Hi I need help with my geomorphology lab Attachment Preview: 376_lab1_sed_properties-F14.pdf Download Attachment This is an unformatted preview. Please download the attached document for the original format. GEOG 376: Laboratory 1 Fall 2014 University of Victoria -­? Department of Geography GEOG376 PROCESS GEOMORPHOLOGY Instructor: Dr. Dan H. Shugar LABORATORY 1: GEOTECHNICAL PROPERTIES OF SEDIMENTS Introduction: Sedimentary deposits and soils are known as three-­?phase composite materials that consist of a matrix of solid particles and void spaces filled with water and/or air. The matrix consists of a range of grain sizes (‘particle-­?size distribution’) that is classified broadly as fine-­?grained (clay and silt) and coarse-­? grained (sand and gravel) deposits. Within the matrix are essentially two main sources of strength: i) interparticle friction and ii) cohesion. Frictional resistance results from surface-­?to-­?surface friction, interlocking of particles, packing, and any rearrangement (e.g., compaction or expansion/dilation) that occurs during applied forces (shearing stress, ?). Cohesive force results from: chemical cementation between particles, electrostatic and electromagnetic forces, and moisture content. Imagine these forces at work between billions of grains in any sedimentary deposit. Combined, these forces represent the shear strength (S) of a deposit. See pages 101-­?109 in the Ritter et al. text also. In nature, soils and sediments often experience changes in both applied shearing stresses and internal shear strength. Often the outcome is for the deposit to deform, or change shape (known as strain). The nature of this deformation depends on how the forces are transferred through the deposit and how resistant the substance is to these applied forces. Rheology is the geotechnical study of stress-­? strain responses, or how substances deform in response to applied shear stresses. Responses can include fracture like a brittle solid (e.g., rock), plastic deformation (e.g., ice), or viscous liquid flow (e.g., mudflow). Moisture and air trapped within deposits can affect rheological responses by exerting pressure within the matrix. Negative (suction) pressures typically enhance shear strength while positive pressures reduce shear strength by reducing interparticle friction. For example, if shear force is applied faster than the air and/or water can escape, the pore air or water pressure increases, causing effective or interparticle forces to decrease, which weakens the soil. In soils with appreciable water content, when external shear forces equals the internal pore pressure, the soil can liquefy and flow. Figure 1 shows the effect of shearing stress on sand particles and resulting change in particle alignment and packing density1. As shearing stress is applied, resistance of the sediment (shear strength) is a function of interparticle friction and packing arrangement. As particles rotate over one another, the packing density changes, which causes sediment volume to increase (dilation) or decrease (compression) depending on particle arrangement. For example, in stage (1) a large void in the matrix is maintained by particle interlocking; (2) counterclockwise strain and particle rearrangement causes the void to collapse; (3) continued shear causes more voids to form or enlargen; (4) voids may collapse as stress direction changes. Imagine how this may play out during an earthquake or landslide, for example. 1 Modified from Youd (1977) as in NASA Educational Brief EB-2002-02-53-MSFC 1 of 10 GEOG 376: Laboratory 1 Fall 2014 5 Purpose & objectives: buildings, managing undeveloped land, and handling The purpose of granular is to conduct experiments to test the shear strength of soils. The lab powdered and this lab materials in chemical, agricultural, and other industries. involves two tests used by geomorphologists and geotechnical engineers to characterize the rheology of sediments and their potential for of ass wasting. soil The weightless environment m space allows mechanics experiments at low effective stresses with Notes: very low confining pressures to proceed slowly for detailed tstudy. Specimen weight is no longer a factor, ust submit individual lab reports. • For his lab, please work in groups but each of you m and the stressll questions in a lab report that includes any results components (tables, figures, plots, etc.). • Answer a across the specimen is constant. This yields measurements tthat canspreadsheet package & word processor in preparing