Geosynthetic-encased stone columns: analytical calculation model

This paper presents a newly developed design method for non-encased and encased stone columns. The developed analytical closed-form solution is based on previous solutions, initially developed for non-encased columns and for non-dilating rigid-plastic column material. In the present method, the initial stresses in the soil/column are taken into account, with the column considered as an elasto-plastic material with constant dilatancy, the soil as an elastic material and the geosynthetic encasement as a linear-elastic material. To check the validity of the assumptions and the ability of the method to give reasonable predictions of settlements, stresses and encasement forces, comparative elasto-plastic finite element analyses have been performed. The agreement between the two methods is very good, which was the reason that the new method was used to generate a parametric study in order to investigate various parameters, such as soil/column parameters, replacement ratio, load level and geosynthetic encasement stiffness on the behaviour of the improved ground. The results of this study show the influence of key parameters and provide a basis for the rational predictions of settlement response for various encasement stiffnesses, column arrangements and load levels. The practical use of the method is illustrated through the design chart, which enables preliminary selection of column spacing and encasement stiffness to achieve the desired settlement reduction for the selected set of the soil/column parameters. (C) 2010 Elsevier Ltd. All rights reserved

Delineation of risk area in Log pod Mangartom due to debris flows from the Stoze landslide

The paper shows in detail the case of delineation of risk area in the village of Log pod Mangartom in the Koritnica River valley due to possible debris flows that might in future be triggered on the Stoze slope above the Mangart Mountain pasture. On the basis of field and laboratory investigations of the debris flow of November 17, 2000, that devastated the Koritnica River valley, the possible scenarios of triggering new debris flows on the Stoze slope were investigated. For the determination of debris flow hazard area in the Koritnica River valley, the results of one- and two-dimensional modelling of selected debris flows of known magnitudes and different viscosities were applied. For the determination of risk area, the existing and the possible new infrastructures were taken into account, and the risk area was divided into 3 zones. The paper presents the expert bases summarised by the legislator in the relevant decree issued by the Government of the Republic of Slovenia on the conditions and limitations governing the construction in the debris-flow risk area of Log pod Mangartom. This regulation is the first of its kind in Slovenia

Mitigation of large landslides and debris flows in Slovenia, Europe

In Slovenia, a small central European country, in the second half of the 20th century minor landslides of different forms (shallow landslides, slides, slumps – average volume of 1000 m3, rarely 10,000 m3) were prevailing, mainly triggered during short and intense rainfall events or after prolonged rainfall periods of moderate intensities. Unfavorable geological conditions are\ud the main causes for a high slide density (≈ 0.4 slide per 1 km2) in Slovenia, despite good vegetation conditions (more than 60% covered by forests).\ud Experiences with mitigation of large landslides were rare until the last decade, when four large landslides (Stože, Slano Blato, Strug, and Macesnik) with volumes of the order of 1 million m3 were triggered and urged for fast mitigation. They can be placed in the category of rainfall-induced landslides that became active in unfavorable geological conditions.\ud The Stože Landslide with a volume of around 1.5 million m3 was initiated in November 2000 as a debris landslide on the Stože slope in morainic material above the village of Log\ud pod Mangartom in W Slovenia after a wet autumn period with no snow accumulation but rising runoff coefficients. It turned from a debris landslide on a hill slope into a catastrophic debris flow due to low inertial shear stress caused by high water content.\ud The Slano Blato Landslide also formed in fossil landslide masses on a contact of calcareous and flysch formations during wet autumn period in November 2000. It is ever since\ud progressively enlarging behind the main scarp via retrogressive slumping of new and freshly weathered material that due to high water pore pressures turns into a viscous earth flow.\ud The Strug Landslide is a very good example of a complex slope movement, which started in December 2001 as a rockslide with a consequent rock fall that triggered secondary landslides and caused occasional debris flows. In 2002 over 20 debris flows were registered in the village of Koseč below the Strug Landslide, mainly on days with a daily rainfall accumulation of 20 to 30 mm. In 2003 and 2004 no further debris flows could be observed,\ud therefore these events in the Strug landslide area were defined as material and not rainfall driven events.\ud The Macesnik Landslide above the village of Solčava in N Slovenia near the border with Austria was triggered in autumn 1989. Till 1994 there were no activities on the landslide. In the period between 1994 and 1998 the advancement of the landslide on the slope was utmost\ud intense. Firstly, the landslide destroyed state road, and a new pontoon bridge had to be built instead. In 1996, the landslide advanced and destroyed a turn on the same state road. In 1999, a large rock outcrop stopped the advancement of the landslide. Further advancement would possibly destroy several farmhouses on its way down the valley towards the Savinja River. Possible damming of this alpine river would cause a catastrophic flooding. The ongoing mitigation of these landslides is subjected to a special law adopted in 2002 (revised in 2005). The final mitigation is planned to be finished before the end of 2010, with\ud estimated costs of 60.5 Mio € for all activities planned. These costs should be added to the estimated sum of 83.5 Mio € as the final remediation costs for all other registered active small-sized landslides in Slovenia. Practical experiences in Slovenia with large landslides up\ud to now show that only strict and insightful co-ordination, interdisciplinary approach and adequate financial support may lead to a successful mitigation

