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Version: Written by: Chase Williams Last updated on October 08, Allow the dish to air dry about 6 hours until the color of the soil pat becomes lighter. Then put the dish with the soil into the oven to dry. Determine the mass of the dish and the oven-dry soil pat W3 in grams. Remove the soil pat from the dish.

In order to find the volume ofthe shrinkage limit dish Vi , fill the dish with mercury. Note: The dish should be placed on a watch glass. Use the three-pronged glass plate and level the surface of the mercury iIi the dish. The excess mercury will flow into the watch glass. Determine the mass of mercury in the dish W4 in grams..

In order to determine the volume of the dry soil pat VI ' fill the glass cup with mer- cury. The cup should be placed on a watch glass. Using the three-pronged glass plate, level the surface of the mercury in the glass cup. Remove the excess mercury on the watch glass.

Place the dry soil pat on the mercury in the glass cup. The soil pat will float. Now, using the three-pronged glass plate, slowly push the soil pat into the mercury until the soil pat is completely submerged Fig. The displaced mercury will flow out of the glass cup and will be collected onthe watch glass.

Determine the mass of the displaced mercury on the watch glass Ws in grams. Determination of the volume of the soil pat Step' Calculate the initial moisture content of the soil at molding.

Calculate the shrinkage limit. A sample calculation is shown in Table If the ratio of LLISL is large, the soil in the field may undergo undesirable volume change due to change in moisture. New foundations constructed on these soils may show cracks due to shrinking and swelling of the soil that result from seasonal moisture change.

Another parameter called shrinkage ratio SR may also be determined from the shrinkage limit test. Referring to Fig. Also,depending on the type and quantity of clay minerals present, the plastic properties of soils Chapters 6, 7 and 8 may be very different.

Various types of engineering works require the identification and classification of soil in the field. In the design of foundations and earth-retaining struc-. For engineering purposes, there are two major systems that are presently used in the United States. These two systems will be discussed in this chapter.

This classification system has under-gone several changes since then. This system s presently used by federal, state, and county highway departments in the United States. GroupA-i is divided into two subgroups: A-i-a and A-i-b. Soils under group A-7 are also divided into two subgroups: A andA The importance of group index can be ex- plained as follows.

Let us assume that two soils fall under the same group; however, they may have different values of OJ. The soil that has a lower value of group index is likely to perform better as a highway sub grade material. Proceed to Steps 2 and 4.

For this, go to Steps 3 and 5. Determination of Groups or Subgroups 2. For coarse-grained Soils, determine the percent passing U. Then proceed to Table 9. Start from the top line and compare the known soil properties with those given in the table Columns 2 through 6. Go down one line at a time until a line is found for which all the properties of the desired soil matches. The soil group or subgroup is determined from Column I..

For fme-grained soils, determine the liquid limit and the plasticity index. Then go to Table 9. Start from the top line. By matching the soil properties from Columns 2, 3 and 4, determine the proper soil group or subgroup. Determination of Group Index 4. To determine the group index Ol of coarse-grained soils, the following rules need to be observed. If the 01 is positive, round it off to the nearest whole number.

Nonplastic Fine sand I Excellent to A 35 max. Silty and A-2 I clayey gravel A! Silty soil Fair to poor A-5 36 min. I 10 max.

Silty soil.. Fair to poor A-6 36 min. Clayey soil Fair to poor 11 min. A 36 min. A j. However, if it is positive, round it off to the nearest whole number. Expression for Soil Classification 6. The final classification of a soil is given by first writing down the group or subgroup followed by the group index in parenthesis.

ClassifY the soils according to the. Soil A: Percent passing No. So this is a coarse-grained soil. From Equation 7. From Table , by matching, the soil is found to belong to subgroup A From Equation 9. So, the soil can be classified as A O. Soil B: 1. So this is a fine-grained soil. The liquid limit of the soil is From Table , the soil is either A or A So this soil isA Soil Mechanics Laboratory Manual 57 4.

So the soil is classified asA JO. This work was conducted on behalf of the U. Anny Corps of Engineers. At a later date, with the cooperation of the United States Bureau of Reclamation, the classification was modified.

