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1
Sample-Lord, Kristin M., Wenjie Zhang, Shan Tong, and Charles D. Shackelford. "Apparent salt diffusion coefficients for soil–bentonite backfills." Canadian Geotechnical Journal 57, no. 5 (May 2020): 623–34. http://dx.doi.org/10.1139/cgj-2019-0058.
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Apparent diffusion coefficients, Da, were measured for two soil–bentonite (SB) backfills characteristic of those used in SB vertical cutoff walls for subsurface control of contaminant migration. The base soils for the backfills comprised either a natural lean clay or sand–bentonite mixtures. The base soils were mixed with 5% bentonite–water slurry to obtain a slump of 125 mm, resulting in total bentonite contents ranging from 4.76% to 7.31%. Values of Da for sodium chloride were measured using a recently developed dialysis-leaching test method. The Da values for the clay–bentonite and sand–bentonite backfills ranged from 2.5 × 10−10 to 5.3 × 10−10 m2/s and from 1.4 × 10−10 to 8.1 × 10−10 m2/s, respectively. Values of Da for both backfills increased with increasing average salt concentration in the specimen (Cave). Values of Da decreased by ≤50% with increasing backfill bentonite content. For all Cave values, the clay backfills exhibited lower Da than the sand–bentonite backfills, likely due to additional fines from the lean clay. Results of this study enhance understanding of solute diffusion through SB cutoff walls, as well as support future use of the dialysis-leaching test method to measure diffusion properties of SB backfills.
2
Tang, Yanan, Weidong Song, and Jianxin Fu. "Damage constitutive model of stratified cemented backfill based on coupling macroscopic and mesoscopic deformations." E3S Web of Conferences 194 (2020): 05024. http://dx.doi.org/10.1051/e3sconf/202019405024.
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The mechanical properties and stress-strain relationship of cemented backfills with different stratified structure have a direct effect on the mining-filling cycle and the mining of adjacent pillars. To obtain the stress-strain evolution curves, the uniaxial compressive strength tests were performed on backfills with stratified numbers of 0, 1, 2 and 3. The deformation of stratified backfill under the compressive load is regarded as a compound of closed deformation of the macroscopic stratified structure and elastic deformation of material. The damage constitutive model of cemented backfills with different stratified structure are established by considering the influence of compacted section. Comparative analysis reveals that the calculated curve based on the established sectional damage constitutive model conforms well to the trial curve. The maximum closed strain of the structural plane has a more significant effect on the mechanical properties of backfill. In the Weibull distribution, with the increase of the parameter m, the peak strength of backfill gradually increases and then reaches to a certain value, and the stress-strain curve gradually becomes steeper, which shows that m is a reflection of the concentration level of micro-unit strength distribution in the backfill..
3
Mitchell, Robert J. "Centrifuge model tests on backfill stability." Canadian Geotechnical Journal 23, no. 3 (August 1, 1986): 341–45. http://dx.doi.org/10.1139/t86-048.
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The 6 m diameter, 30 g-tonne geotechnical centrifuge at Queen's University is described. Results from eight model tests, carried out on plain cemented sand samples representing mine backfills, are presented. These data show that the stable prototype backfill heights obtained from centrifuge tests exceed the failure heights predicted from unconfined compression testing by factors averaging about 1.8. This factor is explained by a combination of geometrical and behavioural effects. Still photographs of typical backfill failures in the centrifuge are included and these indicate that unacceptable ore dilution and recovery costs would be associated with the prototype failures in plain cemented tailings backfills. Key words: geotechnical centrifuge, mine backfill, model tests, cemented sand.
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Fan, Ridong, Yuling Yang, and Songyu Liu. "Impact of In Situ Soil in Soil-Bentonite Cutoff Wall Backfill on Compressibility and Hydraulic Conductivity." Advances in Civil Engineering 2021 (January 19, 2021): 1–12. http://dx.doi.org/10.1155/2021/9350604.
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Soil-bentonite cutoff walls, consisting of excavated in situ soil and bentonite as backfills, are used extensively as vertical barriers for groundwater pollution control. Sand mixed with high-quality natural sodium bentonite (NaB) is commonly used as a research object to investigate the hydraulic and compression properties of soil-bentonite backfills. However, pure sand could rarely be found in real conditions, and natural NaB may not be available readily in some countries such as China, India, and Turkey. This paper presents a comprehensive laboratory investigation on the compressibility and hydraulic conductivity (k) of soil-bentonite backfills created by simulated in situ soil and low-quality sodium activated calcium bentonite (SACaB). The simulated in situ soils are prepared using sand-natural clay mixtures with sand to natural clay mass ratios ranging from 0.5 to 6.0, and the bentonite content (BC) in the base mixture ranges from 0 to 15%. The result indicates that BC dominates the compression index (Cc) of the backfill, and a unique relationship between void ratio at effective vertical compression stress of 1 kPa and compression index is proposed for various types of soil-bentonite backfills. An increase in either BC or clay size fraction (CF) in simulated in situ contributes to reducing k, but the impact of CF in simulated in situ soil on k tends to be insignificant for backfill with BC higher than 6%. A new characteristic parameter based on the concept of void ratio of bentonite (eb), named apparent void ratio of clay size fraction (eC), is developed for predicting soil-bentonite backfills created by in situ soils and bentonites with various contents.
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Deng, Hongwei, Yao Liu, Weiyou Zhang, Songtao Yu, and Guanglin Tian. "Study on the Strength Evolution Characteristics of Cemented Tailings Backfill from the Perspective of Porosity." Minerals 11, no. 1 (January 15, 2021): 82. http://dx.doi.org/10.3390/min11010082.
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At present, the filling mining method is widely used. To study strength evolution laws of cemented tailings backfill (CTB) under different curing ages, in the experiment, mine tailings were used as aggregates, ordinary Portland cement (PC32.5) was used as cementing materials, and different additives (lime and fly ash) were added to make filling samples with the solids mass concentration at 74% and the cement-sand ratios 1:4, 1:6 and 1:8. Based on the nuclear magnetic resonance (NMR) technology, the porosity test of filling samples with curing ages of 3 d, 7 d and 28 d was carried out, and the uniaxial compressive strength test was carried out on the servo universal material testing machine. The relationship between the uniaxial compressive strength and porosity of backfills and the curing age in the three groups was studied, and change laws of the porosity variation and strength growth rate of backfills were analyzed. Based on the variation in porosity, the strength evolution model of the CTB under different curing ages was established, and the model was fitted and verified with test data. Results show that the uniaxial compressive strength, porosity, porosity variation, and strength growth rate of the three groups of backfills gradually increase with the increase of the curing age, the porosity of backfill basically increases with the decrease of the cement–sand ratio, and the porosity of backfill decreases with the increase of the curing age. Porosity variations and relative strength values of the three groups of backfills under different cement-sand ratios obey an exponential function, and the two have a good correlation, indicating that the established filling strength evolution model can well reflect strength evolution laws of the CTB with the change of curing age.
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Yang, Yu-Ling, Krishna R. Reddy, Wen-Jie Zhang, Ri-Dong Fan, and Yan-Jun Du. "SHMP-Amended Ca-Bentonite/Sand Backfill Barrier for Containment of Lead Contamination in Groundwater." International Journal of Environmental Research and Public Health 17, no. 1 (January 6, 2020): 370. http://dx.doi.org/10.3390/ijerph17010370.
