Adding water increases slope instability. It lubricates rock fragments so that they slide down slope more easily. Mass wasting occurs more readily in rainy seasons for this reason. It turns out that a small amount of water in the soil can aid slope stability because of increased surface tension.
What role does water play in each of the types of mass wasting? Water is the critical factor in mass wasting. When soil is saturated with water, it becomes less viscous and is more likely to flow down slope. Similarly, as the amount of water in soil increases, rate of movement tend to increase.
Water in pores and cracks displaces air, so water adds to the mass of soil and broken rock on a slope. If pores and cracks are saturated (filled with water), the pore pressure tends to push the material particles apart, further promoting failure and downslope movements.
The maximum angle at which loose material can be inclined without sliding down is called the angle of repose. 3. A slope that is steeper than the angle of repose is unstable and will cause material to slide downhill.
The Role of Water Water can seep into the soil or rock and replace the air in the pore space or fractures. Since water is heavier than air, this increases the weight of the soil. Weight is force, and force is stress divided by area, so the stress increases and this can lead to slope instability.
When the normal force, i.e., friction, is greater than the shear force, then the block does not move downslope. However, if the slope angle becomes steeper or if the earth material is weakened, shear force exceeds normal force, compromising shear strength, and downslope movement occurs.
Slope material that becomes saturated with water may develop a debris flow or mud flow. The resulting slurry of rock and mud may pick up trees, houses, and cars, thus blocking bridges and tributaries causing flooding along its path.
How does water affect mass movement processes? Large amount of water fills the pores between sediment, destroying the sediment's overall cohesion. When few water is added to make the sediment on a slope slightly damp, the sediment sticks together and resists downward pull.
When water is added to weathered particles, the mass of the sediment is increased, which can cause slope instability. d. Water enhances the ability of vegetation to grow on weathered particles, promoting mass wasting.
In water saturated sediments all the pore spaces are filled with water. Water pressure and water's buoyancy forces reduce the friction between the grains thereby decreasing the angle of repose and possibly causing mass wasting.
Numerous factors, such as the angle of internal friction, grain size and shape, density, moisture content, interface friction angle, stratification, roughness of the base at which the material is heaped, segregation, pull-out velocity of the hollow cylinder (a measurement instrument for the angle of repose), mass of ...
Angle of repose was found to increase as moisture content increases. The study concludes that variety and changes in moisture content significantly (P < 0.05) affected most of the engineering properties determined.
What role does water play to cause mass wasting of the slope? The surface tension of pore water helps to hold sediments in a slope together, provided the amount of water is small.
How does water affect mass movement processes? Large amount of water fills the pores between sediment, destroying the sediment's overall cohesion. When few water is added to make the sediment on a slope slightly damp, the sediment sticks together and resists downward pull.
Answer and Explanation: Rock falls are the fastest form of mass wasting. This is because falling rocks can attain speeds in excess of 60 miles per hour. Falling rocks can attain these speeds because they experience relatively little air resistance.
What is the significance of the angle of repose to mass movement? If a slope becomes any steeper than the angle of repose, then material will start moving downslope.
The angle of repose is important in understanding how well a powder will flow through your machine. LFA has developed this Angle Of Repose Calculator to help you quickly and easily calculate any angle of repose.
What does Angle of Repose Mean? Definition of Angle of Repose in Construction: The angle of repose is the normal and natural angle that dirt, sand, gravel, stone, or other natural site-work material will take, if left to seek its own equilibrium.If an excavator is digging in a damp clay material, and there is a natural ability for the material to stand on its own, there could be a 90 degree ...
The angle of repose is important for the design of processing, storage, and conveying systems of particulate materials. When the grains are smooth and rounded, the angle of repose is low. For very fine and sticky materials the angle of repose is high.
The angle of repose is determined by either tilting box, fixed funnel, revolving cylinder, or hollow cylinder methods, in all of which the containers are filled with a sample and gradually lifted up, allowing the sample to accumulate and form a conical heap on the surface. Then, the angle of repose can also be calculated from the ratio of the height to the base radius of the heap formed based on different mathematical models ( Al-Hashemi and Al-Amoudi, 2018 ).
There are many empirical tests used to assess powder flowability, including measurement of Hausner ratio, angle of repose (Fig. 12.8) with a greater angle being indicative of a more cohesive powder, Carr indices ( Carr, 1965 ), flow through a defined opening, and compression testing. These tests are not useful in the design of hoppers and silos for reliable flow. However, they may be useful in quality control, where a change in a measured value may be indicative of change in the flow behaviour of a given material.
Material bulks like flax seed are known as freely flowable and usually have angle of repose less than 30 degrees, whereas materials with angle of repose greater than 55 degrees are extremely cohesive/sticky/caking and nonflowable ( Al-Hashemi and Al-Amoudi, 2018 ). Table 3.2.