In the pre-sent form, it is widely used by foundation engineers all over the world. If it is peat i. For all other soils, determine the percent of soil passing through U. Determine the percent retained on U. For fine-grained soils i. If the soil is organic, the group symbol can be OH or OL. Determine the percent of sand. For inorganic soils, determine the liquid limit LL and the plasticity index Pl. Go to Step 4e. Figure shows a plasticity chart with group symbols for fine-grained soils.

For coarse-grained soils: a. If R4 ,;; 0. Assume Soil B to be inorganic. So it is a coarse-grained soil. Skip Step 4. Step 5. Thus Cu and Cc values are not needed. Soil B: Step 1. So it is a fine-grained soil. Several relations between k and the void ratio, e, for sandy soils have been proposed.. They are of the form They are a the constant head test and b th.

In this chapter, the constant head test method will be discussed. Soil Mechanics Laboratory Manual Equipment 1. Constant head permeameter 2. Graduated cylinder cc or cc 3. Balance, sensitive up to O. Thermometer, sensitive up to 0. Rubber tubing 6. Stop watch Constant Head Perrrieameter A schematic diagram of a constant head permeameter is shown in Fig. This can be assembled in the laboratory at very low cost. It essentially consists of a plastic soil specimen cylinder, two porous stones, two rubber stoppers, one spring, one constant head chamber, a large funnel, a stand, a scale, three clamps, and some plastic tubes.

The plastic cylinder may have an inside diameter of2. This is because 2. The length of the specimen tube may be about 12 in. Determine the mass of the plastic specimen tube, the porous stones, the spring, and the two rubber stoppers WI ' 2.

Slip the bottom porous stone into the specimen tube, and then fix the bottom rubber stopper to the specimen tube. Collect oven-dry sand in a container. Note: By changing the degree of compaction, a number of test specimens having different void ratios can be prepared. When the length of the specimen tube is about two-third the length of the tube, slip the top porous stone into the tube to rest firmly on the specimen.

Place a spring on the top porous stone, ifnecessary. Fix a rubber stopper to the top of the specimen tube. Note: The spring in the assembled position will not allow any expansion of the speci- men volume, and thus the void ratio, during the test. Measure the length L of the compacted specimen in the tube. Assemble the permeameter near a sink, as shown in Fig. Run water into the top of the large funnel fixed to the stand through a plastic tube from the water inlet.

The water will flow through the specimen to the constant head chamber. After some time, the water will flow into the sink through the outlet in the constant head chamber. Schematic diagram of constant head permeability test setup. Adjust the supply of water to the funnel so that the water level in the funnel remains constant. At the same time, allow the flow to continue for about 10 minutes in order to saturate the specimen.

Note: Some air bubbles may appear in the plastic tube connecting the funnel to the specimen tube. Remove the air bubbles:. After a steady flow is established that is, once the head difference h is constant , col- lect the water flowing out of the constant head chamber Q in a graduated cylinder. Record the collection time t with a stop watch.

Repeat Step 12 three times. Keep the collection time t the same and determine Q. Then find the average value of Q. Change the head difference, h, and repeat Steps II, 12 and 13 about three times. Record the temperature, T, of the water to the nearest degree. Note: This value is sufficiently accUrate for this type of test. Calculate the void ratio of the compacted specimen as follows: Dry density, Pd' of the soil specimen as Thus So calculate kio0c as Soil Mechanics Laboratory Manual 73 Table Variation of Ilrcill2o"c 15 1.

Mass of tube with fittings and specimen, Wz g The falling head penneability test is another experimental procedure to detennine the coefficient of penneability of sand. Falling head penneameter 2. Thennometer 4. Stop watch Falling Head Permeameter A schematic diagram of a falling head penneameter is showb. This consists of a specimen tube essentially the same as that used in the constant head test.

The top of the specimen tube is connected to a burette by plastic tubing. The specimen tube and the burette are held vertically by clamps from a stand. The bottom of the specimen tube is connected to a plastic funnel by a plastic tube. The funnel is held vertically by a clamp from another stand. A scale is also fixed vertically to this stand. Sland f L I- Plastic tut e Figure Schematic diagram of falling head permeability test setup.

