The ‘Attributer limits tests’ are a series of empirical tests, the results of which can be used to estimate engineering properties. The methods for conducting these tests are found in the British standards OBSESS: part 2: 1990 The liquid limit (AL) is the minimum water content at which the soils will flows under a specified small disturbing force. The plastic limit (PL) is the minimum water content at which the soil can be deformed plastically. The plasticity index (P’) is the range of water content over which the soil is in the plastic condition.
Where Considering the above, in order to calculate the moisture content which in the context of this laboratory, it is defined as the mass of water in a soil, expressed as a argental of the dry soil as shown below : Moisture content, w (%) = Mass of water = Mass of soil mm – mm mm- ml Three masses must be taken into consideration: – ml : Mass of container – mm : Mass of container + wet soil mm : Mass of container + dry soil (wet soil = soil + water) In pursuance of computing the liquid limit in the experiment which uses the cone pentameter apparatus, the graph of moisture content against penetration was plotted.
Additionally, to calculate the liquid limit using the one point test, the following equation was used: – Liquid limit(%) = moisture content x factor (from BBS 1377) . 2 Particle size distribution The second part of this experimental programmer was completed in to obtain the particle size distribution. The particle size distribution (SD) of a soil is a characteristic of central importance as it controls multiple characteristics of a soil such as: Permeability Dry density / unit weight Effective angle of friction A standardized system of classification helps to eliminate human error.
The usual method is based on the determination of the SD, by shaking a dried sample of the soil (in this particular experiment, sea dredged sand was used) through a set of fives and recording the mass retained on each sieve. The classification system adopted by the British Standards Institution is the MIT (Massachusetts Institute of Technology) system.
The mathematical equation used in order to calculate the correct mass on each sieve is: where: m is the correct mass on each sieve Mr. is the mass retained on the sieve ml is the initial sample mass met is the total mass retained The percentage retained on each sieve and the pan was also calculated by using the following equation: ( , in order to then obtain the cumulative percentage passing, which is equal to: 100- the percentage retained by that sieve and all larger sieves). Finally the coefficient of Uniformity (Cue) is a crude shape parameter which is determined by the equation below: cue = Where: DAD is the grain diameter at 60% passing, DID is the grain diameter at 10% passing. 3. Experimental procedures and results 3. 1. Experimental procedures All the following tests were carried out in accordance with British Standards BAOBABS: Part 2:1990. The type of soil used for the plastic and liquid limit tests was clay, whereas sand was used for the particle size distribution experiment Plastic limit – hand rolling method.
First of all a ball of soil (clay) weighing approximately 20 grams was rolled between the palms of the hand until small cracks started to form on the surface. O The sample was the broken into two equal sub-samples and then each sample was divided into four pieces. O After that each piece of clay was then rolled back and forth on a glass plate until the point where horizontal and radial cracks started to occur in the surface of the sample at a diameter of mm. In the case of cracks not appearing at 3 mm the soil had to be dried further by molding it between the fingers, forming it into a thread and rolling it on the plate sing the full length of the hand exactly in the same way as the previous step. If the cracks had appeared before the sample had reached the 3 mm diameter, water was added to increase its moisture. O From there on, the samples which had cracks on their surface were then placed into a pre-weighted moisture content tin and put in the tray with the samples from the other tests.
Thenceforth they were placed inside the oven in order to be dried. The temperature of the oven was ICC and the samples stayed inside for 24 hours. O Finally the two moisture contents were within 0. 5 %. The average of those two intents was found and the value was expressed to the nearest whole number which was the plastic limit 5 Liquid limit – cone pentameter apparatus o A cone pentameter apparatus was used for this experiment which calculated the penetration in mm. O First of all, the clay was placed on a glass plate and water was added until the appropriate moisture content was reached.
The sample was mixed using palette knives. O A portion of the clay was then placed in a cone of stainless steel. The suitable moisture content should give penetration of around mm. Two readings could be used if they were within 0. Mm or three if they were within 1 mm and if that was not achieved the sample had to be remixed and the procedure should be repeated. O After the penetration had been measured and the results were satisfying I. E two readings of around mm, a moisture content determination was carried out using the metal containers and a conventional oven. The moisture content was then increased and the same procedure was followed to give penetrations of approximately mm and mm. O Finally the graph of moisture content against penetration could then be plotted and using that graph, the liquid MIT, which is the moisture content at which the penetration is mm, could be found. Liquid limit – Greensand apparatus – one point test o For this test, as stated in the title, a Greensand apparatus was used along with a grooving tool. O Firstly, the clay sample was placed in the cup which was resting on the rubber base of the Greensand apparatus.