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This study investigated the feasibility of using sodium hexametaphosphate (SHMP)- amended calcium (Ca) bentonite in backfills for slurry trench cutoff walls for the containment of lead (Pb) contamination in groundwater. Backfills composed of 80 wt% sand and 20 wt% either Ca-bentonite or SHMP-amended Ca-bentonite were tested for hydraulic conductivity and sorption properties by conducting laboratory flexible-wall hydraulic conductivity tests and batch isothermal sorption experiments, respectively. The results showed that the SHMP amendment causes a one order of magnitude decrease in hydraulic conductivity of the backfill using tap water (1.9 to 3.0 × 10−10 m/s). Testing using 1000 mg/L Pb solution resulted insignificant variation in hydraulic conductivity of the amended backfill. Moreover, SHMP-amendment induced favorable conditions for increased sorption capacity of the backfill, with 1.5 times higher retardation factor relative to the unamended backfill. The Pb transport modeling through an hypothetical 1-m-thick slurry wall composed of amended backfill revealed 12 to 24 times of longer breakthrough time for Pb migration as compared to results obtained for the same thickness slurry wall with unamended backfill, which is attributed to decrease in seepage velocity combined with increase in retardation factor of the backfill with SHMP amendment. Overall, SHMP is shown to be a promising Ca-bentontie modifier for use in backfill for slurry trench cutoff wall for effective containment of Pb-contaminated groundwater.
7
Sobhi, Mohamed Amine, Li Li, and Michel Aubertin. "Numerical investigation of earth pressure coefficient along central line of backfilled stopes." Canadian Geotechnical Journal 54, no. 1 (January 2017): 138–45. http://dx.doi.org/10.1139/cgj-2016-0165.
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The earth pressure coefficient K, defined as the horizontal to vertical normal (effective) stresses ratio (σh/σv), is a key parameter in analytical solutions for estimating the stresses in backfilled stopes. In the case of vertical stopes, the value of K has sometimes been defined using the at-rest earth pressure coefficient K0, while others have applied Rankine’s active earth pressure coefficient Ka. To help clarify this confusing situation, which can lead to significantly different results, the origin and nature of the at-rest and Rankine’s active coefficients are first briefly recalled. The stress state in backfilled stopes is then investigated using numerical simulations. The results indicate that the value of K can be close to Ka for cohesionless backfills along the vertical central line (CL) of vertical stopes, due to sequential placement and partial yielding of the backfill. For inclined stopes, simulations show that the ratio between the minor and major principal stresses (σ3/σ1) along the CL in the backfill, which differs from σh/σv, can also be close to Ka. A simple expression is shown to represent the horizontal to vertical stresses ratio σh/σv (= K) along the CL of such inclined stopes well. A discussion follows on the effects of backfill properties and simulation approach.
8
Siddiqua, Sumi, James Blatz, and Greg Siemens. "Evaluation of the impact of pore fluid chemistry on the hydromechanical behaviour of clay-based sealing materials." Canadian Geotechnical Journal 48, no. 2 (February 2011): 199–213. http://dx.doi.org/10.1139/t10-064.
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The results of an experimental program undertaken to evaluate the impact of pore fluid salinity on the hydromechanical performance of light and dense backfill materials are presented. Light and dense backfills are engineered barrier materials that are being examined in the Canadian concept for storage of spent fuel in a deep geological repository. The current research investigates the impact of pore fluid chemistry on the swelling, compressibility, stiffness, and hydraulic conductivity parameters of light and dense backfills that are required as material parameters for analysis and design. In these tests, pore fluid chemistry was selected to represent groundwater within potential host units including granite and limestone rock. Results show that the performance of light backfill is significantly affected by changes in pore fluid chemistry. The swell potential of light backfill decreases with increasing salinity of the solution. The hydraulic conductivity decreases with increasing effective montmorillonite dry density and specimens saturated with saline solution have higher hydraulic conductivity than those saturated with distilled water. Conversely, the behaviour of dense backfill is governed mainly by the crushed granite component and therefore changes to the pore fluid chemistry have relatively little effect. Results of dense backfill tests confirm the material performance as a sealing material.
9
Zhao, Jack Q., Balvant B. Rajani, and Lyne Daigle. "Thermal performance of trench backfills used for frost protection of water service lines." Canadian Geotechnical Journal 38, no. 1 (February 1, 2001): 161–74. http://dx.doi.org/10.1139/t00-085.
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This paper describes the thermal performance of different configurations of trenches using various trench geometries and backfill and insulation materials. A limited number of laboratory tests were conducted to confirm the thermal properties of the backfills reported in the literature. The frost protection of water service is measured in terms of the number of days it takes for the frost front to reach the depth of water service lines under sustained subzero surface temperatures. The study specifically included typical granular materials used within the City of Ottawa (formerly the Region of Ottawa-Carleton), but the findings can be equally applied to other urban areas in Canada where the surficial terrain is rocky. The thermal analyses of the trenches were conducted using the finite element method that appropriately represents phase changes when the temperature falls below the freezing point of water. The analyses indicate that the use of sandwich insulation is ineffective, and that latent heat of backfill and native soils has a great impact on the frost protection of water service lines. A list of possible trench depths with different backfills and their thermal performance is provided.Key words: backfill, thermal performance, frost penetration, water service, finite element analysis.
10
Siddiqua, Sumi, James Blatz, and Greg Siemens. "Experimental study on the performance of light and dense backfills." Canadian Geotechnical Journal 48, no. 2 (February 2011): 214–25. http://dx.doi.org/10.1139/t10-057.
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Numerical modeling is a cost-effective and important approach to examine the long-term performance of engineered materials. However, to identify the appropriate constitutive model for a particular material it is necessary to measure physical properties in a laboratory. Laboratory experiments provide the data from which the input parameters for the selected model can be interpreted. This paper studies the mechanical behaviour of two clay-based sealing materials — light backfill and dense backfill — recommended for use in disposal of nuclear waste in a proposed Canadian repository. Test specimens of light and dense backfills were saturated in a triaxial cell and then subjected to specified isotropic and shearing stress paths to measure consolidation and shear characteristics. The triaxial results are interpreted in a critical state context. The light backfill results suggest that it has similar stress–strain behaviour to a bentonite–sand buffer, which has a similar composition, but different preparation procedures and design requirements. Results from testing of dense backfill indicate that it is a much stiffer and stronger material than light backfill. Dense backfill is expected to provide mechanical support to the used-fuel container and other sealing components of the Canadian repository, and the mechanical behaviour of dense backfill satisfies these requirements.
11
Shen, Sheng-Qiang, and Ming-Li Wei. "Hydraulic Conductivity of Polymer-Amended Sand-Bentonite Backfills Permeated with Lead Nitrate Solutions." Advances in Civil Engineering 2018 (December 13, 2018): 1–12. http://dx.doi.org/10.1155/2018/9435194.
