Ziang Wang, Tony Liang-Tong Zhan, Haihua Zhang, Liangfeng Zheng, Ting Kang
Low-strength and highly compressible excavated clayey soils are common in geotechnical engineering, which cannot serve as a bearing stratum and typically end up being disposed of in landfills. Autoclaved aerated concrete powder (AACP) is a lightweight and porous waste material, with its stockpiles rapidly accumulating worldwide. To promote sustainable development in geotechnical engineering, a type of composite admixture consisting of cement and AACP was developed to modify clayey soils in this study. The physical and mechanical properties of untreated and the composite admixture-treated soil samples were investigated via Atterberg limits, compaction, bender element, constraint compression, free swell, and unconfined compressive strength (UCS) tests. The physicochemical and microstructural observations, including soil pH, SEM, and MIP analyses, were conducted to interpret the macroscopic mechanical behaviors. Test results showed that the incorporation of AACP improved the workability of clayey soils, while cement further enhanced their mechanical properties. Hydration compounds primarily filled the voids with a diameter ranging from 0.1 to 1 μm. From the perspective of volume change behavior, 8% cement content was recommended. Shear wave velocity showed a strong correlation with the UCS, demonstrating that the bender element technique was an effective non-destructive tool for assessing the strength of compacted samples.
{"title":"Compaction, strength, and volume change characteristics of excavated clayey soil stabilized with composite admixture of cement and autoclaved aerated concrete powder","authors":"Ziang Wang, Tony Liang-Tong Zhan, Haihua Zhang, Liangfeng Zheng, Ting Kang","doi":"10.1139/cgj-2023-0352","DOIUrl":"https://doi.org/10.1139/cgj-2023-0352","url":null,"abstract":"Low-strength and highly compressible excavated clayey soils are common in geotechnical engineering, which cannot serve as a bearing stratum and typically end up being disposed of in landfills. Autoclaved aerated concrete powder (AACP) is a lightweight and porous waste material, with its stockpiles rapidly accumulating worldwide. To promote sustainable development in geotechnical engineering, a type of composite admixture consisting of cement and AACP was developed to modify clayey soils in this study. The physical and mechanical properties of untreated and the composite admixture-treated soil samples were investigated via Atterberg limits, compaction, bender element, constraint compression, free swell, and unconfined compressive strength (UCS) tests. The physicochemical and microstructural observations, including soil pH, SEM, and MIP analyses, were conducted to interpret the macroscopic mechanical behaviors. Test results showed that the incorporation of AACP improved the workability of clayey soils, while cement further enhanced their mechanical properties. Hydration compounds primarily filled the voids with a diameter ranging from 0.1 to 1 μm. From the perspective of volume change behavior, 8% cement content was recommended. Shear wave velocity showed a strong correlation with the UCS, demonstrating that the bender element technique was an effective non-destructive tool for assessing the strength of compacted samples.","PeriodicalId":505159,"journal":{"name":"Canadian Geotechnical Journal","volume":"37 10","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-01-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139441384","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}
M. Roustaei, J. Pumple, Michael T. Hendry, Jordan Harvey, Duane Froese
Freeze-thaw cycling is a critical issue in cold-climate engineering because these cycles impact the mechanical properties of soils due to the translocation of water and ice at temperatures near 0 °C. Reinforcement methods have been developed to decrease these adverse effects, including the use of polypropylene (PP) fibers. However, few macrostructural investigations have been able to demonstrate the underlying physical basis for their effectiveness. This study used computed tomography (CT) images of clay samples reinforced with 2% PP fibers and subjected to unconfined compression (UC) and Brazilian tests before and after up to 10 closed-system freeze-thaw cycles (FTCs). Significant effects of the FTCs on soil structure include a reduction in macropores and an increase in mesopores. The addition of PP fibers reduces this change in the number of macropores from 28% to 18% following 10 FTCs. Unreinforced samples also show more localized propagation of shear/tensile cracks during tests than reinforced samples as a result of having a higher failure strength and ductility. The bridging effect of fibers, deviation of the failure path, and formation of microcracks around fibers are clearly illustrated in the CT images. This study provides significant insights relevant to engineering design in cold regions.
{"title":"Effect of freeze-thaw cycles on the macrostructure and failure mechanisms of fiber-reinforced clay using industrial computed tomography","authors":"M. Roustaei, J. Pumple, Michael T. Hendry, Jordan Harvey, Duane Froese","doi":"10.1139/cgj-2023-0136","DOIUrl":"https://doi.org/10.1139/cgj-2023-0136","url":null,"abstract":"Freeze-thaw cycling is a critical issue in cold-climate engineering because these cycles impact the mechanical properties of soils due to the translocation of water and ice at temperatures near 0 °C. Reinforcement methods have been developed to decrease these adverse effects, including the use of polypropylene (PP) fibers. However, few macrostructural investigations have been able to demonstrate the underlying physical basis for their effectiveness. This study used computed tomography (CT) images of clay samples reinforced with 2% PP fibers and subjected to unconfined compression (UC) and Brazilian tests before and after up to 10 closed-system freeze-thaw cycles (FTCs). Significant effects of the FTCs on soil structure include a reduction in macropores and an increase in mesopores. The addition of PP fibers reduces this change in the number of macropores from 28% to 18% following 10 FTCs. Unreinforced samples also show more localized propagation of shear/tensile cracks during tests than reinforced samples as a result of having a higher failure strength and ductility. The bridging effect of fibers, deviation of the failure path, and formation of microcracks around fibers are clearly illustrated in the CT images. This study provides significant insights relevant to engineering design in cold regions.","PeriodicalId":505159,"journal":{"name":"Canadian Geotechnical Journal","volume":"8 7","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-01-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139439890","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}
An accurate understanding of the cyclic behavior of clays and plastic silts is important for system performance predictions during earthquake loading. This paper presents the results of a numerical investigation into the individual and combined influences of static shear stress and viscous strength gain on the cyclic resistance of clays and plastic silts. Using the viscoplastic constitutive model PM4SiltR implemented in the finite difference program FLAC 8.1, the cyclic behaviors of the plastic soils were simulated using single-element cyclic direct simple shear simulations. A parametric analysis was performed with different combinations of viscous strength gains and static shear stresses. The effects of static shear stress and viscous strength gain varied under monotonic and cyclic loading conditions. Empirical correlations developed using scant laboratory data may not accurately predict the reduction of cyclic strengths with increasing static shear stress. Furthermore, sizeable magnitudes of monotonic viscous strength gains only produced a marginal increase in cyclic strengths. The findings from this study highlight the need for future experimental laboratory testing to validate the numerical findings, in order to improve the accuracy of performance predictions of geosystems constructed with clays and plastic silts during and following earthquake loading.