this report. You are expected o use a be applied to larger problems on Earth. • To save time, conduct experiments FIRST to collect data for your analyses. Experiments can be done in any order, so rotate amongst stations. Save your calculations and analyses for afterward (e.g. MGM has flown twice on the Space Shuttle (STSweek 2 Figure 4), involving nine dry sand 79 and -89; ) 4. An astronaut a soil sample module into specimens. These were highly successful, showing Figureexperiment in insertswill Shuttle middeck. data to • Use the spreadsheet (provided) to compile your data. For apparatus 2 the Space provide your (NASA) you the MGM strengthTA who will compile ALL times greater and the properties two to three of the data for your section and you will use this master dataset to stiffness properties ten times greater than conventional theory predicted. On the STS-107 mission answer the questions. (scheduled for 2002), MGM scientists will investigate conditions with water-saturated sand resem• USE CARE in your experiments. Aim to produce repeatable results. Sloppy work = sloppy data! bling soil on Earth. Three sand specimens will be used in nine experiments. MGM can also benefit • fromDo not contaminate (mix) samples. Place all wet samples in the respective collection simu- for extended tests aboard the International Space Station, including experiments under dishes lateddrying. and ure to clean up all workspaces when finished. lunar Be s Martian gravity in the science centrifuge. The heart of MGM is a column of 1.3 kg (2.8 lbs.) of sand, 7.5 cm in diameter by 15 cm tall (3 x Experiment 1: Displacement shear test 6 in.). This is Ottawa F-75 banding sand, a natural quartz sand (silicon dioxide) with fine grains 0.1 to 0.3 mm in diameter.aw from GEOG103, which used inhat the amount of hexperiments and force (T) Recall Coulomb’s Friction L Ottawa sand is widely states t civil engineering orizontal shearing evaluations. The sand is contained in a latex block over a flat surface with a normal cameras canload of N, is required to initiate the movement of a sleeve printed with a grid pattern so (resistance) record changes inbshape and (position. ???? = ???????? metal plates on three guide rods cap each end of the Tungsten described y Equation 1): (1) specimen. The specimen assembly is contained in a test cell N where ? is coefficient of static friction between the block and a shaped like an equilateral prism and comprising a Lexan flat slip plane. Equation (2) expresses confine and stabilize jacket filled with pressurized water toCoulomb’s law for sand, ????! = ????! ???????????????? (2) the specimen during launch and re-entry. An electric stepper motor moves the top platen to compress and relax the to T/A T where ?f is shear stress along a slip plane equivalent sand column. A load cell measures forces. The test cell is held on a (where T is shear force at point of slippage and A is area of a rigid test/observation pad mounted between an array of plane parallel to T), ?n is the normal stress on the plane (equal to three CCD cameras. Because this mechanism is too complex (?n)f N/A, where N is the normal force), and the internal friction angle to replicate in a classroom, this exercise uses a simpler device. Slip plane ? is related to ? (i.e., tan ? = ?). At the condition of slippage, complete failure (mass wasting) of the sediment mass may not Coulomb’s Friction Law necessarily occur but the initiation of movement begins between You may the two layers. recall Coulomb’s friction law from your physics courses. If a wooden block is pushed horizontally across a Figure 2 (right)2 horizontal force (T) required to initiate table (Figure 5), thedemonstrates Coulomb’s Friction Law by ?f showing movement of a b Equation (1) where µ esponse to an the movement is given inlock on a flat surface in ris the coeffiapplied shearing force, T, and the block and the table and N cient of static friction betweennormal (resisting) force, N. The lower figure force. The friction angle ø is related to µ (tan ø is the normal shows a slippage plain in a sediment matrix and Figure 5. (a) Slip of a wooden block, (b) A slip plane in i soil mass (Budhu, 2000). =related termssof stress,aCoulomb’s tress for ), which are both a function of anternal friction angle, ?. µ). In shear tress (?f) nd normal s law (?n sand is expressed Mechanics of Granular Materials 2 EB-2002-03-53-MSFC from NASA Educational Brief EB-2002-02-53-MSFC or see also Fig. 4.20 in the Ritter text. 2 of 10 cial apparatuses that meet certain