The process of consolidation - Lab Report Example

The process of consolidation Introduction Consolidation refers to the process of the gradual reduction in volume as the result of applying a load on a fully saturated soil. The reduction in volume occurs due to the load effect causing drainage of pore water. The process of consolidation continues to the point when the excess pore pressure result from the increase in total stress completely goes diminished. The hydrostatic pressure therein becomes gradually dissipated thereby shifting the load to the soil solid thereby triggering decrease in volume of the soil mass. It is worth noting that the rate at which water escapes is dependent on the permeability of the soil in question. In which case, the escape of the pore water as the result of long time static load makes up consolidation. Consolidation test is usually carried engineers in the design of engineered structures and performance evaluation of a structure. In which case, consolidation test yield results which are useful in estimating the magnitude of primary and secondary consolidation settlement of a given structure (The Constructor). Purpose The major purpose of this experiment was to determine the magnitude and rate of volume decrease witnessed by a soil specimen when subjected to load. The data obtained from this experiment is significant in determination of compression index and/or recompression index of a given soil. Further, coefficient of consolidation can also be determined using the data. Methodology Apparatus 1 bench, 3 sample cells of soil, 3 dial gauges which can be either analogue or digital, 1 weight set Procedure Soil sample was cut from a big soil block using a rigid confining ring with sharp edge. Excess soil from the process was sliced away to leave a sample with a diameter to height ratio of at least three. Porous stones were placed on the top and bottom of the soil sample in order to give way for drainage. A stiff loading cap was placed on top of the upper porous stone followed by placing the set up on in a loading frame. Load was imposed on the frame by positioning different weights on the loading frame. Measurement of soil sample compression over time was recorded by looking at the dial indicator. The deflection value data was used to measure the point at which the soil sample reached the primary consolidation end. Another load was placed on the sample and the aforementioned process repeated. The load was reduced bit by bit after a significant application. A load increment ratio of 0.5 was used to establish an appropriate framework for description of relationship between effective stress and void ratio. As the test continued, the water level in the cell was checked from time to time to ensure that it stayed above the top of the porous stone. After the completion of the test, the soil sample was removed followed by recording thickness and water content details. Results Figrure 1: Data Sheet showing results obtained Container No. Clay A Mass of wet soil + container (m2) g 63.6 Mass of dry soil + container (m3) g 50.6g Mass container (m1) g 9.6 Mass of moisture (m2-m3) g 13 Mass of dry soil (m3-m1) g 41 Moisture content % 31.71% Calculation of flow rate Mass = 0.7172 h = 0.105 m L = 0.1 m t= 20.1 seconds q = Aki representing Darcy law equation (Brown) for our results A is calculated using the equation πd2/4 = π x 0.0752/4 = 4.418 x 10-3 K is the coefficient of permeability and is calculated using the following equation K = QI/tAL whereby Q = M/Density of water = 0.7172/1000 = 7.172 x 10-4 m3 K = 7.172 x 10-4 x 0.1/(20.1 x 4.418 x 10-3 x 0.105 = 7.692 x 10-3 m/s i = h/L = 0.105/0.1 = 1.05 q = AKi = 4.418 x 10-3 x 7.692 x 10-3 x 1.05 q = 3.568 x 10-5 m3/s Determination of void ratio Dry mass of specimen Md = 80 gm  Diameter of soil sample = 63.5 mm, Area =0.00317m2 HS = = 1.792 cm Height of water before test = = Height of water after test Hwf = = = 0.683 Change in height of specimen after test = 0.257 cm Height of specimen after test, Hf = Hi - Σ∆H = 2.7 – 0.257 = 2.443 cm Void ratio test e0 = = = 0.506 Void ratio after test, ef = = = 0.3617 Discussion and conclusion The lab was successful in meeting the major objective the magnitude and rate of volume decrease witnessed by a soil specimen when subjected to load. This was made possible by determining the void ratio in relation to the effective stress imposed by the load. As seen in the results, the void ratio test reduced from 0.506 to 0.3617 before and after test. This insinuates the influence of water expelled out of the void after water was expelled out by the impact of load. Initially, the voids were filled with water but due to addition of the load a decrease in volume occurs hence confirming the consolidation process. In essence, the use of oedometer test carried out on the saturated soil specimen helps in determining the consolidation and swelling perimeters of the soil determined. This shows the usefulness of consolidation test in geotechnical laboratory testing. Even though the experiment was successful, possible sources of error might have contributed to limitations between real life applications and the experimental test results of the consolidation test. This could be because of errors in estimating of rate of settlement, whereby the practical applications normally have shorter settling time than that evident in experimental test results. This deviation could be attributed to sample size since the sample size was not big enough compared to the soil fabric and its characteristic deep effects on drainage conditions. The slight deviation produced by sampling impacts on the results leading to information slightly different from practical application. Work cited The Constructor. Consolidation Test Of Soil. The Constructor Organization Retrieved from: http://theconstructor.org/geotechnical/consolidation-test-of-soil/3054/ Brown, Glenn. Darcy's Law Basics and More. Oklahoma State University, 2014, Retrieved from: http://biosystems.okstate.edu/darcy/LaLoi/basics.htm Consolidation Test. 2015, Retrieved from: http://home.iitk.ac.in/~madhav/expt13.html Read More