Geotechnical Issues In Engineering - Research Paper Example

Insert the name of your institution here Insert course name here Insert course code here Insert the name of your tutor here Insert your name here Insert date of submission here Table of Contents 1.0.Introduction 2 2.0.Background studies on causes of landslides 4 3.0.Procedures of Assessing Landslide Causes 5 3.1.Event Tree Analysis (ETA) 5 3.2.Free Tree Analysis (FTA) 6 3.3.Cause Consequence Analysis 6 3.4.Multi-risk analysis 6 4.0.Review of Major Causes of Landslide 7 5.0.Human Related Errors Causing Landslide 9 6.0.Conclusion 11 7.0.References 13 A Review of the Cause of Significant Geo-environmental Disaster---A case of Landslide 1.0. Introduction Based on recent instances of landslide, geo-mechanical process considers everything in the ground as causative agent until it is engineered and quantified. It has also emerged that assessment and review of the cause of landslide in the ground is a critical determinant in the success of major geotechnical engineering projects and significant geo-environmental disasters. However, for this process to be conceptualized there is need for comprehensive investigation and assessment of all possible hazards associated with landslides. Within the scope of geotechnical engineering Takara et al. (2010) defined identification of causes of landslide as a systematic process of recognizing, planning, analyzing, monitoring and responding to cases of landslide induced hazards like debris and dam-break floods and surges giving examples of reservoir landslides or submarines. As geotechnical engineering continues to be wider, specific causes of different types of landslides have become priority (Hungr et al., 2014). For instance, there has been need to assess and mitigate causes associated with dam-break floods and surges. Dam-break floods and surges in particular have been associated with disasters and engineering failures for long. This study therefore focuses on different categories of landslides and possible source landslide induced hazards including recently witnessed giant landslides. Literature on the recent causes of landslides have tended to focus on secondary hazards such as debris without giving consideration to issues such as heavy rainfalls or earthquakes in different geological environments. This report seeks to contribute to the already existing knowledge on causes of such disasters when it comes to geo-mechanical issues and geotechnical engineering at large. It will achieve the goal by investigating and laying out major issues that have resulted in the recently witnessed landslides citing examples of such cases. This report recognizes that existing literatures have assessed factors such as earthquake-induced landslides and failure mechanisms of gravitational issues as main causes of landslides but these literatures failed to link them as geo-environmental disasters. It further highlights practical examples that helps to show the value of getting additional geotechnical information that reduce such causes. 2.0. Background studies on causes of landslides Studies agree that probabilistic cause assessment is one of the most widely-used approaches when it comes to finding causes of landslides (Xu et al. 2012; Malehmir et al. 2013). However, there is need to assess how the approach can be effective when it comes to fragile geological environment, rugged and steep terrain and high seismic activities. This report attempts to integrate mechanisms, prediction theory, understanding and warning systems landslides, burst, large deformation of major underground geotechnical engineering, or water inrush. Bednarczyk (2008) in his research noted that contemporary geotechnical practices relating to soil lack optimal design methodology when it comes to underground engineering under conditions such as karst, high stress, weak rock or high water pressure. These are variables that have been argued to be acting as major causes when it comes to geotechnical engineering. In as much, there seems to be a gap between these risks factors and holistic strategies of assessing and managing them. For conceptualization of different causes of landslides within the scope of geotechnical engineering, this report briefly considers definitions of different terms. To begin with, the definition given by Australian Geo-mechanics Society Subcommittee on landslide causes and management will be adopted for analysis and reporting. However, this definition differs marginally and significantly from other scholars such as Hervás & Bobrowsky (2009). In accordance with the committee, landslide is the movement of debris, rock or earth along the slope. The definition thus indicates that the process will result in the effect of uncertainty on objectives and a risk source as an element which alone or in combination has the potential to give rise to a risk. Consequently, magnitude of landslide related or geotechnical risks has been defined as risks or group of related risks that can be expressed in terms of the group of consequences and their chances of occurring (Hervás and Bobrowsky, 2009; Bednarczyk, 2008). A review of landslides therefore means providing a guiding principle and model that helps in the identification of hazards that leads to the movement of debris, rock or earth along the slope. In conclusion, the report therefore recognizes that within the scope of geotechnical engineering, the cause analysis, cause identification and cause evaluation are steps that sum up the process of cause assessment. However, in the process of investigating causes as will be outlined, there are differing approaches, sometimes differing in detail as they have been used by other organization, countries or individual researches (for instance, the International Tunneling Association used a different approach as outlined by (Hervás and Bobrowsky, 2009). 