall and runout, and minimum values of energy lost to friction and of energy used in creating new rock surface area by fragmentation, the energy budget showed a substantial energy deficit; the available potential energy almost matched the energy lost to friction, leaving very little energy available for creating the new surface. This deficit was much less prominent if sub-micron fragments were ignored as in earlier energy budgets, because about 90% of total fragment surface area occurred on sub-micron fragments. Close examination of possible sources of error in the calculated budget leads to the conclusion, supported by published data, that only a small proportion of the energy used to create new rock surface transforms to surface energy, while a large proportion of it remains available in the form of elastic body-wave energy.

Sedimentological characteristics and application of machine learning techniques for landslide susceptibility modelling along the highway corridor Nahan to Rajgarh (Himachal Pradesh), India

The aim of this study is to investigate the causes of landslides in the Himalayan region and analysis of their sedimentary characteristics. The Himalayan region is unique to topographic as well as geological formations; each range has different litho-tectonic setting such as the Siwalik, the Lesser andthe Great Himalayan ranges. Particularly, the Lesser Himalayan ranges are highly susceptible to landslide during the monsoon season. In this study, a highway corridor is selected passing through the Siwalik and the Lesser Himalayan range. The study comprises of two parts; a) investigates landslide sedimentary characteristics such as particle size, plasticity limit, slope geometry, and land cover; b) comparative analysis of four machine learning methods to find out a best suitable model for landslide susceptibility analysis. In order to achieve the objectives detailed landslide inventory of the area is prepared based on repeated field visits and multi-dated satellite imageries. The field investigation reveals that debris fall and debris flow mostly confined; (a) along the road in proximity to the streams, particularly in scrubs and wasteland; and (b) along the streams due to river undercutting process. Sedimentological characteristics are examined to understand the grain size, plasticity limit, rock mass strength, and its relationship to slope failure mechanism. Landslide susceptibility is analyzed using boosted regression tree (BRT), generalized linear model (GLM), random forest (RF) and support vector machine (SVM) for the study area. These model results are validated using landslide test dataset with the area under curve (AUC) method. The AUC values of BRT (0.85), GLM (0.786), RF (0.904), and SVM (0.865) reveals the high prediction rate for spatial modelling of landslide in the area. The validation results show satisfactory agreement between the computed landslide susceptibility maps and the existing landslides occurred along the highway corridor.

ASSIMILATING GEOSPATIAL METAMODEL AND INVENTORY MAPPING FOR NON-STRUCTURAL MITIGATION OF LANDSLIDE

Abstract. In Malaysia, issues related to disaster management are always given attention in society and by the responsible parties. However, in general, citizen do not think of the consequential impact of disaster due to less of knowledge regarding the early phase in disaster management. Therefore, citizen in those areas will be more vulnerable to landslide as the citizen face difficulties in identifying specific areas with the tendency of landslides. This paper presents a geospatial metamodel approach for non-structural mitigation of landslide using data from airborne LiDAR and aerial photograph. Disaster management metamodel with geospatial element combines activity for managing disaster along with geospatial database that makes it handy for appreciating the metamodel. On the other hand, the digital terrain model (DTM) from LiDAR and aerial photograph is required to produce landslide inventory mapping. The case study area is located in Kundasang, Sabah, where landslides occur frequently. In order to get better visual in identifying landslides in the study area, three types of data are required to carry out image interpretation. The three types of data are hillshade, topographic openness and colour composite. The result of the landslide inventory map shows that there are five types of landslide, which is debris flow, debris fall, mud flow, deep-seated landslide and shallow landslide. Finally, the result of landslide inventory map will be integrated into the developed metamodel for presentation to the users. This landslide inventory map is used as a non-structural mitigation step in one of disaster management phases that is suitable to prepare and use in mitigating the landslide hazard impact.

Terrestrial Laser Scanning (TLS) data for the analysis of coastal tuff cliff retreat: application to Coroglio cliff, Naples, Italy.

