settlement of tools and techniques in technology

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1. Settlement of Shallow Foundations

+ Immediate or elastic, S.: during or
immediately after construction
(calculated for both sand and clay)

+ Consolidation settlement, S.: occurs
over time (only for clay)

e Storm = Se + Se

S for foundations on saturated clay

Se = AyAs (q0B / Es)
do = net pressure on foundation and E, = soil
modulus of elasticity

S, for both sands and clays
If you know the elastic parameters E, and {.:

4, = NET BEARIN

Few correlations

SPT: E,=8N (in tsf)

CPT: E,=2.5 q. (square, circular) 7 outa wee
= 3.5 q. (strip/continuous) a +

See Tables for many other correlations!!

2. Equations for stress-strain modulus E, by several test methods

PT, divide kPa by 50 to obtain ksf The N valuessho

Soil SPT CPT

= 210.49,
Da.

Sand (saturated

Sand (overconsolidated) E, = 6 to 304

Sravelly sand and gravel

Clayey sa E, =3 to 69,

Silty sand E, = | 10 24,

Soft clay = 310 84,

ainied shear strength s, in units of sa
€ nic E,= $008

Klastic Parameters of Various Soils

‘Type of soil

Loose Sand

2500-4,000 5-040

Medium dense sand
Dense sand 5,000-8,000 0-045
| Silty sand 1500-2500 10.85-17.25 020-040

50 015-035

| Sand and gravel 10,000-25,000 62.00
| Soft clay 600-3000 41207

| Medium clay 3,000-6,000 207-414 020-050
|

Stiff day 6000-1400 414-966

3. 3.0

10

0.5

settlement

4,

Flexible
foundation
settlement

‘oisson’s ratio

E, = Moduius of elasticity

For circular foundation

— — y = 085
= 0.88

|
3 4 E 6 7 8 9

4. Y FIGURE Values of A, and A, for immediate settlement calculation

5. Elastic Settlement in Sands
(Schmertmann, 1970; 1978)

Determine the variations of E with depth. Use CPT, SPT or
other in-situ test data.

Establish depth of influence: 2B for square; 4B for
continuous; from base of footing

yy = Depth Below Bocom of Footing
3 = widen of Footing
L = Length of Footing

6. Divide the zone of influence into layers and assign E values
to each layer. Thickness and number of layers depend on
CPT profile, SPT variations, or other data.

Elastic Settlement, S. = f(Strain Influence Factor, I,)
Establish variation of I, with depth. Find I, at the middle of
each layer.

4
L, =05+01 2

©.

vp

qo = Bearing Pressure
6 = Vertical Effective Stress a @ level of T,p

I,, occurs: @z/B=0.5 (square and circular); and
@ 7/8 = 1.0 (continuous)

Square and Circular: L/B=1
When z;/B = 0- 0.5

7. © When zYB = 0.5 - 2

+ When zy/B = 0; T, = 0.1
=0.5;L=Lp
=2;L=0

Continuous: L/B > 10

° When 2,/B = 0—- 1.0

e When z/B=1-4

+ When z/B = 0; I, = 0.2
1.0;
=451,

8. Rectangular: L>B

I. = L for continuous footing
L, = I, for square footing

STEP 5
Compute Settlement

Called the Depth Factor

q | =Effective stress at foundation level

qo = Bearing pressure

9. Called the Secondary Creep Factor

ime since application of load; t > 0.1 year

Called the Shape Factor
n =number of soil layers
L, =L @ middle of soil layer

= Thickness of layer i

E, = Modulus of soil layer i

10. The results of a CPT sounding performed at McDonald's Farm near Vancouver, British
Columbia, are shown in Figure 7.9. The soils at this site consist of young, normally
consolidated sands with some interbedded silts. The groundwater table is at a depth of 2.0 m
below the ground surface.

A 375 kN/m load is to be supported on a 2.5 m x 30 m footing to be founded at a
depth of 2.0 m in this soil. Use Schmertmann's method to compute the settlement of this
footing soon after construction and the settlement 50 years after construction.

0

—“— ge (Cone Profile)
qe (Soil Layers)

120
Cone Bearing, g. (kg/cm?)

11. pe un/m

207 Kfm”

25

STEPS 1-2

2-3
3-5
5-6
6-7
7-8
8-9
9-12

gonzu oe

LAXER HE DEP

20
30

40
Fo
90
so
no

L/B = 32212510 > contmuovs FOUNDATION

DEPTH OF INFLUENCE = Det BS RAI RM

=

Te
Cégle) 00)

6560
10250
13720
24010
30870
20580
37730

353,
Vrg/em? > 22 pat
= Ka

LAYERS START

e

FooTin& LEVEL

12. L= BFE Ke _
5m z

Se (a dll raz 5=4-5m)

E EN

150 KPa

= e «Seo» so
ar = 0.50 [2
= 2 Taie
sacs À 2
E
Ci= SS, 6-86
150
<2= ı +02 44 [St Jo [soon aerer comstavc mon]
= 140.2 Lgl &P]= 7537 [so venas nares]
C3 = 703-003%12 2 0-672 0-73
2
A
wer ds Eh Zi Hi ae = À
A 6860 05 peadié 1 425 x1075 De z
ES SL
2 1290 20 05664 2 DE 28 4
“5 3
3 13720 3-5 0 56% ! LHS 10 Ray 2
-5 do =
4 24010 es OTHER 1 210 + Beg
5 aaar
5 30870 55 03944 I 1.273810 ES 3
-5 DS
6 20580 65 0-306 | 4910 x E
2 34730 85 dam 3 100810°

Je AF FEROS
Se= 0-586x 1 X 0-73 X 150 x 27-7 610 52 0-0267m XF mm

Se(soxas) = R78 11539 X 42 mm