YCEF WEEKLY TECHNICAL INTERACTIVE SESSION

Transcription

1 YOUNG CIVIL ENGINEERS FORUM SOIL RELATIVE COMPACTION TEST. PRESENTED BY HABEEB OLADAPO OLAWOLE FOR YCEF WEEKLY TECHNICAL INTERACTIVE SESSION MAY 2018

2 This paper is purposely for the presentation of YCEF weekly technical interactive session which usually holds every Saturday by 20:00hrs on Telegram. The paper is aimed at discussing Soil Relative Compaction Test considering Standard Proctor for the laboratory test and sand pouring replacement for the in-situ test. In geotechnical engineering, soil compactionis the process in which a stress applied to a soil causing densification as air is displaced from the pores between the soil grains. When stress is applied that causes densification due to water (or other liquid) being displaced consolidation, from not between the compaction, has soil grains, occurred that's because consolidation deals with expulsion of water while compaction deals with expulsion of air voids. Normally, compaction is the result of heavy machinery compressing thesoil, but it can also occur due to the passage of animal feet and other heavy equipments.

3 In essence, compaction is a form of stabilizing soil in order to maintain, improve or increase the natural of soil. It's the mechanical pressing together of soil particles to increase its density and expel air voids Soil compaction is a vital part of the construction process. It is used for support of structural entities such as building foundations, roadways, walkways, and earth retaining structures et al. For a given soil type, certain properties may deem it more or less desirable to perform adequately for a particular circumstance. In general, the preselected soil should have adequate strength, be relatively incompressible so that future settlement is not significant, be stable against volume change as water content or other factors vary, be durable and safe against deterioration, and possess proper permeability. When an area is to be filled or backfilled the soil is placed in layers called lifts. The ability of the first fill layers to be properly compacted will depend on the condition of the natural material being covered. If unsuitable material is left in place and backfilled, it may compress over a long period under the weight

4 of the earth fill, causing settlement cracks in the fill or in any structure supported by the fill. In order to determine if the natural soil will support the first fill layers, an area can be proofrolled. Proofrolling consists of utilizing a piece heavy construction equipment (typically, heavy compaction equipment or hauling equipment) to roll across the fill site and watching for deflections to be revealed. These areas will be indicated by the development of rutting, pumping, or ground weaving To ensure adequate soil compaction is achieved, project specifications will indicate the required soil density or degree of compaction that must be achieved. These specifications are generally recommended by a geotechnical engineer in a geotechnical engineering report. The soil type that is, grain-size distributions, shape of the soil grains, specific gravity of soil solids, and amount and type of clay minerals, present - has a great influence on the maximum dry unit weight and optimum moisture content. It also has a great influence on how the materials should be compacted in given situations. Compaction is accomplished by use of heavy equipment. In sands and gravels, the equipment usually vibrates,

5 to cause re-orientation of the soil particles into a denser configuration. In silts and clays, a sheepsfoot roller is frequently used, to create small zones of intense shearing, which drives air out of the soil While soil under structures and pavements needs to be compacted, it is important after construction to decompact areas to be landscaped so that vegetation can grow. Determination of adequate compaction is done by determining the in-situ density of the soil and comparing it to the maximum density determined by a laboratory test Compaction methods There are several means of achieving compaction of a material. Some are more appropriate for soil compaction than others, while some techniques are only suitable for particular soils or soils in particular conditions. Some are more suited to compaction of non-soil materials such as asphalt. Generally, those that can apply significant amounts of shear as well as

6 compressive stress, are most effective. The available techniques can be classified as: 1.Static - a large stress is slowly applied to the soil and then released. 2.Impact - the stress is applied by dropping a large masson to the surface of the soil.3.vibrating - a stress is applied repeatedly and rapidly via a mechanically driven plate or hammer. Often combined with rolling compaction. 4.Gyrating - a static stress is applied and maintained in one direction while the soil is a subjected to a gyratory motion about the axis of static loading. Limited to laboratory applications. 5.Rolling - a heavy cylinder is rolled over the surface of the soil. Commonly used on sports pitches. Roller-compactors are often fitted with vibratory devices to enhance their effectiveness. 6.Kneading - shear is applied by alternating movement in adjacent positions. An example, combined with rolling compaction, is the 'sheepsfoot' roller used in waste compaction at landfills. Test methods in laboratory

