Foundation, Concrete and Earthquake Engineering

Sampling Difficulties of Collapsible Soil: Loess

Dear reader we have discussed about many aspects of loess so far in this blog; now we will discuss about sampling difficulties of loess soils. We have already learnt about different sampling method, disturbance in soil sampling and measuring disturbance in soil sampling in our previous posts. The equation which produces a measure of collapse potential is as follows:

Collapse potential of collapsible soil

Where, Cp=estimate of changing in height of undisturbed specimen expressed in percentage 

hp=change in length of tube sample under consolidation pressure as expected in field. The sample is obviously undisturbed as in ‘Cp’.

Trying to take block soil sample in loess plateau
hp׳=change in length of tube sample that is saturated under identical consolidation pressure as in hp. The initial length (h) for both samples must be same.

This is a simple equation and seems to be very simple to assess Cp but actual difficulty lies in the term ‘undisturbed sample’. Dear reader perhaps we have read about block sampling, discussed in this blog. This is the best way to collect sample of loess soil. But we know that it is very difficult and practically impossible in many situations.

In case of application of thin walled tube sampler, the sample may subject to some degree of compression when sampling process is executed. If we have no way to avoid this sampler, the boreholes must be made dry or without water.

The disturbance may be happened while cutting/trimming sample, placing it into testing arrangement and providing load to required pressure (with minimum side friction or lateral resistance). The depth of saturation zone provides major problems as saturation initiates collapse to such soil.

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