Effect of grain size on the strength characteristics of cement-stabilized lateritic soils

Lateritic soils are readily available all over Nigeria and as such have attracterd several research studies in recent times, the obvious aim being its utilization in the construction industry. This paper gives an account of the work done to further classify the usefulness and limitations of lateritic soils.Cement was used as the stabilizer and the lateritic soils used were obtained from the Ifewara deposits located about 10 km along Ife-Ifewara Road. A sieve analysis of the sample was made. Five different grain size ranges, from coarse to fine, were extracted from the samples. Cubes were moulded by mixing each grain size range with cement in five different proportions, the optimum water/cement ratio of each mix proportion being determined beforehand. The compressive strengths of the cubes were determined after 7, 21, and 28 days of curing in water, respectively. It was established that the higher the laterite/cement ratio, the lesser the compressive strength, and that the finer the grain size range, the higher the compressive strength. Finally, it was observed that cubes made using laterite/cement mix proportions 1:1 and 3:1 kept gaining strength with age while the others were losing strength.     

Effect of different factors on the validity of determinations made for the compactability characteristics of cohesive soils

Conclusions 1. A linear relationship, the range of applicability of which is a critical moisture content close to the maximum content of bound water in the soil, exists between the optimum compactability characteristics and the logarithm of the maximum contact pressures. The effective compaction of a soil is possible with moisture contents greater than the critical values.2. The results of compaction of cohesive soils, which are distinguished one from the other by the percentage of a clayey fraction of constant mineralogical composition, are characterized in W_opt-logo_max coordinates by a family of linear W_opt =f(logo_max) relationships obtained for moisture contents greater than the maximum content of bound water in the soil.The gradation and mineralogical composition of the coarse-disperse component affects the character of the relationships between the optimum compactability characteristics and the stress state in the soil being compacted.4. The optimum compactability characteristics for the same soil are variable quantities; the development of an objective method of evaluating the compactability is therefore possible in cases where the selection of impact-load parameters during laboratory compaction is determined by the magnitude of the maximum contact pressures applied under the action of a soil-compacting mechanism. Use of the laws that we have developed makes it possible to evaluate the optimum compactability characteristics of cohesive soils more reliably during their compaction under working conditions.Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 6, pp. 13–15, November–December, 1977.     

Effect of fiber-reinforcement on the strength of cemented soils

This study aims to verify the differences in the strength of an artificially cemented sandy soil with and without fiber reinforcement. The controlling parameters evaluated were the amount of cement, porosity, moisture content, and voids/cement ratio. A series of unconfined compression tests and suction measures were carried out. The results show that fiber insertion in the cemented soil, for the whole range of cement studied, causes an increase in unconfined compression strength. The UCS increased linearly with the amount of cement and reduced with the increase in porosity (η) for both the fiber-reinforced and unreinforced specimens. A power function fits well as the relation between unconfined compressive strength (UCS) and porosity (η). Finally, it was shown that the voids/cement ratio is a good parameter in the evaluation of the unconfined compressive strength of the fiber-reinforced and unreinforced cemented soil studied.     

基于大型真三轴试验的粗粒料强度特性研究

基于长江科学院自主研制的大型微摩阻土工真三轴仪,对某土石坝粗粒料开展不同中主应力系数(等b)条件下的真三轴试验,探讨三向应力条件下粗粒料强度变化特征。研究表明:(1)中主应力对粗粒料强度影响显著,强度随b值增加而增加,特别是b值在0~0.25区间内,相较于常规三轴试验其强度指标显著增长;(2)经与几种经典强度准则对比,拉德–邓肯强度准则能相对较好地反映粗粒料在三向应力状态下强度演化趋势;(3)通过一组平面应变试验认为,不同围压下当偏应力接近峰值时,b值基本稳定在0.17~0.19,实际工程在试验条件有限的情况下,平面应变试验成果可用于粗略估算粗粒料在复杂三向应力状态下的强度。研究成果可为合理确定粗粒料复杂应力状态下强度参数及精细化研究粗粒料强度准则提供参考。     

Refinement of design rules for beds and foundations on soils prone to slump-type settlement

Suggestions are given for refinement of rules governing the design of beds and foundations on soils prone to slump-type settlement; these suggestions are based on consideration of additional settlements and zones of compression of the underlying soil stratum prone to slump-type settlement, calculation of the bearing capacity of piles from results of static probing of the soils, and determination of additional loads on the piles due to forces of loading friction throughout the mass of soil suspended on the piles. __________ Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 4, pp. 25–30, July–August, 2008.     

Multifunctional combined foundations on permafrost soils

The writers examine the construction of multifunctional combined foundations on permafrost soils, as approved for strengthening the foundation system of an administrative-industrial building in Norilsk. Such foundations make it possible to control the building deformations developed as a result of increase in the pile loads or in the settlements of the piles due to decrease in their bearing capacity when the soil base temperature increases.Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 5, pp. 26–28, September–October, 1992.     

纤维加筋非饱和黏性土的剪切强度特性

纤维加筋是近些年发展起来的一种土质改良技术,系统掌握纤维加筋土的力学性质对评价纤维加筋土工程的稳定性和进一步推广该技术在工程中的应用具有重要意义。为了了解纤维加筋的剪切强度特性,以非饱和黏性土为研究对象,以聚丙烯纤维为加筋材料,在控制含水率和干密度条件下开展了一系列直剪试验。借助扫描电镜,从微观的角度探讨了纤维的增强机理,并对相关宏观力学性质进行了分析。结果表明：纤维加筋能有效提高土体的抗剪强度,且抗剪强度随纤维掺量的增加而增加;相对于内摩擦角,纤维对黏聚力的增强效果要明显得多;纤维加筋土的抗剪强度随含水率的增加而减小,随干密度的增加而增加;总体上,低含水率和高密实度条件有利于发挥纤维的拉筋效果,提高纤维对强度的贡献。此外,纤维加筋在提高土体峰值剪切强度的同时,还能增加土体破坏时对应的应变及破坏后的残余强度,改善土体的破坏韧性。由扫描电镜分析可知,单根纤维一维拉筋作用和纤维网三维拉筋作用是纤维加筋土的主要增强机理,增强效果则取决于纤维-土界面力大小;剪切面上的纤维在剪切过程中呈现拔出和拉断两种失效模式。     

Effect of chemical composition of soils on the strength and deformability of frozen saline soils

The possibility of deriving a generalized relationship between strength characteristics of frozen saline soils and homological temperature is established. An equation for determination of the freezing point of saline soils is obtained on the basis of the Rayleigh-Van't Hoff law and confirmed experimentally. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 6, pp. 18–22, November–December, 1994.