7 Soil compactors are used to perform test methods which cover laboratory compaction methods used to determinethe relationship between molding water content and dryunit weight of soils. Soil placed as engineering fill is compacted to a dense state to obtain satisfactory engineering properties such as, shear strength, compressibility, or permeability. In addition, foundation soils are often compacted to improve their engineering properties. Laboratory compaction tests provide the basis for determining the percent compaction and molding water content needed to achieve the required engineering properties, and for controlling construction to assure that the required compaction and water contents are achieved. Test methods such as EN , EN , ASTM D698, ASTM D1557, AASHTO T99, AASHTO T180, AASHTO T193, BS 1377:4 provide soil compaction testing procedures. The scope of this presentation is targeted at relating the valued in-situ density of soil to its maximum dry density in the laboratory ASTM D698/ AASHTO T99 for the laboratory test and sand pouring replacement for the in-situ test shall be discussed

8 The compaction test covers the determination of the mass of dry soil per cubic meter when the soil is compacted in a specific manner over a range of moisture content including the mass of dry soil per cubic meter. Taking Standard proctor (ASTM D698/ASH TOT99) for presentation Equipments for Proctor s Test for Compaction of Soil 1.Compaction mould, capacity 1000ml. 2.Rammer, mass 2.5kg (5.5lb) 3.Detachable base plate 4.Collar, 60mm high 5.IS sieve, 4.75 mm 6.Oven 7.Desiccator 8.Weighing balance, accuracy 1g 9.Large mixing pan 10.Straight edge 11.Spatula 12.Graduated jar 13.Mixing tools, spoons, trowels, etc. Procedure of Proctor s Test for Compaction of Soil

9 1. Take about 20kg of air-dried soil. Sieve it through 20mm and 4.7mm sieve. 2. Calculate the percentage retained on 20mm sieve and 4.75mm sieve, and the percentage passing 4.75mm sieve. 3. If the percentage retained on 4.75mm sieve is greater than 20, use the large mould of 150mm diameter. If it is less than 20%, the standard mould of 100mm diameter can be used. The following procedure is for the standard mould. 4. Mix the soil retained on 4.75mm sieve and that passing 4.75mm sieve in proportions determined in step (2) to obtain about 16 to 18 kg of soil specimen. 5. Clean and dry the mould and the base plate. Grease them lightly. 6. Weigh the mould with the base plate to the nearest 1 gram. 7. Take about kg of soil specimen. Add water to it to bring the water content to about 4% if the soil is sandy and to about 8%if the soil is clayey. 8. Keep the soil in an air-tight container for about 18 to 20 hours for maturing. Mix the soil thoroughly. Divide the processed soil into 6 to 8 parts. 9. Attach the collar to the mould. Place the mould on a solid

10 base. 10. Take about 2.5kg of the processed soil, and hence place it in the mould in 3 equal layers. Take about one-third the quantity first, and compact it by giving 25 blows of the rammer. The blows should be uniformly distributed over the surface of each layer. The top surface of the first layer be scratched with spatula before placing the second layer. The second layer should also be compacted by 25 blows of rammer. Likewise, place the third layer and compact it. The amount of the soil used should be just sufficient to fill the mould ad leaving about 5mm above the top of the mould to be struck off when the collar is removed. 11. Remove the collar and trim off the excess soil projecting above the mould using a straight edge. 12. Clean the base plate and the mould from outside. Weigh it to the nearest gram. 13. Remove the soil from the mould. The soil may also be ejected out. 14. Take the soil samples for the water content determination from the top, middle and bottom portions. Determine the water content. 15. Add about 3% of the water to a fresh portion of the processed soil, and repeat the steps 10 to 14 until there's fall in

11 the dry density of the soil. Note: computation will be going on simultaneously during the test procedures so as to know the dry density at each set of test. Field Density Test Determination of field density of cohesion less soil is not possible by core cutter method, because it is not possible to obtain a core sample. In such situation, the sand replacement method is employed to determine the unit weight. In sand replacement method, a small cylindrical pit is excavated and the weight of the soil excavated from the pit is measured. Sand whose density is

