GEOTECH 1 — Geotechnical Engineering 1 UNIVERSITY OF THE CORDILLERAS
College of Engineering and Architecture
Module 6 — Soil Compac on
OBJECTIVES, CLOs & TLOs 4. Proctor/Modified Proctor Test Per nent Equa ons
CLO 3: The student is able to discuss the uses and advantages of com- Laboratory procedures to determine the maximum dry unit weight
pac ng soil and shall be able to use exis ng methodologies to reflect of soil. Standard procedures are respec vely represented by ASTM D
parameter per nent to soil compac on. 1140 and ASTM D 1557.
MTTLO 5: The Student is able to explain the advantages of and compute
values per nent to soil compac on. Ecomp—Energy of compaction per unit
volume.
OUTLINE
mh—Mass of hammer
1. Recall hd—Height of drop
2. Compac on of Soil Nb—Number of Blows
2a. Key points Nl—Number of layers
2b. Defini on of terms, Per nent concepts γzav— Unit weight at 0 air voids
2c. Per nent Equa ons ***Above equa ons are usually used to aid the analysis of test results.
2d. Sample Problems Compac on problems usually come in the form of test results analysis
RECALL as will be shown in the next part of the handout.
Phase rela onship of soils—Recall that soil is considered to consist of
three parts: soil solids, water and air. Sample Problem
Basic defini ons—Soil index proper es: dry unit weight/density, satura- The standard and modified proctor test may be summarized as fol- The data from a standard proctor test are tabulated and follows.
on, void ra o, specific gravity etc. lows. Dry soil is mixed with water and placed into the cylindrical mold. From said data, determine the maximum dry unit weight and the op -
COMPACTION OF SOIL This soil is then compacted by the repeatedly raising (25 blows) the mum water content and determine the degree of satura on at the
KEY POINTS ram (2.5 kg, 4.54 kg) to a specified height (305 mm, 457 mm) and al- maximum dry unit weight. Following also are data per nent towards
Soil compac on lowing the ram to fall freely. This is done repeatedly for each layer (3, sa sfying the above requirements.
Soil compac on is essen ally the densifica on of soil through the ex- 5) and repeatedly for each sample. The water content is then plo ed Diameter of mold 101.4 mm
pulsion of air and rearrangement of par cles through the addi on of as abscissa against the dry unit weight as the ordinate to obtain the Height of mold 116.7 mm
water and introduc on of compac on efforts. Basic tests to determine compac on curve. Interpola on is then applied to determine the op - Mass of mold 4196.50 grams
the maximum dry unit weight a soil can a ain include proctor tests. mum water content and maximum dry unit weight. Specific Gravity 2.69 for soil solids
Soil Compac on Advantages 5. Field Density Tests
Increased soil strength, increased load bearing capacity, lower com- Tests that can be done in the field to determine/inves gate the Mass of wet mass of can mass of can and
mass of can
pressibility, reduc on of seepage, reduc on of swelling and contrac- field/in-situ density of soils. Basic procedure include sand cone test soil and mold and wet soil dry soil
on, increased soil stability. Improper compac on may lead to soil ero- (ASTM D-1556) and the rubber balloon method (ASTM D-2167). 5906 108.12 105.1 42.1
sion, differing se lements through the soil profile, poten al structural 6. Compac on Tools/Equipment 6013 98.57 94.9 40.9
damages to buried structures etc.
6135 121.9 114.7 42.7
DEFINITION OF TERMS, PERTINENT CONCEPTS
1. Soil Compac on 6156 118.39 110.5 42.5
The densifica on of soil through the expulsion of air. 6103 138.02 126.8 41.8
Achieved by adding water into the soil to facilitate easy ***mass are given in terms of grams, weight in terms of kN and
re-arrangement of soil par cles into a denser state dur- volumes in terms of cubic meter
ing the introduc on of compac ng forces. Usually done Solu on:
in the field by mechanical compactors, rollers and ram- From the above data, the water content is easily established as
mers. shown
2. Maximum Dry Unit Weight (γd(max)) Mass of wet soil Mass of dry soil Water content
The maximum dry unit weight a soil can a ain given a 66.02 63 4.793651%
compac on procedure. 57.67 54 6.796296%
3. Op mum Water Content (wopt)
79.2 72 10%
The water content required for soil to a ain its maxi-
mum dry unit weight given a compac on procedure. Images and tables taken from “Soil Mechanics and Founda ons”, Budhu (2003) 75.89 68 11.60294%
96.22 85 13.2%
GEOTECH 1 — Geotechnical Engineering 1 UNIVERSITY OF THE CORDILLERAS
College of Engineering and Architecture
Module 6 — Soil Compac on
S ll from the given data, the moist unit weight/density in the mold can The solu on for the satura on at the maximum dry unit weight can
be established. Knowing the water content, the dry unit weight/density is
also therefore proceed as follows
also easily established right a er.
Mass of Wet Weight of Wet soil Moist Unit Dry unit weight
1709.5 0.016770195 17.795198 16.98118
1816.5 0.017819865 18.909025 17.70569
1938.5 0.019016685 20.178995 18.34454 It can be observed from the graph that the 97% of dry unit weight
1959.5 0.019222695 20.397597 18.27693 and the compac on curve has two points of intersec on, P6 and P7.
The water content between this two points, 7.5% to 12.5%, are within
1906.5 0.018702765 19.845888 17.5317
the possibili es of water content to a ain the required 97% of maxi-
***It would be intui ve for the students to recall that these values are mum dry density. It must be noted however that for course grained
simply taken by concepts already discussed in prior topics. It would be soils, it would be op mal to use water content on the le side of the
more intui ve however if students ask ques ons for any point of confu- op mum water content or call the dry of op mum. For fine grained
sion or for any concepts that have been forgo en. soils, it would be op mal to use the right side of the op mum water
content or called the wet of op mum.
The solu on may therefore proceed by graphing the dry unit weights It must also be noted that soil types have corresponding compac on
against the water content and finally determining the maximum dry unit methods that are more effec ve or not effec ve at all.
weight and op mum water content.
γd(max) = 18.4 kN/m3 Pmax (10.8%,
P3 (10%, 18.34 kN/m3)
P4 (11.60%, 18.28 kN/m3)
***assuming project specs require compac-
on degree of 97%. (17.848 )
` `
P6 (7.5%, 17.848 kN/m3) P7 (12.5%, 17.848 kN/m3)
P2 (6.8%, 17.71 kN/m3)
P5 (13.2%, 17.53 kN/m3)
P1 (4.79%, 16.98 kN/m3)
wopt = 10.8%