Dry nanoparticles powders are characterized via a tap density test and a test for angle of repose which will give a measure about the flowability of dry powders and will be important for powder inhaler formulations. The tapped and untapped (bulk) densities are determined by demarcating a small cuvette with known volumes, then inserting a small mass of powder into the cuvette (bulk density) and tapping it vertically against a padded bench top 50 times (tapped density). The mass is divided by the initial and final volumes. From these values, the Hausner ratio (tapped density/bulk density) and Carr's index (Ci) ( (tapped density–bulk density)/tapped density × 100%) are also determined for each of the samples.
The coefficient of friction between granular materials is equal to the tangent of the angle of internal friction of the material. The angle of repose is the angle made by a material, with respect to the horizontal when piled. While it is generally assumed that the angle of friction and the angle of repose are approximately equal, for some materials, such as sorghum, magnitudes of the two angles can be different. There are two angles of repose, i.e., a static angle of repose taken up by a granular solid that is about to slide upon itself, and a dynamic angle of repose that arises in all cases where the bulk of the material is in motion, such as during discharging of solids from bins and hoppers.
In environments where dry ravel occurs, large volumes of sediment may accumulate in topographic depressions on hillslopes and along the margins of headwater tributaries and second-order stream channels ( Fig. 6; Florsheim et al., 1991, 2016; DiBiase and Lamb, 2020 ). Deposits of sediment at the base of hillslopes derived from dry ravel may appear as an inverted cone or semi-rectangular or irregular shapes composed of relatively well sorted gravel-sized grains ( Florsheim et al., 2016 ). These relatively fine-grained deposits are subject to subsequent channel erosion (discussed in subsequent sections). Variables that affect the dry ravel sediment yield from a particular fire include the rate of rock weathering that generates the noncohesive sediment volume available for transport, the density of re-established vegetation that enables hillslope sediment storage, and the time since the last fire ( Shakesby, 2011 ). Steep hillslopes are subject to dry ravel during the remainder of the dry season following the fire. Over time, as vegetation re-establishes, dry ravel rates are greatly reduced.
The angle of repose is important for the design of processing, storage, and conveying systems of particulate materials. When the grains are smooth and rounded, the angle of repose is low. For very fine and sticky materials the angle of repose is high.
The angle of repose is determined by either tilting box, fixed funnel, revolving cylinder, or hollow cylinder methods, in all of which the containers are filled with a sample and gradually lifted up, allowing the sample to accumulate and form a conical heap on the surface. Then, the angle of repose can also be calculated from the ratio of the height to the base radius of the heap formed based on different mathematical models ( Al-Hashemi and Al-Amoudi, 2018 ).
There are many empirical tests used to assess powder flowability, including measurement of Hausner ratio, angle of repose (Fig. 12.8) with a greater angle being indicative of a more cohesive powder, Carr indices ( Carr, 1965 ), flow through a defined opening, and compression testing. These tests are not useful in the design of hoppers and silos for reliable flow. However, they may be useful in quality control, where a change in a measured value may be indicative of change in the flow behaviour of a given material.
Material bulks like flax seed are known as freely flowable and usually have angle of repose less than 30 degrees, whereas materials with angle of repose greater than 55 degrees are extremely cohesive/sticky/caking and nonflowable ( Al-Hashemi and Al-Amoudi, 2018 ). Table 3.2.
Dry nanoparticles powders are characterized via a tap density test and a test for angle of repose which will give a measure about the flowability of dry powders and will be important for powder inhaler formulations. The tapped and untapped (bulk) densities are determined by demarcating a small cuvette with known volumes, then inserting a small mass of powder into the cuvette (bulk density) and tapping it vertically against a padded bench top 50 times (tapped density). The mass is divided by the initial and final volumes. From these values, the Hausner ratio (tapped density/bulk density) and Carr's index (Ci) ( (tapped density–bulk density)/tapped density × 100%) are also determined for each of the samples.
The coefficient of friction between granular materials is equal to the tangent of the angle of internal friction of the material. The angle of repose is the angle made by a material, with respect to the horizontal when piled. While it is generally assumed that the angle of friction and the angle of repose are approximately equal, for some materials, such as sorghum, magnitudes of the two angles can be different. There are two angles of repose, i.e., a static angle of repose taken up by a granular solid that is about to slide upon itself, and a dynamic angle of repose that arises in all cases where the bulk of the material is in motion, such as during discharging of solids from bins and hoppers.
In environments where dry ravel occurs, large volumes of sediment may accumulate in topographic depressions on hillslopes and along the margins of headwater tributaries and second-order stream channels ( Fig. 6; Florsheim et al., 1991, 2016; DiBiase and Lamb, 2020 ). Deposits of sediment at the base of hillslopes derived from dry ravel may appear as an inverted cone or semi-rectangular or irregular shapes composed of relatively well sorted gravel-sized grains ( Florsheim et al., 2016 ). These relatively fine-grained deposits are subject to subsequent channel erosion (discussed in subsequent sections). Variables that affect the dry ravel sediment yield from a particular fire include the rate of rock weathering that generates the noncohesive sediment volume available for transport, the density of re-established vegetation that enables hillslope sediment storage, and the time since the last fire ( Shakesby, 2011 ). Steep hillslopes are subject to dry ravel during the remainder of the dry season following the fire. Over time, as vegetation re-establishes, dry ravel rates are greatly reduced.