| 1. |
- Ahmadi Naghadeh, Reza, 1982, et al.
(författare)
-
A laboratory characterisation of the response of intact chalk to cyclic loading
- 2022
-
Ingår i: Geotechnique. - : Thomas Telford Ltd.. - 0016-8505 .- 1751-7656. ; In Press
-
Tidskriftsartikel (refereegranskat)abstract
- This paper reports the cyclic behaviour of chalk, which has yet to be studied comprehensively. Multiple undrained high-resolution cyclic triaxial experiments on low- to medium-density intact chalk, along with index and monotonic reference tests, define the conditions under which either thousands of cycles could be applied without any deleterious effect, or failure could be provoked under specified numbers of cycles. Intact chalk's response is shown to differ from that of most saturated soils tested under comparable conditions. While chalk can be reduced to putty by severe two-way displacement-controlled cycling, its behaviour proved stable and nearly linear visco-elastic over much of the one-way, stress-controlled loading space examined, with stiffness improving over thousands of cycles, without loss of undrained shear strength. However, in cases where cyclic failure occurred, the specimens showed little sign of cyclic damage before cracking and movements on discontinuities led to sharp pore pressure reductions, non-uniform displacements and the onset of brittle collapse. Chalk's behaviour resembles the fatigue response of metals, concretes and rocks, where micro-shearing or cracking initiates on imperfections that generate stress concentrations; the experiments identify the key features that must be captured in any representative cyclic loading model.
|
|
| 2. |
- Bergström, Anders, et al.
(författare)
-
Field test of a floating thermal pile in sensitive clay
- 2021
-
Ingår i: Geotechnique. - 0016-8505 .- 1751-7656. ; 71:4, s. 334-345
-
Tidskriftsartikel (refereegranskat)abstract
- The response of floating pile foundations in deep deposits of soft clay is governed by the settlements within the clay deposit surrounding the piles. A long-duration thermal response test (TRT) has been performed to assess the impact of heating and cooling on the geotechnical performance of a vertically loaded slender tubular steel pile in a deep deposit of sensitive clay. The results from the instrumented test site indicate that negligible excess pore water pressures, up to 3 kPa during heating and down to -1·1 kPa during cooling, were generated in the soil adjacent to the pile for a 50 W/m heat flux. The heating rate was sufficiently low to facilitate the drainage of pore water. The influence radius for the excess pore water pressures, however, extended beyond the soil volume affected by temperature change. The absence of thermally triggered creep settlements could be explained by the overlap between the remoulded zone resulting from pile installation, the extent of the heating, and the low creep susceptibility of remoulded sensitive clay for moderate temperature changes. Furthermore, no difference in the ultimate bearing capacity was found between the thermal pile and the reference pile, which was only loaded with a serviceability load during the test series. The current test data, therefore, indicate that driven floating piles in a deep deposit of soft clay also function as heat exchanger piles with minimal detrimental effects, for similar operational conditions as used in the TRT. It should be noted, however, that other pile types that do not extensively remould the clay adjacent to the pile shaft may show more significant influence of the thermal changes.
|
|
| 3. |
- Birmpilis, Georgios, 1988, et al.
(författare)
-
Experimental quantification of 3D deformations in sensitive clay during stress-probing
- 2022
-
Ingår i: Geotechnique. - : Thomas Telford Ltd.. - 0016-8505 .- 1751-7656. ; 73:8, s. 655-666
-
Tidskriftsartikel (refereegranskat)abstract
- Unique four-dimensional (4D) deformation data are collected during drained triaxial tests on intact specimens of a natural sensitive clay. This requires the development of a miniature triaxial cell for advanced stress path testing, specifically designed for X-ray computed tomography. Salient features include the omission of a membrane, and a mounting procedure that minimises disturbance by the experimenter. Three distinct drained stress ratios are studied for pseudo-isotropic, K-0, and highly deviatoric loading paths. The results indicate that the K-0 path shows the most uniform deformation mechanism, where the measured ratio of deviatoric and volumetric strain increments reach the stress ratio applied at boundary value level for large magnitudes of total strain. The pseudo-isotropic test also reaches a strain ratio close to eta at large total strain levels; however, the deformation field is less uniform. Furthermore, the highly deviatoric stress path shows the most heterogeneous deformation fields commensurate with the applied stress ratio, although the ratio of deviatoric and volumetric strain increments falls above the eta applied. The mean value of the three-dimensional spatial fields of strain corresponds well with the changes observed at boundary level, supporting prior research on drained stress-probing on clays for which there are no 4D deformation data available.
|
|
| 4. |
- Bolton, Malcolm D., et al.
