Question 5
Trench excavation precaution and procedures differ from sandy and clayey soil soils.
Clayey Soil
Due to the clay particles cohesiveness dependency, trench evacuation in a clayey soil to a certain depth is possible. For example, a two-meter depth trench that would be dag in heavy clay can support a structure by itself. However, if there is a requirement to carry out a deep trench evacuation compared to the safe working depth, the probability of the trench wall collapse will be high.
To protect the walls from collapsing, one must support the trenches’ sides with struts and shuttering. Since clay can support loads, shuttering should not be applied again and again in the trenches. The best shoring and workable option that support loads of passive and active pressure of any soil whose scale is larger is the use of a permanent retaining structure.
There are also sands called cohesion-less, which are not like clays; the soil does not have cohesive strength that overcomes such pressure. Due to this, there is a continuous fall of the trench walls in the trench. The soil’s repose angle is depended by the sandy soil trench excavation, which is achieved through the implementation of a particular excavation method (benching method).
Part 2
Question 4
General shear failure, commonly known as the foundation’s ultimate bearing capacity, is the bearing pressure, which is at its maximum point and is forced on a foundation before it fails.
The footing surface at D= 0 for the mounted surface case would be assumed to have no weight the footing base on Pandtl argument. Furthermore, based on Ressine views, the foundation bearing capacity would be maximized by adding components that would influence the surcharge pressure effect on the ground surface level. The concept was embraced by Terzaghi, who stated that over-burden or surcharge pressure would be active in case the footing would be located at a certain distance that would be below the ground level under the assumption that that the soil would act at equivalent.
Question 5
All the zones of Terzaghi experience a significant size change on the broader footing. These changes will, therefore, generate friction force and internal cohesion beneath a foundation. It would theoretically raise the foundation soil bearing capacity loads. Some implications will be drawn from this enlargement of the footing itself and the foundation based on some conditions.
Zones enlargement:
Zone 1: this zone is not affected significantly. Since this zone can be elastically compress easily, it contains a boost with no strength of the footing effect.
Zone 2: the volume of this zone of the earth increases. Due to this increment, the slip surface enlargement will occur. The rise will mean that more cohesive and frictional forces develop gradually on the slip’s surface before failing.
Zone 3: due to the shearing slip section enlargement in zone 2, more soil volume should be raised upwards before the foundation’s failure and should also be passively sideways.
Last but not least, the foundation’s bearing capacity increment will come up if footing will be widened up since more soil is required for the enlargement and has to be push upwards and sideways.
Question 6
The surface soil’s mounted case tends to collect majorly on a particular section due to the overburden pressure test. The shearing would be stress on one of the sides of the plywood strip that would act as a footing. The occurrence of this scenario would be base on several factors, but in this case, it would be place on the plywood that would not be leveled or centered perfectly. Additional assumptions would be base on the rigidity of the footing and soils incompressible.
Furthermore, more water ingress increases the general-bearing failure, which later increases the soil’s habit of shear. Therefore, there will be an easy flow of high saturated soil under the foundation of the building.