In this study, we present the results of an analysis of Terrestrial Laser Scanning ( TLS) datasets, referred to multi-temporal (2013-2015) acquisition, aimed at evaluating volumetric changes and average retreat rates of the Coroglio tuff cliff, located in the western sector of Naples (Italy) in the Campi Flegrei caldera. The multi-temporal analysis was carried out in two steps: firstly, we developed a preliminary 3D Cloud-to-Cloud comparative analysis of point clouds obtained by TLS data processing, providing a view on geomorphological evolution; secondly, we obtained quantitative information by analyzing in GIS processing the differences between multi-temporal Digital Elevation Models. Finally, a morphometric analysis was carried out in order to evaluate retreat both retreat and failure rates. Four types of landslides (rock fall, debris fall, earth flow, and soil slip) have been accurately mapped in the different sectors of the cliff. The morphological analysis shows that several morphological variations have been recognized in different areas of the cliff with a maximum retreat of 8 m at the foot of the cliff due to the erosive action of the sea on poorly lithified deposits. We estimated that the average linear retreat rate related to the Coroglio cliff between 2013-2015, was equal to 0.07 m/yr; the linear retreat rate is higher (0.34 m/yr) at the base of the cliff, directly beaten by the sea waves. The results of the statistical analysis of the relationship between volume and area calculated for rock falls are consistent with the results of previous studies. Geo-structural analysis confirms that some discontinuity sets strongly control the failure kinematisms.

Structural and thermal controls of rockfall frequency and magnitude within rockwall–talus systems (Swiss Alps)

AbstractBoth from a systemic and natural hazard perspective, it is essential to understand the causes and frequency of rockfalls in mountain terrain and to predict the block sizes deposited at specific locations. Commonly, rockfalls are studied either retrospectively, using talus slopes, or directly by rockwall surveys. Nevertheless, our understanding of rockfall activity, particularly at the lower magnitude spectrum, is still incomplete. Moreover, the explanatory framework is rarely addressed explicitly. In this study, we investigate two rockwall–talus systems in the Swiss Alps to estimate the rockfall frequency–magnitude pattern and their key controls. We present a holistic approach that integrates deductive geotechnical and thermal investigations of the source rockwalls with abductive talus‐based explanations of rockfall volume and frequency.The rockwalls' three‐dimensional (3D) joint pattern indicates that 75% of the blocks may be released as debris fall (< 14 m3) and boulder falls (14–61 m3), which is mirrored in the corresponding talus material. Using two‐year records of near‐surface rockwall temperatures as input for a 1D heat conduction model underlines the destabilizing role of seasonal ice segregation. Deepest frost cracking of 300 cm may occur on the north‐northeast (NNE)‐exposed, snow‐rich rockwall, with peaks at the outermost surface. The synthesis of all data suggests that infrequent, large planar slides (approximately every 250 years) overlain by smaller, more frequent wedge and toppling failures (approximately every 17–50 years) as well as high‐frequency flake‐like clasts (3–6 events/year) characterize the rockfall frequency–magnitude pattern at Hungerli Peak.Here, we argue that small‐size rockfalls need more scientific attention, particularly in discontinuous permafrost zones. Our study emphasizes that future frequency–magnitude research should ideally incorporate site‐specific structural and thermal properties, rather than just focusing on climatic or meteorological triggers. We discuss how holistic rockwall–talus approaches, as proposed here, could help to increase our process understanding of rockfalls in mountain environments. Copyright © 2017 John Wiley & Sons, Ltd.

Geology and Slope Stability Analysis using Markland Method on Road Segment of Piyungan – Patuk, Sleman and Gunungkidul Regencies, Yogyakarta Special Region, Indonesia

Road segment of Piyungan - Patuk is a part of Yogyakarta - Wonosari highway, fairly dense traversed by vehicles, from bicycles tobuses and trucks. This road crosses hilly topography, causing its sides bounded byquite steep slopes or cliffs. Steep slopes and cliffs are potentialto create mass movement. Geologic condition of the surrounding area is built of various volcanic lithology such as breccia, siltstone, sandstone and tuff. There are also geologic structures of joints and faults that affect the stabilityof the slopes around this road. Slope stability analysis for road segment of Piyungan – Patuk was conducted by applying Markland method. Laboratory testings were done to determine the mechanical and physical properties ofrocks that influence the slope strength. Results ofthe testings show that cohesion and friction angle of volcanic breccia are c = 20.0441 kg/cm2 and  = 56.38˚; cohesion and friction angle of sandstone are cr = 0.6862 kg/cm2, cp = 4.6037 kg/cm2, r = 26.37˚, and p = 32.79˚; cohesion and friction angle of tuff is cr = 1.677 kg/cm2, cp = 7.5553 kg/cm2, r = 17.85˚, and p = 24.19˚. Based on the analysis, some slopes in the study area are potential to move. The movements canbe classified into rock fall, debris fall, and rock slides with the sliding plane categorized as planar and wedge. On the other hand, landslide prone zones in the study area can be divided into: Areas with high vulnerability, Areas withmoderate vulnerability, and Areas with low vulnerability. Areas prone to landslide should be managed by a series of measures, among others understand natural phenomena, recognizing symptoms of avalanche, attempting to reduce the risk, and land use regulation. The management activities should involve all stakeholders in anintegrated manner ofimplementation. Keywords: Road segment, Markland method, slope stability, factor of safety, vulnerability

