This paper explores the relative contributions of wetting (suction reduction) and its associated volume change on the small-strain shear stiffness, G0, in compacted loess from Xi’an, China. Results from one-dimensional compression tests with measurements of the shear wave velocity upon wetting and loading paths are presented. The experimental results show that the softening caused by wetting compete with the densification caused by plastic deformation and their effects on G0 are strongly controlled by stress level applied prior to wetting. Below the compaction stress, suction effects are dominant and G0 reduces irrespective of the magnitude of the collapse strain. With the increase in the stress level, the reduction in G0 caused by saturation is compensated by the plastic deformation triggered by soil collapse. This behaviour is clearly observed when the soil is first loaded to the compaction stress, where the maximum collapse strain is measured upon wetting. Volume change is dominant once the compaction stress is exceeded so that G0 tends to increase upon wetting. A wetting-induced stiffness factor D is defined to demonstrate that the change in G0 varies linearly with the stress level and this behaviour is independent of the compaction conditions.
{"title":"Competing effects of wetting and volume change on G0 in compacted loess","authors":"M. Ge, J. Pineda, D. Sheng","doi":"10.1680/jgele.22.00125","DOIUrl":"https://doi.org/10.1680/jgele.22.00125","url":null,"abstract":"This paper explores the relative contributions of wetting (suction reduction) and its associated volume change on the small-strain shear stiffness, <i>G</i><sub>0</sub>, in compacted loess from Xi’an, China. Results from one-dimensional compression tests with measurements of the shear wave velocity upon wetting and loading paths are presented. The experimental results show that the softening caused by wetting compete with the densification caused by plastic deformation and their effects on <i>G</i><sub>0</sub> are strongly controlled by stress level applied prior to wetting. Below the compaction stress, suction effects are dominant and <i>G</i><sub>0</sub> reduces irrespective of the magnitude of the collapse strain. With the increase in the stress level, the reduction in <i>G</i><sub>0</sub> caused by saturation is compensated by the plastic deformation triggered by soil collapse. This behaviour is clearly observed when the soil is first loaded to the compaction stress, where the maximum collapse strain is measured upon wetting. Volume change is dominant once the compaction stress is exceeded so that <i>G</i><sub>0</sub> tends to increase upon wetting. A wetting-induced stiffness factor <i>D</i> is defined to demonstrate that the change in <i>G</i><sub>0</sub> varies linearly with the stress level and this behaviour is independent of the compaction conditions.","PeriodicalId":501470,"journal":{"name":"Géotechnique Letters","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-11-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138535396","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This paper describes direct shear testing of a range of sand-bentonite slurry mixes, identified as a gap in the literature. In the absence of a concrete interface, there was an apparent transition zone from sand-governed strength (bentonite content ≤30%) to clay-governed strength (bentonite content ≥80%), which was linked to the sample void ratio. When a concrete interface was introduced, the critical stress ratio (critical state shear stress normalised by the effective normal stress) was found to change linearly with bentonite slurry content, reflecting an interface sliding failure mechanism. The testing also considered the effect of shearing rates ranging from 0.0025 mm/min to 10 mm/min on interface shear strength. The mixtures containing greater bentonite slurry content displayed a greater decrease in the critical stress ratio with increasing shear rate. Very few studies have explored the influence of the relative sand-clay mix composition on interface shear resistance; these results provide a better understanding of their mechanical behaviour and forms a basis for future research in this area.
{"title":"Critical state shear strength at concrete-sand-bentonite slurry interfaces: mix proportions and rate effects","authors":"K. G. O'Dwyer, B. A. McCabe, B. B. Sheil","doi":"10.1680/jgele.22.00086","DOIUrl":"https://doi.org/10.1680/jgele.22.00086","url":null,"abstract":"This paper describes direct shear testing of a range of sand-bentonite slurry mixes, identified as a gap in the literature. In the absence of a concrete interface, there was an apparent transition zone from sand-governed strength (bentonite content ≤30%) to clay-governed strength (bentonite content ≥80%), which was linked to the sample void ratio. When a concrete interface was introduced, the critical stress ratio (critical state shear stress normalised by the effective normal stress) was found to change linearly with bentonite slurry content, reflecting an interface sliding failure mechanism. The testing also considered the effect of shearing rates ranging from 0.0025 mm/min to 10 mm/min on interface shear strength. The mixtures containing greater bentonite slurry content displayed a greater decrease in the critical stress ratio with increasing shear rate. Very few studies have explored the influence of the relative sand-clay mix composition on interface shear resistance; these results provide a better understanding of their mechanical behaviour and forms a basis for future research in this area.","PeriodicalId":501470,"journal":{"name":"Géotechnique Letters","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2022-11-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138535401","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Soil water adsorption strength represents the changing rate of adsorptive water content with regard to soil suction or water potential changes, dictating the magnitude of the soil water-retention curve at the dry end. Non-isothermal conditions are frequently encountered in energy and environmental geotechnics, posing the requirement to assess temperature effects on soil water adsorption strength. Yet, it remains challenging in assessing the temperature effects at the high suction range due to limitations in available experimental techniques. Here, the grand canonical Monte Carlo (GCMC) simulation was explored as a method to address this challenge. A series of GCMC simulations has been performed to assess the temperature effect on the external surface adsorption of three representative soil minerals – that is, K-muscovite, Na-montmorillonite and α-quartz. Molecular simulation results preliminarily reveal that the water adsorption strength of the external surface of these soil minerals only demonstrates marginal dependence on temperature. This observation is consistent with experimental results, substantiating the feasibility of the proposed method.
