摘要:

InPart Iof this report the results are given from 43 months of measurements of forces and bending moments on two instrumented precast piles driven through 40 m (130 ft) of soft clay and 15 m (50 ft) into underlying silt and sand. The force in the piles increased due to negative skin friction. After the first 5 months a force of nearly 40 tons was observed at the bottom of the clay layer. During this time the reconsolidation of the clay after the driving took place. The force due to the reconsolidation effect amounted to about 30 tons, while the rest was due mainly to negative skin friction caused by a small regional settlement. The latter force increased linearly with time by about 15 tons per year. Seventeen months after the driving the pile heads were loaded with 44 tons and one year later another 36 tons were added. The load on the pile head eliminated the negative skin friction, which however started to return with the continued regional settlements.InPart IIof the report general design formulae for piles considering negative skin friction are given. The formulae should be used to check that the permanent and transient working loads, which have been chosen according to ordinary design rules, are not too large when negative skin friction develops.When settlements due to negative skin friction are not acceptable, the negative friction can be reduced by applying a thin coat of bitumen to the piles. References are made to investigations concerning reduction of skin friction, and practical difficulties are pointed out.

ISSN:0008-3674    

DOI:10.1139/t72-037

出版商:NRC Research Press    

年代:1972

数据来源: NRC

摘要:

The deformation characteristics of sand and other granular materials under hydrostatic compression are studied in the conventional triaxial apparatus using 4 × 4 in. (10 × 10 cm) specimens. Modifications have been made for measuring small axial strains and free end platens were used. The errors in testing have been estimated and their effect was evaluated. Different kinds of granular materials were tested to study the effect of the physical properties of the material on its deformational behavior.The results showed that the total deformation of a mass of sand subjected to a hydrostatic compression is generally not recoverable, and can be divided into elastic (recoverable) and sliding (irrecoverable) components. It has also been found out that for a dense specimen of sand most of the total deformation is recoverable, since the sliding component of deformation represents only a small fraction of the total deformation. The results also showed that for the very dense specimen axial and radial strains were nearly equal which implies that the material behaves isotropically. On the other hand for a loose specimen the sliding component of deformation becomes large and thus the total deformation of the specimen cannot be considered completely elastic. Furthermore axial and radial strains of the loose specimen were not equal.

ISSN:0008-3674    

DOI:10.1139/t72-038

出版商:NRC Research Press    

年代:1972

数据来源: NRC

摘要:

This paper outlines research on large model piles and some full-scale piles driven into insensitive clay to study the phenomena of load transfer and the effect of pile driving on the soil. It is divided into two parts. Part I deals with the stress field set up by driving a large model pile into an instrumented clay bed and the stresses measured for some full-scale timber piles. Part II presents an evaluation of the load carrying capacity of the model pile and compares the results with full-scale pile load tests. The soil properties are evaluated in terms of effective stress for an estimate of the bearing capacity of the piles.The measured soil displacements near the shaft and base agree well with plastic theory, while the observed magnitude of the pore pressures in the clay due to driving are smaller and the rate of pore pressure dissipation is greater than expected theoretically.The magnitude of the total and effective radial stresses surrounding the pile is mainly related to the stress changes in the soil due to placing the pile and subsequent stress changes are relatively small. On the other hand, the tangential and vertical stresses vary appreciably with time and the latter stresses depart considerably from estimates based on elastic theory, due to locked-in-soil stresses.An approximate theory is presented to estimate the average effective radial stress on the pile shaft in connection with the ultimate shaft capacity. This proposed approach is supported by observations in some clays of low sensitivity, but requires further research in other type of clays.