3.0. Procedures of Assessing Landslide Causes These procedures have been based on literatures reviewed, disasters that have been experienced in the past and more importantly, personal view of issues that have been reported with regard to geotechnical engineering. 3.1. Event Tree Analysis (ETA) Taking a case of Longxi and Zana landslides which took place along Longyangxia hydropower station, Lundström et al. (2009) reported that ETA will help in drawing a systematic mapping of events that are realistic as it has the potential of detecting a major incident. Causes identification will thus incorporate ETA since the system provides numerical estimates of the likelihoods of occurrence of the component landslide and the escalated event. 3.2. Free Tree Analysis (FTA) Considering records of landslide events held by Pittwater Council, it can be noted that one of the critical aspect of landslide cause assessment is to integrate Free Tree Analysis (FTA). FTA identifies, quantifies and represents, in tabular and diagrammatic form, the failures and faults that can lead to landslides. Recent research has indicated that FTA is an effective tool in the assessment of landslide causes specifically in the instances where there are slope movement featured by the lateral extension of a more rigid mass of soil over a deforming the underlying materials. This report therefore suggests the procedures especially in cases where there are slope movements by which there are displacements of materials less or more coherently. 3.3. Cause Consequence Analysis This has been viewed as the combination of the above processes (ETA and FTA). It is a method showing the relationship between the cause of a given landslide and the outcome and or consequence of the occurrence. According to Crosta & Frattini (2008) this method is effective when the failure or slide logic is simple since diagrammatic representation of ETA or FTA has been seen to be complex. 3.4. Multi-risk analysis This method has been included due to its usefulness in the assessment of multi-risks associated with different types of soils. Taking a case of gravity-based structure, Crosta & Frattini (2008) noted that gravity-based structure can be more vulnerable to liquefaction of given layer compared with a piled foundation which has the ability of penetrating well below the liquefiable strata. This now provides a good example where multi-risk analysis has been adopted as a process that can help in understanding of the causes of landslides as it was the case with Bayview and Avalon. On the other hand, Baum & Godt (2010) define multi-risk analysis as probable computational method used in the calculation of risks involving multiple statistically related hazards or independent risks that are each dealt with as stochastic variables. What Baum & Godt (2010) suggest is that as a model, multi-risk analysis gives a method for understanding uncertainty and perhaps used in the estimation of chances of occurrence of landslides. Conceptualizing this model within the scope of the study is that there are cases where projects experience overruns as there have been no site investigations for occurrence of slides. Therefore multi-risk analysis as a model has been adopted as a method that can be used in understanding major causes of landslides caused in the following categories; Falls Topples Lateral spreading and Flows 4.0. Review of Major Causes of Landslide Factors related to the cause of slides significantly depend on regions. However, researches have agreed that gravity, geology, groundwater, weather, human activities and wave actions are major causes of slides (Cascini et al., 2009; Baum & Godt, 2010). Taking a case of debris flow or rapid mass movement where loose soils matter combine with water and entrained air to form slurry, landslides have been reported to able to occur as river bluffs or ground failure that may accompany building excavations or mine waste piles. There are also cases of underwater landslides which involve small slope gradient and areas of low relief in reservoirs and lakes or offshore marine settings (Cascini et al., 2009). On a different perspective, the cause of major landslides involves sliding planes. Baum & Godt (2010) note that the breakthrough of the sliding plane is represents progressive destruction that ultimately results in landslide. Going by recent investigation on landslides such as Soldan Khad and Alma-Ata debris flow, slides are sometimes caused by deep toppling and locking-section dominated failures. However, Yalcin (2011) gave a different view arguing that the processes of large-scale landslides are grouped differently: retaining wall collapse, sliding-tension, soft base collapse, cracking-sharing and toppling and dislocation shifting focus