What are the bearing capacity values of different types of soils such as clay, sand, gravel, rocks etc.?
Slope stability is the process of calculating and assessing how much stress a particular slope can manage before failing. Examples of common slopes include roads for commercial use, dams, excavated slopes, and soft rock trails in reservoirs, forests, and parks. Considering the importance of slope stRead more
Slope stability is the process of calculating and assessing how much stress a particular slope can manage before failing. Examples of common slopes include roads for commercial use, dams, excavated slopes, and soft rock trails in reservoirs, forests, and parks. Considering the importance of slope stability to their work, it’s beneficial for civil engineers to understand how to properly evaluate slope stability and leverage various techniques to achieve slope stabilization.
Evaluating Slope Stability
Civil engineers evaluate slope stability on the following premise: if a slope is stable enough to resist movement, then it is considered stable; whereas if the movement is too strong for a slope, then it is considered unstable. There are a number of elements that factor into determining slope stability and are analyzed through a series of tests by civil engineers. Four of the most prominent factors include:
- Relief – height differences amongst the slope’s terrain.
- Material Strength – the strength of the material used in creating the slope.
- Soil Water Content – relative amount of water in the soil surrounding the slope.
- Vegetation – plants and vegetation covering and/or surrounding the slope area.
Another factor which civil engineers must keep in mind is whether they are interested in determining short-term stability, long-term stability, or both. In either of these cases, civil engineers will need to evaluate the soil and determine if there is potential for slippage or sliding. In analyzing for long-term stability, engineers will also need to consider a number of factors, such as evaluating the potential quality of the soil in five or ten years or potential environmental events that could rupture or alter the soil.
Techniques for Stabilization
There are a number of techniques that civil engineers can leverage in achieving stabilization, some of which include:
- Anchor blocking – where blocks are strategically placed across the slope to resist the movement of sliding soil.
- Soil nailing – stabilization is achieved through the use of steel nails, which help provide support to the slope and/or infrastructure.
- Gabions – attempt to provide stability through the use of walls (similar to blocks) formed with the soil. These walls are capable of being temporary for stability rehabilitation or permanent.
- Micropile slide stabilization system – uses micropiles, concrete beams, and at times anchors to achieve stabilization. With this system, civil engineers insert a concrete beam into the ground then drill micropiles into the beam at various angles. Once complete, the connected micropiles will provide enough stability to protect an infrastructure from any sliding forces it may encounter.
One of the more recent trends in slope stability is the implementation of sustainable slopes, particularly for flood protection systems. This process has become quite complicated as a result of the numerous variables that come with introducing a new and powerful element such as water. Due to these variables, civil engineers have had to expand and tighten their assessment and calculation skills as they deal with new uncertainties, such as the exact strength and power of a given flood.
3D slope analysis is another growing trend for achieving and maintaining slope stability. Although not always necessary, 3D slope analysis has developed into a unique component of the slope stability process as it provides civil engineers with the capability to observe and analyze the actual state of the slope, as opposed to 2D which often relies upon assumptions to simplify the process. Furthermore, 2D slope analysis can be done only once a civil engineer knows the configuration and soil framework, whereas 3D slope analysis is able to manage more complex and potentially unknown factors. Examples of when 3D slope analysis may be used include:
- Slopes featuring complex geometry
- Differences in the geometry of slope and slip surface
- Locally surcharged slope
Slope stability has become a crucial component of America’s expanding infrastructure ecosystem. By calculating slope stability, civil engineers are able to create beautiful and innovative infrastructures in regions and areas that in the past were deemed unsafe for a building. Furthermore, the insight gained by determining slope stability has given civil engineers an expanded understanding of natural laws and forces, which they can study to improve future projects, as well as progress the civil engineering industry as a whole.
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aviratdhodare
Follwoing are the values of safe bearing capacity as per IS:1904–1978 - Rocks - a) hard sound rock - 330 t/m2 or 3240 KN/m2 b) leminated rock - 165 t/m2 or 1620 KN/m2 c) residual deposit of shattered and broken rocks- 90 t/m2 or 880 KN/m2 d) soft rock - 45 t/m2 or 440 KN/m2 Non Cohesive Soil (sandRead more
Follwoing are the values of safe bearing capacity as per IS:1904–1978 –
Rocks –
a) hard sound rock – 330 t/m2 or 3240 KN/m2
b) leminated rock – 165 t/m2 or 1620 KN/m2
c) residual deposit of shattered and broken rocks- 90 t/m2 or 880 KN/m2
d) soft rock – 45 t/m2 or 440 KN/m2
Non Cohesive Soil (sand & gravel ) –
a) compact gravel, sand and gravel – 45 t/m2 or 440 KN/m2
b) compact and dry coarse sand – 45 t/m2 or 440 KN/m2
c) compact and dry medium sand – 25 t/m2 or 245 KN/m2
d) find sand – 15 t/m2 or 150 KN/m2
e) loose gavel or sand – 25 t/m2 or 245 KN/m2
f) loose and dry fine sand – 10 t/m2 or 100 KN/m2
Cohesive soil –
a) hard or stiff clay, soft shale – 45 t/m2 or 440 KN/m2
b) medium clay – 25 t/m2 or 245 KN/m2
c) moist clay and sand clay mixture – 15 t/m2 or 150 KN/m2
d) soft clay – 10 t/m2 or 100 KN/m2
e) very soft clay – 5 t/m2 or 50 KN/m2
f) black cotton soil , peat – by soil investigation
This is bit difficult to state like this. Generally, in fields, we deal with layered soil systems where in you need to work out settlement of each layer and then compare the same to allowable settlement of the subject structure. The allowable settlement for each structure in different and hence the criterion changes all the time.
More than shear criteria, the settlement criteria generally governs the safe bearing capacity of a soil. So, it is difficult to standardize the bearing capacity values in case of soils. May be, in the case of rock, you can standardize the values as the rock does not settle more than 3–4 mm.
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