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Hydraulic conductivity of sand-bentonite (SB) backfills amended with polyanionic cellulose (PAC) to lead nitrate (Pb(NO3)2) solutions was evaluated experimentally in this study. PAC-amended sand-bentonite (PSB) backfills were synthesized by mixing sand-bentonite mixture with 0.3 to 1.2% dry PAC (by total dry mixture mass) and mixed with a certain weight of conventional bentonite (CB) slurry. The rheology properties including the filtrate loss, viscosity, density, and pH testes of slurry with various bentonite dosages were measured to determine the reasonable CB dosage of slurry. The slump tests on PSB backfills with various mass slurries were conducted to determine the corresponding water content of backfills with slump 125 ± 5 mm. Under the applied pressure 100 kPa, the hydraulic conductivity to Pb(NO3)2 solutions (kc) of PSB backfills with various PAC contents was evaluated based on the modified filter press (MFP) tests, to ascertain the optimum PAC content of PSB backfills when permeated with Pb(NO3)2 solutions. Index properties, including the specific gravity (Gs) and liquid limit (wL) of PSB backfills, were measured after MFP tests. The MFP tests for PSB backfills were then conducted under various applied pressures to obtain the relationship between void ratio (e) and hydraulic conductivity of backfills. Finally, the flexible-wall permeability test (FWP test) under osmotic pressure 100 kPa was conducted to verify the effectiveness of the MFP test. The results indicate that slurry with 8% bentonite dosage is the reasonable choice in slurry wall construction. PSB has lower GS and higher wL compared to SB; increasing Pb concentration leads to GS of PSB increased and wL of PSB decreased. PSB with 0.6% PAC content is supposed as the optimum proportion of backfills when permeated with concentrated Pb(NO3)2 solution. PAC adsorbs large amount of bound water, which leads to higher water content (w) and e of PSB backfills, while lead ions (Pb) cause the diffuse double layer (DDL) of bentonite compressed and e of PSB backfills reduced. The kc of PSB-0.6 remains lower than 10−9 m/s and increases less than 10 times though the Pb concentration was up to 500 mM, demonstrating that the hydraulic performance of backfills can be improved effectively in Pb(NO3)2 solution by the additive PAC. The comparison results between k from MFP tests and FWP tests show that the MFP test is an effective and easy evaluation of hydraulic conductivity of backfills.
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Zhang, Xinguo, Jinhai Zhao, Lin Xin, Kun Wang, and Haiyang Pan. "Monitoring and Assessment of Cemented Paste Backfill Containing Coal Gangue and Fly Ash in an Underground Mine." Advances in Materials Science and Engineering 2021 (February 23, 2021): 1–15. http://dx.doi.org/10.1155/2021/5946148.
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Cemented coal gangue paste backfill (CCGPB) containing coal gangue and fly ash is a backfilling technique newly developed in coal mines in China that allows environmentally hazardous products, such as gangue and fly ash, to be reused in underground stopes. CCGPB materials provide efficient ground support for the caving of strata and reduce surface subsidence. In this paper, field monitoring of CCGPB properties was conducted in an underground coal mine, which mainly included the measurement of the longwall face temperature, humidity, CCGPB internal hydration temperature, stress conditions inside the backfills, and displacement. First, the components of the backfills, paste technique, slurry generation procedures, coalfield geology, and mining conditions were introduced. Then, a monitoring system was designed in the field. An online monitoring system was installed. The results of the field monitoring showed that the curing temperature significantly varied, i.e., from 26°C near the main gate to 37°C near the tailgate. The curing humidity had the same trends, increasing from 60% relative humidity (RH) near the main gate to 81% RH near the tailgate. The internal hydration process of the paste was divided into four stages, i.e., the rapid hydration stage, slower hydration stage, rapid decline hydration stage, and relatively stable stage. The highest hydration temperature was 50°C, which was measured on the second day after the backfill process. The temperature approached stability at 41°C. The evolution of the roof stress applied on the CCGPB was divided into four stages: the development stage, regulation stage, rapid growth stage, and relatively stable stage. The maximum roof loading was 12 MPa in the middle of the longwall face. The deformation of the backfill experienced four stages, i.e., the rapid deformation stage, slow deformation stage, relatively stable stage, and long-term stable stage. The maximum deformation was 104.3 mm, appearing in the middle of the face. In addition, the compression ratio of the backfill was approximately 4%. The results of this study showed that the working conditions of backfills in the field were different from those in the laboratory. This paper provides guidance for the design of the CCGPB technique and the predictions of surface subsidence induced by the production process of underground mining.
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Nnadi, G. N., and R. J. Mitchell. "Behaviour of cemented sandfills under repeated loadings." Canadian Geotechnical Journal 28, no. 5 (October 1, 1991): 746–52. http://dx.doi.org/10.1139/t91-089.
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Two series of tests were conducted to study the behaviour of cemented tailings backfills materials under repeated loading conditions. Drained triaxial and drained plane strain boundary conditions were used in this experimental work. Two distinct patterns of behaviour were found to exist, and these were separated by a critical stress level close to the static strength of the cemented materials. These materials can sustain instantaneous repeated loading deviatoric stresses of 1.2 times the static strength for up to a dozen stress applications but generally reach a failure state with multiple applications of repeated loads in excess of 0.9 times the static failure loads. The behaviour of the cemented backfill was found to progressively become more plastic with increased number of stress applications. The resilient modulus was found to initially decrease before increasing with increased number of stress applications. Key words: repeated loadings, cemented backfills, resilient modulus.
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Stuyts, Bruno, David Cathie, and Toby Powell. "Model uncertainty in uplift resistance calculations for sandy backfills." Canadian Geotechnical Journal 53, no. 11 (November 2016): 1831–40. http://dx.doi.org/10.1139/cgj-2016-0056.
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Trenching and backfilling is one of the most practical and cost-effective methods for protection and stabilization of offshore pipelines. Defining the geotechnical properties of backfill material resulting from mechanical backfilling or jet trenching is an area of substantial uncertainty and the resistance against pipeline uplift provided by these backfills needs to be characterized accounting for these uncertainties. This paper compares the properties of sandy backfill material and the available calculation models for uplift resistance against a database of more than 300 controlled pipeline uplift tests. The model uncertainty for uplift resistance calculations is derived from a back-analysis of the uplift tests. The uncertainties on uplift resistance and mobilization distance are correlated and characterized using a joint probability distribution. The selected distributions are applied to an example uplift resistance problem. When compared against this probabilistic formulation, the factors applied to uplift resistance in pipeline analysis can be refined to lead to a more cost-effective solution.
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Li, Changhong, Qiantian Ma, Guoliang Chen, and Hai Shao. "Study on Creep Characteristics of Cemented Waste Rock Backfills." Open Civil Engineering Journal 9, no. 1 (October 29, 2015): 957–61. http://dx.doi.org/10.2174/1874149501509010957.
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Slip instability and tensor instability are two kinds of failure modes of cemented waste rock backfills. In order to simulate the creep characteristics of cemented waste rock backfills, PFC was carried out. The results show that: rocks inside the models will have displacement under load. The expansion is caused by large lateral displacement of the rocks. A non-stationary creep model of cemented waste rock backfills was established based on the results of simulation. This model can be used to describe the whole creep characteristics of cemented waste rock backfills better.
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Conard, B. E., R. A. Lohnes, F. W. Klaiber, and T. J. Wipf. "Boundary Effects on Response of Polyethylene Pipe Under Simulated Live Load." Transportation Research Record: Journal of the Transportation Research Board 1624, no. 1 (January 1998): 196–205. http://dx.doi.org/10.3141/1624-23.