{"title":"Assessing temperature dependence of soil water adsorption strength by molecular simulation","authors":"Jianbo Wang, Zemin Qiu, Chao Zhang, Renpeng Chen","doi":"10.1680/jgele.21.00126","DOIUrl":"https://doi.org/10.1680/jgele.21.00126","url":null,"abstract":"Soil water adsorption strength represents the changing rate of adsorptive water content with regard to soil suction or water potential changes, dictating the magnitude of the soil water-retention curve at the dry end. Non-isothermal conditions are frequently encountered in energy and environmental geotechnics, posing the requirement to assess temperature effects on soil water adsorption strength. Yet, it remains challenging in assessing the temperature effects at the high suction range due to limitations in available experimental techniques. Here, the grand canonical Monte Carlo (GCMC) simulation was explored as a method to address this challenge. A series of GCMC simulations has been performed to assess the temperature effect on the external surface adsorption of three representative soil minerals – that is, K-muscovite, Na-montmorillonite and <i>α</i>-quartz. Molecular simulation results preliminarily reveal that the water adsorption strength of the external surface of these soil minerals only demonstrates marginal dependence on temperature. This observation is consistent with experimental results, substantiating the feasibility of the proposed method.","PeriodicalId":501470,"journal":{"name":"Géotechnique Letters","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2022-05-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138535307","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
R.-M. Yang, R.-W. Wei, Z.-N. Zhang, T.-L. Zheng, L. Ma
To investigate effects of initial water content on compression behaviour of municipal sewage sludge and clarify its intrinsic compression characteristics. Oedometer tests were conducted on sludge with various initial water content of 0·13–1·48 times the liquid limit. It is observed that the sludge is organic high liquid limit silt, whose e–log σ′v compression curves are inverse ‘S’ shape due to organic floc structure of sludge potentially. When the effective vertical stress σ′v > 100 kPa, a clear gap of compression curves of various initial water content still exists, different from Burland's viewpoint that compression curves tend to be consistent. Burland's concept of intrinsic compression line (ICL) is adopted for correlating compression curves of sludge well, and an ICL of the sludge is derived. The ICL of sludge is below ones reported by Hong and Burland when σ′v < 100 kPa, due to the difference in initial water content. A generalised void index is tentatively proposed by introducing generalised intrinsic parameters e*y1 and e*y2, which may be related to the loading history of the soil and the maximum load that the soil may bear in future engineering, respectively.
研究初始含水量对城市污水污泥压缩特性的影响，阐明其固有的压缩特性。对初始含水率为0·13-1·48倍液限的污泥进行了Oedometer试验。结果表明，污泥为有机高液限淤泥，其e-log σ ' v压缩曲线可能受污泥有机絮体结构的影响呈倒S形。当有效垂直应力σ ' v > 100 kPa时，不同初始含水率的压缩曲线仍然存在明显的差距，与Burland认为压缩曲线趋于一致的观点不同。采用Burland的本征压缩线(intrinsic compression line, ICL)概念对污泥井的压缩曲线进行关联，推导出污泥的本征压缩线。当σ ' v < 100 kPa时，由于初始含水量的差异，污泥的ICL低于Hong和Burland报道的ICL。通过引入广义本征参数e*y1和e*y2，初步提出广义孔隙指数，这两个参数可能分别与土体的加载历史和土体在未来工程中可能承受的最大荷载有关。
{"title":"Effects of initial water content on compression behaviour of municipal sewage sludge","authors":"R.-M. Yang, R.-W. Wei, Z.-N. Zhang, T.-L. Zheng, L. Ma","doi":"10.1680/jgele.21.00112","DOIUrl":"https://doi.org/10.1680/jgele.21.00112","url":null,"abstract":"To investigate effects of initial water content on compression behaviour of municipal sewage sludge and clarify its intrinsic compression characteristics. Oedometer tests were conducted on sludge with various initial water content of 0·13–1·48 times the liquid limit. It is observed that the sludge is organic high liquid limit silt, whose <i>e</i>–log <i>σ</i>′<sub arrange=\"stack\">v</sub> compression curves are inverse ‘S’ shape due to organic floc structure of sludge potentially. When the effective vertical stress <i>σ</i>′<sub arrange=\"stack\">v</sub> > 100 kPa, a clear gap of compression curves of various initial water content still exists, different from Burland's viewpoint that compression curves tend to be consistent. Burland's concept of intrinsic compression line (ICL) is adopted for correlating compression curves of sludge well, and an ICL of the sludge is derived. The ICL of sludge is below ones reported by Hong and Burland when <i>σ</i>′<sub arrange=\"stack\">v</sub> < 100 kPa, due to the difference in initial water content. A generalised void index is tentatively proposed by introducing generalised intrinsic parameters <i>e</i>*<sub arrange=\"stack\">y1</sub> and <i>e</i>*<sub arrange=\"stack\">y2</sub>, which may be related to the loading history of the soil and the maximum load that the soil may bear in future engineering, respectively.","PeriodicalId":501470,"journal":{"name":"Géotechnique Letters","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2022-05-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138535308","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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