standards. This educational brief illustrates the standard direct shear test to determine the shear strength of soils. The standard procedure is modified to enable students (grades 9-12) to perform experiments using materials available at local hardware stores. Note: This experiment should only be used for educational demonstrations because it uses nonGEOG 376: Laboratory 1 standard equipment. The results will not be valid in a real-world civil engineering application. Fall 2014 The DST apparatus consists of a horizontally split box (Figure 6) and a frame to apply a horizontal shear load (T) under constant normal load (N). It is known as a shear box. Soil is placed in Experimental Procedure: the shear box, where the top half is moved relative to the horizontal plane (AB). Normal (or vertical) force (N) is applied through a platen or plate resting on the top of the soil. The shear force (T) This experiment tests the smotor strength of soils using aby weights through a pulley tandard direct shear test is applied through a hear for displacement control or modified version of a s system for load control. Usually, three or more tests are f a sample c a soil sample using three different (DST). The DST apparatus or ‘shear box’ consists ocarried out on hamber that is split horizontally to facilitate a constant vertical forces. Failure is determined when the soil cannot resist any further increment of failure plain (horizontal), a cap that covers the box slips). If and plotulley system to anormal stress, you shear stress Figure 3 force (i.e., when the upper chamber, you a p shear stress versus pply a horizontal get a straight line with a slope ediment is placed (T) under a constant normal load (N). Sequal to ? (Figure 7). in the shear box and the top half can move relative N ?n T Possible failure zone ? A B Shear Stress (?f) to the horizontal plane (AB). Normal (vertical) force (N) is applied through the cap resting on the top of the sediment sample chamber. Shear stress (T) is applied by attaching weights to the pulley system. ? Normal Stress (?n) Slip or failure plane Figure 6. Shear box (Budhu, 2000). Figure 7. Coulomb shear stress versus normal stress relation. Figure 3 shows the operating principle of the shear box apparatus (left) and a plot of shear stress versus normal stress (right)3. Typically, three or more tests are conducted on a sample using three different constant normal stresses. Failure occurs when the soil cannot resist any further shear stress and the upper half of the shear box slips. If you plot shear stress versus normal stress, you get a straight line with a slope Mechanics of Granular Materials EB-2002-03-53-MSFC • Attach equal to ? the m m-­?1) pulley andrweight platform to the eye hook (in string, (Figure 3, ight). on the top half of the shear box. 9 Experiment Procedure Cap Record all data on the data sheet at the end of this brief. • Obtain a sample of about 3000 grams (~6.5 lb) of dry, clean sand. You can purchase it from local hardware stores or from swimming pool supply stores (uniform sand is used as a filter material in many applications). H1 H3 Direct Shear Box H0 Sand specimen H2 • Weigh the cap and record its mass (Mcap). mbled DST box with H0 = H1 + H2 - H3 • Assemble DST box at startshear(left) and and mount it on displacement Figure 10. the direct of test box, weight is added to cause the laboraFigure 11. Determining the height of the sand (right). Figure 4 (Figure 10). the experiment (left) and after failure tory benchshows a cross-­?section of the shear box at the start of specimen. (middle) in response to a critical shearing stress. Cross-­?section of the sample chamber (right) shows • Measure the depth, H2, ofor the experiment. the height, H3, of the top cap as shown in Figure important measurements f the shear box and Materials list and estimates prices for shear strength of sand experiment 11. Record these measurements. nsity fiberboard (0.5 in. x 2 x 2 ft.)*** quantity* price /unit total price** 1 4.00 4.00 • Weigh the dish filled with the sand to be tested. Place the sand in a container (e.g., beaker or dish) x 1.57 weigh the dish with the sand and record the weight. 7 x 105.4 x 40 mm (0.5 x 4.15 thenin.) 