UoB No: Soil Mechanics (CSE5009-B) Laboratory Experiment #1 Compaction test 1.0 PURPOSE OF MEASUREMENT Compaction is the process which causes the particles of a soil to become closer in order to increase the density of the soil medium by reducing the volume of air present. It is used to increase the shear strength and to reduce the settlement or compressibility of soils. The degree of compaction is measured in terms of dry unit weight (loose or dense). The compaction of a soil can be performed in the laboratory using a Standard Proctor test. The technician will show you how this test is performed. This test measures the compaction characteristics of the soil. The soil is compacted in a cylindrical mould using a standard compactive effort. In this test the soil (with all particles larger than 20 mm removed) is compacted using a rammer consisting of a 2.5 kg mass falling from 300 mm. Two types of compaction tests are routinely performed: (1) The Standard Proctor Test, and (2) The Modified Proctor Test. Each of these tests can be performed in three different methods as outlined in the attached Table 1. In the Standard Proctor Test, the soil is compacted by a 5.5 lb hammer falling a distance of one foot into a soil filled mold. The mold is filled with three equal layers of soil, and each layer is subjected to 25 drops of the hammer. The Modified Proctor Test is identical to the Standard Proctor Test except it employs, a 10 lb hammer falling a distance of 18 inches, and uses five equal layers of soil instead of three. There are two types of compaction molds used for testing. The smaller type is 4 inches in diameter and has a volume of about 944 cm³, and the larger type is 6 inches in diameter and has a volume of about 2123 cm³. If the larger mold is used each soil layer must receive 56 blows instead of 25. Lecturer's signature: 1 UoB No: Significance: Mechanical compaction is one of the most common and cost effective means of stabilizing soils. An extremely important task of geotechnical engineers is the performance and analysis of field control tests to assure that compacted fills are meeting the prescribed design specifications. Design specifications usually state the required density (as a percentage of the "maximum" density measured in a standard laboratory test), and the water content. In general, most engineering properties, such as the strength, stiffness, resistance to shrinkage, and imperviousness of the soil, will improve by increasing the soil density. The optimum water content is the water content that results in the greatest density for a specified compactive effort. Compacting at water contents higher than (wet of) the optimum water content results in a relatively dispersed soil structure (parallel particle orientations) that is weaker, more ductile, less pervious, softer, more susceptible to shrinking, and less susceptible to swelling than soil compacted dry of optimum to the same density. The soil compacted lower than (dry of) the optimum water content typically results in a flocculated soil structure (random particle orientations) that has the opposite characteristics of the soil compacted wet of the optimum water content to the same density. Equipment: Molds, Manual rammer, Extruder, Balance, Drying oven, Mixing pan, Trowel, #4 sieve, Moisture cans, Graduated cylinder, Straight Edge. 2 Lecturer's signature: UoB No: Lecturer's signature: ELE Figure 1. Compaction test setup. 3 UoB No: Test Procedure: 1. About 5 kg of air dried soil is collected. 2. The soil is then thoroughly mixed with enough water to give a fairly low value of water content (3~5 % for sands and ~10% for clays) 3. The soil is then compacted in three equal layers. Each layer receives 25 blows with the rammer. 4. levelled. After filling the mould, the collar is removed and the surface of the compacted soil is 5. The mould and soil sample are weighed. 6. A sample is taken from the middle of the mould and its water content is determined using the method described below. 7. A suitable increment of water is thoroughly mixed with the soil and the compaction is repeated. 8. The test should involve at least five trials but it is usually continued until the weight of the wet soil in the mould passes some maximum value and begins to decrease. 9. The water content corresponding to each compaction trial should be determined. 10. Compute the amount of initial water to add by the following method: (a) Assume water content for the first test to be 8 percent. (b) Compute water to add from the following equation: (soil mass in grams)8 water to add (in ml) = 100 Where "water to add” and the “soil mass” are in grams. Remember that a gram of water is equal to approximately one millilitre of water. Lecturer's signature: 4 UoB No: Analysis: (1) Calculate the moisture content of each compacted soil specimen by using the average of the two water contents. (2) Compute the wet density in grams per cm3 of the compacted soil sample by dividing the wet mass by the volume of the mould used. (3) Compute the dry density using the wet density and the water content using the following formulas: Moisture Content: W = (Mass of container + Wet Soil (g)) - (Mass of container + Dry Soil (g)) (Mass of container + Dry Soil (g)) - Mass of container (g) x 100 Pb = (Total mass of soil + Mould (g)) - (Mass of Mould (g)) Volume of Mould (cm³) = g/cm³ 3 d = Ph 1+W =g/cm³ = (4) Plot the dry density values on the y-axis and the moisture contents on the x-axis. Draw a smooth curve connecting the plotted points. (5) Identify and report the optimum moisture content and the maximum dry density. Lecturer's signature: 5/n Faculty of Engineering and Informatics CSE5009-B- Soil Mechanics - Laboratory practice – Individual Report Assignment Introduction This module runs in Semester 1 and 2. The aim of laboratory exercises is to give you an opportunity to understand the main instruments, apparatuses and their application in the geotechnical material laboratory to obtain skills through specific designed laboratory exercises. The laboratory exercises will support your further learning in Stage 3 and 4. Individual Coursework Report You are required to complete an individual coursework report. This report should be around 2000 words. You are requested to write about the six laboratory practicals, discuss the data collected, plot graphs and include pictures. The following structure should be applied to each individual practical. Practical structure: Part 1: Introduction. Part 2: Brief description of the practical (do not include the practical hand out). In the first semester four practical's will be covered, which include: • Compaction test • Permeability • Seepage tank • Consolidation test In the second semester two practical's will be covered, which include: • Shear box • Triaxial test Part 3: Results and data analysis, include any salient trends in the data. Plot graphs and show data in tables. Part 4: Discussion/Conclusions. Summarise your findings. Part 5: References and appendixes