ISSN:0008-3674    

DOI:10.1139/t72-039

出版商:NRC Research Press    

年代:1972

数据来源: NRC

摘要:

Duisburg on the Rhine, at the heart of the Ruhr, one of Europe's greatest industrial areas, is the world's largest inland port. Located at the junction of the Rhine and Ruhr Rivers, its harbour includes twenty major docks with a total of 45 km of wharves over which more than 45 million tons of cargo are handled each year.Starting in the middle of the nineteenth century, the course of the Rhine has been improved by straightening, cleaning, and dredging. A serious drop in upstream water levels has been the inevitable result, 2 m at Duisburg since 1900, with the prospect of a similar drop by the end of this century.Geological strata beneath the harbour area include three valuable coal seams, mining of which had been prohibited for centuries. After careful study it was decided to extract most of this coal by controlled mining, in this way securing settlement of the whole harbour area to counterbalance the drop in river level. Mining was started in 1956; by 1968, when work had to stop, most of the harbour had been lowered as much as 1.5 m, with no interference with its normal operation.

ISSN:0008-3674    

DOI:10.1139/t72-040

出版商:NRC Research Press    

年代:1972

数据来源: NRC

摘要:

The paper is divided into two parts. The first part deals with the systematic program of measurements undertaken on an open braced cut in dense sand at the Greenway Pollution Control Centre in London, Ontario. In the second part, the experimental data are analyzed and a new solution is presented based on Dubrova's analysis, which related qualitatively and quantitatively the active earth pressure distribution to the mode of deformation of a retaining structure.The roughly L-shaped excavation measured 68 × 42 ft (20.7 × 12.8 m) for the longest leg, the other leg was 30 × 23 ft (9.1 × 7.0 m). The temporary bracing system consisted of interlocking steel sheet piles (Larssen IIIN), and wales and struts from wide-flanged steel sections. The maximum depth of the cut was 50 ft (15.2 m) below ground elevation of 722 ft (220.1 m). The soil consisted of fine uniform dense sand having a relative density varying from medium to very dense. The natural water level was approximately 20 ft (6.1 m) below the ground surface prior to construction.The instrumentation program was carried out during the 6-month construction period (January–June 1964) and consisted of measuring: (1) The strut loads with a mechanical strain indicator (Whitmore gauge) over 8 in. (20.3 cm) gauge lengths, (2) The deformation of the north wall in a horizontal and a vertical plane, (3) The water levels and water pressures from borehole and standpipe observations, and (4) The active and passive earth pressures over the cut with 'Geonor vibrating-wire pressure transducers mounted flush on two adjacent sheet piles of the north wall.Field and laboratory tests supplied the necessary soil data.Comprehensive measurements of this kind in deep cuts in sand, prior to this London investigation, had only been made in Berlin, Munich, and New York. But at London, for the first time the actual distribution of earth pressures in sand were measured on a full-scale braced wall.The analysis of the experimental data showed that the earth pressure distribution can be approximated by the extended Dubrova’s solution. The agreement between the total active earth pressure obtained from the pressure cells and the corresponding Coulomb values varied from excellent (upper bound) to good (lower bound).An experimental relationship between the horizontal soil strain and the variation ofK-values over the depth of the cut was established.The different theories for predictingKo-values do not seem to apply to over consolidated dense sand deposits. The experimentalKo-values, rather, agree with other published experimental values for similar soils.The strut load readings were somewhat erratic, not necessarily corresponding to the excavation progress. The total strut loads were lower than the corresponding forces from the earth pressure cells or the corresponding Coulomb values.

ISSN:0008-3674    

DOI:10.1139/t72-041

出版商:NRC Research Press    

年代:1972

数据来源: NRC

摘要:

In this paper, the different factors that contribute to progressive failure are briefly reviewed, and the necessary conditions for its occurrence delineated.Experiments on specimens trimmed from block samples of several clays were performed to study the post-peak stress deformation behavior. It is shown that the stiffness of the testing system has an important influence on the post-peak characteristics. A method of obtaining the effective 'residual' angle of friction from drained triaxial tests is developed.Because of the localization of deformation in the failure zone, both in the laboratory and in the field, the laboratory nominal post-peak stress–strain relationship cannot be directly applied to field problems. Based on laboratory and field observations on the mechanism of deformation, the ratio of the shear modulus of the failure zone to that of the pre-peak range is proposed as a deformation parameter to be used in analysis of progressive failure.A simplified theory for the solution of the problem of progressive failure is then developed, and a case record of a first time slide in sensitive Leda clay is analyzed to illustrate the practical application of the approach.

