ONE DIMENTIONAL CONSOLIDATION TEST REPORT

1.  INTRODUCTION

The oedometer is a comparatively  simple  laboratory test that, if carefully conducted  and interpreted, can yield very useful data for the prediction of consolidation settlement. In the oedometer, a disc of soil of 75mm or 50mm diameter can be compressed, while drainage to or from the sample is possible through porous stones at both ends of the sample. Loads can be applied to the sample by adding weights to a hanger and the settlement (or vertical compression) is monitored by the dial gauge above the arm that applies the load to the top cap. This system will allow you to understand, for each load increment, how the settlement occurs with time (dissipation of the excess pore-pressure) and how the sample reduces in volume with the increase of vertical stress or load increments applied.

2.  OEDOMETER TEST

Oedometer tests have been performed in kaolinite clay and a mixture of quartzitic sand and kaolin and the objective of this coursework is to calculate and analyse the data This report will investigate the consolidation or compression/swelling behaviour of kaolinite clay and a mixture of kaolinite and sand and your team need to calculate

•   For each compression stage, calculate the final void ratio,e, by working from the void ratio at the start of the loading derived from the initial water content and making use of the change in sample thickness, ΔH. Note that for H measured vertically upwards, Δe/(1+e) = ΔH/H. Plot e against logσv ' and determine the compression and swelling indices Cc  and Cs.

•   Plot e against σv ' and determine values of mv  in m2/kN for each load:

mvi  = (de/dσv ')/(1+ei); the suffix i refers to values at the start of each loading stage.

•   For the consolidation stages and the swelling stages, plot the dial gauge reading against √t. Use the graphs to determine values of cv  (in mm2/s) for each of these stages.

•   For the loading stages and the unloading stages, calculate the coefficient of permeability k (in m/s).

3.  POINTS FOR DISCUSSION

The discussion points below should be covered for both soils (Clay and Clay + Sand), therefore comparisons between both soils are required.

•   How do your consolidation data conform to the theory?

•   How do mv  (compression), ms  (swelling), k (permeability) and cv vary with stress level and overconsolidation ratio and how do mv  and k control cv? Please do not attempt to explain the formulae. Think about what it physically means to the soil behaviour.