2.

.

V. I. Krutov, I. G. Rabinovich, and B. A. Sal'nikov, "A new method of constructing foundations on soils prone to slump-type settlement," Promyshlennoe Stroitel., No. 7 (1971). Consolidation of Soils Prone to Slump-Type Settlement [Russian translation], Stroiizdat, Moscow (1974).

PERFORMANCE CHARACTERISTICS OF HORIZONTALLY LOADED PILES LOCATED NEAR A TRENCH Ya. Sh. Ziyazov

UDC 624.131.531.6

In designing buildings and structures for modern industrial establishments, it is sometimes necessary to consider the effect of trenches or pits for underground services installed in the vicinity of a pile foundation. To determine this effect, we conducted investigations on the proving ground operated by the Scientific-Research Institute of Industrial Buildings and Structures in Ufe. The soils at the experimental site were clayey loams of semihard consistency with a volumetric mass of 1.91 tons/m 3, an internal-friction angle of 2-4 ° , a cohesion of 0.07 MPa, and a void ratio of 0.462. The resistance of the soils to static probing ranged from 7.2-8.8 MPa on stabilization. Metallic piles fabricated from two No. 27 channel irons each 6 m long were employed in the experiments. Resistance strain gauges with a gage length of 30 mm and identical electrical characteristics were glued 50 cm apart on the inner surface of the piles along their longitudinal axis. The sensors were well insulated from the external medium by glue, commercial vaseline, and an ED-6 epoxy resin. The air tightness of the sensor insulation was checked by holding in water for 48-72 h, while that of the welded joints in the two channel irons was tested under an air pressure of 3 atm. The sensor readings were calibrated by bending the pile under a concentrated load, like a beam on two supports. The piles were loaded using upright diesel hammers. Testing of the piles commenced after a six-day rest period. A horizontal load was generated by a 200-kN hydraulic jack on drawing the piles together in pairs (Fig. i) and increased by steps, the magnitude of which was assigned within the limits of i/i0 of the expected ultimate load (corresponding to a i0 mm displacement of the pile at the point of load application). The piles were first tested to the point where a 6-8-mm displacement occurred at the ground surface with no trench excavated. After stabilization of the displacement rate of the pile, the load was reduced to zero, and a trench with a depth h = 4d, a length of 4 m, and width of 2d (where d is the transverse dimension of the pile) was opened at a distance a = 6d from the pile. The piles were then retested to the ultimate load, after which the latter was reduced to zero, the trench expanded by 2d in the direction of the pile, and the testing repeated. Similar tests were conducted at trench depths of 7.5d. Pile displacements at the points of load application were observed using Aistov deflectometers~ The displacement of the anchor or control pile, which was located at a distance of more than 4.5 m from the trench, was measured simultaneously. Deflectometer readings were recorded every 15 min. A 15-min variation of 0.i mm in pile displacement was adopted as stabilization criterion. The strain gage readings were recorded on stabilization of pile displacement due to each step.

Scientific-Research Institute of Industrial Buildings and Structures. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 3, pp. 13-14, May-June, 1976o This material is protected b y copyright registered in the name o f Plenum Publishing Corooration, 227 West 1 7th Street, N e w York, PC.Y. 70071. N o part o f thispublication may be reproduced, stored in a re t~qeval system, or transmitted, in any form or b y any means, elee tronic, mechanical, pt~otocopying, microfilming, recording or otherwise, w i t h o u t written permission o f the publisl2er. A copy o f this article is available from the publisher f o r $ Z 5 0 .

165

0

a

/0

20 JO 4kN b 0

10 20 ~ g kN

2

2

4

2

2

8

J <'~

2

2@"

fo

/0

f2

I2

gmm ~mm

Fig. 1

Fig. 2

Fig. i, Diagram showing horizontal-load test of piles with trench excavated in their vicinity (Roman numerals refer to testing sequence). !) Test pile; 2) deflectometers; 3) jack; 4) control pile; 5) trench. Fig. 20 Load-displacement curves for piles installed in vicinity of trench, a) Depth of 1.2 m; b) depth of 2.25 m; !) test without excavation; 2, 3, 4, 5) with trench excavated at distances of 1.8, 1.2, 0.6, and 0 my respectively, from pile.