ISSN:0008-3674    

DOI:10.1139/t72-042

出版商:NRC Research Press    

年代:1972

数据来源: NRC

摘要:

The bearing capacity of rigid vertical and batter piles under inclined loads in sand has been determined for model piles of different depth/diameter ratios. The first part of this paper deals with vertical piles and the second part will consider batter piles. The results of loading tests on free standing and piled foundations under inclinations of load varying from vertical to horizontal are analyzed. On the basis of plastic theory, a new approach for analysis of rigid vertical piles under horizontal loads is developed by extending Brinch Hansen's method; and previous methods of analysis by Meyerhof are extended to estimate the bearing capacity of vertical piles under inclined loads in sand. Loads on vertical piles are found to be in reasonable agreement with the proposed theories.

ISSN:0008-3674    

DOI:10.1139/t72-043

出版商:NRC Research Press    

年代:1972

数据来源: NRC

摘要:

This paper presents the complete record of the laboratory investigations and field observations made in conjunction with the construction of expressway embankments built by preloading over a muskeg. The peat deposit, located on the north shore of the Saint-Laurent River, was initially 10–19 ft (3.0–5.8 m) thick and is underlain by sand. Settlements of the highway fills ranging from 5 to 11 ft (1.5 to 3.3 m) were measured during construction.Laboratory and field tests were performed before and during construction. Field vane tests made at the end of the preloading stage indicated a considerable gain in the shear strength as a result of consolidation. Compressibility characteristics of the peat measured in the laboratory are compared with the field behavior.Periodical field level observations were taken during the 4 years after the removal of the temporary surcharge and have shown that the highway embankments heaved 2–3 in. (5.0–7.5 cm) over a period of 12 months at a gradually decreasing rate. The rebound was followed by long-term secondary settlements totaling 0.5–1.5 in. (1.3–3.8 cm) over the following 3 years of observations. Analysis of the settlement records shows that preloading has been beneficial in reducing the coefficient of secondary compression of the peat. Preloading was simulated in the laboratory by means of oedometer tests on peat samples; both the laboratory results and the field observations revealed a remarkable agreement between the duration of the surcharge stage and the time for rebound to be complete after removal of the surcharge.

ISSN:0008-3674    

DOI:10.1139/t72-044

出版商:NRC Research Press    

年代:1972

数据来源: NRC

摘要:

An examination has been made of the behavior of a half space of elastic material of constant Poisson's ratio, whose Young's modulus increases linearly with depth, and which is subject to a strip or circle of uniform load. Poisson's ratio was considered in the range zero to one-half, and the surface modulus ranged from zero to the value corresponding to a homogeneous material.Numerical values are presented for vertical surface displacement due to a load uniformly distributed over a circular area for Poisson's ratio = 1/2, 1/3 and 0, and for a wide range of inhomogeneity.

ISSN:0008-3674    

DOI:10.1139/t72-045

出版商:NRC Research Press    

年代:1972

数据来源: NRC

摘要:

The prediction of the coupled response to horizontal forces is of major importance for the design of footings exposed to dynamic effects. The theory of surface footings greatly overestimates the real response and neglects the fact that the footings are founded beneath the surface of the ground,i.e. partly embedded. This latter factor considerably affects the footing vibrations in that it reduces the resonant amplitudes and increases the resonant frequencies.An approximate analytical solution was developed in this paper and the theoretical response curves were compared with field experiments. Closed form formulas were obtained that are simple enough to be directly used in design. The approximate analytical solution is better able to predict the coupled response of embedded footings than that of surface footings. The response is usually dominated by the first resonant peak with the second resonant peak entirely suppressed. The derived formulas for equivalent stiffnesses and damping coefficients due to soil can be introduced into the solution of any structure.

ISSN:0008-3674    

DOI:10.1139/t72-046

出版商:NRC Research Press    

年代:1972

数据来源: NRC