Numerical analyses of tunnel collapse and slope stability assessment under different filling material loadings: a case study

To transfer the excess water from Sabzkouh River in central Iran to cities beyond the river, a mechanized tunnel is being excavated. During construction and support installation in the first 100 m, tunnel roof collapse occurred and was followed by ground settlement, so that a cavity was developed in ground surface. The cavity had to be filled in a short time before rainy season, since the water flow through cavity could extend the collapse area in both tunnel roof and ground surface. In order to fill the cavity, some filling methods with different materials consist of in situ soil, lightweight concrete, and pumice aggregate lightweight concrete (PALWC) were suggested. To analyse the load distribution and minimize the costs, a three-dimensional analysis was carried out. Tunnel support system was simulated numerically to further evaluate loading state on support system under different material loadings. Mohr-Coulomb material model was used to allow material failure. The modelling procedure was based on actual construction procedure. Firstly, in situ model was modelled without any excavation and was run to establish pre-stresses and displacement, then slope was supported, the tunnel was excavated and support was installed and finally cavity was simulated. The numerical results show that filling the cavity with soil will result in over loading on the support system and leads to instability of the slope. Other two suggested filling materials have acceptable load on support system, but PALWC was selected as the best filling material having minimum loading and guarantees slope stability.     

Integrated tsunami intensity scale based on maxima of tsunami amplitude and induced current

As with earthquakes, river floods, water waves, and wind intensities, a tsunami intensity has to be synthetic and comprehensive to be efficient. Tsunami impact is complex because the effects can be felt on the beach, on inundated areas and also at berths and anchors. Within the same local area, a tsunami may severely impact the population on the coast, while its effects may be negligible on marine bodies (boats). Most existing tsunami intensity scales are based either on water elevation or on induced currents. However, it is commonly admitted that both variables should be considered simultaneously. Several existing intensity scales were integrated and were made consistent with each other. An original intensity scale is then derived based on analysis of the interdependency between the maxima of tsunami amplitude and induced current: The dimension of the couple composed by two variables is analyzed, in particular through the derivation of a linear relationship using the long wave theory and the use of a fully nonlinear numerical experiment. Our intensity scale is particularly well adapted to numerical studies, for which the two variables are naturally derived within an entire computational grid. Once the tsunami intensity scale was set up, it was briefly applied to a particular case study: the impact of the Sumatra tsunami, dated December 26, 2004, on the coast of Sri Lanka. Indeed, the tsunami scales proposed herein represent an initial framework of study and can be further improved through new or revisited tsunami observations.

     

Short and Long-term Behaviours of Bored Tunnels in Port-Said Clay

Geotechnical and Geological Engineering - This study investigates the behaviour of bored tunnels in the Port-Said very soft to firm clay deposit in El-Tina Plain, north-eastern Egypt. Recent...     

Shaking table tests of a full-scale flat-bottom manufactured steel silo filled with wheat: Main results on the fixed-base configuration

This paper reports on a series of shaking table tests on a full-scale flat-bottom steel silo filled with soft wheat, characterized by aspect ratio of around 0.9. The specimen was a 3.64-m diameter and 5.50-m high corrugated-wall cylindrical silo. Multiple sensors were used to monitor the static and dynamic response of the filled silo system, including accelerometers and pressure cells. Numerous unidirectional dynamic tests were performed consisting of random signals, sinusoidal inputs, and both artificial and real earthquake records. The objectives of this paper are (i) to provide a general overview of the whole experimental campaign and (ii) to present selected results obtained for the fixed-base configuration. The measured data were processed to assess the static pressures, the dynamic overpressures (related to the effective mass) and the accelerations of monitored points on the silo wall, and to identify the basic dynamic properties (fundamental frequency of vibration, damping ratio, dynamic amplification factors) of the filled silo. The main findings are discussed and compared with the predictions given by available theoretical models and code provisions. It is found that the fundamental frequency slightly decreases with increasing acceleration, while it slightly increases with increasing compaction of the granular material. For close-to-resonance input, the dynamic amplification (in terms of peak values of accelerations) increases along the height of the silo wall up to values of around 1.4 at the top surface of the solid content. The dynamic overpressures appear to increase with depth (differently from the EN1998-4 expectations), and to be proportional to the acceleration.     

Experimental Study of Bearing Capacity of Granular Soils,Reinforced with Innovative Grid-Anchor System