from debris flow as one of the issues associated with landslides. He added that these groups occur under a given soil structure conditions which have unique failure mechanism. Jongmans et al. (2009) assessed geological factors and its relationship with landslides. Their research noted that where there is a geologic setting there will be gravels and permeable sands rising above impermeable layers of clay and silt, or bedrock. This will lead to water seeping downward through the upper materials accumulating on the top of the underlying units thus forming a layer of weakness. This view however is different from the research by Baum & Godt (2010) who noted that when it comes to geological factors, landslides are formed when slopes around the plateau are underlain by interbedded series of siltstone, laminite, quartz and sandstone of the Narrabeen Formation which exhibit strongly developed bedding and jointing. While taking a case of Thangi slide, Gratchev and Towhata (2010) found that seismic or earthquake activities are associated with landslides in different parts of world. Earthquakes come as a result of plate tectonics and whenever this happens, the soil that covers it moves with it. When there is occurrence of earthquake on regions with steep slopes, there will be slipping of soils causing landslides. The sudden collapse of strato volcanoes have been linked with landslides more so during wet conditions (Quinn et al., 2010). Quinn et al. (2010) cited a case of the magma which moved high into the cone of Mount St. Helens. This led to the huge landslide which removed the summit, the bulge and the inner core of the mountain thus triggering a series of massive landslides. Yalcin (2011) later explained it differently arguing that the strato volcano conditions often prevail after the eruptions that sweep vegetation over areas and spread loose volcanic soils over the landscape. During subsequent rainy seasons, rivers will erode the new deposits thus generating lahars. 5.0. Human Related Errors Causing Landslide This section identifies some of the causes associated with geo-mechanical engineering practices. It is significant to note that the recognition of these causes, including underground soils come as a result of errors or uncertainty. Some of these errors or uncertainties have been discussed in other studies as; Omissions Model uncertainty Random or systematic measurement errors Load uncertainty and Temporal variability and inherent spatial This report finds that some common causes of landslide are associated with mass classification schemes in the design of underground excavations. Basically, this will always come in two groups. The first one is the error intrinsic to the classification of scheme used. This has been broadly classified as errors of super-fluousness, errors of taxonomy linked with the requirement to select a given classification rating value for a geo-mechanical property and errors related to omissions during engineering projects (Yalcin, 2011). The second group of errors leading to landslide includes errors of ignoring variability, errors of convenience, and errors of ignoring uncertainty. Taking a case of Pacific Highway upgrade geotechnical inspection, there were errors committed due to convenience and the group that was tasked to inspect the project discovered that there were risks that could lead to landslide (Hungr et al. 2014). Engineers failed to design parameters to be used for RE wall design, wall and culvert foundations, ground investigation for concrete batching plant, and earthworks requirements for reinstatement of contamination spill. Relating this case with multi-risk analysis model as presented earlier, the cause of landslide is therefore a failure to act on ground investigation report, ground investigation for concrete batching plant and earthworks requirements. This report further finds that poor probabilistic risk assessment was to blame for Khait landslide (Hungr et al., 2014). Though Hungr et al. (2014) found that Khait landslide was as a result of soil slides which transformed into large granite and loess debris avalanche. Engineers who were working within the site failed in their risk evaluation thus triggering the debris (Takara et al., 2010). Just as it was the case with Hurstville Railway Line of the Sydney Rail Transport network, risk evaluation will mean carrying out comprehensive analysis and investigation of all stages in the construction of projects such as railway line so that any activity that may cause slides would be avoided. In such cases, Takara et al., (2010) suggest the adoption of Free Tree Analysis and 3D numerical modeling as it will ensure that assessment of issues such as stresses, loads or groundwater pressure are given considerations. However, it is important to note that when integrating Free Tree Analysis and 3D numerical modeling in averting landslides then risks carried out in engineering projects may be at best, semi-quantifiable or qualitative. This means that strength of soil will be considered as the shear strength. In summary, this report encourages the adoption of 3D modeling in in avoiding errors that ultimately leads to landslides as it enables engineers to optimize structural design as compared with the 2D which has been seen to be resulting in substantial project wastage. Another error committed by engineers is the estimation of activity risk. According to Muntohar & Liao (2009), estimation of activity risk will involve using a combination of different methods. Taking a case study of ground investigation which was conducted during Canberra International Airport Hotel, one of the critical errors committed was failing to give consideration to rock related activities or hazards (Solberg et al., 2009). Rocks and soils are connected therefore interference with the arrangement of rocks leads to massive slides. This was the case with Vaiont Reservoir landslide which came as a result of poor estimation of activity risk in the Vaiont Dam (Solberg et al., 2009). 