Modelling of rockfall motion

An analysis of natural hazards caused by rockfalls (common expression for falling stones and boulders; and other similar forms of gravitational mass movements) is an important element of risk management in mountainous regions. Due to their energy and velocity rockfalls represent an especially dangerous hazard factor. Because of that rockfalls are given much attention all over the world and they are modelled in different ways – simulating their paths and run-out distances. In this paper, a literature review of the main characteristics of the most important non-comprehensive rockfall models is presented. The dispositional models are those that tell us where a hazardous process may occur. The process-based models simulate rockfall process dynamics. They can be classified in relation to the process approach into empirical models and into analytical models. Empirical process-based models are generally based on the relationship between topographic factors and rockfall run-out zone. Analytical process-based models are composed of a trajectory model and a friction model. They describe and provide 2-D or 3-D simulation of the movement of the rockfall masses and can be differentiated regarding the way how the rockfall mass (lumped mass, rigid body shape) and the movement on the slope (bouncing, rolling, sliding) are described, respectively. The GIS-based models use the advantages of this system and work in three steps: the determination of rockfall source areas, the determination of trajectories of single boulders, and the determination of run-out distances and run-out zones. The main aim of the review on modelling of rockfall motion is to make it easier for the professionals to choose an adequate rockfall model at local and regional scales

Stepwise mitigation of the Macesnik landslide, N Slovenia

The paper gives an overview of the history of evolution and mitigation of the Macesnik landslide in N Slovenia. It was triggered in 1989 above the Solcava village, but it enlarged with time. In 2005, the landslide has been threatening a few residential and farm houses, as well as the panoramic road, and it is only 1000 m away from the Savinja River and the village of Solcava. It is 2500 m long and up to more than 100 m wide with an estimated volume in excess of 2 million m(3). Its depth is not constant: on average it is 10 to 15 m deep, but in the area of the toe, which is retained by a rock outcrop, it reaches the depth of 30 m. The unstable mass consists of water-saturated highly-weathered carboniferous formations. The presently active landslide lies within the fossil landslide which is up to 350 m wide and 50 m deep with the total volume estimated at 8 to 10 million m3. Since 2000, the landslide has been investigated by 36 boreholes, and 28 of them were equipped with inclinometer casings, which also serve as piezometers. Surface movements have been monitored geodetically in 20 cross sections. This helped to understand the causes and mechanics of the landslide. Therefore, landslide mitigation works were planned rather to reduce the landslide movement so that the resulting damages could be minimized. The construction of mitigation works was made difficult in the 1990s due to intensive landslide movements that could reach up to 50cm/day with an average of 25 cm/day. Since 2001, surface drainage works in the form of open surface drains have mainly been completed around the circumference of the landslide as the first phase of the mitigation works and they are regularly maintained. As a final mitigation solution, plans have been made to build a combination of subsurface drainage works in the form of deep drains with retaining works in the form of concrete vertical shafts functioning as deep water wells to drain the landslide, and as dowels to stop the landslide movement starting from the slide plane towards its surface. Due to the length of the landslide and its longitudinal geometry it will be divided into several sections, and the mitigation works will be executed consecutively in phases. Such an approach proved effective in the 800 m long uppermost section of the landslide, where 3 parallel deep drain trenches (250 m long, 8 to 12 m deep) were executed in the autumn of 2003. The reduction of the movements in 2004 enabled the construction of two 5 in wide and 22 m deep reinforced concrete shafts, finished in early 2005. In Slovenia, this sort of support construction, known from road construction, was used for the first time for landslide mitigation. The monitoring results show that the landslide displacements have been drastically reduced to less than I cm/day. As a part of the stepwise mitigation of the Macesnik landslide, further reinforced concrete shafts are to be constructed in the middle section of the landslide to support the road crossing the landslide. At the landslide toe, a support construction is planned to prevent further landslide advancement, and its type is still to be defined during the procedure of adopting a detailed plan of national importance for the Macesnik landslide

Back Analyses of Anchored Retaining Structures

Finite element step-by-step back analyses were performed on four typical instrumented test sections of several anchored, bored-pile walls, located on the Vransko - Blagovica section of the Celje - Ljubljana motorway. A sufficiently accurate numerical model was obtained in the early stages of the construction sequence, so that it was possible to predict with confidence in advance the critical stages which were encountered at the end of the construction works. The back analyses were carried out using the computer program Plaxis, assuming the simple Mohr-Coulomb constitutive relationship and a simplified geological structure. The results of these analyses were compared with those obtained using the more sophisticated back analyses performed by Vukadin [2001], which took into account the Hardening Soil model and a more detailed geological structure. It was found that, even though the more sophisticated model provided slightly more accurate results, the results obtained by using the simplified model were very similar, which makes the use of such a model and the observational method very attractive for practicing engineers

