6585844958

153

USSR

The formula (10) was successfully used for the determining of the bearing capacity of piles during some years. Howeyer, in some cases the load ■test of piles si— multaneously with sounding showed that sometimes deyiations are unallcwable*

The inyestigations have reyealed that the accuracy of the determination of the bearing capacity of piles by the data of the static sounding can be substantial— ly improyed by introducing yariable coef-fioients of transition from the soil resistanoe under a o one to the soli rasie tan ca under a pile point and from spe-cific friction on a sounding tubę to specific friotion on a pile depending res-peotiyely on mean oone resistanoe (q™) and mean speoific friction on a sounding tubę (f_m)*

Table 7

5 • 2    4    6    8    10    12

% a²

1    0.50    0.21    0.17    0.15    0.14    0.12

2    0.50    0.55    0.27    0.24    0.22    0.20

5    0.50    0.40    0.53    0.29    0.26    0.23

H    0.50    0.50    0.50    0.50    0.50    0.50

Notę: Prom the depth c£ 3»0 m to H m ooeffioient is determined by inter-polation* ^

The allowabia bearing c usually taken by the formuia:

^fm⁼

UsH

E

(11)

^pa=°’^{7 P}u

(14)

where H- deptE to a pile point*

At present the ultimate resistanoe (Pn) of a driyen friotion pile under an axTal yertical load by the results of the static sounding is determined: when sounding with a oone and a casing-acoording to the formula:

(12)

^Pu°>£l^<łm4p⁺>52^f mAs

when so\mding with a oone and a sleeve-according to the fomula:

The results of comparison of the ultimate resistanoe of piles determined by formula (12)- (Pg) and by pile load tests (Pfc) for 153 piles at 57 yarious sites (Trofimenkoy et al*_f1973) are giyen in Fig*7« The depth <£ pile penet-ration yaried from 5 bo llm₉ oross seo-tion of piles - from 25x25 to 35x35 cau The mean point resistanoe (q_m) was with-in 8 to 320 kg/cm²9 the totai skin friotion Q- from 0*5 to 9*7 t. The ultimate resistanoe of piles (Pt) yaried from 12 to 120 t.

P_u=0_ł5q_JttŁp+

A

s

(13)

where Ap - oross section and aide are a and Ag of a pile

jg± - ooeffioient of transition from ^ speoific resistanoe of a oone to speoific resistanoe of a pile point taken according to Table 5*

qtt	t/m^2 250 500 150	1000 1500	2000
jl	0*75 0.60 0.50	0.40 0.30	0.25

- ooeffioient of transition from speoific friction on a sounding tubę to speoific friction on a pile taken according to table 6«

Table 6

o to » soto30eo 7060sofiomttoisotoisoteoR

f_B t/m² 2    4    6    8    10

1.5 1.0 0.7 0.5

0.4

Eig*7 Comparison of the pile resistanoe* determined by the results of static sounding and load tests*

ooeffioient of transition from ^ mean speoific friotion on a sleeye in "i" layer (f^) of the thiokness l^to specific friotion on a pile depending on the depth of a oonsi-dered layer₉ Ha and taken according to Table 7.

As Gan be seen in Fig*7 the oomparieon shows good agreement* The mean value of erros is 4*20 per cent and -16 per cent* The possibility of the determination of the pile bearing capacity by the total resistanoe oz a sounding tubę (without separating to oone resistanoe and skin friotion) is of a great inte-rest, The prodessing of 153 ezperiments by this method gave the following formula for the determining of the ultimate resistanoe of a pile: