Géotechnique Letters

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EISSN : 2045-2543
Published by: Thomas Telford Ltd. (10.1680)
Total articles ≅ 563
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C. Deng, S.K. Haigh
Published: 1 September 2021
Géotechnique Letters, Volume 11, pp 1-21; https://doi.org/10.1680/jgele.21.00046

Abstract:
A series of centrifuge tests was conducted to explore the earth pressures mobilised in loose and dense sand for a complete set of active movement modes of a rigid retaining wall: rotation about the base, translation and rotation about the top. Earth pressures behind the wall were measured by a Tekscan pressure mapping system. This paper reveals that earth pressures at all depths decrease simultaneously with active wall rotation about the base, while those in shallow layers can increase with active wall translation and rotation about the top. A linkage between earth pressures and shear strains was built as a simplified constitutive law, together with deformation mechanisms, allowing designers to predict flexible wall deflections during construction as well as ultimate collapse.
G. Mortara
Published: 1 September 2021
Géotechnique Letters, Volume 11, pp 221-229; https://doi.org/10.1680/jgele.20.00161

Abstract:
The scope of this paper is to give an alternative to the use of an explicit plastic potential in elastoplastic models for soils. This is possible through the definition of a stress-dilatancy relationship and a simple expression for an auxiliary surface inlieu of a given expression of the plastic potential surface. This approach results in a flexible definition of the model and to very simple expressions of the auxiliary plastic potential derivatives.
H. A. Amundsen, A. Emdal, V. Thakur
Published: 1 September 2021
Géotechnique Letters, Volume 11, pp 179-186; https://doi.org/10.1680/jgele.21.00052

Abstract:
A new method for storing mini-block samples was developed by the Norwegian University of Science and Technology. The method consists of storing samples inside a pressurised storage cell in order to minimise the effects of stress relief. The pilot study consists of nine mini-block samples that were stored and tested at the sampling site. The samples were sealed with a rubber membrane and storage cell at the site, shortly after sampling. Thereafter an isotropic pressure was applied and kept constant throughout the storage period of up to two months while the excess water was monitored. The results indicate that the storage method reduce/minimises the effects of stress relief and ageing during the time delay between sampling and testing. The conducted tests indicate that samples stored inside the pressurised storage cell result in geotechnical parameters that are close to the 0 days’ samples, which were tested less than an hour after the sampling.
C. Deng, S.K. Haigh
Published: 1 September 2021
Géotechnique Letters, Volume 11, pp 202-208; https://doi.org/10.1680/jgele.20.00116

Abstract:
A series of centrifuge tests was conducted to explore the earth pressures mobilised in loose and dense sand for a complete set of active movement modes of a rigid retaining wall: rotation about the base, translation and rotation about the top. Earth pressures behind the wall were measured by a Tekscan pressure mapping system. This paper reveals that earth pressures at all depths decrease simultaneously with active wall rotation about the base, while those in shallow layers can increase with active wall translation and rotation about the top. A linkage between earth pressures and shear strains was built as a simplified constitutive law, together with deformation mechanisms, allowing designers to predict flexible wall deflections during construction as well as ultimate collapse.
J. Prasomsri, ,
Published: 1 September 2021
Géotechnique Letters, Volume 11, pp 209-214; https://doi.org/10.1680/jgele.20.00089

Abstract:
Internal instability or suffusion is one of the mechanisms of internal erosion in cohesionless soils, which is described by the loss of integrity of soil by seepage flow and is associated with the migration of finer particles. The contribution of the non-plastic finer fraction in a material is a key factor governing internal instability susceptibility. This study presents the experimental investigation of the influence of the fines content on the onset of internal instability of gap-graded sands using a pressure-controlled triaxial erosion device. The results indicate that the finer fraction in the soil has a significant influence on the hydraulic gradient at the onset of erosion. The underfilled soil with fines content less than 30% is vulnerable to suffusion at a relatively small hydraulic gradient. The transitional soil, whose fines content is between 30 and 35%, also exhibits suffusion, but the erosion onset hydraulic gradient significantly increases with increasing fines content. The overfilled soil with fines content larger than 35% exhibits suffosion or internal stability at a larger hydraulic gradient. The results also highlight the necessity of the multiple indices, such as mass loss, volumetric change and change in permeability, in evaluating the onset of various instability phenomena.
A. Saha, S. Sekharan, U. Manna
Published: 1 September 2021
Géotechnique Letters, Volume 11, pp 164-170; https://doi.org/10.1680/jgele.21.00015

