Is it possible to alter the slope condition

Instead, it broke into pieces and rebounded into the air. Residents in Untertal, on the opposite side of the valley from the slide, saw the mass of rebounded rock coming at the them and ran uphill. But the mass of rock continued up the walls of the valley and buried them. The avalanche killed people.

The valley runs along the bottom of a geologic structure called a syncline, wherein rocks have been folded downward and dip into the valley from both sides see cross section below. The rocks are mostly limestones, but some are intricately interbedded with sands and clays. These sand and clay layers form bedding planes that parallel the syncline structure, dipping steeply into the valley from both sides. Fracture systems in the rocks run parallel to the bedding planes and perpendicular to bedding planes.

The latter fractures had formed as a result of glacial erosion which had relieved pressure on the rocks that had formed deeper in the Earth. Some of the limestone units have caverns that have been dissolved in the rock due to chemical weathering by groundwater.

Furthermore, the dam site was built near an old fault system. During August and September, , heavy rains drenched the area, rasing the water table and adding weight to the rocks above the dam. On October 9, at P. The slide mass was 1. As the slide moved into the reservoir it displaced the water, forcing it meters above the dam and into the village of Casso on the northern side of the valley. Subsequent waves swept up to meters above the dam.

Although the dam did not fail, the water rushing over the dam swept into the villages of Longorone and T. Vaiont, killing 2, people. Waves also swept up the reservoir where they first bounced off the northern shore, then back toward the Pineda Peninsula, and then back up the valley slamming into San Martino and killing another people.

The debris slide had moved along the clay layers that parallel the bedding planes in the northern wall of the valley. A combination of factors was responsible for the slide.

First filling of the reservoir had increased fluid pressure in the pore spaces and fractures of the rock. Second, the heavy rains had also increased fluid pressure and also increased the weight of the rock above the slide surface.

After the slide event, parts of the reservoir were filled up to m above the former water level, and even though the dam did not fail, it became totally useless.

This event is often referred to as the world's worst dam disaster. In this area the rocks have been folded into a synclinal structure with rock layers dipping gently toward the Pacific Ocean.

Rocks near the surface consist of volcanic ash that has been altered by chemical weathering to an expanding type clay called bentonite. Below these altered ash layers are shales that are interbedded with other thin volcanic ash layers that have been similarly altered to bentonite clay. The area had the appearance of an earth flow, with a very hummocky topography with many enclosed basins filled with lakes.

Prior to the s the area had been used for farming. In the s demand for ocean views led to the development of the area as an upscale suburb. But, no sewer system was available, so wastes were put into the ground via septic tanks. In the area began moving down slope toward the ocean. Rates of movement were fastest several months after the end of the winter rainy season and slowest during the summer dry season. In the next three years the earthflow moved as much as 20 meters, but in the processes the expensive homes built on the flow became uninhabitable.

Movement was caused by a combination of wave erosion along the coast removing some the mass resisting flow, added water due to the disposal of wastes, watering of lawns, and rainfall causing the bentonite clays to expand and weaken, and by the added weight of development on top of the flow. Property owners looked desperately for someone to sue, and eventually won a suit against the county of Los Angeles who had added fill dirt to build a road into the development note that since the property owners could not sue themselves, nor could they sue the clay layers responsible for the movement they found the only agency with deep pockets that was available.

Examples - We have previously discussed the mudflows and debris avalanche produced by the eruption of Mount St. Helens, and the devastating mudflows that killed 23, people in Armero that resulted from an eruption of Nevado del Ruiz volcano in Columbia.

Changes in Slope Strength. Anything that acts to suddenly or gradualy change the slope strength can also be a triggering mechanism. For example, Weathering creates weaker material, and thus leads to slope failure. Vegetation, holds soil in place and slows the influx of water. Trees put down roots that hold the ground together and strengthen the slope. Removal of tress and vegetation either by humans or by a forest fire, often results in slope failures in the next rainy season.

Assessing and Mitigating Mass Movement Hazards. As we have seen mass movement vents can be extremely hazardous and result in extensive loss of life and property.

But, in most cases, areas that are prone to such hazards can be recognized with some geologic knowledge, slopes can be stabilized or avoided, and warning systems can be put in place that can minimize such hazards. Hazard Assessment. If we look at the case histories of mass movement disasters discussed above, in all cases looking at the event in hindsight shows us that conditions were present that should have told us that a hazardous condition existed prior to the event. Because there is usually evidence in the form of distinctive deposits and geologic structures left by recent mass movement events, it is possible, if resources are available, to construct maps of all areas prone to possible mass movement hazards.

More detailed state and local maps can be found and most are available on the internet. Planners can use such hazards maps to make decisions about land use policies in such areas or, as will be discussed below, steps can be taken to stabilize slopes to attempt to prevent a disaster. Short-term prediction of mass movement events is somewhat more problematical. For earthquake triggered events, the same problems that are inherent in earthquake prediction are present.