The pull-out resistance of reinforcing elements is one of the most significant factors in increasing the bearing capacity of geosynthetic reinforced soils. In this research a new reinforcing element that includes elements (anchors) attached to ordinary geogrid for increasing the pull-out resistance of reinforcements is introduced. Reinforcement therefore consists of geogrid and anchors with cubic elements that attached to the geogrid, named (by the authors) Grid-Anchor. A total of 45 load tests were performed to investigate the bearing capacity of square footing on sand reinforced with this system. The effect of depth of the first reinforcement layer, the vertical spacing, the number and width of reinforcement layers, the distance that anchors are effective, effect of relative density, low strain stiffness and stiffness after local shear were investigated. Laboratory tests showed that when a single layer of reinforcement is used there is an optimum reinforcement embedment depth for which the bearing capacity is the greatest. There also appeared to be an optimum vertical spacing of reinforcing layers for multi-layer reinforced sand. The bearing capacity was also found to increase with increasing number of reinforcement layer, if the reinforcement were placed within a range of effective depth. The effect of soil density also is investigated. Finally the results were compared with the bearing capacity of footings on non-reinforced sand and sand reinforced with ordinary geogrid and the advantages of the Grid-Anchor were highlighted. Test results indicated that the use of Grid-Anchor to reinforce the sand increased the ultimate bearing capacity of shallow square footing by a factor of 3.0 and 1.8 times compared to that for un-reinforced soil and soil reinforced with ordinary geogrid, respectively.     

Analysis of subsurface magnetic features of the southeast of Al-Muwayh quadrangle,Saudi Arabia,using aeromagnetic data

Aeromagnetic data have been utilized to investigate the subsurface features of the southeast of Al-Muwayh quadrangle. Several techniques have been comprehensively used in an integrative way to reach the goals. Local phase and normalized standard deviation filters are used in this study as edge detectors, showing the possible occurrences of structural lineaments/faults in the quadrangle. Magnitude magnetic transform filters are used to produce anomalies that are closer to the true horizontal position of magnetic sources to enhance the interpretation. Among these transforms, a transform which has been used as edge detectors and the other two transforms are used to show the shallow and the shallowest magnetic sources within the study area. Tilt angle is mainly used to delineate the main magnetic contacts (faults), their locations, and their expected depths. The integration between these different filters show clearly the possible occurrences of edges (contacts/faults), the direction of these lineaments, the source locations of magnetic anomalies, the shallow and the shallowest causative targets, and the location and the depths of the main faults deduced from the tilt angle approach.     

Immune deficiency causes annual late summer brown trout (Salmo trutta) mortality in Austrian prealpine river systems

For several years, severe brown trout (Salmo trutta) mortality has been observed in different prealpine river systems of Austria, Southern Germany, and Switzerland during late summer and early autumn. Often, the skin of the effected fish shows a medium to intense black pigmentation, and therefore this phenomenon is called “Schwarze Bachforelle Phänomen” or “proliferative darkening syndrom”. The present study was conducted to gain insight about its presence. From middle of May to end of August, brown trout and rainbow trout were kept in experimental tanks supplied with water from an effected river system. In brown trout, samples for blood diagnostics and histological investigations were taken after 0, 47, 62, and 77 days, and in rainbow trout after 0 and 107 days. Brown trout from a wild population were investigated for comparative purposes. Brown trout showed no abnormalities till the end of June. All fish sampled in the second half of July suffered from severe immune deficiency as the numbers of peripheral blood granulocytes and lymphocytes, plasma lysozyme activity, and plasma immunoglobulin levels significantly decreased. During August, the number of erythrocytes decreased and the osmotic fragility of the erythrocytes increased. Senescent erythrocytes became more frequent and the hematopoietic tissue of spleen and kidney enlarged. Also, the cellular composition of the spleen changed as the number of hemoblasts and normal erythroblasts decreased while the number of atypical erythroblasts increased. In the pronephros and hematopoietic tissue of the mesonephros, aggregation of macrophages and tissue disintegration was frequently observed. This was similar for brown trout from the field experiment and from the wild population. High mortality occurred in the end of July and during August. Death of the fishes might have been caused by secondary infections with microorganisms. Almost similar changes were observed in rainbow trout, however, the mortality was lower.     

Exploring Groundwater Resources and Recharge Potentialities at El-Gallaba Plain,Western Desert,Egypt

Egypt has a fast-growing population rate of 2.5%/year; consequently, there is an increase in the water demand for living and launching different development plans. Meanwhile, there is intensive construction of several dams in the upstream Nile basin countries. Thus, it is necessary to search for new water resources to overcome the expected shortages of the Nile water supply by focusing on alternative groundwater resources. El-Gallaba Plain area is one of the most promising areas in the western desert of Egypt attaining the priority for new reclamation projects; however, its hydrogeological setting is not well understood. The present work aims at identifying the recharge potential of the groundwater aquifers in El-Gallaba Plain, as well as exploring the role of geologic structures as natural conduits, and evaluating the groundwater types, origin and distribution. The integration of hydrogeophysical studies (aero and land magnetic surveys, vertical electrical sounding), hydrochemical analyses and remote sensing were successfully used for assessing the groundwater development potential. The hydrogeophysical studies show a large graben bound aquifer with thickness exceeding 220 m. The hydrochemical results indicate the presence of three major water types; Na mix, Na Cl, Na Cl HCO₃ with salinities ranging between 227 and 4324 mg/L. The aquifer receives little recharge from the western fractured calcareous plateau from past pluvial periods and scarce present flashfloods. There is no indication for recent recharge from Lake Nasser to the aquifer domain. Further modeling studies are essential for establishing sustainable abstraction levels from this aquifer.