Supply water using a plastic tube from the water inlet to the burette. The water will flow from the burette to the specimen and then to the funnel.

Check to see that there is no leak. Remove all air bubbles. Allow the water to flow for some time in order to saturate the specimen. When the funnel is full, water will flow out of it into the sink. Using the pinch cock, close the flow of water through. The pinch cock is located on the plastic pipe connecting the bottom of the specimen to the funnel. Measure the head difference, hI cm see Fig. Open the pinch cock. Water will flow through the burette to the specimen and then out of the funnel.

Record time t with a stop watch until the head difference is equal t6 h2 cm Fig. Close the flow of water through the specimen using the pinch cock. Soil Mechanics Laboratory Manual 77 5. Determine the volume Vw of water that is drained from burette in cm3. Add more water to the burette to make another run.

However, hi and h2 should be changed for each run. Record the temperature, T, of the water to the nearest degree 0C. Calculation The coefficient of permeability can be expressed by the relation. Proctor developed a laboratory compaction test procedure to determine the maximum dry unit weight of compaction of soils which can be used for specification of field compaction. This test is referred to as the' standard Proctor compaction test and is based on the compaction of the soil fraction passing No, 4 U.

Compaction mold 2. Standard Proctor hammer 5. Large flat pan 7. Jack 8. Steel straight edge 9. Moisture cans Drying oven Equipment for Proctor compaction test. Proctor Compaction Mold and Hammer A schematic diagram of the Proctor compaction mold, which is 4 in. There is a base plate and an extension. The inside of the mold is Iho ft3 ;9 cm3. Figure b shows the schematic diagram of a standard Proctor hammer.

The hammer can be lifted and dropped through a vertical distance of 12 in. Obtain about 10 lb 4. Break all the soil lumps. Sieve the soil on a No. Collect all of the minus-4 material in a large pan. This should be about 6lb 2. Now attach the extension to the top of the mold. Each layer should be com- pacted uniformly by the standard Proctor hammer 25 times before the next layer of loose soil is poured into the mold.

Standard Proctor mold and hammer. Note: The layers of loose soil that are being poured into the mold should be such that, at the end ofthe three-layer compaction, the soil should extend slightly above the top of the rim of the compaction mold. Remove the top attachment from the mold. Be careful not to break off any of the compacted soil inside the mold while removing the top attachment. Now the top of the compacted soil will be even with the top of the mold. Remove the base plate from the mold.

Take a moisture can and determine its mass, W3 g. Place the moisture can with the moist soil in the oven to dry to a constant weight. Break the rest ofthe compacted soil to No. Excess soil being trimmed Step 8. Repeat Steps 6 through Continue the test until at least two successive down readings are obtained.

Soil Mechanics Laboratory Manual This can be given by Table shows the calculations for Yzav for the soil tested and re- ported in Table Also dete. Figure shows the results of calculations made in Tables and Weight of mold, WI lb Weight of moist soil, W2 - WI 3. Moisture can number 6. Mass of moisture can, W3 g I Plot of Vd VS. For further discussion on this topic, refer to Das However, ASTM and AASHTO have four different methods for the standard Proctor com- paction test that reflect the size of the mold, the number of blows per layer, and the maximum particle size in a soil used for testing.

Summaries of these methods are given in Table Because of this, in the initial stages of com- paction, the dry unit weight of compaction increases.

However another factor that will control the dry unit weight of compaction of a soil at a given moisture content is the energy of com-paction.

The hammer used for this test weighs 10 lb and drops through a vertical distance of 18 in. Figure 13'-1 shows the standard and modified Proctor test hammers side by side. The compaction mold used in this test is the same as described in Chapter 12 i. Comparison of the standard and modified Proctor compaction hammer. Note: The left-side hammer is for the modified Proctor compaction test. Procedure The procedure is the same as described in Chapter 12, except for Item 6.