7 x 105.4 x 105.4 mm (0.5 x 4.15 x 4.15 in.) 7 x 80 x 40 mm (0.5 x 3.14 x 1.57 in.) 7 x 105.4 x 60 mm (0.5 x 4.15 x 2.36 in.) • Pour the sand slowly into the shear box while the pins hold the two parts of the shear box together. Compact the1 sand with a rubber 1.88 tamper or gently vibrate the table with your fist. The al pins ~3 x 85mm (1/8 x 3.3"; only 2 needed) 1.88 shear box should be filled with4.00 enough material so that the depth of sand in the shear box is mm shims 1 4.00 3 k 79mm x 79mm x 50mm 1 0.31 0.31 above the slip or failure plane NASAabout 80 mm deep). (i.e., Educational Brief EB-2002-02-53-MSFC modified from Budhu (2000) as in 7 x 80 x 60 mm (0.5 x 3.14 x 1.57 in.) 1" phillips screws e hooks 1 3.89 5.00 1 0.83 0.83 8 0.53 4.24 3 of 10 • Weigh the container with the leftover sand not poured into the box to determine the weight of 1 3.50 3.50 et (weight platform) the sand used in the test. 1 2.00 2.00 GEOG 376: Laboratory 1 Fall 2014 Materials: sand sample (in bin), shear box (DST) device, electronic balance, calculator, spreadsheet, mm ruler or tape measure, various weights, curiosity and/or enthusiasm. Steps: A. Assemble the shear box on the laboratory bench as shown in Fig. 4 (above, left). Ensure that: a) the pins that hold the two parts of the shear box together are in place, and b) the shims that separate the two parts of the shear box are also in place. B. Weigh the sample chamber cap (with rubber bands) and record its mass (Mcap). Record ALL measurements and related calculations in Table 1 (below). You will submit this table with your writeup. A digital copy will also be provided. C. Weigh the sample container (beaker) that holds the sand to be tested. Record this value. D. Fill the sample chamber slowly with the sand sample to a height above the failure plane that is approximately equal to the depth below it. E. Level the sand surface by gently shaking the chamber once or twice, and gently place the cap onto the sample. DO NOT compress the sample. Gently tap the chamber with your finger to allow the sample to settle. F. Weigh the sample container again with the leftover sand to determine the weight of the sample used in the test. Refill the beaker with sand. G. Fill a red bottle with ~250g sand. DO NOT fill bottles with water! Record the mass in table. Place the mass (MN) on top of the cap to provide the normal load, N. H. Measure and record the initial height, H0, of the sand sample as shown in Figure 4. I. Carefully remove the shims and the pins from the shear box. J. Weigh the weight platform (bucket or 2L pop bottle) and record the weight. Carefully attach it to the shear box cable below the pulley (see Figure 4). Avoid disturbing the shear box sample chamber while doing this. a) Note: the shear box should NOT move or displace under the weight of the bucket alone. If it does, you must reset the sample chamber and start again. K. Gently add weight in small increments (~50 g) by pouring sand slowly in to the bucket/pop bottle. Carefully watch the top half of the shear box for movement. Keep adding weight until the top half of the shear box starts sliding along the shear plane (Figure 4, middle). L. Record the mass (MS) that caused the shearing by weighing the bucket with sand. M. Take the shear box apart and remove the sand. Place it back into the sample container. N. Repeat the test (steps 3 through 13) for two other different normal loads (MN2 and MN3, or one 500g weight and one 1kg weight). O. Repeat the test (steps 3 through 13) for a sample that has been compacted by tapping the cap a few times with a solid object (e.g., hammer, textbook, etc. NOT a beaker!). Apply the same normal load (MNC) that you used for the second test (MN2 500g). 4 of 10 GEOG 376: Laboratory 1 Fall 2014 Calculations4 (10 marks): • For EACH of the 4 experiments (i.e., three MN values + MNC) record ALL measurements and calculate the following quantities (REMEMBER TO CHECK UNITS!). Compile values into Table 1. o Initial volume of the sand sample (V0) in m3 by multiplying the sample chamber dimensions by H0 (i.e., 0.08 x 0.08 x H0) o Sample cross-­?sectional area, A, as the cross-­?sectional area of the sample chamber in m2. o Sample dry unit weight, ?d = [(mass of sand in kg) x g]/V0, where g = 9.81 m s-­?2 o Normal force, N = (MN + Mcap) x g o Shear force, T = (MN + MS + Mcap) x g o Normal stress, ?n = N/A o Shear stress at failure, ?f = T/A Experiment 1 Questions (27 marks): 1. Explain the difference between shearing force (T) and shearing stress (?f) in terms of both fundamental dimensions (e.g., M L T) and actual physical quantities. How do the units of measurement differ for each? Hint: refer to the various equations provided above. Physically, what do these units measure and how are they different? (4 marks) 2. Plot the ?n vs. ?f relation (see Figure 3) in a