(författare)
-
Centrifuge cone penetration tests in sand
- 1999
-
Ingår i: Geotechnique. - : Thomas Telford Ltd.. - 0016-8505 .- 1751-7656. ; 49:4, s. 543-552
-
Tidskriftsartikel (refereegranskat)abstract
- When performing centrifuge tests, it is necessary to carry out in-flight tests such as the cone penetration test (CPT). Recently, miniature CPTs have formed one collaboration entitled 'European Program of Improvement in Centrifuging' (EPIC). This article provides information on both the random and the consistent variations which have been observed with CPTs in sand when identical prototypes have been modeled in the different laboratories.
|
|
| 5. |
- Cusack, M., et al.
(författare)
-
Relic aragonite from Ordovician-Silurian brachiopods : Implications for the evolution of calcification
- 2011
-
Ingår i: Geotechnique. - 0016-8505 .- 1751-7656. ; 39:10, s. 967-970
-
Tidskriftsartikel (refereegranskat)abstract
- Understanding the influence of aragonite/calcite sea conditions on the evolution of biocalcification relies strongly on the correct interpretation of the original composition of calcareous taxa. Aragonite dissolves or inverts into calcite over geological time, and its preservation is currently unknown to predate the Pennsylvanian. Here we present direct evidence for the common occurrence of relic aragonite in Ordovician and Silurian trimerellid brachiopods, thereby extending the known range of aragonite preservation by more than 130 million years. Together with associated hypercalcifying taxa of putatively original aragonite or high-magnesium calcite composition and considerations of the temperature dependence of aragonite and calcite precipitation, our results suggest that the evolution of aragonite biomineralization might have presented an adaptive advantage in shallow marine tropical waters of calcite seas. A targeted search for Paleozoic aragonite should both resolve the original composition of consistently recrystallized taxa and enable the reassessment of the aragonite/calcite sea paradigm in a paleoenvironmental context.
|
|
| 6. |
- de Frias Lopez, Ricardo, et al.
(författare)
-
Force transmission and soil fabric of binary granular mixtures
- 2016
-
Ingår i: Geotechnique. - : ICE Publishing. - 0016-8505 .- 1751-7656. ; 66:7, s. 578-583
-
Tidskriftsartikel (refereegranskat)abstract
- The effect of fines content on force transmission and fabric development of gap-graded mixtures under triaxial compression has been studied using the discrete-element method. Results were used to define load-bearing soil fabrics where the relative contributions of coarse and fine components are explicitly quantified in terms of force transmission. Comparison with previous findings suggests that lower particle size ratios result in higher interaction between components. A potential for instability was detected for underfilled fabrics in agreement with recent findings. It was also found that the threshold fines content provides an accurate macroscopic estimation of the transition between underfilled and overfilled fabrics.
|
|
| 7. |
- Degago, S.A., et al.
(författare)
-
Use and misuse of the isotache concept with respect to creep hypotheses A and B
- 2011
-
Ingår i: Geotechnique. - 0016-8505 .- 1751-7656. ; 61:10, s. 897-908
-
Tidskriftsartikel (refereegranskat)abstract
- Time-dependent settlements of thick in situ clay layers are normally analysed based on results of thin laboratory specimens. However, the time used to complete primary consolidation is significantly different for laboratory specimens and in situ soil layers. Two totally different cases, referred to as creep hypotheses A and B, have been used as a basis of discussion to assess the effect of creep during the primary consolidation phase. Several laboratory and field experiments have been conducted to study the effect of soil layer thickness on the time-dependent compressibility of a soil layer. Some of these tests seemed to support hypothesis A, others hypothesis B, and in some cases showed a behaviour between the two. As a result this question has continued to be a controversial topic among researchers, and remains to be an issue that needs to be resolved. In this study, some relevant experimental investigations from the literature are thoroughly studied and critically reviewed, and also explained consistently using the isotache concept. This work indicates that the isotache approach can capture the main characteristics of the time-dependent compressibility of clays during both the primary and secondary consolidation phases. It is also shown that the misuse of the isotache concept, as reported in the literature, may give a confusing picture of reality. Based on the considered data, it is demonstrated that the measured time-dependent compressibility of clays agrees well with hypothesis B.
|
|
| 8. |
- Larsson, Stefan, et al.