The moist soil has to be poured into the mold in five equal layers. Each layer has to be compacted by the modi- fied Proctor hammer with 25 blows per layer.

Soil Mechanics Laboratory Manual 91 Comparison of standard and modified, Proctor compaction test results for the soil reported in Tables and General Comments 1. The modified Proctor compaction test results for the same soil as reported in Tables and and Fig. A comparison ofy dVs. However, for a given void ratio, an increase in the angularity of the soil particles will give a higher value of the soil friction angle. The general range of the angle of friction of sand with relative density is shown in Fig.

Direct shear test machine strain controlled 2. Large porcelain evaporating dish 4. Tamper for compacting sand in the direct shear box " 5.

Spoon Figure shows a direct shear test machine. It consists primarily of a direct shear box, which is split into two halves top and bottom and which holds the soil specimen; a proving ring to measure the horizontal load applied to the specimen; two dial gauges one horizontal and one vertical to measure the deformation of the soil during the test; and a yoke by which a vertical load can be applied to the soil specimen.

A horizontal load to the top half of the shear box is applied by a motor and gear arrangement. In a strain-controlled unit, the rate of movement of the top half of the shear box can be controlled.

General range of the variation of angle of friction of sand with relative density of compaction. Figure shows a direct shear test machine. It consists primarily of a direct shear box, which is split into two halves top and bottom and which holds the soil specimen; a proving ring to measure the horizontal load applied to a specimen; two dial gauges one horizontal and one vertical to measure the deformation of the soil during the test; and a yoke by which a vertical load can be applied to the soil specimen.

In a strain-controlled unit, the rate of movement on the top half of the shear box can be controlled. Figure shows the schematic diagram of the shear box. The shear box is split into two halves-top and bottom. The top and bottom halves of the shear box can be held together by two vertical pins. There is a loading head which can be slipped from the top of the shear box to rest on the soil specimen inside the box. There are also three vertical screws and two horizontal screws on the top half of the shear box.

Remove the shear box assembly. Back off the thrt;e vertical and two horizontal screws. Remove the loading head. Insert the two vertical pins to keep the two halves of the shear box together. Weigh some dry sand in a large porcelain dish, WI' Fill the shear box with sand in small layers.

A tamper may be used to compact the sand layers. The top of the compacted specimen should be about Y. Level the surface of the sand specimen. A direct shear test machine. Determine the dimensions of the soil specimen i. Slip the loading head down from the top of the shear box to rest on the soil specimen. Put the shear box assembly in place in the direct shear machine. N, on the specimen.

This can be done by hanging dead weights to the vertical load yoke. The top crossbars will rest on the loading head of the specimen which, in tum, rests onthe soil specimen. Remove the two vertical pines which were inserted in Step 1 to keep the two halves ofthe shear box together.

Advance the three vertical screws that are located on the side walls of the top half of the shear box. This is done to separate the two halves of the box. Schematic diagram of a direct shear test box. Set the loading head by tightening the two horizontal screws located at the top half of the shear box.

Now back off the three vertical screws. After doing this, there will be no connection between the two halves of the shear box except the soil. Attach the horizontal and vertical dial gauges 0. Apply horizontal load, S, to the top half of the shear box.

The rate of shear displace- ment should be between 0. For every tenth small division displacement in the horizontal dial gauge, record the readings of the vertical dial gauge and the proving ring gauge which measures horizontal load, 8.

Continue this until after a the proving ring dial gauge reading reaches a maximum and then falls, or b the proving ring dial gauge reading reaches a maximum and then remains constant. Soil Mechanics Laboratory Manual Table Specimen length, L in. Specimen width, B in: 2 3. Specimen height, H in. Dry unit weight of specime. Specific gravity of soil solids, Gs 2. Plot of shear stress and vertical displacement vs. Plot of s vs. Note: The results for tests with 0.

The unconfined compression test is a quick method of determining the value of Cu for a clayey soil. The unconfined strength is given by the relation [for further discussion see any soil mechanics text, e.

