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Greece

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cted according thc well known etnpirical formula Hz 15 ♦ l/₂ (N“- 15).

b)    A rough estimation of allowable pressure of footings resting on granular soils is usually madę by means of the formula(in Kg/ cm²),

o i, • X • N/₁₀ where A s 1,0 for dry sands and X^a= 2/3 for saturated sands. Such an allowable prce-surę corresponds to a settlement of approximate-ly 3 cm.

c)    As far as the correlation between penetra*

tion resistance and the "elastic" modulus C_s is conccmed, the following empirical forsyla    is

found useful for Greek soils:

_E(kg/cm2) _ _{a t C}(_N±6) _{f where a}=40 for N > 15

a= 0 for H < 15

Soil type    C

Silt with sand	3
Fine sand	3,5
Medium sand	•*,5
Coarse sand	7
Sand with gravel	10
Gravel with sand	12

3.2.2 Cohesive soils

In the case of cohesive soils the following, well known, table of Terzaghi-Peck is generally u-sed, relating N-values, consistency and unconfined compressiye strength in clayey soils:

N	Consistency	(Kg/cm^2)
<2	very soft	<0,25
2 t 4	soft	0,25 t 0,50
4 * 8	medium soft	0,50 * 1
8 ?15	stiff	1:2
15 ?30	very stiff	2 ? 4
>30	hard	> 4

Special attention is paid in using the term " co-hesive"; the content of granular materiał possi-bly results in higher N-values, without a similar increase in consistency.

The samples taken out by means of the Raymond-Ty-pe sampler during the performance of SPT are used for classiflcation purposes and, sometimes,for unconfined compression tests- Hevertheless the limi-tations of such a use of standard-spoon samples a-re taken into consideration.

4. SIĄIię.ęOHĘ.TEST 4.1 Test Procedurę

Dutch penetrometersof 10 tons capacity(Gouda type) are mainly used in Greece. The standard 60° cone (10 cm² in section) is generally used. Friction sleeves (Beqema&&-type) are also used, in order to estimate the local-friction down through the various layers. During the test, the cone is driven first for 7,5 cm; the correspoding pressure being measured; the casing is subseąuently brought down to the same depth. Then, the neces-sary pressure is measured in order to forward the whole of the column (cone plus casing) for ano-ther 12,5 cm. The difference between these two pressures, expresses the apparent lateral friction of the total length of the casing. The whole procedurę is repeated every 20 era through the whole depth of interest.

In the case that a friction sleeve is used, the procedurę is slightly modified; An initial dri-ving of the cone alone for only 4 cm, is followed by pushing down the sleeve for local friction mea-sureraent. Finally the whole column of casing,slee-ve and cone are forwarded.

Readings are madę by means of manometers of 100 kg/cio and 600 kg/cm². a morę sensitive mano-meter of 50 kg/cm² is used when indications are relatively Iow.On the presentation log, cone pressures and total friction pressures and/or local friction pressures are separately noted. In the latter case the ratio f_s/q_c is also noted at each layer (local friction pressure over cone resistan ce).

4.2 Interpretation of results

4.2.1    Cohesion

In case of saturated frictionless soils, the value of ^,łquick-non-drained" cohesion is esti-mated by means of the expressions C_u=q_c/₁5'?q_c/^Q (for relatively shallow layers).

4.2.2    JeteraJL friction

The lateral friction available is measured directly by means of friction sleeves.

4.2.3    Soiljclas sification

On the basis of f_s/q_c values the naturę of the respective layers can be guessed. The following characteristic values have been proved va-lid in some cases in Greece: f

=1*2% , Gravel and sand (provided they are not ^    in loose State).

" =2*5% , Sand ♦ silt+clay

" > 5% , Clay.

These values do not seem to be clearly influenced by ground water level.

4.2.4    Estimatian_of sett1 ements

In case of fine~granular soils in a relative-ly dense State (q_c > 30 kg/cm²), settlements of footings are estimated on the basis of ^,,elastic^,ł moduli E_s 5 1,5^ , where q_c denotes the cone resistance of the respective layer.

In case of mixte loose soils (silt-clayey sands, q_c 5 5 to 15 kg/cm²), a different expression ,

E_s r 3,0.q_c, has been found appropriate is some cases in this Country.

In any case, settlement values estimated on the basis of the above formulaeare approximative only.

4.2.5    Allowable loading

a) Shallow foundations: Allowable pressu-res of footings resting on sands are roughr ly estimated (in preliminary design, only) by means of the empirical relationship

°all ⁼ ^€^40 •

corresponding to a probable settlement of the order of 3 cm .When ground water level is found at a depth less than the footings width, below foundation level, the above value has to by divided by 1,5.