6.0. Conclusion As already noted, landslides are caused by different factors---both natural and human triggered or engineering problems. However, this report notes that some of the major causes reviewed do not exhaust the list. Therefore any technique chosen in the assessment of the causes should not be a combination of strategies or models that will enable engineers to identify possible causes and their outcomes but provide a model assessing currently trends in landslides. Literatures reviewed have also shown that geotechnical assessment of causes of landslides is not perfect way in understanding all causative agents when it comes to landslides. Recent cases such as Hurricane Mitch that took place in Guatemala show that there is need for a model that will predict and assess all factors causing slides. This will act as a foundation from which engineers will be able to construct even-incident as well as cause-consequence-frequency relationships. Citing cases where engineers will be required to do contamination assessment of highway upgrade for instance, this report suggests that it will be prudent that the process of geotechnical cause identification as well as assessment follow well established format or system that ensures that all possible activities, situations or scenarios are identified and analyzed in accordance with the magnitude of the slides and type of soil in the region associated. 7.0. References Baum, R. L., & Godt, J. W. (2010). Early warning of rainfall-induced shallow landslides and debris flows in the USA. Landslides, 7(3), 259-272. Bednarczyk, Z. (2008). Landslide geotechnical monitoring network for mitigation measures in chosen locations inside the SOPO Landslide Counteraction Framework Project Carpathian Mountains, Poland. In The First World Landslide Forum, Tokyo International Consortium of Landslides (ICL), United Nations University Tokyo (UNU) (pp. 71-75). Cascini, L., Cuomo, S., Pastor, M., & Sorbino, G. (2009). Modeling of rainfall-induced shallow landslides of the flow-type. Journal of Geotechnical and Geoenvironmental Engineering. Crosta, G. B., & Frattini, P. (2008). Rainfall‐induced landslides and debris flows. Hydrological processes, 22(4), 473-477. Gratchev, I., & Towhata, I. (2010). Geotechnical characteristics of volcanic soil from seismically induced Aratozawa landslide, Japan. Landslides, 7(4), 503-510. Hervás, J., & Bobrowsky, P. (2009). Mapping: inventories, susceptibility, hazard and risk. In Landslides–Disaster Risk Reduction (pp. 321-349). Springer Berlin Heidelberg. Hungr, O., Leroueil, S., & Picarelli, L. (2014). The Varnes classification of landslide types, an update. Landslides, 11(2), 167-194. Jongmans, D., Bievre, G., Renalier, F., Schwartz, S., Beaurez, N., & Orengo, Y. (2009). Geophysical investigation of a large landslide in glaciolacustrine clays in the Trièves area (French Alps). Engineering geology, 109(1), 45-56. Lundström, K., Larsson, R., & Dahlin, T. (2009). Mapping of quick clay formations using geotechnical and geophysical methods. Landslides, 6(1), 1-15. Malehmir, A., Bastani, M., Krawczyk, C. M., Gurk, M., Ismail, N., Polom, U., & Persson, L. (2013). Geophysical assessment and geotechnical investigation of quick-clay landslides–a Swedish case study. Near Surface Geophysics, 11(3), 341-350. Muntohar, A. S., & Liao, H. J. (2009). Analysis of rainfall-induced infinite slope failure during typhoon using a hydrological–geotechnical model. Environmental geology, 56(6), 1145-1159. Quinn, J. D., Rosser, N. J., Murphy, W., & Lawrence, J. A. (2010). Identifying the behavioural characteristics of clay cliffs using intensive monitoring and geotechnical numerical modelling. Geomorphology, 120(3), 107-122. Solberg, I. L., Hansen, L., Rønning, J. S., Haugen, E. D., Dalsegg, E., & Tønnesen, J. F. (2012). Combined geophysical and geotechnical approach to ground investigations and hazard zonation of a quick clay area, mid Norway. Bulletin of Engineering Geology and the Environment, 71(1), 119-133. Takara, K., Yamashiki, Y., Sassa, K., Ibrahim, A. B., & Fukuoka, H. (2010). A distributed hydrological–geotechnical model using satellite-derived rainfall estimates for shallow landslide prediction system at a catchment scale. Landslides, 7(3), 237-258. Xu, C., Xu, X., Dai, F., Xiao, J., Tan, X., & Yuan, R. (2012). Landslide hazard mapping using GIS and weight of evidence model in Qingshui river watershed of 2008 Wenchuan earthquake struck region. Journal of Earth Science, 23, 97-120. Yalcin, A. (2011). A geotechnical study on the landslides in the Trabzon Province, NE, Turkey. Applied Clay Science, 52(1), 11-19. Read More

