Engineering Techniques for Stabilizing Landslides - Research Paper Example

Engineering techniques for stabilizing landslides: Introduction: Land sliding is the downhill movement of the soil that takes place because of unstable ground. The instability in ground may either be caused by natural disturbance in the form of earthquakes or heavy rains, or manual intervention in the form of construction. Alteration of ground geometry without adequate understanding of the soil dynamics and equilibrium induces instability in it, and it may slide any time to release the stresses in order to regain its lost equilibrium. The different techniques for controlling landslide are case sensitive and do not necessarily prove right for all conditions or types of soil. Some techniques have even been abandoned because of their insufficient tendency to control land sliding. Review of the techniques: Techniques to reduce the verisimilitude of land sliding include but are not limited to reprofiling the geometry of soil surface, draining the water from soil or lowering the water table, anchoring the soil by natural means like growing trees or artificially and providing structures to support the load like retaining walls etc (Popescu and Sasahara). Anchoring and restraining are in-place stabilization techniques that tend to limit the susceptibility of sliding without altering the profile of soil. Each of them is discussed below: Excavation: This technique involves drainage of the land. In this technique, the suspected land is excavated in order to make room for the drains that are installed to remove excess water from the soil. Once the subsurface drains are laid, the soil is backfilled so as to achieve a stable slope. This technique is frequently employed to restrain the soil movement. Anchoring: It is not always possible to remove or excavate the soil for laying drainage pipes because of dense construction or limitation of space that renders it impossible to move in the excavation equipment. In such circumstances, in-place stabilization techniques are made use of in order to control land sliding. To achieve in-place stabilization, retaining walls, pilings, and other nailing procedures are used. Retaining walls are supporting cantilever walls that are designed in a way that they can adequately stand the pressure of soil. Their reinforcement adequately takes the moment induced by the lateral loading. Its base resists overturning of the retaining wall as well as sliding. Piling: Drill piers and piles reinforce the soil in order to provide it with added stability because of congestion. They also do not require much space to be drilled in the soil, hence are suitable for areas with limited space. Piles are driven in the unstable soil to the depth that they ultimately rest upon or even protrude a bit in the stable layer underneath. As the piers are drilled into the soil, they produce shear resistance in the soil along their individual surfaces. However, piles are very costly to be installed given the complexity of operation. In order to reduce the size of piers, they may be used together with tie-back anchors which further adds to the cost of operation. Selection criteria for landslide prevention technique: The following figure explains the requirement of application of different slope stabilization techniques as per the condition of soil.  Fig: Selection criteria for landslide stabilization techniques (FAO) Limitations: All of the mechanical stabilization techniques require comprehensive site investigations with particular reference to mechanics of the soil, its composition, type and ground water table. Soil nailing design requires considerable understanding of the properties of soil and the geometry of area. Such designs are hence, very cumbersome to be made. Empirical designs have been conventionally employed, though they are not appreciated much because they do not include sufficient provision of the factor of safety (Carte and Knight). In a vast majority of cases, the most effective design can not be achieved because of limitation of experience of the design engineers. Also, little maintenance is provided once the technique has been used. These techniques require formulation and installation of structures that proves very costly. Therefore, use of mechanical techniques that require installation of stabilizing structures should be taken as the last resort. Retaining walls require extensive excavation in order for the heavy foundations to be laid. This increases the susceptibility of land sliding temporarily as the existing restraints have to be removed so that retaining wall can be placed. In order to achieve temporary control, tie-back anchors are often employed. However, space or economic constraints often impose difficulty in their employment and hence, the placement of retaining walls can itself cause land sliding. The most cost effective and environment friendly technique to make the land stabilized against sliding is thick vegetation. The roots of plants serve as reinforcement for the disintegrated soil particles and the susceptibility of land to slide decreases considerably. How we know what we know? The jargon of literature we have regarding methods to prevent land sliding comes from years of research into the field. The techniques have been applied a large number of times and the results have been as intended. That tells us that the techniques we know are valid and functional. Many nations have big contributions in spreading knowledge about such techniques. Particularly, Japanese Engineers have come up with many of them. We believe Japanese engineering techniques for stabilizing slopes because Japan has always been quite susceptible to earthquakes. Much of land sliding conventionally takes place as a result of the earthquakes. Therefore, there is no wonder that Japanese engineers would have identified these techniques after having applied them in a number of occasions and places in their own land. That is why, they are often consulted for stabilizing extensive areas against sliding. For example, Japanese engineers were invited to give their suggestion on the stabilizing technique in The Point in Rancho Bernardo area in San Diego, US that was about 14.5 acre commercial development land (GiB). After comprehensive site investigations, ground anchors and buried structural beams were installed. Facts, theories and hypotheses: We all know that knowledge in any field is generated through research. Research starts with a hypothesis. After the research has been conducted, the hypothesis is either rejected or accepted. In either case, a theory is formulated. Once, the results upon application of the theory are acceptable and help remove the trouble, the theory is justified and becomes a fact. Likewise, all engineering techniques for slope stabilization and land sliding prevention have been validated by practical application and evaluation. After years of application and successful results, we can render them as facts. Though, it should be remembered that certain techniques are not suitable for application ever where. Technique for prevention of land sliding must be chosen as per the soil mechanics, availability of funds and location of the area. Data gaps; Tsunami hypothesis: There is considerably less information regarding underwater land sliding as compared to exposed land sliding. A number of theories have been put forward to explain the causes of Tsunami catastrophe that had occurred few years ago. The difficulty in realizing the true cause of underwater land sliding is because of the limitations of technology. Land sliding fundamentally happens because of geological upsets. However, it is very difficult to maneuver geological conditions as per the requirements of research. Wiegel (1955 cited in Watts) had performed experiment on landslide tsunamis, yet the research made use of nuclear bombs instead of natural geological events. Knowledge we have till now regarding tsunami land sliding has grey areas, though more research is in progress to reveal the underlying causes. We can say that open landslide prevention techniques are based upon facts and underwater landslide prevention techniques are based upon doubtable theories and hypotheses. Works cited: Carte, Joseph D. and Knight, John R. System and method for stabilizing landslides and steep slopes. 2010. Web. 13 Dec. 2010. . Food and Agriculture Organization of the United Nations. Chapter 5: Surface and slope protective measures. n.d. Web. 15 Dec. 2010. . Gib. The largest landslide stabilization project in California. 2009. Web. 15 Dec. 2010. Popescu, Mihail E. and Sasahara, Katsuo. Engineering Measures for Landslide Disaster Mitigation. n.d. Web. 13 Dec. 2010. . Watts, Philips. Some opportunities of the landslide tsunami hypothesis. N.d. 15 Dec. 2010. < http://www.appliedfluids.com/SciTsuHaz.pdf>. Read More