摘要:

This lecture describes the investigation of large and damaging settlements in the One Lombard Building in San Francisco Calif. The cause of the settlements was a mystery. Although it was known that settlement began during construction of a major new sewer near the building, it was not clear how the settlements could be related to the sewer construction activities. The paper explains the cause of the settlements and describes the technique used to remedy the problem. The legal and insurance aspects of the case, in some ways more mysterious than the technical aspects, are also described.Key words: settlement, foundations, clay, dewatering, pile driving, underpinning.

ISSN:0008-3674    

DOI:10.1139/t92-001

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

A precast concrete pile was driven 11.0 m into a sand deposit and subjected to three compression and one tension static loading tests. By means of strain-gage instrumentation, the loads imposed in the pile during the tests were determined. The observed load distributions appeared to suggest the existence of a critical depth. However, when the load data were supplemented with the residual load acting before the start of the tests, the appearance of critical depth disappeared. Instead, the analysis of the tests showed that the load distribution was a function of the effective overburden stresses in the soil over the full pile length, with β-ratios ranging from 0.40 through 0.65 and a toe bearing coefficient of 30. The shaft resistance degraded slightly from test to test. The shaft resistance in tension was about equal with the shaft resistance in compression. The β-ratios and the toe bearing coefficient derived from the test were applied unchanged to the results of compression tests on a second test pile, a 15 m long identical pile, and the calculated capacity agreed with the capacity found in the static loading test.Key words: instrumented pile, sand, loading test, residual load, load transfer.

ISSN:0008-3674    

DOI:10.1139/t92-002

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

A nonlinear finite element analysis was carried out to model the pile tests presented in the companion paper which included a new procedure to calculate the residual load in the test pile. The soil at the site consists of sand, and this second paper applies a bounding surface plasticity model in a finite element analysis to describe the behavior of the sand subjected to repeated loading. A close agreement was achieved between the calculated and measured values for the applied load versus pile head movement, load transfer, and shaft resistance in compression and tension testing. In addition, the analysis demonstrated a reduction in shaft resistance and a buildup of toe resistance with repeated loading. The finite element calculations as well as the measurements indicate that the critical-depth concept is incorrect.Key words: pile, sand, residual load, load transfer, finite element, constitutive model.

ISSN:0008-3674    

DOI:10.1139/t92-003

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

The performance of a 6 m high anchored steel sheet pile retaining wall, constructed to allow CN Rail to twin its main-line track, is presented. The instruments installed gave measurement of the load and its variation along the tieback anchors; the distribution of the strain along the height of the wall which allowed an earth-pressure distribution to be postulated; and the lateral deflection of the wall. The earth-pressure distributions, inferred from the field measurements, were adequately predicted using the Terzaghi and Peck recommendation coupled with the Boussinesq procedure to account for the train loads. The best-fit lateral pressure distributions were in turn used to calculate displacement profiles by modelling the wall as a beam. The results matched the measured profiles reasonably well, thus endorsing a simplified technique for predicting displacements of an anchored wall.Key words: retaining wall, tieback, earth-pressure distribution, wall deflection, railway.

ISSN:0008-3674    

DOI:10.1139/t92-004

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

A number of simplified approaches have been used by various researchers to estimate the three-dimensional stress changes and ground deformations due to shallow tunnels in soft soils. The effectiveness of these simplified analyses, such as (i) axisymmetric analysis, (ii) longitudinal plane strain analysis, and (iii) empirical cumulative probability distribution approach, has been examined by comparison of results with those from a full three-dimensional elastoplastic finite-element analysis. For tunnels located at shallow depths, axisymmetric analyses are generally found to be unable to predict the correct magnitude of displacement around a tunnel heading. However, the trend of the three-dimensional deformation behaviour near the tunnel heading can be reasonably approximated by the average of the normalized displacement curves predicted by the two axisymmetric assumptions as described in this paper. The three-dimensional distribution of the displacement near the ground surface, on the other hand, can be approximately predicted by the cumulative probability approach, provided that the three empirical parameters required by the equations are reasonably estimated. In this paper, these parameters were estimated from the result of a two-dimensional plane strain cross-sectional analysis. Finally, it was found that modelling of three-dimensional deformations by a longitudinal plane strain analysis did not give good results for the cases examined.Key words: tunnelling, soft ground, analysis.