The unconfined compressiou strength is determined by applying an axial stress to a cylin- drical soil specimen with no confining pressure and observing the axial strains corresponding to various. The stress at which failure in the soil specimen occurs is referred to as the unconfined compression strength Figure For saturated clay specimens, the unconfined compression strength decreases with the increase in moisture content.

Unconfined compression strength-definition Equipment 1. Unconfined compression testing device 2. Specimen trimmer and accessories if undisturbed field specimen is used 3. Harvard miniature compaction device and accessories if a specimen is to be molded for classroom work 4. Scale 5. Porcelain evaporating dish Unconfined Compression Test Machine An unconfined compression test machine in which strain-controiled tests can be performed is shown in Fig.

The machine essentially consists of a top and a bottom loading plate. The bottom of a proving ring is attached to the top loading plate. The top of the proving ring is attached to a cross-bar which, in tum, is fixed to two metal posts. The bottom loading plate can be moved up or down. Obtain a soil specimen for the test. If it is an undisturbed specimen, it has to be trimmed to the proper size by using the specimen trimmer. The cylindrical soil specimen should have a height-to-diameter LID ratio of be- tween 2 and 3.

In many instances, specimens with diameters of 1. Soil Mechanics Laboratory Manual Figure An unconfined compression testing machine. Measure the diameter D and length L of the specimen and detennine the mass of the specimen. Place the specimen centrally between the two loading plates of the unconfined com- pression testing machine. Move the top loading plate very carefully just to touch the top of the specimen. Set the proving ring dial gauge t.

A dial gauge [each small division of the gauge should be equal to 0. Set this dial gauge to zero. Turn the machine on. Record loads i. At the initial stage of the test, readings are usually taken every 0. How- ever,. Continue taking readings until a. A soil specimen after failure b. Load reaches a maximum value and remains approximately constant thereafter take about 5 readings after it reaches the peak value ; or c.

This may happen in the case of soft clays. Figure shows a soil specimen after failure. Unload the specimen by lowering the bottom loading plate. Remove the specimen from between the two loading plates. Draw a free-hand sketch of the specimen after failure. Show the nature of the failure. Put the specimen in a porcelain evaporating dish and determine the moisture content after drying it in an oven to a constant weight.

Calculation For each set of readings refer to Table : I. Calculate the vertical strain Column 2 M Column 3 x calibration factor Proving ring calibration factor: 1 div. This is the unconfined compression strength, qu' of the specimen. In the detennination of unconfined compression strength, it is better to conduct tests on two to three identical specimens. The average value of qu is the representative value.

Based on the value of qu' the consistency of a cohesive soil is as follows,: Very soft Soft Medium Stiff stiff 3. For many naturally deposited clayey soils, the unconfined compression strength is greatly reduced when the soil is tested after remolding without any change in moisture content.

In this chapter, the procedure of a one-dimensional laboratory consolidation test will be described, aud the methods of calculation to obtain the void ratio- pressure curve e vs. Consolidation test unit 2. Specimen trimming device 3. Wire saw 4. Balauce sensitive to 0. Stopwatch 6. Moisture cau 7. Oven Consolidation Test Unit The consolidation test unit consists of a consolidometeraud a loading device.

The consolido- meter cau be either 1 a floating ring consolidometer Fig. The floating ring consolidometer usually consists of a brass ring in which the soil specimen is placed.

One porous stone is placed at the top ofthe specimen aud auother porous tone at the bottom. The soil speCimen in the ring with the two porous stones is placed on a base plate. A plastic ring surrounding the specimen fits into a groove on the base plate.

Load is applied through a loading head that is placed on the top porous stone. Schematic diagram of a floating ring consolidometer; b fixed ring consolidometer.

The fixed ring consolidometer essentially consists of the same components, i. The ring surrounds the soil specimen.

A stand pipe is attached to the side of the base plate. This can be used for permeability determination of soil. In the fixed ring consolidometer, the compression of the specimen occurs from the top towards the bottom.

The specifications for the loading devices of the consolidation test unit vary depending upon the manufacturer. Figure shows one type ofloading device. During the consolidation test, when load is applied to the soil specimen, the nature of variation of side friction between the surrounding brass ring and the specimen are different for the fixed ring and the floating ring consolidometer, and this is shown in Fig.