{"title":"The influence of viscous behavior and static shear stress on the cyclic strengths of plastic soils: a numerical study","authors":"Tyler J. Oathes, Trevor Carey","doi":"10.1139/cgj-2023-0060","DOIUrl":"https://doi.org/10.1139/cgj-2023-0060","url":null,"abstract":"An accurate understanding of the cyclic behavior of clays and plastic silts is important for system performance predictions during earthquake loading. This paper presents the results of a numerical investigation into the individual and combined influences of static shear stress and viscous strength gain on the cyclic resistance of clays and plastic silts. Using the viscoplastic constitutive model PM4SiltR implemented in the finite difference program FLAC 8.1, the cyclic behaviors of the plastic soils were simulated using single-element cyclic direct simple shear simulations. A parametric analysis was performed with different combinations of viscous strength gains and static shear stresses. The effects of static shear stress and viscous strength gain varied under monotonic and cyclic loading conditions. Empirical correlations developed using scant laboratory data may not accurately predict the reduction of cyclic strengths with increasing static shear stress. Furthermore, sizeable magnitudes of monotonic viscous strength gains only produced a marginal increase in cyclic strengths. The findings from this study highlight the need for future experimental laboratory testing to validate the numerical findings, in order to improve the accuracy of performance predictions of geosystems constructed with clays and plastic silts during and following earthquake loading.","PeriodicalId":505159,"journal":{"name":"Canadian Geotechnical Journal","volume":"17 12","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-01-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139443785","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}
In order to study the problems of large deformation of surrounding rock and water-rich dense fracture zones during tunnel construction through fault fracture zone, the NPR anchor cable control method is studied based on the Tabaiyi tunnel. Firstly, the mechanical deformation mechanism of surrounding rock is analyzed by geological conditions, lithology and strength of surrounding rock, and different surrounding rock zones are obtained. Then, based on the self-developed high-prestressed NPR anchor cable, the tunnel prevention and control measures are designed. The high stress NPR anchor net technology is used to support the common large deformation and fault fracture zone, while in the water-rich dense fracture zones, the combined support of double gradient grouting technology and high stress NPR anchor net technology is adopted. Finally, in order to evaluate the control effect of the support design scheme, the deformation of surrounding rock, the axial force of NPR anchor cable and the pressure of steel arch are monitored in real time. The results show that the high stress NPR anchor net technology can effectively control the large deformation of tunnel surrounding rock caused by fault zone. And in the water-rich zones, the double gradient grouting technology can provide sufficient anchoring force for the NPR anchor cable. The two technologies control the maximum deformation of surrounding rock within 300 mm, and realize the stability of tunnel primary support.
{"title":"Research on energy-absorption active control method for large deformation of tunnel surrounding rock through multi-fault fracture zone","authors":"Zhigang Tao, Yuting Mao, Jihao Sun, Xiaoyun Zhang, SS. Huo, Manchao He","doi":"10.1139/cgj-2023-0318","DOIUrl":"https://doi.org/10.1139/cgj-2023-0318","url":null,"abstract":"In order to study the problems of large deformation of surrounding rock and water-rich dense fracture zones during tunnel construction through fault fracture zone, the NPR anchor cable control method is studied based on the Tabaiyi tunnel. Firstly, the mechanical deformation mechanism of surrounding rock is analyzed by geological conditions, lithology and strength of surrounding rock, and different surrounding rock zones are obtained. Then, based on the self-developed high-prestressed NPR anchor cable, the tunnel prevention and control measures are designed. The high stress NPR anchor net technology is used to support the common large deformation and fault fracture zone, while in the water-rich dense fracture zones, the combined support of double gradient grouting technology and high stress NPR anchor net technology is adopted. Finally, in order to evaluate the control effect of the support design scheme, the deformation of surrounding rock, the axial force of NPR anchor cable and the pressure of steel arch are monitored in real time. The results show that the high stress NPR anchor net technology can effectively control the large deformation of tunnel surrounding rock caused by fault zone. And in the water-rich zones, the double gradient grouting technology can provide sufficient anchoring force for the NPR anchor cable. The two technologies control the maximum deformation of surrounding rock within 300 mm, and realize the stability of tunnel primary support.","PeriodicalId":505159,"journal":{"name":"Canadian Geotechnical Journal","volume":"29 7","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-01-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139447542","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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