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The objective of this paper is to evaluate the deflection response of polyethylene pipes when loaded near their ends. Tests were conducted on pipes loaded at the center and near their ends to simulate loading of a vehicle at the center of a roadway and on the shoulder. The tests were performed on 900-mm (36-in.) and 1200-mm (48-in.) diameter polyethylene pipes with 610-mm (2 ft) cover and a variety of backfills. Loads were applied through a 93 025-mm2 (1-ft2) plate that provides very severe loading conditions. At high contact stresses, the load test plate punched into the soil cover so that the crown of the pipe was subjected to stresses in excess of those that would have occurred if the soil surface were paved or stabilized or a less severe loading condition better representing a truck tire had been used. At contact stresses equivalent to moderate highway tire pressures, pipe deflections are slightly higher near the ends of the pipes than at the center. Except for low-density till, the percent deflections are not excessive and the pipe-soil systems have adequate stiffness. For contact stresses near the upper limit of truck tire pressures and when loaded near the ends, the pipes with sand and till backfills fail by local wall bending. For flowable-fill backfill, the ultimate capacity of the pipes is nearly twice that for the soil backfills.
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Khatami, Hamidreza, An Deng, and Mark Jaksa. "Passive arching in rubberized sand backfills." Canadian Geotechnical Journal 57, no. 4 (April 2020): 549–67. http://dx.doi.org/10.1139/cgj-2018-0672.
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The deformation and stress profiles of passive arching in a coarse sand and two rubberized sand backfills were investigated using a trapdoor apparatus. The trapdoor apparatus was instrumented with high-speed imaging equipment and a series of pressure sensors. The images of the deformation process in the backfills were analysed using the digital image correlation technique. The effect of a local surcharge on the deformation and stress profiles was also examined. It was observed that the rubber inclusions helped reduce the deformation of the backfills. Passive arching moduli and stress variations between the backfills examined are compared.
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Watson, Gary W., Gary Kupkowski, and Kerstin G. von der Heide-Spravka. "Influence of Backfill Soil Amendments on Establishment of Container-grown Shrubs." HortTechnology 3, no. 2 (April 1993): 188–89. http://dx.doi.org/10.21273/horttech.3.2.188.
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Cotoneaster apiculata and Juniperus chinensis `Pfitzeriana Compacta' were planted on a site with compacted clay soil. Plants were placed in holes the same size as the root ball (no backfill), or in holes three times the diameter of the root ball with sloping sides. The three backfill soils used were composed of site-soil (50%) amended with sand (40%) and leaf compost (10%), site-soil (75%) amended with mushroom compost (25%), and unamended site-soil. After 14 months, root density was not different in any of the treatments, and root densities were not different in the compacted clay soil outside of the planting hole, indicating that root growth was not inhibited at the interface between the backfill soil and the compacted site clay soil. Shoot growth of C. apiculata grown in backfill amended with sand and leaf compost was larger than shoot growth of plants grown in other backfills.
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Wang, Zhi-zhihui, Ai-xiang Wu, and Hong-jiang Wang. "A Strength Design Method of Cemented Backfill with a High Aspect Ratio." Advances in Civil Engineering 2020 (February 19, 2020): 1–11. http://dx.doi.org/10.1155/2020/7159208.
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To calculate the required strength of a cemented backfill with high aspect ratio, the confirmation of lateral pressure is fundamental and needs to be determined first. As for the backfill with a high aspect ratio of height to length, the shape of the slip surface is not straight when in the active state due to the limited space, which is different from the general backfill. For this reason, a formulation of the slip surface with a curved shape and a lateral pressure calculation method based on this curved slip surface were proposed. The proposed equation of the slip surface is affected by the geometry parameters of the backfill, internal friction angle of the backfill, and the friction angle of the backfill-rock interface. Then, by the combination of the minor principal stress trajectory method and the horizontal slice method, an ordinary differential equation of stresses was established and then solved numerically. Finally, the method based on Mitchell’s three-dimensional limit equilibrium model was used to calculate the required strength of the cemented backfill. The calculated results were compared with previous studies and validated with numerical models. The results showed good consistency for the backfills with high aspect ratios.
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Xu, Li-Wei, and Yu-Jian Lin. "Experimental Study on the Active Earth Pressure of Narrow Cohesionless Backfills against Rigid Retaining Wall under the Translation Mode." Advances in Civil Engineering 2020 (November 12, 2020): 1–9. http://dx.doi.org/10.1155/2020/8889749.
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In engineering, the new retaining walls are often constructed near the existing structure owing to the space limitation. The backfill behind the retaining wall is narrow, which causes an overestimation in the active earth pressure by using Coulomb’s earth pressure theory. In previous studies, experimental observations for the failure modes of narrow backfills are still rare. To confirm the failure mode of the narrow backfill, the experimental method and the geotechnical particle image velocimetry method are employed to observe the active failure process of the cohesionless narrow backfill with various widths under the translation mode. The experimental results revealed that the decrease in the length of the backfill width led to the increase in the inclined angle of the sliding surface. When the backfill width was sufficiently small, the sliding surface developed from the wall toe to another wall face, and then another sliding surface occurred as a reflection. In addition, the active earth pressure of the narrow backfill is significantly smaller than that calculated using Coulomb’s method. The active failure calculation models are established based on the experimental results. The active earth pressure of the narrow cohesionless backfill under the translation mode is derived by using the limit equilibrium methods. The proposed method was validated by comparing with the previous method and the experimental data.
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Boone, Lorne C., David C. Sego, and S. Peter Dozzi. "Field performance of thin wall foundations." Canadian Journal of Civil Engineering 23, no. 2 (April 1, 1996): 315–22. http://dx.doi.org/10.1139/l96-037.
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The feasibility of building residential basement foundation walls of unreinforced concrete thinner than the conventional 200 mm thick wall is investigated. An optimum thickness of 150 mm was determined for an unreinforced 2400 mm high foundation wall based on the use of equivalent fluid pressures with sand and gravel backfill material. For walls backfilled with other than clean sand and gravel, or with a submerged condition, it was found that the theoretical maximum backfill heights for both 150 and 200 mm walls are substantially less than those presently specified by the Alberta Building Code. The primary purpose of the study described in this paper was to test under actual field conditions the performance of a 150 mm unreinforced concrete wall under varying lateral loads imposed by different soil types, and to compare measured and calculated lateral loads with the equivalent fluid pressure specified as a criterion in the Alberta Building Code. The lateral earth pressures resulting from the backfilling of 150 mm thick concrete foundation walls were investigated for two backfills, namely sandy lean clay (clay till) and sand. The findings indicate that for longer term placement conditions, the resulting pressure distribution supports the hypothesis of a triangular soil pressure distribution and can be described using traditional earth pressure theory. Two design methods based on the concept of equivalent fluid density were evaluated and compared with the field measurements. Key words: thin wall foundations, earth pressure, field measurement.
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Mitchell, Robert J., and David M. Stone. "Stability of reinforced cemented backfills." Canadian Geotechnical Journal 24, no. 2 (May 1, 1987): 189–97. http://dx.doi.org/10.1139/t87-024.
