Department of Civil, Environmental and Mining Engineering
CIVL 4430
TRANSPORTATION AND PAVEMENT ENGINEERING
Laboratory Manual
1. LABORATORY EXPERIMENT - #1
COMPACTION TEST
1.1 INTRODUCTION
In geotechnical engineering, soil compaction is the process in which stress applied to a soil causes densification as air is displaced from the pores between the soil grains and in the process increases soil density and removing air, usually by mechanical means. The size of the individual soil particles does not change, neither is water removed. Purposeful compaction is intended to improve the strength and stiffness of soil.
Soil compaction is necessary to increase the bearing capacity and stiffness of in-situ (natural state) or chemically modified soils. Compaction increases the shear strength of soils by adding friction from the interlocking of particles.
The compaction test aims to establish the maximum dry density that maybe attained for a given soil with a standard amount of compaction effort. When a series of soil samples are compacted at different water content, the plot usually shows a peak.
The compaction test of soil is carried out using Proctor’s test to understand compaction characteristics of different soils with change in moisture content. Compaction test of soil is to find the optimal moisture content at which a given soil type becomes most dense and achieve its maximum dry density by removal of air voids. It is the process of densification of soil by reducing air voids. The degree of compaction of a given soil is measured in terms of its dry density. The dry density is maximum at the optimum water content. A curve is drawn between the water content and the dry density to obtain the maximum dry density (MDD) at the optimum moisture content (OMC).
Dry density of soil = M / V
(-1 + w)
Where M = total mass of the soil, V = volume of soil, w = water content
1.2 TEST PROCEDURE
The test is conducted for 5 moisture contents to obtain the optimum moisture content for which the value of the dry unit weight is maximum.
A sample with a certain percentage of sand and clay have been provided for your test.
2.1 SAMPLE PREPARATION
(1) Mix the provided sample thoroughly in a tray.
(2) Split out five representative portions of the soil, each of sufficient quantity to produce a compacted volume in excess of the volume of the mould.
(3) Take a portion of the soil as prepared above in a mixing bowl, take the weight, add around 8% water, and thoroughly mix the soil.
(4) Clean the mould, collar, and baseplate. Grease them lightly. Inspect and clean the rammer and ensure that it is free in the guide.
(5) Determine the mass (m1) of the mould, plus baseplate and measure the diameter and height of the mould to calculate the volume
(V) of the mould.
(6) Assemble the mould, collar and baseplate and place the assembly on the rigid foundation.
(7) Compact the specimen as follows:
(i) Take the mixed soil and compact it into the mould in three layers, so that the compacted height of the soil in the mould is 38mm to 43mm in the first layer, 77mm to 82mm in the second layer and 116mm to 120mm in the third layer.
(ii) Compact each layer by 25 uniformly distributed blows of the rammer falling freely from a height of 300mm.
(8) Free the material around the inside of the collar and then carefully remove the collar.
(9) Trim the compacted soil level with the top of the mould by means of the straightedge; use some sample to patch up any holes developed in the surface developed during trimming.
(10) Determine the mass (m2) of the mould and soil with baseplate.
(11) Immediately remove the soil specimen from the mould and obtain a representative sample from the full height of the specimen. Determine the moisture content (w) of the sample.
(12) Discard the used soil. Do not reuse soil from a previously compacted specimen.
(13) Repeat steps 4 to 12 excluding step 5 with the other portions of prepared soil with different water content to obtain at least four points, at least two of which must be dryer, and one wetter, than optimum moisture content, to satisfactorily define the dry density / moisture content relation.
(14) If the optimum moisture content has not been straddled or is imprecisely defined use additional soil portions prepared in the same manner as in step 3 and compact these at appropriate moisture contents as in steps 4 to 12.
2.2 CALCULATIONS
Calculate as follows:
(a) For each specimen, the density of wet soil
(p) from the equation:
p = (m2 – m1)
V
where,
p = density of wet soil, in tonnes per cubic meter
m2 = mass of mould plus baseplate plus specimen, in grams
m1 = mass of mould plus baseplate, in grams
V = measured volume of the mould, in cubic centimetres
(b) For each specimen, the density of dry soil (pd) from the equation:
pd = 100 × p
100 + w
where,
pd = density of dry soil, in tonnes per cubic meter
p = density of wet soil, in tonnes per cubic meter
w = moisture content of the specimen, in percent
(c) Plot the dry densities obtained from the compacted specimens against their moisture contents.