spreadsheet. Fit a linear regression model (best-­?fit line) through the data. Include the equation of the regression model and R2 value on the plot. Also include full ancillary information (name, SID, instructor, lab section, title, legend, scales, units, etc) (4 marks) a. Describe any general patterns or trends that you see in your data. For instance, how does your plot compare to the example in Figure 3? What does your plot indicate, generally, about the relationship between ?n and ?f. Is it a strong or weak relationship (and how do you know this)? Is it positive or negative and what does that mean? Are there any oddities in your plot and what might those indicate. (5 marks) b. Using the slope of your regression line, calculate the value of the internal friction angle (?) in degrees. Recall, slope can be determined from the equation of the regression model (i.e., in the form y = m x + b, where m is slope) and converted to degrees. (2 marks) c. What does the internal friction angle mean, physically? How does your value compare to the typical angle of repose5 for dry sand (34°). Explain why these values are different or the same. (4 marks) 3. How did your compacted sample experiment (MNC) compare to the uncompacted sample runs (MN1-­?3)? With specific reference to the basic forces at work within the sediment matrix (see Figure 2 and equation 2), explain any differences. Based on this (albeit limited) observation, what effect(s) might compaction have on the strength of sedimentary deposits? (4 marks) 4. How might the addition of moisture affect the response of this same sand to applied stress? Again, refer to the basic forces at work and consider our discussion in lecture on the roles of moisture in sedimentary deposits. (4 marks) 4 Pay close attention to unit conversions here. Usually, SI units are used in such calculations (e.g., L as m, etc.) Recall from your experiments in GEOG103 where you measured the resting angle of loose sand grains that angle of repose is a measure of static friction within a sediment matrix. 5 5 of 10 GEOG 376: Laboratory 1 Fall 2014 Table 1: Experimental data for direct shear test experiment. Use this for recording during the experiment, but please enter these data into the spreadsheet provided on CourseSpaces. (10 marks, see Calculations above) Date: Experiment conducted by: Lab section: Lab instructor: Experimental condition: MN1 MN2 MN3 MNC A) Sample Data 1. Sample area, A (m2) 2. Mcap (g) 3. Mass of full sample container (beaker, g) 4. Mass of sample container after sand placed in chamber (g) 5. Mass of the weight platform (bucket) (g) 6. H0 (mm) 7. Normal mass, MN (g) 8. Shear mass, MS (g) 7. Mass of sand sample in chamber [(3) – (4)] (g) 8. Initial sample volume, V0 (m3) 9. Sample dry unit weight, ?d (kN m-­?3) 10. Normal force, N (kN) 11. Normal stress, ?n (kN m ) 12. Shear force, T (kN) B) Calculations -­?2 -­?2 13. Shear stress, ?f (kN m ) 6 of 10 GEOG 376: Laboratory 1 Fall 2014 Experiment 2: Testing Liquid and Plastic Limits for sediment deformation and failure Usually, sandy soils are stable and provide good support to applied normal loads (e.g., building foundations, road bases, circus tents) so long as they are not subjected to dynamic (changing) load conditions (e.g., shaking). Under normal conditions then, packing density and moisture content (dry vs. fully saturated pore spaces) are the main factors that control shear strength within sediment deposits and, in turn, how they respond to more dynamic load conditions such as earthquakes. In many areas, soils and sedimentary deposits extend below the groundwater table where the matrix becomes fully saturated. During an earthquake as sediments rearrange (Figure 1) some of this moisture is relocated as the pore matrix changes and pore water pressures rise. In response, particles lose contact (i.e., interparticle friction decreases) and soil flowage or liquefaction can occur. After the pore water pressure decreases, sediment particles typically settle in a denser condition, which results in ground subsidence (settling). The amount of settling depends on the amount of liquefaction and the normal load that existed on top of the sediments. Atterberg limits In 1911, a series of simple tests were devised by a Swedish physicist (Atterberg) to correlate moisture content and ‘plasticity’ of sediment samples. This technique is still used widely today to describe and classify cohesive soils (i.e., not unconsolidated sediments) and to determine properties related to their strength and