lecture soil compaction

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Soil Compaction COSC 323: Soils in Construction

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Page 1: Lecture  soil compaction

Soil Compaction

COSC 323: Soils in Construction

Page 2: Lecture  soil compaction

Question The contractor, during construction of the soil embankment,

conducted a sand-cone in-place density test to determine whether the required compaction was achieved. The following data were obtained during the test:

Weight of sand used to fill test hole and funnel of sand-cone device = 845 g.

Weight of sand to fill funnel = 323g. Unit weigh of sand = 100 lb/ft3

Weigh of wet soil from test hole = 600g Moisture content of soil from test hole = 17%.

Based on the contract, the contractor is supposed to attain the 95% compaction. Will you approve the contractor’s work?

Page 3: Lecture  soil compaction

Compaction

Compaction – expelling air from the void space Consolidation – extrusion of water

Effects of compaction Increase soil’s shear strength Decrease in future settlement of the soil Decrease in its permeability

How to quantify – use dry unit weight of soil

content moisture

tunit weigh wet 1

w

wd

Page 4: Lecture  soil compaction

Compaction

What does water do for compaction? Lubricant Too much water lesser density Optimum moisture content

(=maximum dry unit weight) best compaction

How to use maximum dry unit weight? Target unit weight at the job site

Need to know how much the soil can be compacted.

Page 5: Lecture  soil compaction

Compaction Test

ASTM D 698 Standard Proctor Compaction Test Hammer: 5.5 lb Drop Height: 12in

ASTM D 1557 Modified Proctor Compaction Test Hammer: 10 lb Drop Height: 18in For higher value of dry unit weight

Page 6: Lecture  soil compaction
Page 7: Lecture  soil compaction

Compaction Test

Dry out soil sample Add water to the soil sample Compact the soil sample in the compaction mold Measure wet unit weight () Measure moisture content (w) Calculate dry unit weight

Repeat 4 times with different moisture contents

wd

1

Page 8: Lecture  soil compaction

Proctor Curve

Page 9: Lecture  soil compaction

Example

ConditionThe combined weight of a mold and the

specimen of compacted soil it contains is 9.0 lb.

The mold’s volume is 1/35ft3

The mold’s weight is 4.35 lb.The specimen’s water content is 12%.

What is dry unit weight of the specimen?

Page 10: Lecture  soil compaction

Example

A set of laboratory compaction test data and results is tabulated as follows. Determine the soil’s maximum dry unit weight and optimum moisture content.

Determination Number 1 2 3 4 5

Dry unit weight (lb/ft3) 112 115 115 113 109

Moisture content(%) 5 10 15 20 25

Page 11: Lecture  soil compaction

What affects Compaction?

Moisture content Compaction effort

Compaction energy per unit volume (function of number of blows per layer)

For the stand proctor test: 12,400 ft-lb/ft3

For the modified proctor test: 56,000 ft-lb/ft3

Type of soil Grain size distribution Specific gravity of solids Type and amount of clay materials

Page 12: Lecture  soil compaction

Compaction

Page 13: Lecture  soil compaction

Facts about Compaction

Maximum dry unit weight Min: Organic soils (60lb/ft3) Max: Well-graded granular material (145 lb/ft3)

Optimum moisture contents Min: Granular material (5%) Max: Elastic silts and clays (35%)

Higher optimum moisture contents = Lower dry unit weight

Page 14: Lecture  soil compaction
Page 15: Lecture  soil compaction
Page 16: Lecture  soil compaction

Field Compaction

Compacted in layers 8 in. loose horizontal layer compacted to a

thickness of 6 in.

Sprinkling or drying to control moisture content Scarifying to provide bonding between layers. Equipments

Tempers – Limited in scope and compacting ability Rollers

Smooth wheel roller, Sheepsfoot roller, Pneumatic roller, Vibratory roller

Page 17: Lecture  soil compaction

Field Compaction

Smooth wheel roller Provide a smooth finished grade Used for paving

Page 18: Lecture  soil compaction

Field Compaction

Sheepsfoot roller Greater compaction pressure Effective for compacting fine-grained soil

Page 19: Lecture  soil compaction

Field Compaction

Pneumatic roller Effective for compacting clayey soil and silty soils

Page 20: Lecture  soil compaction

Field Compaction

Vibratory rollerEffective for compacting granular materials:

clean sands and gravels

Page 21: Lecture  soil compaction

Dynamic Compaction

When Existing surface or near-surface soil is poor with

regard to foundation support

For which soil? Both cohesive and cohesionless soils

How Drop a very heavy (2~20 tons) weight onto the soil

from a relatively great height (20 ~ 100 ft) Dropping weight randomly? a closely spaced grid

pattern is selected.