2. LABORATORY EXPERIMENT - #2
CALIFORNIA BEARING RATIO (CBR)
2.1 INTRODUCTION
The California Bearing Ratio (CBR) is a measure of the strength of the subgrade of a road or other paved area, and of the materials used in its construction. The ratio is measured using a standardised penetration test first developed by the California Division of Highways for highway engineering.
The CBR is the ratio of the bearing load that penetrates a material to a specific depth compared with the load giving the same penetration into crushed stone. The test measures neither Stiffness Modulus nor Shear Strength directly but gives a combined measure of both.
Penetration is measured by applying the bearing load on the sample using a standard plunger of diameter 50mm at the rate of 1.0mm/min. The CBR is expressed as a percentage of the actual load causing the penetrations of 2.5mm or 5.0mm to the standard loads on crushed stone.
The CBR test is performed in construction materials laboratories to evaluate the strength of soil subgrades and base course materials. For designing and engineer highways, airport runways and taxiways, parking lots and other pavements you rely on CBR test values when selecting pavement and base thicknesses.
The CBR test is a simple strength test that compares the bearing capacity of a material with that of a well- graded crushed stone. It is primarily intended for, but not limited to, evaluating the strength of cohesive materials.
2.2 TEST PROCEDURE
From your compaction test you will get your MDD and OMC values. Based on these values you will need to prepare your sample for CBR and leave it for curing.
2.3 SAMPLE PREPARATION
(1) Mix the provided sample thoroughly in a mixing bowl.
(2) Add the required amount of water as your OMC value to dampen the soil.
(3) Mix thoroughly and allow the soil to cure for an appropriate time. Note down the duration of curing.
2.4 UNSOAKED CBR
(1) Determine the mass of the mould (m1) and measure the diameter and height of the mould to calculate the volume (V1) of the mould.
(2) Insert the spacer disc, clamp the mould with the extension collar attached to the baseplate and place a filter paper on top of the spacer disc.
(3) Prior to compaction, thoroughly mix the cured soil and determine the moisture content (w1) of a representative fraction of the test portion.
(4) Compact the specimen uniformly in the mould to 95% of your MDD value.
(5) Take the mixed soil and compact it into the mould in three layers, so that the compacted height of the soil in the mould is 39mm to 44mm in the first layer, 78mm to 83mm in the second layer and 117mm to 122mm in the third layer.
(6) Free the material around the inside of the collar and then carefully remove the collar.
(7) While the baseplate is still attached, trim the surface of the compacted specimen level with the top of the mould by means of a straightedge. Use small size material to patch any holes developed in the surface from removal of coarse material during trimming.
(8) Remove the perforated baseplate, spacer disc and filter paper and determine the mass of the mould plus compacted soil (m2).
(9) Place a filter paper on the perforated baseplate, invert the mould plus the compacted soil and place it on the baseplate. Clamp the baseplate to the mould with the compacted soil in contact with the filter paper.
(10) Perform. the penetration test.
(11) Place the 4.5kg annular surcharge on the soil surface and then place the mould plus specimen plus baseplate in the loading machine. Seat the penetration piston with the smallest possible load not exceeding 50N.
(12) Read or set to zero the load and the displacement readings before applying the load.
(13) Apply the load with a constant rate of penetration of 1mm/min. Record load readings at penetrations of 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 4.0, 5.0, 7.5, 10.0 and 12.5 mm.
(14) Remove the soil from the mould and determine the moisture content of the top 30mm layer (w30) and the bottom remaining specimen.
2.5 SOAKED CBR
(1) Determine the mass of the mould (m1) and measure the diameter and height of the mould to calculate the volume (V1) of the mould.
(2) Insert the spacer disc, clamp the mould with the extension collar attached to the baseplate and place a filter paper on top of the spacer disc.
(3) Immediately prior to compaction, thoroughly mix the cured soil and determine the moisture content (w1) of a representative fraction of the test portion.
(4) Compact the specimen uniformly in the mould to 95% of your MDD value.
(5) Take the mixed soil and compact it into the mould in three layers, so that the compacted height of the soil in the mould is 39mm to 44mm in the first layer, 78mm to 83mm in the second layer and 117mm to 122mm in the third layer.
(6) Determine the mass of the baseplate plus mould plus specimen (m3).
(7) Place the stem and perforated plate on the compacted soil specimen in the mould and apply surcharges of 4.5kg.