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Mining with backfill has been the subject of several international meetings in recent years and a considerable research effort is being applied to improve both mining economics and ore recovery by using backfill for ground support. Classified mill tailings sands are the most commonly used backfill material but these fine sands must be stabilized before full ore pillar recovery can be achieved. Normal portland cement is generally used for stabilization but the high cost of cement prohibits high cement usage. This paper considers the use of reinforcements in cemented fill to reduce the cement usage. It is concluded that strong cemented layers at typical spacings of about 3 m in a low cement content bulk fill can reinforce the fill and reduce the overall cement usage. Fibre reinforcements introduced into strong layers or into bulk fills are also known to be effective in reducing cement usage. Some development work is needed to produce the ideal type of anchored fibre in order to realize economic gains from fibre-reinforced fills. Key words: mining, backfilling, ground support, soil–cement, fibre reinforcement.
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Wilson, Patrick, and Ahmed Elgamal. "Full-scale shake table investigation of bridge abutment lateral earth pressure." Bulletin of the New Zealand Society for Earthquake Engineering 42, no. 1 (March 31, 2009): 39–46. http://dx.doi.org/10.5459/bnzsee.42.1.39-46.
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During strong seismic excitation, passive earth pressure at the abutments may provide resistance to longitudinal displacement of the bridge deck. The dynamic pressure component may also contribute to undesirable abutment movement or damage. Current uncertainty in the passive force-displacement relationship and in the dynamic response of abutment backfills continues to motivate large-scale experimentation. In this regard, a test series is conducted to measure static and dynamic lateral earth pressure on a 1.7 meter high bridge abutment wall. Built in a large soil container, the wall is displaced horizontally into the dense sand backfill, in order to record the passive force-displacement relationship. The wall-backfill system is also subjected to shake table excitation. In the conducted tests, lateral earth pressure on the wall remained close to the static value during the low to moderate shaking events (up to about 0.5g). At higher levels of input acceleration, a substantial portion of the backfill inertial force started to clearly act on the wall.
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Bergado, D. T., R. Shivashankar, C. L. Sampaco, M. C. Alfaro, and L. R. Anderson. "Behavior of a welded wire wall with poor quality, cohesive–friction backfills on soft Bangkok clay: a case study." Canadian Geotechnical Journal 28, no. 6 (December 1, 1991): 860–80. http://dx.doi.org/10.1139/t91-103.
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A full-scale and extensively instrumented experimental mechanically stabilized earth (MSE) wall with steel grid reinforcements was built on soft clay foundation. Three different locally available poor to marginal quality backfills were used in each of three sections along its length. The soft Bangkok clay in the subsoil is about 6 m thick, overlain by a surficial 2 m thick weathered clay crust and underlain by a layer of stiff clay. It was observed that the amount of subsoil movement greatly influenced the variation in the vertical pressure beneath the wall, as well as the tension in the reinforcement. Pullout resistances in the field were also found to be very much affected by the arching effects due to the presence of inextensible reinforcement in combination with the subsoil movements. The wall showed no signs of instability both during construction and in the postconstruction phases, despite the large settlements and lateral movements. Its overall performance has been satisfactory. It was concluded that the steel grid reinforcement can be effectively used to reinforce poor to marginal quality backfill in walls and embankments on soft clay foundations. Key words: mechanically stabilized earth, inextensible reinforcements, soft clay foundation, poor quality backfills, base pressures, settlements, lateral movements, lateral pressures, compaction, arching.
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Jiang, Xi Yan, and Su Wei Di. "Active Earth Pressure on Retaining Walls with Layered Cohesive Backfills and Considering Cracking." Advanced Materials Research 243-249 (May 2011): 2786–89. http://dx.doi.org/10.4028/www.scientific.net/amr.243-249.2786.
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Based on the method of level-layer analysis, with the sliding harmonious condition of layered backfills considered , the theoretical answers to the unit earth pressures , the resultant earth pressures and the points of application of the resultant earth pressures on retaining walls with layered cohesive backfills are set up . The comparisons are made with Rankine’s formula.
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Jiang, Xi Yan, and Zhan Xue Zhou. "Research and Analysis of Active Earth Pressure on Retaining Walls with Layered Non-Cohesive Backfills." Applied Mechanics and Materials 275-277 (January 2013): 269–72. http://dx.doi.org/10.4028/www.scientific.net/amm.275-277.269.
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Based on the method of level-layer analysis , with the sliding harmonious condition of layered backfills considered , the theoretical answers to the unit earth pressures , the resultant earth pressures and the points of application of the resultant earth pressures on retaining walls with layered non-cohesive backfills are set up . The comparisons are made with Coulomb’s formula.
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Take, W. A., and A. J. Valsangkar. "Earth pressures on unyielding retaining walls of narrow backfill width." Canadian Geotechnical Journal 38, no. 6 (December 1, 2001): 1220–30. http://dx.doi.org/10.1139/t01-063.
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Arching theory predicts a significant reduction in earth pressures behind retaining walls of narrow backfill width. An extensive series of centrifuge tests has been performed to evaluate the use of flexible subminiature pressure cells in the centrifuge environment and their subsequent use to measure lateral earth pressures behind retaining walls of narrow backfill width. Although the flexible earth pressure cells exhibit hysteresis and nonlinear calibration behaviour, the extensive calibration studies indicate that stiff diaphragm type earth pressure cells may be used with replicate models to measure earth pressures. Measurements of lateral pressures acting on the unyielding model retaining walls show good agreement with Janssen's arching theory. Tests on backfills bounded by vertical planes of dissimilar frictional characteristics indicate arching theory with an average interface friction angle provides a reasonable estimate of lateral earth pressures.Key words: fascia retaining walls, silos, earth pressures, pressure cells, centrifuge modelling.
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Silvestri, Vincenzo. "Limitations of the theorem of corresponding states in active pressure problems." Canadian Geotechnical Journal 43, no. 7 (July 1, 2006): 704–13. http://dx.doi.org/10.1139/t06-035.
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This paper analyzes the application of the theorem of corresponding states or the correspondence rule, as found in a number of advanced soil mechanics textbooks, and shows that it results in approximate solutions to limit-state problems. The limitations of the rule are made apparent by applying it to the determination of active pressures exerted on vertical retaining walls by cohesivefrictional backfills with inclined ground surfaces. A correct derivation of the correspondence rule is obtained for this case. An example is given that illustrates the inadequacy of this rule when boundary conditions are not properly accounted for in the analysis.Key words: theorem of corresponding states, active pressure, vertical retaining wall, inclined ground surface, cohesivefrictional backfill.
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Brandon, T. L., J. K. Mitchell, and J. T. Cameron. "Thermal Instability in Buried Cable Backfills." Journal of Geotechnical Engineering 115, no. 1 (January 1989): 38–55. http://dx.doi.org/10.1061/(asce)0733-9410(1989)115:1(38).
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Rollins, Kyle, Amy Fredrickson, and Eric Scott. "Effect of Interface Friction on Passive Force on Bridge Abutments." E3S Web of Conferences 92 (2019): 13013. http://dx.doi.org/10.1051/e3sconf/20199213013.