Page 22: Lecture  soil compaction

Dynamic Compaction

Page 23: Lecture  soil compaction

Dynamic Compaction

How deep soil will be affected?Approximate depth of influence of dynamic

compaction (D)

(m)height :

tons)(metric Weight :

(m) compaction dynamic of influence ofDepth :

soil cohesive :

soil sscohesionle:5.0

h

W

D

WhD

WhD

Page 24: Lecture  soil compaction

Dynamic Compaction

How many drops do we need?Typically 5~10 dropsAdditional drops beyond 10 drops improves

littleWhat about craters?

Need to be backfilled and compacted by other means

Page 25: Lecture  soil compaction

In-Place Soil Unit Weight Test

Destructive testing methodSand-coneRubber-balloon methods

Nondestructive methodNuclear moisture-density apparatus

Soil unit weight is inversely proportional to the amount of radiation that reaches the detector.

Speedy Moisture Tester

Page 26: Lecture  soil compaction

In-Place Test: Sand-cone method

Page 27: Lecture  soil compaction

Example

During construction of a soil embankment, a sand-cone in-place unit weight test was performed in the field. Weight of sand used to fill test hole and funnel of

sand-cone device = 867g Weigh of sand to fill funnel = 319g Unit weigh of sand = 98.0 lb/ft3

Weigh of wet soil from the test hole = 747g Moisture content of soil from test hole = 13.7%

Page 28: Lecture  soil compaction

Example 4-3

33

33

33

/8.117137.01

/9.133

1

/9.1330123.0

/6.453/747 place-in soil oft unit weighWet

0123.0/0.98

/6.453/548 hole test of Volume

548g319g-867g

funel fill tosand of Weight - funnel and hole test fill tosand ofWeight

holein test used sand ofWeight

ftlbftlb

w

ftlbft

lbgg

ftftlb

lbgg

d

Page 29: Lecture  soil compaction

In-Place Test: Rubber-balloon

Page 30: Lecture  soil compaction

In-Place Test: Nuclear Apparatus

Nuclear moisture-density apparatus

Page 31: Lecture  soil compaction

Field Control of Compaction

Required percent of compaction the required in-place dry unit weight

= ----------------------------------------------------- x 100%

the maximum laboratory dry unit weight

Minimum number of field unit weight tests required.

Maximum thickness of loose lifts (layers) Methods to obtain maximum dry unit weight Methods to determine in-place unit weight

Page 32: Lecture  soil compaction

Example

Given Soil from a borrow pit to be used for construction of an

embankment gave the following laboratory results when subjected to the ASTM D 698 Standard Proctor test

Maximum dry unit weight = 118.5 lb/ft3

Optimum moisture content = 12.5% The contractor, during construction of the soil

embankment, achieved the following Dry unit weight reached by field compaction = 117.8 lb/ft3

Actual water content = 13.7%

Required Percent of compaction achieved by the contractor

Page 33: Lecture  soil compaction

Example

Solution

%4.99100/5.118

/8.117

100tunit weighdry laboratory Maximum

tunit weighdry place-In

achieved compactionProctor Standard ofPercent

3

3

ftlb

ftlb

Page 34: Lecture  soil compaction

Example Given

A borrow pit’s soil is being used as earth fill at a construction project.

The in situ dry unit weight of the borrow pit soil was determined to be 17.18 kN/m3

The soil at the construction site is to be compacted to a dry unit weight of 18.90 kN/m3

The construction project requires 15,000m3 of compacted soil fill. Required

Volume of soil required to be excavated from the borrow pit to provide the necessary volume of compacted fill.

Page 35: Lecture  soil compaction

Example

Solution

33

33

500,1617.18kN/m

283,500kN

pit borrow thefrom obtained be torequired soil of Volume

283,500kN))(15,000m(18.90kN/m

pit borrow thefrom excavated be torequred soil of dry weight Total

fill compacted efurnish th torequired dry weight Total

m

Page 36: Lecture  soil compaction

Example

Given The in situ void ratio of a borrow pit’s oil is 0.72. The borrow pit soil is to be excavated and transported

to fill a construction site where it will be compacted to a void ratio of 0.42.

The construction project requires 10,000 m3 of compacted soil fill.

Required Volume of soil that must be excavated from the

borrow pit to provide the required volume of fill

Page 37: Lecture  soil compaction

Example

Solution

3

3

3

042,7)(

000,10)(42.0)(

000,10)()(

)())(42.0(

)(

)(42.0

fill in the soil

mV

mVV

mVV

VfV

V

V

f

V

Ve

fs

fsfs

fvfs

fvs

fs

fv

s

v

Page 38: Lecture  soil compaction

Example

Solution

333

3

3

112,12042,7070,5)()()(

3070,5)(

)()042,7)(72.0(

042,7)()(

)())(72.0(

)(

)(72.0

pit borrow in the soil

mmmVVV

mV

Vm

mVV

VV

V

V

b

bvbvb

bv

bv

fsbs

bvbs

bs

bv