Retreat rates, modalities and agents responsible for erosion along the coastal chalk cliffs of Upper Normandy: The contribution of terrestrial laser scanning

In order to follow all the changes affecting the coastal chalk cliff face in Upper Normandy and improve knowledge about cliff erosion, repeated terrestrial laser scanning (TLS) surveys were carried out frequently between 2010 and 2013 (every 4–5 months). They were conducted at two sites with similar lithostratigraphic characteristics but different exposures to marine actions (the former being an abandoned cliff and the latter an active cliff). They provide a quantification of the production of debris with centimeter precision (from ±0.01 to 0.04m). These surveys provided three major outcomes: 1) cliff retreat rates were measured at high spatial resolution with retreat values, unsurprisingly, 3–4 times higher for an active cliff than for an abandoned cliff. This result highlights that marine actions should be seen as not only a transport agent but also a particularly effective erosion agent; 2) a significant proportion of debris fall production (about 25%) in the total active cliff retreat was identified; and 3) one of the modalities of retreat was visualized as the creation of a basal notch, which propagates instability towards the upper part of the cliff face. Later, this instability generates rock falls coming from the whole cliff face.

Micromorphological Features of Pan Horizon in the Soils Derived from Different Parent Materials

We have five soil series of pan soils in South Korea out of 391 series: Gangreung, Bugog, Yeongog, Jangweon, and Pogog. Productivity decreases in pan soils as pan horizons impede percolation and capillary rise of water and interrupt root extension. This study was performed to investigate pedogenic processes of pan soils mainly located in footslope and river terrace by analyzing physicochemical properties and soil micro-morphology. Korean pan soils belong to Alfisols, Ultisols, or Inceptisols and have udic or aquic soil moisture regime, mesic temperature regime, and mixed mineral substances. Texture of pan horizons selected for the present study was mainly silty clay loam with clay contents ranging from 26.3 to 45.3%. Bulk density of the pan horizons ranged from 1.4 to <TEX>$2.1Mg\;m^{-3}$</TEX> and their soil structure were subangular or angular structure. In terms of micro-morphological structure, Bt horizon of Gangreung series was formed as platy and striated b-fabric structure possibly affected by uplift of coastal terrace following clay sedimentation by flood. Jangweon series showed micro-morphology of massive structure and crystallic b-fabric as macropores between coarse debris established by debris fall in slope were filled with silt-sized particles. The Bt horizons having massive structure and striated b-fabric in Yeongog, Pogog, and Bugog series implies that those horizons experienced horizontal mass flow after clay accumulation.

Greater risk of physical damage caused by debris fall to understory plants and tree seedlings in old-growth forests than in young forests

Falling canopy debris causes injury and mortality of tree seedlings and understory plants in a wide variety of forests. Canopy structure and dynamics differ between young and old-growth forests: old forests are taller and have more aboveground biomass and greater annual mortality of bole biomass. I predicted that risk of damage caused by debris fall in the understory is greater in old-growth forests than in young forests. I tested this prediction by tracking for 1 year the fates of artificial seedlings placed in young (stand age 31 to 61 years) and old-growth (stand age circa 500 years) Pseudotsuga–Tsuga forests. The risk of physical damage caused by debris fall in old-growth forests was significantly greater than in young forests (P = 0.001). Seedling models were damaged by falling debris at a rate of 4.4%·year−1 and 0.8%·year−1 in old-growth and young forests, respectively. More seedling models were damaged by fallen coarse woody debris in old-growth forests than in young forests, although this trend was not significant (P = 0.134). Approximately 25% of seedling models in both young and old-growth forests were damaged by something other than fallen canopy debris, most likely snow accumulation.