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A correct understanding of passive force-deflection response is important for lateral load evaluations of bridges during extreme events such as earthquakes and from thermal expansion and contraction of the superstructure. In these cases, the ultimate passive force is highly sensitive to the interface friction between the abutment wall and the adjacent geomaterials. These geomaterials may simply consist of compacted sand or gravel; however, for geosynthetic reinforced soil (GRS) backfill a geosynthetic fabric may be placed between the abutment wall and soil which can reduce the interface friction. In still other cases, a zone of compressible material such as geofoam may be used as a barrier between the soil and abutment to reduce lateral earth pressures. To evaluate the effect of the interface friction on passive force-deflection curves, large-scale testing was performed with a test abutment that was 3.35 m wide and 1.68 m high. Backfill materials consisted of sand, gravel, GRS backfill, and a geofoam inclusion between a sand backfill and the abutment. As a result of lower interface friction, the GRS backfills only developed 80% of the force developed by the unreinforced gravel. The geofoam inclusion decreased the passive force by about 70% as a result of reduced interface friction.
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Eshun, S. N., Solomon Senyo Robert Gidigasu, and S. K. Y. Gawu. "The Effect of Clay Pozzolana-Cement-Composite on the Strength Development of a Hydraulic Backfill." Ghana Mining Journal 18, no. 1 (June 28, 2018): 32–38. http://dx.doi.org/10.4314/gm.v18i1.4.
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The study sought to investigate the potential application of clay pozzolana as a supplement for cement in hydraulic backfill, using classified tailings from AngloGold Ashanti, Obuasi Mine. The percentage of the Portland cement that could be substituted with the clay pozzolana to produce backfill with best strength was determined. 10%, 25%, 30%, 35% and 40% of the ordinary Portland cement were replaced with clay pozzolana and then mixed with tailings and water. The slurry produced was cast into cylindrical specimen of 50mm diameter by 120mm high and tested for compressive strength after curing for 7, 14, 21, 28 and 56 days. The results indicate that, clay pozzolana-cement composite has potential for application in hydraulic back fill production without increased risk to safety and dilution. It was noted that hydraulic backfill with 10%, 25%, 30% and 35% of the ordinary portland cement replaced with clay pozzolana had strengths greater than those obtained for ordinary portland cement alone. Ten percent (10%) pozzolana content gave the maximum strength followed by 25% pozzolana. It is recommended that for safety and economic considerations, the cement content should be replaced by 25% pozzolana in the production of backfills. Keywords: Hydraulic Backfill, Portland Cement, Clay Pozzolana, Unconfined Compressive Strength
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Filz, George M., and James M. Duncan. "Earth Pressures Due to Compaction: Comparison of Theory with Laboratory and Field Behavior." Transportation Research Record: Journal of the Transportation Research Board 1526, no. 1 (January 1996): 28–37. http://dx.doi.org/10.1177/0361198196152600105.
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Compaction of backfill adjacent to stiff and unyielding structures induces earth pressures in the compacted fill that exceed normal at-rest earth pressures. A numerical method that can be used to calculate compaction-induced lateral earth pressures has been proposed by Duncan and Seed. The purpose of the study described in this paper is to evaluate the theory by comparing calculated and measured compaction-induced lateral earth pressures. The data for the comparisons is from values measured in backfills behind three stiff, unyielding walls: the instrumented retaining wall in the Transport and Road Research Laboratory in Crawthorne, England; the instrumented retaining wall in the Virginia Tech Geotechnical Laboratory in Blacksburg, Virginia; and the lock walls at Eisenhower and Snell Locks in New York state. The lock walls were found to be cracked, apparently by high earth pressures induced by compaction, and an extensive rehabilitation program was required. The measurements from all three walls confirm the existence of compaction-induced lateral earth pressures. For clean sand backfill, pressures calculated using the theory of Duncan and Seed are shown to be in reasonable agreement with measured values. Laboratory test data indicate that for moisture-sensitive silty sand backfill the applicability of the Duncan and Seed theory, which does not include considerations of pore water pressure development during backfill placement and compaction, depends on the degree of saturation of the backfill.
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Sepehr, K., and L. E. Goodrich. "Frost protection of buried PVC water mains in western Canada." Canadian Geotechnical Journal 31, no. 4 (August 1, 1994): 491–501. http://dx.doi.org/10.1139/t94-058.
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Although desirable for many reasons, controlled low-strength material – controlled density fill (nonshrinkable fill) has the potential to promote rapid frost penetration within the trench when used as a backfill material in waterworks construction and repair projects. This paper describes results of a two-dimensional finite-element heat-transfer model study carried out to investigate the effectiveness of various insulation systems for frost and frost-heave protection of buried waterlines. Combinations of nonshrinkable fill with horizontal insulation boards, cylindrical pipe insulation, and inverted U-shaped insulations were investigated. It was shown that, while moderate thicknesses of insulation could be found to protect the pipe from freezing, thermal-bridging effects make the location of the maximum frost penetration depth sensitive to details of the insulation geometry. The use of different combinations of insulating backfills was also investigated, and it was shown that a backfill layer of moderate insulating value placed high in the trench may be most advantageous. Key words : frost, frost protection, insulation, waterlines, nonshrinkable fill, numerical analysis.
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Haldar, Asim, VSN Prasad Yenumula, and T. R. Chari. "Full-scale field tests on directly embedded steel pole foundations." Canadian Geotechnical Journal 37, no. 2 (April 1, 2000): 414–37. http://dx.doi.org/10.1139/t99-119.
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The results of eight full-scale tests on directly embedded steel pole foundations are presented. Fully instrumented poles were tested to measure the various design parameters. Different types of backfills such as sand, in situ gravelly sand, crushed stone, and flowable material were used. Various parameters were measured, including applied moment, ground line deflection-rotation, rotation of the pole below the ground level, soil pressures, and bending moments in the poles. The behaviour of these foundations was explained through ultimate capacity and moment-rotation characteristics. Based on these test results, it was found that the capacity of the directly embedded pole foundation depends primarily on the compaction levels of backfill and the embedment length of the pole. Flowable backfill material, which does not require any compaction, was found to be most effective and promising. Even when the backfill was loose, the lateral capacity significantly increased by the addition of a baseplate or by installing the pole with an additional embedment depth. Various theories developed for laterally loaded rigid piles were used to predict the moment-rotation behaviour and the ultimate capacity of the directly embedded pole foundation with different types of backfill material. Results from the analytical investigations were compared with those obtained from the full-scale load tests. Comparisons show that the ultimate capacities predicted by the models ranged from 0.30 to 2.20 times the measured capacities.Key words: backfill, compaction, full-scale tests, laterally loaded rigid piles, transmission steel poles, ultimate moment.
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Bohnhoff, Gretchen L., and Charles D. Shackelford. "Hydraulic Conductivity of Polymerized Bentonite-Amended Backfills." Journal of Geotechnical and Geoenvironmental Engineering 140, no. 3 (March 2014): 04013028. http://dx.doi.org/10.1061/(asce)gt.1943-5606.0001034.
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Bohnhoff, Gretchen L., and Charles D. Shackelford. "Consolidation Behavior of Polymerized Bentonite-Amended Backfills." Journal of Geotechnical and Geoenvironmental Engineering 140, no. 5 (May 2014): 04013055. http://dx.doi.org/10.1061/(asce)gt.1943-5606.0001079.
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Yeo, Sang-Sik, Charles D. Shackelford, and Jeffrey C. Evans. "Membrane Behavior of Model Soil–Bentonite Backfills." Journal of Geotechnical and Geoenvironmental Engineering 131, no. 4 (April 2005): 418–29. http://dx.doi.org/10.1061/(asce)1090-0241(2005)131:4(418).