However, there is need to assess how the approach can be effective when it comes to fragile geological environment, rugged and steep terrain and high seismic activities. This report attempts to integrate mechanisms, prediction theory, understanding and warning systems landslides, burst, large deformation of major underground geotechnical engineering, or water inrush. Bednarczyk (2008) in his research noted that contemporary geotechnical practices relating to soil lack optimal design methodology when it comes to underground engineering under conditions such as karst, high stress, weak rock or high water pressure.

These are variables that have been argued to be acting as major causes when it comes to geotechnical engineering. In as much, there seems to be a gap between these risks factors and holistic strategies of assessing and managing them. For conceptualization of different causes of landslides within the scope of geotechnical engineering, this report briefly considers definitions of different terms. To begin with, the definition given by Australian Geo-mechanics Society Subcommittee on landslide causes and management will be adopted for analysis and reporting.

However, this definition differs marginally and significantly from other scholars such as Hervás & Bobrowsky (2009). In accordance with the committee, landslide is the movement of debris, rock or earth along the slope. The definition thus indicates that the process will result in the effect of uncertainty on objectives and a risk source as an element which alone or in combination has the potential to give rise to a risk. Consequently, magnitude of landslide related or geotechnical risks has been defined as risks or group of related risks that can be expressed in terms of the group of consequences and their chances of occurring (Hervás and Bobrowsky, 2009; Bednarczyk, 2008).

A review of landslides therefore means providing a guiding principle and model that helps in the identification of hazards that leads to the movement of debris, rock or earth along the slope. In conclusion, the report therefore recognizes that within the scope of geotechnical engineering, the cause analysis, cause identification and cause evaluation are steps that sum up the process of cause assessment. However, in the process of investigating causes as will be outlined, there are differing approaches, sometimes differing in detail as they have been used by other organization, countries or individual researches (for instance, the International Tunneling Association used a different approach as outlined by (Hervás and Bobrowsky, 2009). 3.0.

Procedures of Assessing Landslide Causes These procedures have been based on literatures reviewed, disasters that have been experienced in the past and more importantly, personal view of issues that have been reported with regard to geotechnical engineering. 3.1. Event Tree Analysis (ETA) Taking a case of Longxi and Zana landslides which took place along Longyangxia hydropower station, Lundström et al. (2009) reported that ETA will help in drawing a systematic mapping of events that are realistic as it has the potential of detecting a major incident.

Causes identification will thus incorporate ETA since the system provides numerical estimates of the likelihoods of occurrence of the component landslide and the escalated event. 3.2. Free Tree Analysis (FTA) Considering records of landslide events held by Pittwater Council, it can be noted that one of the critical aspect of landslide cause assessment is to integrate Free Tree Analysis (FTA). FTA identifies, quantifies and represents, in tabular and diagrammatic form, the failures and faults that can lead to landslides.

Recent research has indicated that FTA is an effective tool in the assessment of landslide causes specifically in the instances where there are slope movement featured by the lateral extension of a more rigid mass of soil over a deforming the underlying materials. This report therefore suggests the procedures especially in cases where there are slope movements by which there are displacements of materials less or more coherently. 3.3.

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