Prepare a soil specimen for the test. The specimen is prepared by trimming an undis- turbed natural sample obtained in shelby tubes. The shelby tube sample should be about V. Soil Mechanics Laboratory Manual 11 9 Figure Consolidation load assembly. In this assembly, two specimens can be simultaneously tested. Lever arm ratio for loading is Note: For classroom instruction purposes, a specimen coo be molded in the laboratory. Collect some excess soil that has been trimmed in a moisture can for moisture content determination.

Collect some of the excess soil trimmed in Step I for determination of the specific gravity of soil solids, Gs' 4. Determine the mass of the consolidation ring WI in grams. Place the soil specimen in the consolidation ring.

Use the wire saw to trim the speci- men flush with the top and bottom of the consolidation ring. Record the size of the specimen, i. Nature of variation of soil-ring friction per unit contact areas in a fixed ring consolidometer; b floating ring consolidometer. Determine the mass of the consolidation ring and the specimen W2 in grams. Saturated the lower porous stone on the base of the consolidometer. Place the soil specimen in the ring over the lower porous stone.

Place the upper porous stone on the specimen in the ring. Attach the top ring to the base of the consolidometer. Add water to the consolidometer to submerge the soil and keep it saturated. In the case of the fixed ring consolidometer, the outside ring which is attached to the top of the base and the stand pipe connection attached to the base should be kept full with water. This needs to be done for the entire period of the test.

Place the consolidometer in the loading device. Attach the vertical deflection dial gauge to measure the compression of soil. It should be fixed in such as way that the dial is at the beginning of its release run. Take the vertical deflection dial gauge readings at the following times, t, counted from the time of load application-O min. Soil Mechanics Laboratory Manual 1 21 Repeat Step 15 for soil pressure magnitudes of2 tonlft2 At the end of the test, remove the soil specimen and determine its moisture content.

S iii 0. Plot of dial reading vs. Determination of t 90 by square-root-of-time method. Calculation and Graph The calculation procedure for the test can be explained with reference to Tables and and Figs.

Collect all of the time vs. Draw a tangent AB to the initial consolidation curve. Measure the lengthBC. In Fig. This technique is referred to as the square-root-of-time fitting method Taylor, The procedure for this is shown in Fig. Consolidation Test Time VS. Moisture Content: Beginning of test The point of intersection of these two lines is A. The vertical dial gauge corresponding to line BC ill d , i.

Complete the experimental data in Columns 1, 2, 8 and 9 of Table Determine the height of solids Hs of the specimen in the mold as see top of Table -. Determine the fmal specimen height, Ht f , at the end of consolidation due to a given load Column 4 in Table Determine the height of voids, Hv, in the specimen atthe end of consolidation due to a given loading, p, as see Column 5 in Table Calculate the coefficient of consolidation, Cv Column 10, Table , from Column 8 as Plot a semilogarithmic graph of pressure vs.

Column 6, Table Pressure,p, is plotted on the log scale and the final void ratio on the linear scale. As an example, the results of Table are plotted in Fig. Note: The plot has a curved upper portion and, after that, e vs. Calculate the compression index, Ce. This is the slope of the linear portion of the e vs.

On the semilogarithmic graph Step 13 , using the same horizontal scale the scale for p , plot the values of C v Column 10 and II, Table Note: Cv is plotted on the linear scale corresponding to the average value of p, i. Plot of void ratio and the coefficient of consolidation against pressure for the soil reported in Table Determine the preconsolidation pressure, Pc' The procedure can be explained with the aid of the e-logp graph shown in Fig.

First, determine point A, which is the point on the e-log p plot that has the smallest radius of curvaC ture. Draw a horizontal line AB. Project the straight line portion of the e-log p plot backwards to meet line AD at E. The pressure corresponding to point E is the preconsolidation pressure. Many correlations for Cc have been proposed in the past for various types of soils. A summary of these correlations is given by Rendon-Herrero Following is a list of some of these correlations.