compressibility – critical factors in the mass wasting process. Read more on p. 101-­?104 in Ritter et al. text and see Figs. 4.23 and 4.24. In general, moisture-­?laden sand to clay-­?sized sediments exist in several rheological states categorized by order of decreasing moisture content, Mc: 1) suspension in liquid, 2) viscous liquid, 3) plastic solid, 4) semi-­? plastic solid, 5) solid. In each state, the sediment will behave differently to an applied stress. This is because water exerts pressure within pore spaces (p) and the amount of pressure changes with moisture content. In general, p becomes more positive (outward pressure) with increasing moisture vs. more negative (suction pressure) for drier sediments. So, for different sediments and Mc there will be some threshold at which the deposit changes from behaving as a cohesive solid to a deformable plastic or viscous fluid that can fail or flow. These moisture contents (or consistency limits) define the Plastic Limit (PL) and Liquid Limit (LL) respectively (see Fig. 4.23 in text). The limits are derived experimentally with 2 relatively simple tests. Liquid Limit (LL): the threshold between liquid & plastic states characterized by the minimum Mc at which a sediment will flow under it's own weight. Defined by the Mc at which 25 taps in a LL device will close a standard groove in the sample. Plastic Limit (PL)6: the threshold between plastic & semi-­?solid states characterized by the minimum Mc at which soil can be rolled into a thread 3mm in diameter on a glass plate without breaking. The range in Mc between these limits defines how the deposit responds to this transition in rheological response (i.e., greater range, larger threshold transition). This is described using the Plasticity Index, PI = LL – PL. In general, LL and PL both increase as sediments become finer. 6 Note that cohesionless sediments (e.g., sand & gravel) will have no ‘plastic’ stage and thus, the LL and PL coincide. 7 of 10 GEOG 376: Laboratory 1 Fall 2014 NOTES: • Provide your data from this experiment to your TA who will compile it into a master dataset that you will use to answer the questions. • Someone in your group must return 24hr after the experiment to weigh dried samples and record data. Your TA will collect and email everyone the data shortly thereafter. • USE CARE in your experiments. Aim to produce repeatable results. Sloppy work = sloppy data! • Do not contaminate (mix) samples. Place all wet samples in the respective collection dishes for drying. Be sure to clean up all workspaces when finished. Experiment 2a procedure: Liquid Limit Materials: fine grained sediment sample, Liquid Limit (Atterberg) device, groove tool, spatula, preparation dish, foil weighing dish (tared), plastic wrap, drying oven, electronic balance. Steps: To determine LL, prepare a sample of the fine sediment and test in the Liquid Limit device as follows. Be quick in weighing your samples and recording your results. Evaporation of water from the sample affects not only the accuracy of your results, but will also hold up the rest of the group. A. Weigh two foil dishes and write group name AND experiment number (e.g. 2a or 2b) on bottom in marker. Record empty dish weights. B. Prepare ~100 g of sample in a sample dish. Add distilled water sparingly until the sample has the consistency of a stiff paste. C. Place a portion of the sample in the bowl of the LL device. Level it with a spatula. Make a groove down the centre using the groove tool. The depth of clay should not exceed the depth of the groove. D. Rotate the handle at a slow, steady pace, count the number of taps it takes to close the groove by 1 cm along the length of the groove. The number of taps will depend on the consistency of your sample. If it does not close by 40 taps, you must add moisture (go back to step B). E. Determine the Mc of the sample after closure. To do this, obtain a 20-­?50g sample from along the groove, place quickly in a pre-­?weighed (tared) oven-­?safe foil dish, and weigh the sample. Record the weight of the wet sample (Ww) by subtracting the dish weight (see above). Give dish to TA to place in drying oven at 105°C for 24 hours. Save remainder of sample for experiment 2b (below). • Note: cover the remaining sample in the LL device with plastic wrap. You will obtain a sample for the next experiment. F. Return the next day, remove sample from the oven (or TA will do this for you) and allow to cool to room temperature then weigh the sample again. Estimate Mc as a % using the ratio