12 known is filled into the pit. By measuring the weight of sand required to fill the pit and knowing its density the volume of pit is calculated. Knowing the weight of soil excavated from the pit and the volume of pit, the density of soil is calculated. Apparatus for In-Situ Density Test 1.Sand pouring cylinder 2.Calibrating can 3.Metal tray with a central hole 4.Dry sand (passing through 600 micron sieve and retained in 300 micron sieve) 5.Balance or (any weight determinant) 6.Moisture content bins or speedy moisture tester 7.Glass plate 8.Metal tray 9.Scraper tool 10. Bent spoon dibber 11. Hammer Here are the procedure on how to do in-situ Density test. Place the metal tray. The technician can now place the metal tray as per Consultant or quality engineer preferred location. As a

13 Quality Engineer, you should make sure that the area to be tested is compacted and within the area submitted in the Inspection Request. Digging the soil. A helper will start to dig the soil by a using pointed steel rod (250mm long mm dia.) and a hammer. The head of the rod shall be stricken at slow speed and at conditional pressure. Use gloves for hand protection to prevent hand injury..collect the excavated soil into the tray and weigh the soil (W) Measuring the depth of hole.while the digging progresses, monitor the depth of hole by measuring a ruler, make sure that the depth is 200 mm or 150 mm depending on the requirement of the specification. If the depth is not yet achieved continue digging until it reach the desired or required depth. Pouring silica or calibrated sand in the hole. Once the hole is properly shaped to the diameter of 200 mm just the same diameter that of the hole of the metal tray and the depth has reached. Place the pouring cylinder onto the metal tray. Pour the silica or calibrated sand inside the pouring cylinder make sure

14 no one will hold or touch the pouring cylinder that may cause vibration. Taking the silica or calibrated sand from the hole. The hole, once filled with silica or calibrated sand and when the hole has fully filled, remove the silica and place it to extracontainer it may use again for the next set of compaction. Before pouring the silica or calibrated sand, the weight of the cylinder before pouring, after pouring and weight of sand in hole must be determined respectively. To get the moisture content of the soil sample dug using a speedy moisture tester "though any means can be adopted to determine the moisture content ", the moisture measurements will be made by mixing a weighed sample of material "6g mostly " with a spoon of calcium carbide reagent in the speedy test. The two substances will be mixed by shaking the tester. The speedy moisture content value shall be taken from the speedy tester. This is determined by noting the highest value before fall. The speedy moisture content value is not the actual moisture content value. To get the actual moisture content,w, it's m/(1m/100).taking m as the speedy moisture value and w as the

15 actual moisture content value. Thereafter the dry density of the soil can be determined End- Product Specifications In end- product specifications, the required field dry density is specified as a percentage of the laboratory maximum dry density, usually 90% to95%. The target parameters are specified based on laboratory test results.the field water content working rangeis usually within ± 2% of the laboratory optimum moisture content.it is necessary to control the moisturecontent so that it is

16 near the chosen value. From the borrow pit, if the soil is dry, water is sprinkled and mixed thoroughly before compacting. If the soil is too wet, it is excavated in advance and dried.in the field, compaction is done in successive horizontal layers. After each layer has been compacted, the water content and the in-situ density are determined at several random locations. These are then compared with the laboratory OMC and MDD using either of these two methods: the sand replacement method, or the core cutter method. Note : the consulting geotechnical engineer will give the specifications of the relative compaction value. The above is the

17 result,computation and calculations of laboratory compaction tests and in-situ density test conducted Now let's go for the relative value of the two tests conducted Be reminded that the percentage of field density to laboratory compaction is the relative compaction as the defined earlier. The end product result is stated to be between 90 to 95% Though the specification of the geotechnical engineer must be strictly adhered ro From the lately computed data: FD/LD X 100% will give 1.93/2.1 X 100 = 91.9% which is still in line with the specifications. From the above results, the engineer in charge is on the right track. I'm still Habeeb Oladapo Olawole and very mindful of YCEF mission which is to bridge the openings between all young

18 active and intelligent Civil Engineers #WeAreYCEF References Das, Braga M (2002) Principles of Geotechnical Engineering McCarthy, D and F (2007) Essentials Soil Mechanics and Foundation Olawole, Habeeb O (2013) Effects of CuSO4 contamination on engineering properties of lateritic soil. Habeeb Oladapo Olawole olawoleh.oladapo@live.com