Soil type and liquefaction
The hypothesis that sand will require the most water before soil liquefaction occurs has been proven to be true.
Soil liquefaction can cause serious damage to buildings and property. When the soil that supports the weight of the building and its foundation liquefies, the building will collapse. This will cause loss of lives and damage to property. Soil liquefaction is also responsible for slope failures, resulting in landslides. It is therefore important to understand the conditions under which different types of soil liquefy.
The science fair project may be repeated by filling a pail with several types of soil, compressing the soil and inverting the pail on the ground to create a mound of soil. Then, water may be added until the slopes of the mound collapse.
The experiment may also be done by adding rocks or mixing different types of soil together to compare the results.
Soil liquefaction - http://en.wikipedia.org/wiki/Soil_liquefaction
What is soil liquefaction - http://www.ce.washington.edu/~liquefaction/html/what/what1.html