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Wang, Sheng, Feng Wang, Dawei Yin, Tianqi Jiang, and Zhen Zhang. "Experimental Study on Mechanical Properties of Paste Backfill with Flue-Gas Desulphurisation Gypsum under Combined Action of Dry–Wet Cycles and Chloride Erosion." Minerals 11, no. 8 (August 15, 2021): 882. http://dx.doi.org/10.3390/min11080882.
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Flue-gas desulphurisation gypsum—a solid waste from power plants—can be used to prepare paste backfill for reducing costs. Most paste backfills are exposed to dry–wet cycles and chloride salt-rich water in mines. Therefore, the mechanical properties and damage mechanisms of paste backfill with desulphurised gypsum under the coupling action of erosion due to chloride with different concentrations and dry–wet cycles were investigated using methods such as visual observation, mass measurement, uniaxial compression, acoustic emission, Fourier-transform infrared spectroscopy, X-ray diffraction analysis, and field-emission scanning electron microscopy. With an increasing number of dry–wet cycles, the mass, elastic modulus, and strength of the paste backfill exhibited the trend of increasing first and then decreasing. The failure mechanism changed from mainly vertical fractures to the alternating development of vertical and horizontal fractures. The surface denudation effect of the specimens in a solution with a higher concentration was more severe under the same number of dry–wet cycles. In this study, the laws governing the mass change, strength change, degree of surface denudation, and failure pattern of desulphurised gypsum-filled specimens under different concentrations of chloride salt and different numbers of dry–wet cycles were derived.
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Arciniega, Jose Luis, W. Shane Walker, Soheil Nazarian, and Kenneth L. Fishman. "A Process for Optimizing Gradation of Marginal Backfill of Mechanically Stabilized Earth Walls to Achieve Acceptable Resistivity." Transportation Research Record: Journal of the Transportation Research Board 2672, no. 52 (May 14, 2018): 251–57. http://dx.doi.org/10.1177/0361198118770166.
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The service life of mechanically stabilized earth walls depends on the corrosion rate of the metallic reinforcement used in their construction. The resistivity of the backfill aggregates needs to be measured accurately to estimate realistically the corrosion rate of the reinforcement. Resistivity testing is usually performed using the traditional soil box on the portion of the aggregates that passes a No. 10 or No. 8 sieve to either select or reject the backfill. For a more reasonable characterization of the corrosivity of coarse backfills, it is desirable to use their actual gradations. To that end, several resistivity boxes that were double and quadruple the dimensions of the original box were constructed. In addition to the three standard gradations specified by the Texas Department of Transportation, over 20 backfill materials sampled from sources throughout Texas were fractionated to fines, fine sand, coarse sand, and gravel. Resistivity tests were performed separately on each of these four constituents for each backfill. The results were used to evaluate a relationship that would allow the estimation of the resistivity of any desired backfill gradations from the resistivity values of these four constituents. The proposed model looks promising since the resistivity of the backfill composed of the actual gradation can be estimated with reasonable certainty. The results of this study can potentially help highway agencies and contractors use a number of local quarries that are currently disqualified based on the resistivity values obtained from only testing materials that pass a No. 8 or No. 10 sieve.
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Yan, Baoxu, Xingping Lai, Hanwen Jia, Erol Yilmaz, and Chen Hou. "A Solution to the Time-Dependent Stress Distribution in Suborbicular Backfilled Stope Interaction with Creeping Rock." Advances in Civil Engineering 2021 (March 23, 2021): 1–18. http://dx.doi.org/10.1155/2021/5533980.
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The creep behavior of deep weak rock masses is important due to an underground opening. Appreciating the nature and source of these deformations requires the knowledge of rock mass and ground support interaction. The theoretical solution of the backfill’s internal stresses needs to consider the time-dependent effect. In the present study, the coupling interaction between the creep behavior of the nearby rock material and the internal stresses in the backfilled stope is considered and the interaction characteristics are given analytically. A solution is then proposed regarding the time-dependent stress distribution in suborbicular backfilled stope interaction with creeping rock. Besides, the correctness of the theoretical solution is verified by numerical simulation, while influential parameters such as stope buried depth, lateral pressure coefficient, horizontal stress ratio, creep time of surrounding rock mass, delay time of the backfill, and Young’s modulus are thoroughly discussed. Research shows that when the stope buried depth becomes large as well as the rheological effect of the nearby rock materials becomes significant, the stress distribution in the backfill material exceeds its self-weight stress and presents significant time-dependent characteristics. The delayed backfilling weakens the backfill’s ground support effect on the nearby rock material. Hence, timely and multipoint simultaneous backfilling is needed for a stope with significant rheological deformation of surrounding rock mass. Lastly, this work will offer useful knowledge while designing the backfill materials for underground mines.
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Thiry, Médard, Sabine Huet-Taillanter, and Jean-Michel Schmitt. "The industrial waste land of Mortagne-du-Nord (59) – I – Assesment, composition of the slags, hydrochemistry, hydrology and estimate of the outfluxes." Bulletin de la Société Géologique de France 173, no. 4 (July 1, 2002): 369–81. http://dx.doi.org/10.2113/173.4.369.
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Abstract The industrial waste land in Mortagne-du-Nord has been occupied for over 60 years by a zinc smelter unit linked to a sulfide roasting unit for sulfuric acid production and for a few years a lead smelting unit. The waste land has been systematically explored by drillings and pits ; 58 of these drill holes and pits have been equipped as piezometers and surveyed for 4 years. The site has been back-filled with slags and smelting crucible to a thickness of about 3 meters. The mineralogy of these materials is highly varied. More than 30 heavy metal-bearing (Zn, Pb, Cd, Cu) mineral species have been identified, these are sulfides, sulfates, carbonates, oxides and silicates. High substitution rates characterize these minerals, especially the sulfides and the oxides. Field descriptions and mineralogical analyses lead to distinguish two main types of materials: materials called ≪ active ≫ that are characterized by the presence of sulfides and secondary sulfates,, and materials called ≪ non-active ≫ that look clearly weathered and in which the heavy metals are mainly present as carbonates and oxides. The ≪ active ≫ materials with sulfides bear an average of 7 % of heavy metals (Zn + Pb + Cd), whereas the oxidized and altered ≪ non-active ≫ materials contain less than 3 % of heavy metals. The whole stock of heavy metals in the waste land backfills can be assessed at over 15 000 tons. The hydrochemistry of the surficial groundwater contained in the backfills is directly related to the mineralogy of the material and shows very steep heterogeneities, with heavy metal concentrations increasing 10 or even 100 times over a distance of less than 50 m. The groundwaters adjoining the ≪ non-active ≫ backfills have moderately acidic to neutral pH and are relatively weakly mineralized: SO−4 =700 mg/L, Zn++=10 mg/L, Pb++=0,2 m/L et Cd++=0,1 mg/L. On the contrary, the groundwaters adjoining the ≪ active ≫ backfills are acidic (2,5 < pH < 6,3) and are heavyly mineralized: SO−4 > 4 000 mg/L, Zn++ > 1 000 mg/L, Pb++ > 1,5 mg/L et Cd++ > 50 mg/L. These groundwaters discharge in the water courses alongside the waste land, with in places heavy metal concentrations equivalent to those within the ≪ active ≫ sulfide bearing backfills. The deeper regional aquifer contained in the Sables d’Ostricourt Formation is separated from the surficial groundwater by organic- and pyrite-rich clayey alluviums. Because of this, the deeper groundwater is relatively protected, but nevertheless contaminated. The alluvium acts as both a hydrological and a geochemical barrier, and, leads to the precipitation of a part of the dissolved heavy metals as sulfides. The hydrological modelling of the surficial groundwater allows to calculate the annual fluxes towards the watercourses alongside the waste land. Applying the average concentrations measured in the surficial groundwater to this flux, we can estimate the annual tonnage of heavy metals exported towards the regional watercourses at about 14 000 kg/year of Zn++, 2 kg/year of Pb++ and 25 kg/year of Cd++, merely for the site of the former sulfuric acid plant where the ≪ active ≫ backfills are widespread. This heavy metal export to the watercourses constitutes the site major environmental harm. Regarding the volume of the polluted materials, it is inconceivable to excavate the backfills. A confining and/or processing method of the polluted waters has to be considered instead.