The triaxial compression test is a more sophisticated test procedure for determining the shear strength of soil. In general, with triaxial equipment, three types of common tests can be conducted, and they are listed below.

Triaxial cell 2. Strain-controlled compression machine 3. Specimen trimmer 4. Wire saw 5. Vacuum source 6. Calipers 8. Evaporating dish 9. Rubber membrane Membrane stretcher Triaxial Cell and Loading Arrangement.

Figure shows the schematic diagram of a triaxial celt. It consists mainly of a bottom base plate, a Lucite cylinder and a top cover plate. A bottom platen is attached to the base plate. A porous stone is placed over the bottom platen, over which the soil specimen is placed. A porous stone and a platen are placed on top of the specimen. The specimen is enclosed inside a thin rubber membrane. Inletand outlet tubes for specimen saturation and drainage are provided through the base plate.

Appropriate valves to these tubes are attached to shut off the openings when desired. A hydrostatic chamber pressure, 03, can be applied to the specimen through the chamber fluid. Ah added axial stress, D. During the test, the triaxial cell is placed on the platfonn of a strain-controlled compres- sion machine.

The top of the piston of the triaxial chamber is attached to a proving ring. The proving ring is attached to a crossbar that is fixed to two metal posts. The platfonn of the compression machine can be raised or lowered at desired rates, thereby raising or lowering the triaxial cell.

During compression, the load on the specimen can be obtained from the proving ring readings and the corresponding specimen defonnation from a dial gauge [1 small div. The connections to the soil specimen can be attached to a burette or a pore-water pressure measuring device to measure, respectively, the volume change of the specimen or the excess pore water pressure during the test. Triaxial equipment is costly, depending on the accessories attached to it.

For that reason, general procedures for tests will be outlined here. For detailed location of various components of the assembly, students will need the help of their instructor. Triaxial Specimen Triaxial specimens most commonly used are about 2. In any case, the length-to-diameter ratio LID should be between 2 and 3. For tests on undisturbed natural soil samples collected in shelby tubes, a specimen trimmer may need to be used to prepare a specimen of desired dimensions.

Depending on the triaxial cell at hand, for classroom use, remolded specimens can be prepared with Harvard miniature compaction equipment. The length should be measured four times about 90 degrees apart. The average of these four values should be equal to Lo. To obtain the diameter, take four measurements at the top, four at the middle and four at the bottom of the specimen.

The average of these twelve measurements is Do. Placement of Specimen in the Triaxial Cell I. Boil the two porous stones to be used with the specimen. De-air the lines connecting the base of the triaxial cell.

Attach the bottom platen to the base of the cell. Place the bottom porous stone moist over the bottom platen.. Take a thin rubber membrane of appropriate size to fit the specimen snugly. Take a membrane stretcher, which is a brass tube with an inside diameter of about V. The membrane stretcher can be connected to a vacuum source. Fit the membrane to the inside ofthe membrane stretcher and lap the ends of the membrane over the stretcher.

Then apply the vacuum. This will make the membrane fonn a smooth cover inside the stretcher. Rubber ,,,,,:'.. Membrane stretcher. Slip the soil specimen to the inside of the stretcher with the membrane Step 5. The inside of the membrane may be moistened for ease in slipping the specimen in. Now release the vacuum and unroll the membrane from the ends of the stretcher. Place the specimen Step 6 on the bottom porous stone which is placed on the bottom platen of the triaxial cell and stretch the.

At this time, place the top porous stone moist and the top platen on the specimen, and stretch the top of the membrane over it. For air-tight seals, it is always a good idea to apply some silicone grease around the top and bottom platens before the membrane is stretched over them.

Using some rubber bands, tightly fasten the membrane around the top and bottom platens. Connect the drainage line leading from the top platen to the base of the triaxial cell. Place the Lucite cylinder and the top of the triaxial cell on the base plate to complete the assembly.

Note: 1. In the triaxial cell, the specimen can be saturated by connecting the drainage line leading to the bottom of the specimen to a saturation reservoir. During this process, the drainage line leading from the top of the specimen is kept open to the atmosphere.