Question

1. (1 Point) A sample of soils was taken by using the sand cone method. The sample was placed inside a sealed jar and the total weight jar + sample was 3.08 lbs. The empty jar had weighted 0.75 lbs. before collecting the sample. After collecting the sample, the cone and the calibrated sand bottle were placed on the plate. The sand being used was calibrated in advance and it was determined its relative density was 2.55. The density of water is 62.4 lbs./ft3. The sand was allowed to fill the excavation hole as well as the plate and cone assembly, after which the valve was closed. The calibrated sand bottle weighted 6.25 lbs. before and 3.79 lbs. after being used. During calibration at the lab, it was found that the weight of sand left inside the cone and plate assembly was 0.51 lbs. Using the “Sand Cone test Form.pdf” file provided as a template complete all the necessary calculation to estimate the volume of the excavated hole. Remember that the density of sand can be calculated by multiplying its relative density by the density of water. Please document all your calculations below the given table.

2. (1 Point) Why are Organic soils unstable for foundation support? Please explain with enough detail for the different kinds of organic soil.

Answer 1

Organic soils are unstable for foundation support because the source of origin of organic soil was decomposed vegetation and with time ,they start decaying if used in foundation support. One can say the core of organic soil are rotten plant material (soft and springy) and in their composition, particles are not small enough to fit tightly and leaves spaces for air to fill in between. Ultimately this kind of soil has very low bearing capacity and are prone to shrinkage.

In contrast mineral soil were created through erosion for hard rock with time creating fine closely fitted particles with strong holding capacity and very low compressibility.

Additionally, organic soil also has higher water content result of which with time, the kind of soil can shrink even by several meters.

For instance if we take an example of peat moss, they are not at all suitable for construction because they have a property of making the compact soil loosen with time. Similarly, leaf mold or humus are primarily composed of municipally collected leaves and have got great water holding capacity making the foundation soft and prone.

So overall, one can say construction over organic soil can create a big issue with time due to its typically lower strength and high compressibility.