ISSN:0008-3674    

DOI:10.1139/t92-005

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

A deterministic (GEOSLIDE) and a probabilistic (PROSLIDE) microcomputer code are introduced to aid in performing rock wedge analyses based on the limit equilibrium method. The deterministic code evaluates the stability of a single rock wedge formed by discontinuities in rock through three-dimensional vector algebra,GEOSLIDEundertakes a full kinematic analysis (daylighting and obstruction), analyzes both wedge and plane sliding, and provides for anchor designs and sensitivity analyses (cohesion, friction, and water forces). Through multiple stability analyses,PROSLIDEevaluates the probability of failure for a rock slope by examining the distribution of the factors of safety from all the potential sliding wedges formed by the discontinuities of the rock mass. The probability of failure is expressed as the ratio of kinematically free wedges that have a factor of safety less than unity to the total number of wedges,PROSLIDEcan form and analyze as many as 2000 different pairs of discontinuities in less than 30 min using a 25 MHz 486 IBM-compatible computer. In a worked example, the probability of failure for a fixed slope strike and loading condition is shown to vary with the slope angle, following the characteristic 'S' shape of a cumulative distribution function. The effect of an anchor force is to spread the distribution over a wider range of the factor of safety (SF), pushing many wedges into a potential upslide situation and splitting the distribution about the failure zone of the stability diagram (−1 < SF < 1).Key words: rock slope, rock wedge, stability analysis, factor of safety, probability of failure, Monte Carlo simulation.

ISSN:0008-3674    

DOI:10.1139/t92-006

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

A simplified model of an unconfined dry snow slab is used to derive expressions for the rate at which elastic strain energy is released and for the fracture resistance during the propagation of the rapid brittle fractures that result in slab avalanches. A relatively constant energy release rate is derived based on arguments that associate most of the released energy with the crown fracture. In contrast, advancing basal and crown fractures result in increasing fracture resistance. By assuming fracture propagation will stop when the strain energy release rate is just greater than the fracture resistance, the width of a slab avalanche is found to be proportional to an arrest parameter. This parameter includes the slab thickness, slab tensile strength, and basal shear strength, each of which can be measured prior to avalanching. It is argued that, compared to the three variables which can be measured, the remaining variables have limited influence on the width of unconfined slab avalanches. These less influential variables are grouped into an empirical constant that is evaluated using field data from 13 unconfined slab avalanches. The width of these slab avalanches appears to be related linearly to the arrest parameter and to be independent of whether the avalanches result from natural, skier, or explosive triggering.Key words: avalanche, avalanche width, energy release rate, fracture arrest, fracture resistance, slab tensile strength, basal shear strength.

ISSN:0008-3674    

DOI:10.1139/t92-007

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

This case record describes the performance of two test embankments constructed over a soft compressible clay, one with prefabricated vertical drains and one without. The measured settlements were significantly different from the predicted settlements, and the pore-water pressures were inconsistent with the observed consolidation. The observed performance of the vertical drains is compared with theoretical predictions to assess the sensitivity of the predicted rate of consolidation to input parameters.Key words: case record, consolidation, field observations, prefabricated vertical drains, wick drains, preloading, settlements, test embankments.

ISSN:0008-3674    

DOI:10.1139/t92-008

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

Fluid pressures up to 1.7 times greater than hydrostatic have been measured in argillaceous Paleozoic rocks of low permeability in southern Ontario and western New York State. These supernormal formation fluid pressures were measured at depths of 50–310 m using submersible pressure transducers with straddle packers and multiple-packer casings isolating the test intervals. Measurements were obtained over periods of 7–46 months following casing installations. The pressure measurements from 11 monitoring wells are compiled and supporting hydrogeologic data for 5 selected wells are used as examples to illustrate the occurrence of supernormal fluid pressures in the Ordovician, Silurian, and Devonian sedimentary sequence of southern Ontario and western New York State. Possible explanations for the occurrence of supernormal fluid pressures in sedimentary rock are evaluated considering the available geologic and hydrogeologic information obtained from the monitoring wells. Based on this review, it is hypothesized that gas migration and accumulation from deeper distant sources via permeable vertical pathways is the most plausible explanation for the observed fluid pressures, although secondary contributions from local neotectonic activity are also possible. The implications of such supernormal fluid pressures on regional groundwater flow in sedimentary rocks and related activities such as waste disposal in sedimentary rock are briefly discussed.Key words: supernormal fluid pressure, sedimentary rocks, gas migration.

ISSN:0008-3674    

DOI:10.1139/t92-009

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

Understanding of progressive failure of slopes is of immense interest to geotechnical engineers and others concerned with the occurrence of landslides. One important aspect of research is the development of relevant analytical and numerical techniques. Both deterministic and probabilistic approaches can be used to study the development of progressive failure, provided valid geomechanics models form the basis of such studies. In this paper the risk of failure is simulated within a probabilistic framework. Of particular interest is the increase in the probability of failure, as overstress (and consequent localized failure) is considered to have actually occurred over an increasing proportion of a slip surface within the slope. The perception or interpretation of local failure is often based on observational data from surface measurements and subsurface instrumentation. Knowledge of spatial progression of failure may similarly be based on indirect and direct evidence. In the proposed simulation process the peak and residual shear strength of the slope material are regarded as one-dimensional random fields, and therefore spatial variability of each parameter is taken into consideration.Key words: analysis, clays, failure, shear strength, slopes, stability, landslides, probabilistic analysis, reliability analysis, progressive failure, slip surfaces, risk simulation, statistical analysis.

ISSN:0008-3674    

DOI:10.1139/t92-010

出版商:NRC Research Press    

年代:1992

数据来源: NRC