Part B; Figure 1 shows the cross-section of the ground condition below the propo
ID: 1732650 • Letter: P
Question
Part B; Figure 1 shows the cross-section of the ground condition below the proposed railway line. As it can be seen from the figure, there is a clay layer available below the lm thick embankment fill. The variation of the clay layer thickness along the railway line is given in figure 1 and the properties of the three soil layers (fill, clay and coarse grained sand) are given in Table 1. 1) Discuss about the possibility of settlement in each soil layer that may result due to a seasonal using your Atterberg limits knowledge (without any calculation) 2) Estimate the potential vertical settlement at points A, B, C and D that may result due to an extreme seasonal change of ground moisture content from the wettest to the driest (please note that each soil layer is extensively long (2 2km) and thus lateral movement of the soil has been restricted by the surrounding soil)Explanation / Answer
(1) The proposed railway line shows three layers of soil that are:
1. Hard rock
2. coarse grained sand
3. clay.
If we talk about the seasonal changes majorly affecting the layers, they are:
snowfall, humidity, rainfall, and dry weather.
(a) snowfall: Snowfall afffects the hard rock by increasing the abrassion value between the particles of the rock. Heavy snowfall for a long term would result in sudden settlement of the rock.
The coarse grained soil is affected by the snowfall as in undergoes snow thaw action ultimately creating variation in the saturation point of the soil. Due to snow thaw action, coarse grains loose the stability.
Severe soil freezing can be seen on the layer of clayey soil.
Rainfall as such doesnt affect the hard rock but is always a danger for the layer of clay sue to its liquid limit. Hot and humid temperature has the tendency to develop crack in the clayey layer and would partially and certainly affct the coarse grained soil.