I

p: 30 kN

~'~

j

I

L_~ 5

I

~ # ~

C

i

Fig. 3. Bending-moment diagrams for pile installed in vicinity of trench, a) Depth of 1.2 m; b) depth of 2.35 m at distances from pile: I) ~; 2) 1.8; 3) 1.2; 4) 0.6; 5) 0 m. The control pile was used in reducing the results of pile tests with the trench excavated to exclude the effect of load repeatability and the possible deviations in the forces exerted by the jack (with repeated testing) on these results. A load--displacement relationship (Fig. 2) for different trench spacings was derived from the deflectometer readings, while bending-moment diagrams were plotted from the straingauge readings (Fig° 3). As is apparent from Fig. 3, the moment diagram in the upper section of the pile does not exhibit the concave profile characteristic for a distributed load (due to the pressure of the creeping soil). This is apparently explained by the fact that the 166

displacement rate of the creeping soil during the test period was lower than the rate of pile displacement due to the external load. Below a certain depth, the moment diagram is restricted to a convex curve; this is associated with the development of passive soil pressure on the pile. From the depth of the point of intersection of the rectilinear and curvilinear segments of the moment diagram, we can determine the design depth of pile embedment in the soil

(I)

t~ = t - : ~ ,

where 1 is the depth of pile embedment measured from the surface of the ground, and Xa is the thickness of the upper layer of soil, which does not create a passive pressure on the pile due to the excavation of a trench in its vicinity, or the formation of a gap between the pile and soil during its backfilling. As analysis of the experimental results indicated, the quantity Xa can be determined as a function of the depth h and distance a from the formula la=b-v

!

K ~a

.

(2)

where b is the layer of soil that does not exert a passive pressure on the pile subject to the action of a horizontal load due to the formation of a gap between the pile and soll on backfilling, which, as is apparent from Fig. 3, is approximately equal to the transverse dimension d of the pile when a ÷ ~; h' is the depth of the trench disregarding the upper layer of soil with thickness b; and K is an empirical coefficient, which is dependent on the type of soil and is 0.66-0.76 for the soils in question. It should be noted in conclusion that the effect of the pressure exerted by creeping soil on pile performance could not be evaluated in the studies. These data could be obtained with further observation of soil pressure on a pile. CONCLUSIONS i. The excavation of a trench (pit) in the vicinity of a pile diminishes its ability to resist horizontal loading. This reduces the depth of pile embedment in the soil and depends on the depth of the trench and its distance from the pile. 2. The above-described method of testing piles for horizontal loading with strain gages can be used to determine the design depth of pile embedment in a soil. 3. The upper layer of soil of thickness d exerts no significant influence on the performance of horizontally loaded piles due to the formation of a gap between the pile and soil during its backfilling and can therefore be disregarded in their design.

VIBRATIONS OF FOUNDATIONS OF FUMING FURNACES M. M. Afanas'ev

UDC 624.159.11

Fuming furnaces are widely used in nonferrous metallurgy for processing slags by sublimating them. As a rule, they are installed on framed foundations, which until the present time were designed only for the action of static loads. However, as shown by the operating experience and By investigations carried out, although fuming furnaces operating on gas fuels* do not have rotating or moving parts, they are nonetheless sources of comparatively large dynamic loads, which in certain cases lead to increased vibrations and deterioration of the *Fuming furnaces operating on coal do not generate any perceptible dynamic loads, and they can be regarded as "dynamically tranquil." Mekhanobr Institute, Leningrad. Gruntov, No. 3, pp. 15-17, May-June,

Translated from Osnovaniya, Fundamenty i Mekhanika 1976.

This mqterial is protected by copyright registered in the name o f Plenum Publishing Corporation, 227 West 1 7th Street, N e w York, N. Y. 10011. No part o f thispublication may be reproduced, stored in a retrieval system, or transmitted, in any lotto'or by any means, electronic, mechanical, photocopying, microfilming, recording or otherwise, without written permission o f the publisher. A copy o f this article is available from the publistxer f o r $ Z 5 0 .

167