Slope destabilization and undercutting triggered events require the constant attention of those undertaking or observing the slopes, many of whom are not educated in the problems inherent in such processes. Mass movement hazards from volcanic eruptions can be predicted with the same degree of certainty that volcanic eruptions can be predicted, but again, the threat has to be realized and warnings need to be heeded.

Hydrologic conditions such as heavy precipitation can be forecast with some certainty, and warnings can be issued to areas that might be susceptible to mass movement processes caused by such conditions. Still, it is difficult of know exactly which hill slope of the millions that exist will be vulnerable to an event triggered by heavy rainfall.

Some warning signs can be recognized individual by observations of things around you:. All slopes are susceptible to mass movement hazards if a triggering event occurs. Thus, all slopes should be assessed for potential mass movement hazards. Mass movement events can sometimes be avoided by employing engineering techniques to make the slope more stable. Among them are:.

Some slopes, however, cannot be stabilized. In these cases, humans should avoid these areas or use them for purposes that will not increase susceptibility of lives or property to mass movement hazards. Examples of questions on this material that could be asked on an exam. Natural Disasters. Gravity The main force responsible for mass movement is gravity.

The Role of Water Although water is not always directly involved as the transporting medium in mass movement processes, it does play an important role. When the material becomes saturated with water, the angle of repose is reduced to very small values and the material tends to flow like a fluid.

This is because the water gets between the grains and eliminates grain to grain frictional contact. Groundwater exists nearly everywhere beneath the surface of the earth. It is water that fills the pore spaces between grains in rock or soil or fills fractures in the rock. The water table is the surface that separates the saturated zone below, wherein all pore space is filled with water from the unsaturated zone above.

Changes in the level of the water table occur due changes in rainfall. The water table tends to rise during wet seasons when more water infiltrates into the system, and falls during dry seasons when less water infiltrates. Such changes in the level of the water table can have effects on the factors 1 through 5 discussed above. Another aspect of water that affects slope stability is fluid pressure. It should spread out over a wide area, forming a pile with a slope of only a few degrees.

Water will also reduce the strength of solid rock, especially if it has fractures, bedding planes, or clay-bearing zones. One of the hypotheses advanced to explain the Hope Slide is that the very cold conditions that winter caused small springs in the lower part of the slope to freeze over, preventing water from flowing out.

It is possible that water pressure gradually built up within the slope, weakening the rock mass to the extent that the shear strength was no longer greater than the shear force. Water also has a particular effect on clay-bearing materials. All clay minerals will absorb a little bit of water, and this reduces their strength.

The smectite clays such as the bentonite used in cat litter can absorb a lot of water, and that water pushes the sheets apart at a molecular level and makes the mineral swell. Smectite that has expanded in this way has almost no strength; it is extremely slippery. And finally, water can significantly increase the mass of the material on a slope, which increases the gravitational force pushing it down. In the situation shown in Figure In the previous section, we talked about the shear force and the shear strength of materials on slopes, and about factors that can reduce the shear strength.

Shear force is primarily related to slope angle, and this does not change quickly. But shear strength can change quickly for a variety of reasons, and events that lead to a rapid reduction in shear strength are considered to be triggers for mass wasting.

An increase in water content is the most common mass-wasting trigger. This can result from rapid melting of snow or ice, heavy rain, or some type of event that changes the pattern of water flow on the surface. Rapid melting can be caused by a dramatic increase in temperature e. Heavy rains are typically related to storms. Changes in water flow patterns can be caused by earthquakes, previous slope failures that dam up streams, or human structures that interfere with runoff e.

An example of this is the deadly debris flow in North Vancouver Figure The failure took place in an area that had failed previously, and a report written in recommended that the municipal authorities and residents take steps to address surface and slope drainage issues. Little was done to improve the situation. In some cases, a decrease in water content can lead to failure. This is most common with clean sand deposits e. Freezing and thawing can also trigger some forms of mass wasting.

More specifically, the thawing can release a block of rock that was attached to a slope by a film of ice. One other process that can weaken a body of rock or sediment is shaking. The most obvious source of shaking is an earthquake, but shaking from highway traffic, construction, or mining will also do the job. Soil chemical indicators can be identified through specified considerations based on the existence of certain amount of soil colloids whereas physical indicators can be determined by exploring on certain physical appearances and water-holding capacity of the soils.

Biological indicators are determined by identifying the amount and mass of microorganisms through concentrations of biogeochemical responses or determining the populations of microorganisms in slope soil. The soils of the humid tropic such as highly weathered soil Oxisols and sandy soil have been observed to be problematic, especially with regard to their fertility.

Reviews of research work on current slope soil development in Malaysia, Thailand and Indonesia have significantly shown that such fertility constraints could be improved. Poor fertility of the saprolite is more complex and should be imposed with serious enhancement and management activities.

Furthermore, like all acid soils of the humid tropics, Oxisols soils are low in pH value which causes many potential associating problems, including H, Al, and Mn toxicity, Ca deficiency, low CEC, P fixation and low microbial activities [ 9 ]. The shallow topsoil is highly vulnerable to erosion and if it is not managed properly especially after the process of clearing the vegetation on top of soil surface, it can slowly lose its original fertility and beneficial physical properties which finally will cause shallow slope failure.

Several reviews on the characteristics and management of these soils did not take into account the effect of terracing in exposing saprolites or C horizon. With the surface soils and subsoils already being considered problematic, one could only imagine what kind of impact the saprolites pose to soil fertility. As for unstable soil sample, only slope that collapsed abruptly were collected whereas for stable sample collected from the slope that fully covered by vegetation Figure 1.

Therefore, a total of soils samplings were collected from those two different localities in Peninsular Malaysia. Auger set was used to collect soil sample at the designated area and soil samples were collected in the depth of 30 cm from the surface.

Then, the soil samples were stored in plastic bag and labelled for further analysis. Condition and appearance of stable and unstable slopes soil. The collected samples were air-dried, homogenised and sieved to pass a 2 mm mesh sieve for chromaticity variables analysis by CIELAB spectrophotometer. By using a CIELAB spectrophotometer analysis, 10 g of samples were accurately weighed by using analytical balance and was transferred into polystyrene cell and was placed horizontally under spectrophotometer.

During the measurement, each sample was measured at three points randomly in order to obtain the mean colour and the variability between different points. Readings were entered by hand into an Excel spreadsheet. For analysis, all data gathered were inserted in Microsoft Excel. The mean and standard deviation for each concentration of every experiment was calculated.

One-way ANOVA were conducted to measure the validity of the data and the significance of the variation in the results between the stable slope and unstable slope for each soil property. Soil colours give valuable clues in regard to soil properties, soil classification and interpretation. Scoring with Munsell relies upon human perceived assessment of the three colour attributes: hue, value and chroma. These attributes give valuable clues in soil properties, soil classification and interpretation.

Hue is identified as the basic spectral colour or wavelength Red, Yellow, Blue, or in between, such as Yellow-Red. Value refers to measurement of soil organic matter OM in relation to the lightness or darkness of a colour and the range is from 0 pure black to 10 pure white ; while chroma is a measurement of colouring agents like Iron or Manganese and the range is from 0 no colour to 8 most coloured.

For this study, the analyses by using Munsell Soil Colour Chart showed a slight difference in stable and unstable slopes. The hues for overall samples were YR Yellow-Red and the hues indicating the stable slopes were between 2. Within each letter range, hue became more Yellow and less Red as the numbers increased.

Based on the result, 2. This result is consistent with Fontes and Carvallho [ 11 ] that reported hue 2. It is generally believed that hematite, goethite and probably maghemite are the main pigmenting agents in the soil systems [ 12 ]. Thus, the different Oxisols variant studied for all sites could be categorised into two main groups which are hematitic or red soil comprising most of the samples from stable slope, and goethite or yellow soils made up most of samples from unstable slope.

Therefore, the Munsell chroma combined with the hue value was also used to predict the relative amount of Iron oxides in highly weathered soils [ 11 ]. Iron oxides are reddish, yellow and orange in colour [ 13 ] and showed in a very small particle size in soils in comparison with other soil minerals which favour their capacity for pigmentation.

Summary of overall soil colour analysis by using Munsell Soil Colour Chart in response to stable and unstable slope conditions. Carbonates of Calcium and Magnesium contribute to the white colour of the soils. Moreover, in terms of the differences in the regression equations, Schulze et al. High contents of clay and sand affects the soil colour to become yellowish, reddish and whitish.

Clay is the smallest particle in soils and exhibits colloidal properties. Some of the clays, like Iron oxide clay, play an important role in soil aggregation and in addition impart red to yellow colours to soils. Embrapa [ 16 ] stated that most minerals are not highly coloured and when they are coated with humus and Iron oxides, they take on the colours of humus black or brown , Iron oxides and hydroxides red and yellow.

Table 1 showing summary of overall colour analysis by using Munsell Soil Colour Chart for soil samples in response to stable and unstable slopes. The results of the quantitative measurements of soil colour performed in the laboratory are summarised in Table 2. Since there is a significant difference of colour variables in the comparison of different slope condition, it is possible to conclude the soil colour can be an indicator for early warning of shallow slope failure.

Munsell Soil Colour Charts are develop for colour identification of an object by direct comparison by using set of colour palettes with a sequence of colour samples on each page in it. It works by scanning an object via spectrophotometer and the outcomes were recorded in graph in three dimensional colour space.

This equipment is very effective as supporter to the Munsell colour system. Some complications that make the outcomes an alternative and attractive prospect are inherent to the Munsell colour system for example, a great degree of subjectivity and unpredictability between researchers.

Through the result and analysis using CIELAB spectrometer, variation of soil colours became apparent at different slope conditions.