(författare)
-
On horizontal variability in lime-cement columns in deep mixing
- 2005
-
Ingår i: Geotechnique. - : Thomas Telford Ltd.. - 0016-8505 .- 1751-7656. ; 55:1, s. 33-44
-
Tidskriftsartikel (refereegranskat)abstract
- The variability with respect to results from hand-operated penetrometer tests on lime-cement column cross-sections is investigated by means of spatial correlation structures. Experimental directional semi-variograms are evaluated for a large number of column cross-sections from two field tests. Analyses of variance (ANOVA) are performed in order to investigate the influence of various factors in the installation process on the inherent variability. The paper also briefly discusses the concept of sufficient mixing: the link between the mixing process and the mechanical system. The results have been interpreted within the framework of variance reduction based on an averaging model for axially loaded columns. The results from the two field tests show that the radius is the dominating variable in the variability, and different types of correlation structure can be obtained in spite of the fact that they have been equally installed. The mechanical mixing work does not significantly influence the type of spatial correlation structure. Furthermore, a simple design consideration shows that the variance reduction has a major influence on the determination of the partial factor of safety.
|
|
| 9. |
- Liu, Tingfa, et al.
(författare)
-
An experimental investigation into the behaviour of de-structured chalk under cyclic loading
- 2022
-
Ingår i: Geotechnique. - : Thomas Telford Ltd.. - 0016-8505 .- 1751-7656. ; In Press
-
Tidskriftsartikel (refereegranskat)abstract
- Low-to-medium density chalk can be de-structured to soft putty by high-pressure compression, dynamic impact or large-strain repetitive shearing. These process all occur during pile driving and affect subsequent static and cyclic load-carrying capacities. This paper reports undrained triaxial experiments on de-structured chalk, which shows distinctly time-dependent behaviour as well as highly non-linear stiffness, well-defined phase transformation (PT) and stable ultimate critical states under monotonic loading. Its response to high-level undrained cyclic loading invokes both contractive and dilative phases that lead to pore pressure build-up, leftward effective stress path drift, permanent strain accumulation, cyclic stiffness losses and increasing damping ratios that resemble those of silts. These outcomes are relatively insensitive to consolidation pressures and are distinctly different to those of the parent intact chalk. The maximum number of cycles that can be sustained under given combinations of mean and cyclic stresses are expressed in an interactive stress diagram which also identifies conditions under which cycling has no deleterious effect. Empirical correlations are proposed to predict the number of cycles to failure and mean effective stress drift trends under the most critical cyclic conditions. Specimens that survive long-term cycling present higher post-cyclic stiffnesses and shear strengths than equivalent ‘virgin’ specimens.
|
|
| 10. |
- Pusch, Roland, et al.
(författare)
-
Stochastic model of the creep of soils
- 1980
-
Ingår i: Geotechnique. - : Thomas Telford Ltd.. - 0016-8505 .- 1751-7656. ; 30:4, s. 497-506
-
Tidskriftsartikel (refereegranskat)abstract
- The complex microstructure characteristic of soils points to the need to allow for this heterogeneity in models of plasticity and creep. In particular, the number and heights of thermally activable barriers to slip, in a given volume of soil subjected to a constant deviatoric stress, will vary in space and time. A statistical model embodying such changes in the spectrum of activation energies is outlined. With usual conditions of testing, it yields a linear relation between the creep strain and the logarithm of time. The model is shown to account rather well for typical creep behaviour of undrained clay, and to provide an appropriate framework for the representation and study of the creep of structurally sensitive clay and clayey silt, as well as for less sensitive soils. The determination of the most probable activation energy in the spectrum is discussed.
|
|