(8) Place the tripod and the dial gauge on the mould and record the initial reading before soaking (h1). Mark the point of contact of the tripod with the mould.
(9) Immerse the surcharged specimen in water, allowing free access of water to the top and the bottom of the specimen. Allow the specimen to soak for 4 days. Maintain the water level above the mould during this period.
(10) After soaking is competed, set the reading on the measuring device against the setting piece so that it is the same as that used in Step (8).
(11) Place the tripod on the points of contact marked in Step (8) and record the reading after soaking (h2).
(12) Tilt the specimen to remove the surface water. Return the mould to the vertical position and allow the specimen to drain downward for 15 min. Do not disturb the surface of the specimen during the removal of water.
(13) Remove the surcharges, stem and perforated plate and determine the mass of the baseplate plus mould plus specimen (m4).
(14) Perform. the penetration test.
(15) Place the 4.5kg annular surcharge on the soil surface and then place the mould plus specimen plus baseplate in the loading machine. Seat the penetration piston with the smallest possible load not exceeding 50N.
(16) Read or set to zero the load and the displacement readings before applying the load.
(17) Apply the load with a constant rate of penetration of 1mm/min. Record load readings at penetrations of 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 4.0, 5.0, 7.5, 10.0 and 12.5 mm.
(18) Remove the soil from the mould and determine the moisture content of the top 30mm layer (w30) and the bottom remaining specimen.
2.6 CALCULATIONS
The calculations shall be as follows:
(a) Plot the load-penetration curve.
(b) Read from the load-penetration curve, the force value in kN at penetrations of 2.5mm and 5.0mm and calculate the bearing ratio for each by dividing by 13.2kN and 19.8kN respectively and multiplying by 100.
Record the greater value of the calculated values as the CBR of the material.
(c) Calculate the dry density of the specimen before soaking (ρd) from the following equation:
pd = 1 x m2 - m1 V1 1 + w1
100
where,
pd = dry density of the specimen, in grams per cubic centimetre
m2 = mass of the mould plus compacted soil, in grams
m1 = mass of the mould, in grams
V1 = volume of the specimen before soaking, in cubic centimetres (volume of the mould less the volume occupied by the disc)
W1= moisture content of the material immediately prior to compaction
(d) Calculate the laboratory density ratio (LDR) of the specimen from the following equation:
LDR = MDD/ρd x 100
where,
LDR = laboratory density ratio, in percent
pd = dry density of the specimen, in grams per cubic centimetre
MDD = maximum dry density of the soil, in grams per cubic centimetre
(e) Calculate the laboratory moisture ratio (LMR) of the specimen from the following equation:
LMR = OMC/w1 x 100
where,
LMR = laboratory moisture ratio, in percent
w1 = moisture content of the soil immediately prior to compaction, in percent
MC = optimum moisture content of the soil, in percent
(f) Calculate the swell from the following equation:
S = 117/h2 – h1 x 100
where,
S = the swell of the specimen, in percent
h2 = the reading after soaking, in millimetres h1 = the reading before soaking, in millimetres
(g) Calculate the mass of dry soil in the specimen (m5) from the following equation:
m5 = m2 - m1
1 + w1
100
where,
m5 = mass of dry soil in the specimen, in grams
m2 = mass of mould plus compacted soil, in grams m1 = mass of mould, in grams
w1 = moisture content of the soil immediately prior to compaction, in percent
(h) Calculate the moisture content of the specimen after soaking (ww) from the following equation:
ww = w1 + m5/m4 – m3 x 100
where,
ww = moisture content of the specimen after soaking, in percent
w1 = moisture content of the soil immediately prior to compaction, in percent
m4 = mass of mould baseplate plus mould plus specimen after soaking, in grams m3 = mass of mould baseplate plus mould plus specimen before soaking, in grams m5 = mass of dry soil in the specimen, in grams
(i) Calculate the volume of the specimen after soaking (V2) from the following equation:
V2 = V1[100/100 + S]
where,
V2 = the volume of the specimen after soaking, in cubic centimetres V1 = volume of the specimen before soaking, in cubic centimetres
S = the swell of the specimen, in percent
(j) Calculate the specimen dry density after soaking (ρda) from the following equation:
Ρda = V2/m5
where,
Ρda = dry density of the specimen after soaking, in grams per cubic centimetre m5 = mass of dry soil in the specimen, in grams
V2 = the volume of the specimen after soaking, in cubic centimetres