of mass of moisture to mass of dry soil as follows: Mc = [(Ww – Wd) / Ww] x 100 where Mc = moisture content (%), Ww = wet weight of sample, Wd = dry weight of sample. Note: be sure to subtract the weight of the foil dish from your calculations. G. Estimate the Liquid Limit of the sample by plotting the number of taps against the MC of the sample. Be sure to use data from all lab groups in your section. From the regression equation, the MC at 25 taps defines the LL. 8 of 10 GEOG 376: Laboratory 1 Fall 2014 Experiment 2b procedure: Plastic Limit Materials: sediment sample from Liquid Limit test, glass plate, ruler or calipers, foil weighing dish (tared), drying oven, electronic balance. Steps: Note: As in the previous experiment, be quick & careful in weighing your samples & recording results. A. Take a sample of about 20 g from the remaining prepared paste in the LL device from Exp. 2a. Place it on a glass plate and work the sample into a ball. B. Mould the ball between the fingers and palms of your hands until it has dried sufficiently for slight cracks to appear in the surface. Split the sample into 3 equal sized portions and follow steps C and D for each. C. Roll each sub-­?sample into a thread approx. 6mm in diameter on the glass plate by repeatedly rolling it from finger-­?tip to the second joint of your finger. Continue with enough pressure to reduce the diameter of the thread to about 3mm in five to ten complete rolling motions. Use a ruler or calipers to measure the diameter. Note: it is important to maintain a steady pressure while doing this. D. If cracks occur and the thread crumbles at 3mm, go to next step E. Otherwise, pick up the sample, remould it between the fingers to dry it further and repeat step C. E. Gather crumbled pieces (do not mould them together) and place them into a pre-­?weighed, pre-­?labeled (see above) oven-­?safe foil dish. Place all crumbled portions for all 3 threads into this container. Weigh dish and sample and record weights. F. Determine the Mc of this sample as you did in exp. 2a above. This moisture content is the Plastic Limit for your sample. G. Calculate the Plasticity Index (PI) of your sample. H. Provide results to TA as soon as possible. You will need everyone’s results to complete the questions. Experiment 2 Questions (33 marks): Your TA will gather results from each group in your section and make these data available to you by via email or a spreadsheet on CourseSpaces. Use these results to answer the following questions. 5. Discuss how LL, PL, and PI varied for the sample. Do this by calculating standard deviation and mean values from the group dataset and disscuss the variation in each of these for the dataset. (6 marks) 6. Table 2 below shows typical values of LL, PL and PI for various sediments. How do our grouped results compare for this size of sediment? Explain any discrepancies. (5 marks) Soil Type Clay Silty Clay Silt Sandy Clay Loam Sandy Loam Sand Table 2: Atterberg Limits for Average Soils LL PL 50-­?100+ 25-­?40 40-­?50 20-­?25 30-­?40 20 25-­?30 18 20-­?25 16 15 15 PI 25-­?60 20-­?25 10-­?20 7-­?10 5-­?7 0 9 of 10 GEOG 376: Laboratory 1 Fall 2014 7. Where does our sample sit in the plasticity chart shown in Fig. 4.24 (below)? Does this make sense based on what you know about the properties of the sediment? How do your PI values match the ranges discussed in class? (3 marks) 8. According to our results, at what average Mc will this sediment start to deform under it’s own weight? What are the geomorphic implications of this? (3 marks) 9. Assuming that the average Mc of this sediment in it’s natural setting ranges 10 – 25%, would you consider this an ‘unstable’ sediment? Why or why not? (3 marks) 10. What does our mean PI value express about the threshold response of this sediment? What are the geomorphic implications of this (i.e., for potential mass failure?) (3 marks) 11. What other factors affect the PL and/or LL of a sedimentary deposit? Expand briefly with respect to how this factor affects the fundamental forces at work (2 marks) 12. What possible sources of error do you see with this experiment? (3 marks) 13. Briefly discuss one benefit and one limitation of the techniques used in this lab (DST, LL and PL tests) for determining the potential for mass wasting of sediments. Are they useful for actually predicting mass wasting hazards? Why/not? (5 marks) Figure 4.24 (Ritter et al. 2011) Plasticity chart showing example plots of several problem soils susceptible to expansion. Total: 70 marks 10 of 10