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Yang, Minghui, and Bo Deng. "Simplified Method for Calculating the Active Earth Pressure on Retaining Walls of Narrow Backfill Width Based on DEM Analysis." Advances in Civil Engineering 2019 (April 4, 2019): 1–12. http://dx.doi.org/10.1155/2019/1507825.
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Spaces for backfills are often constrained and narrowed when retaining walls must be built close to existing stable walls in urban areas or near rock faces in mountainous areas. The discrete element method (DEM), using Particle Flow Code (PFC-2D) software, was employed to simulate the behavior of cohesionless soil with narrow width behind a rigid retaining wall when the wall translation moved away from the soils. The simulations focused on the failure model of the soil when the movement of the wall reaches the value where active earth pressure occurs, and the shape of the sliding surface was captured. Then, based on the limit equilibrium method with the obtained slip surfaces in PFC-2D, a simplified analytical method is presented to obtain a solution of the active earth pressure acting on rigid retaining with narrow backfill width. The point of application of the active earth pressure is also obtained. The calculated values agree well with those from physical tests in the previous literature. Furthermore, the effects of the width of the backfill, internal friction angle of soil, and wall-soil friction angle on the distribution of active earth pressure are discussed.
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Rajani, B., and C. Zhan. "On the estimation of frost loads." Canadian Geotechnical Journal 33, no. 4 (August 20, 1996): 629–41. http://dx.doi.org/10.1139/t96-088-309.
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Frost load is an important loading condition to consider for the design of buried pipes. Though frost loads can be much greater than earth loads, it is not presently possible to estimate frost loads except using heuristic arguments. This paper describes the development of simplified methods to estimate frost load. Important variables are identified that can explain how the effects of frost loading can be mitigated. Sensitivity analyses are presented to highlight the importance of the different variables involved in the simplified methods. Frost loads measured in a field case study are compared with calculated frost loads in trenches with clay and sand backfills. Key words: frost load, frost depth, buried pipe, trench backfills, trench width.
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Qiu, Huafu, Fushun Zhang, Lang Liu, Dongzhuang Hou, and Bingbing Tu. "Influencing Factors on Strength of Waste Rock Tailing Cemented Backfill." Geofluids 2020 (October 19, 2020): 1–7. http://dx.doi.org/10.1155/2020/8847623.
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Tailing cement filling is an important development direction in mine filling, as it is a green and environmentally friendly method for efficiently treating solid waste in mines. Adding a certain amount of waste rock can effectively improve the backfill strength and better meet the filling strength requirements. To address the use of waste rock tailings in cemented filling materials, a uniaxial compression test was carried out on backfills with different cement/sand ratios and waste rock contents, and the influence of the cement/sand ratio and waste rock content on the strength of the backfill was studied. This study found that when the waste rock content is certain, the strength of the backfill increases with the increase in the cement/sand ratio, and the increase in strength slows with the increase in the cement/sand ratio until the strength of the backfill reaches a limit and no longer increases. When the cement/sand ratio is constant, the strength of the backfill first increases and then decreases as the waste rock content increases. When the cement content is constant, the addition of a certain amount of waste rock reduces the specific surface area of the solid materials in the backfill, increases the amount of cement per unit area, and improves the strength of the backfill. When the waste rock content is too high, due to the large particle size of the waste rock, the tailings cannot completely wrap around the waste rock, resulting in a weakening of the cement in the backfill, which reduces the strength of the backfill. This study found that the waste rock content and the cement/sand ratio in the backfill have a significant impact on backfill damage. The damage is mainly caused by insufficient cement strength. The presence of waste rock will change the original direction of crack propagation, resulting in more crack bifurcation, and the form of the destruction surface on the backfill is complicated and diverse.
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Clayton, C. R. I., I. F. Symons, and J. C. Hiedra-Cobo. "The pressure of clay backfill against retaining structures." Canadian Geotechnical Journal 28, no. 2 (April 1, 1991): 282–97. http://dx.doi.org/10.1139/t91-034.
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This paper investigates the pressures exerted by clay backfills against retaining structures. The lateral pressures are developed during three main phases: placement, compaction, and burial; horizontal total stress reduction at constant moisture content; and swelling or consolidation under approximately constant vertical stress. Experimental data from laboratory and pilot-scale studies, using clays of intermediate and high plasticity, are presented and used to assess the magnitude of the pressure changes in each phase. The process of compaction is examined and it is concluded that previously developed theories for assessing the pressures on retaining walls developed by compaction of granular soils are inapplicable for cohesive soils. The factors controlling the swelling of cohesive backfill are reviewed and results from a preliminary numerical study are used to provide an indication of the likely effects of plasticity and placement moisture content. Key words: earth pressure, retaining walls, clay, compaction, swelling.
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Shukla, Sanjay Kumar. "Dynamic active thrust from c–ϕ soil backfills." Soil Dynamics and Earthquake Engineering 31, no. 3 (March 2011): 526–29. http://dx.doi.org/10.1016/j.soildyn.2010.10.001.
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Shukla, Sanjay Kumar, and Daryoush Habibi. "Dynamic passive pressure from c–ϕ soil backfills." Soil Dynamics and Earthquake Engineering 31, no. 5-6 (May 2011): 845–48. http://dx.doi.org/10.1016/j.soildyn.2011.01.009.
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Zhang, Zhongjie, Murad Y. Abu-Farsakh †, and Mingjiang Tao ‡. "Evaluation of trench backfills at highway cross-drains." International Journal of Pavement Engineering 6, no. 2 (June 2005): 77–87. http://dx.doi.org/10.1080/10298430500137228.
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Abd, Akram H., and Stefano Utili. "Design of geosynthetic-reinforced slopes in cohesive backfills." Geotextiles and Geomembranes 45, no. 6 (December 2017): 627–41. http://dx.doi.org/10.1016/j.geotexmem.2017.08.004.
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Fall, Mamadou, and Mukesh Pokharel. "Coupled effects of sulphate and temperature on the strength development of cemented tailings backfills: Portland cement-paste backfill." Cement and Concrete Composites 32, no. 10 (November 2010): 819–28. http://dx.doi.org/10.1016/j.cemconcomp.2010.08.002.
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