Abstract:
Water absorbing polymer (WAP) amendment is emerging as a sustainable soil management technique in various geoenvironmental projects for controlling the subsurface water flow in the vadose zone. The addition of WAP can alter the pore structure and improve water retention characteristics of the soil. The existing water retention characteristic curve (WRCC) models for polymer amended soils are complex and require a number of empirical parameters, which cannot be easily obtained through simple laboratory experimentation. The present study proposed a simple predictive WRCC model for WAP amended soils based on the understanding that WAP particles absorb and retain water within their polymer structure and therefore influence the void ratio. The proposed model captures the change in the void ratio of the amended soil through a modified phase relationship for predicting WRCC. The performance of the model was validated for four different textured soils with varying WAP concentrations. The comparison between measured and predicted WRCC indicates that the proposed model can capture the changes in the void ratio as well as the WRCC with adequate accuracy.
V. Hadsari,
Published: 1 September 2021
Géotechnique Letters, Volume 11, pp 187-194; https://doi.org/10.1680/jgele.20.00147

Abstract:
This study investigates the effects of drying and rewetting on the pore size distribution in a silty sand. It is shown that drying reduces the void ratio and at the same time alters the pore size distribution although not with all sizes of pores reducing in volume. As the extent of drying increased the volume fraction of the larger pores increased while the volume fraction of the smaller pores decreased. Subsequent rewetting does not alter or reverse the pore rearrangement in a significant way. Inferred and directly measured soil-water characteristic curves are characterised using fractal theory. Increased drying increases the slopes of scanning curves and reduces air entry and air expulsion suctions. There is no significant change to the fractal dimension of the pore size distribution. In practice, the drying induced pore rearrangement could lead to a stability concern, especially for marginally stable soil deposits, as larger pores become greater in number, a change not erased by rewetting, likely making the soil more prone to collapse or liquefaction.
X. Feng, F. Xue, X. Liu, M. Wang
Published: 1 September 2021
Géotechnique Letters, Volume 11, pp 1-16; https://doi.org/10.1680/jgele.21.00065

Abstract:
This technical note uses bolt-reinforced jointed granite to investigate the relationship between the joint angle and the reinforcing effects of bolt. 3D-printed (3DP) bolts were manufactured with a real bolt as the model prototype, the dimensions and surface geometries were scaled up, and the mechanical properties were similar to those of the prototype bolt. The cylindrical granite specimens were prepared with each separated by a through-going inclined joint plane, the bolt and the granite were combined via bonding agent and nuts. The bearing capacity of the system, the loading status of the bolt, and the displacement/strain changing patterns on the surface of the granite were comprehensively investigated. The results indicated that granite tended to crack when the joint angle was small and that a higher joint angle weakened the bearing capacity of the system, even with the reinforcement of the bolt. For specimens with joint angles of 45° and 60°, a shearing tendency and strain concentration zones nearby the joint plane were clearly observed. This study provide a new methodology for studying the anti-shearing behaviour of bolt in fractured hard rock.
G. De Lima Sonaglio, G. M. A. Do Patrocínio, L. Festugato, M. B. Corte
Published: 1 September 2021
Géotechnique Letters, Volume 11, pp 1-20; https://doi.org/10.1680/jgele.20.00059

Abstract:
Shaft friction degradation in geotechnical problems occurs alongside large uncertainties. Under cyclic loadings, offshore foundations can episodically suffer the loss of stiffness and strength. In such cases, initial in-situ soil state is lost as soil is disturbed during cyclic loading. In this sense, it is important to develop a testing procedure to assess the lateral friction degradation. Considering that a cone is a miniature driven pile, the use of this testing technique allows monitoring the degradation of sleeve friction during cyclic loading. This paper aims to improve the knowledge on the feasibility of using cone testing for the recognition of lateral friction degradation of a dry granular soil. Cyclic mCPT tests were performed in a calibration chamber considering a range of loading conditions. The effect of cyclic displacement amplitude and the confining pressure were investigated. Lateral friction, fs, degrades while repeating the load cycling, resulting in loss of lateral strength due to soil-cone interface friction degradation. After about ten load cycles, degradation tended to stabilize for all tests.
A. Galli, G. Mortara
Published: 1 September 2021
Géotechnique Letters, Volume 11, pp 171-178; https://doi.org/10.1680/jgele.20.00098

Abstract:
The accurate prediction of settlements of shallow foundations under operational condition is still an open issue for both scientists and engineers, in particular in case of complex loading conditions (e.g. combined vertical and horizontal loads). The complexity of the soil mechanical response and the difficulty in managing a multiscale problem (ranging from the local scale of the soil REV to the macro scale of the structure) makes a rigorous modelling of such problems particularly demanding for standard numerical tools such as 3D finite element codes. In this perspective, the well-known macroelement approach may represent a valid simplified approach, capable of overcoming these limitations and allowing a comprehensive description of both SLS and ULS of such systems, particularly useful even for practitioners. In the paper, based on a small-scale 1g experimental campaign on a strip foundation, the effect of embedment is investigated over horizontal loading paths at constant vertical load. In particular, relatively low vertical stress values are considered for the foundations, as it often happens in real structures under usual working conditions. A simple macroelement plastic model, based on a strain hardening law with non-associated flow rule is then proposed and validated over the available experimental data.
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