History and present state of the Slano Blato landslide

The Slano Blato landslide is more than 1290 m long, 60 to 200 m wide and 3 to 11 m deep with a volume of about 700 000 m(3). It is located in the Eocene flysch region of western Slovenia with a limestone overthrust in the direct vicinity, above the landslide. The landslide moves mainly as a viscous earth flow with occurrences of rapid mud flows. In dry periods or in freezing conditions it behaves as a group of several slow to moderate landslides. The landslide follows the course of the Grajscek stream and is presently only 220 m away from Lokavec village. The landslide was first mentioned about 200 years ago. In 1887 it flowed as a liquid flow and reached and destroyed the main road in the valley 2 km away. The Austro-Hungarian monarchy sent one engineer to the site and 17 years later the slide was remediated with a series of torrential check dams. The monarchy prohibited any construction works in the influence, area of the landslide. During the 20th century the region changed from Austrian, Italian, Yugoslav, and finally to Slovenian government in 1991. The relevant Austrian measures and decisions were forgotten during the course of the years, and building permits were issued after the World War II to local people who populated the part of the landslide influence area. Simultaneously, regular maintenance of the excellent past engineering works was neglected. In November 2000 a large landslide of mud and debris was triggered again and it still presents a danger to the relatively new residential houses today. At present, the village is protected against mudflows by a small rockfill dam and by the regulation of the stream bed. In rainy periods removal of mud is necessary to maintain safe conditions for the village. The paper discusses the geological, hydrogeological, hydrological and geotechnical conditions for the occurrence of the Slano Blato landslide. The primary reasons for the Slano blato landslide are the geological and hydrogeological conditions just beneath the overthrust of a Triassic limestone plateau over the Eocene flysch of Vipava valley. The direct reason for triggering the earth flow in 2000 was the intensive precipitation. During the course of years the precipitation threshold for earth flow movements has diminished. The landslide has to be remediated for two main reasons (1) the village below the landslide is endangered, and (2) the landslide is still advancing retrogressively and laterally. The foreseen permanent remediation measures that are currently under construction are briefly presented

Numerical simulation of debris flows triggered from the Strug rock fall source area, W Slovenia

The Strug landslide was triggered in December 2001 as a rockslide, followed by a rock fall. In 2002, about 20 debris flows were registered in the Kosec village; they were initiated in the Strug rock fall source area. They all flowed through the aligned Brusnik channel, which had been finished just before the first debris flow reached the village in April 2002. Debris flow events were rainfall-induced but also governed by the availability of rock fall debris in its zone of accumulation. After 2002 there was not enough material available for further debris flows to reach the village. Nevertheless, a decision was reached to use mathematical modeling to prepare a hazard map for the village for possible new debris flows. Using the hydrological data of the Brusnik watershed and the theological characteristics of the debris material, 5 different scenarios were defined with the debris flow volumes from 1000 m(3) to a maximum of 25 000 m(3). Two mathematical models were used, a one-dimensional model DEBRIF-1D, and a two-dimensional commercially available model FLO-2D. Due to the lack of other field data, data extracted from available professional films of debris flows in 2002 in the Kosec village were used for model calibration. The computational reach was put together from an 800-m long upstream reach and 380-m long regulated reach of the Brusnik channel through the village of Kosec. Both mathematical models have proved that the aligned Brusnik channel can convey debris flows of the volume up to 15 000 m(3). Under the most extreme scenario a debris flow with 25 000 m3 would locally spill over the existing levees along the regulated Brusnik channel. For this reason, additional river engineering measures have been proposed, such as the raising of the levees and the construction of a right-hand side sedimentation area for debris flows at the downstream end of the regulated reach

Geodetic measurements in tunnel Šentvid

This article describes the geodetic monitoring of the\ud impact that the tunnel excavations have on the rock\ud mass at the tunnel face in the Šentvid tunnel. In the\ud preliminary phase, an exploratory gallery was built\ud almost along the main tunnel axis to collect geological,\ud tectonic zone and other relevant data. The exploratory\ud gallery is now being used for geodetic and other\ud monitoring of the impact of tunnel excavations on the\ud surrounding rock mass. Before the beginning, methods\ud of point and station point stabilization, and a\ud measurement method were chosen. Thus, the chosen\ud methods are the method of 3D inner intersection with\ud adjustment of redundant observation for station point\ud determination, and the polar method for calculating\ud 3D coordinates of detail points. The method of\ud determination of station point was chosen because of\ud the far reaching influence that the tunnel excavations\ud have on rock mass behaviour at the tunnel face