Unconfined compressive strength and failure behaviour of completely weathered granite from a fault zone

Understanding the strength characteristics and deformation behaviour of the tunnel surrounding rock in a fault zone is significant for tunnel stability evaluation.In this study,a series of unconfined compression tests were conducted to investigate the mechanical characteristics and failure behaviour of completely weathered granite(CWG)from a fault zone,considering with height-diameter(h/d)ratio,dry densities(ρd)and moisture contents(ω).Based on the experimental results,a regression mathematical model of unconfined compressive strength(UCS)for CWG was developed using the Multiple Nonlinear Regression method(MNLR).The research results indicated that the UCS of the specimen with a h/d ratio of 0.6 decreased with the increase ofω.When the h/d ratio increased to 1.0,the UCS increasedωwith up to 10.5%and then decreased.Increasingρd is conducive to the improvement of the UCS at anyω.The deformation and rupture process as well as final failure modes of the specimen are controlled by h/d ratio,ρd andω,and the h/d ratio is the dominant factor affecting the final failure mode,followed byωandρd.The specimens with different h/d ratio exhibited completely different fracture mode,i.e.,typical splitting failure(h/d=0.6)and shear failure(h/d=1.0).By comparing the experimental results,this regression model for predicting UCS is accurate and reliable,and the h/d ratio is the dominant factor affecting the UCS of CWG,followed byρd and thenω.These findings provide important references for maintenance of the tunnel crossing other fault fractured zones,especially at low confining pressure or unconfined condition.

Improving the Unconfined Compressive Strength of Red Clay by Combining Biopolymers with Fibers

To explore an environmentally friendly improvement measure for red clay,the function and mechanism of xanthan gum biopolymer and polypropylene fibers on the strength properties of red clay were investigated by unconfined compressive strength and scanning electron microscopy tests.The test results demonstrated that the contents and curing ages of xanthan gum had significant influences on the unconfined compressive strength of red clay.Compared with untreated soil,1.5%xanthan gum content was the optimal ratio in which the strength increment was between 41.52 kPa and 64.73 kPa.On the other hand,the strength of xanthan gum-treated red clay increased,whereas the ductility decreased with the increase in curing ages,indicating that the xanthan gum-treated red clay started to gradually consolidate after 3 days of curing and stiffness significantly improved between 7 and 28 days of curing.The results also showed that the synergistic consolidation effects of the xanthan gum–polypropylene fibers could not only effectively enhance the strength of red clay but also reduce the brittle failure phenomenon.The strengths of soil treated with 2.0%xanthan gum-polypropylene fibers were 1.9–2.41 and 1.12–1.47 times than that of red clay and 1.5%xanthan gum-treated clay,respectively.The results of study provide the related methods and experiences for the field of ecological soil treatment.

The Influence of Freeze-Thaw Cycles on Unconfined Compressive Strength of Lignin Fiber-Reinforced Loess

In the seasonal permafrost region with loess distribution,the influence of freeze-thaw cycles on the engineering performance of reinforced loess must be paid attention to.Many studies have shown that the use of fiber materials can improve the engineering performance of soil and its ability to resist freeze-thaw cycles.At the same time,as eco-environmental protection has become the focus,which has been paid more and more attention to,it has become a trend to find new environmentally friendly improved materials that can replace traditional chemical additives.The purpose of this paper uses new environmental-friendly improved materials to reinforce the engineering performance of loess,improve the ability of loess to resist freeze-thaw cycles,and reduce the negative impact on the ecological environment.To reinforce the engineering performance of loess and improve its ability to resist freeze-thaw cycles,lignin fiber is used as a reinforcing material.Through a series of laboratory tests,the unconfined compressive strength(UCS)of lignin fiber-reinforced loess under different freeze-thaw cycles was studied.The effects of lignin fiber content and freeze-thaw cycles on the strength and deformation modulus of loess were analyzed.Combined with the microstructure features,the change mechanism of lignin fiber-reinforced loess strength under freeze-thaw cycles was discussed.The results show that lignin fiber can improve the UCS of loess under freeze-thaw cycles,but the strengthening effect no longer increases with the increase of fiber content.When the fiber content is less than 1%,the UCS growth rate of loess is the fastest under freeze-thaw cycles.And the UCS of loess with 1%fiber content is the most stable under freeze-thaw cycles.The freeze-thaw cycles increase the deformation modulus of loess with 1%fiber content,and its ability to resist deformation is obviously better than loess with 1.5%,2%and 3%fiber content.The fiber content over 1%will weaken the strengthening effect of lignin fiber-reinforced loess,and the optimum fiber content of lignin fiber-reinforced loess under freeze-thaw cycles is 1%.

Estimating Unconfined Compressive Strength of Sedimentary Rocks in United Arab Emirates from Point Load Strength Index

In this paper, three rock types including Sandstone, Mudstone, and Crystalline Gypsum were part of a laboratory study conducted to develop a dataset for predicting the unconfined compressive strength of UAE intact sedimentary rock specimens. Four hundred nineteen rock samples from various areas along the coastal region of the UAE were collected and tested for the development of this dataset and evaluation of models. From the statistical analysis of the data, regression equations were established among rock parameters and correlations were expressed and compared by the ones proposed in literature.

Analysis of influence factors of unconfined compressive strength for composite soil stabilizer-stabilized gravel soil

In order to investigate the effect o f some factors on the unconfined compressive strength(UCS)for composite soil stabilizer-stabilized gravel soil(CSSSGS),the orthogonal test is adopted to set up the experimental scheme.Three levels o f each factor armconsidered to obtain the change laws o f UCS,in which the binder dosages are8%,10%,and12%;the curing times ae7,14and21d;the gradation nae0.3,0.35and0.4;and the degrees of compaction are95%,97%,and99%.The range analysis clearly indicates that the influence degree o f the four factors on UCS is in such an order:dosage,age,gradation,and degree o f compaction.The variance analysis shows that only the composite soil stabilizer dosage can significantly affect UCS.In road construction,the examination o f composite soil stabilizer dosage and base-course maintenance should be given much more attention to obtain satisfactory base-course strength,compared w ith gradation floating and the change of degree o f compaction.

Effect of chloride salt concentration on unconfined compression strength of cement-treated Lianyungang soft marine clay

This study aims to quantify the influence of the amount of cement and chloride salt on the unconfined compression strength （UCS） of Lianyungang marine clay. The clays with various sodium chloride salt concentrations were prepared artificially and stabilized by ordinary Portland cement with various contents. A series of UCS tests of cement stabilized clay specimen after 28 d curing were carried out. The results indicate that the increase of salt concentration results in the decrease in the UCS of cement-treated soil. The negative effect of salt concentration on the strength of cement stabilized clay directly relates to the cement content and salt concentration. The porosity-salt concentration/cement content ratio is a fundamental parameter for assessing the UCS of cement-treated salt-rich clay. An empirical prediction model of UCS is also proposed to take into account the effect of salt concentration. The findings of this study can be referenced for the stabilization improvement of chloride slat- rich soft clay.

Effect of Sample Disturbance on Unconfined Compression Strength of Natural Marine Clays

Quantitatively correcting the unconfined compressive strength for sample disturbance is an important research project in the practice of ocean engineering and geotechnical engineering. In this study, the specimens of undisturbed natural marine clay obtained from the same depth at the same site were deliberately disturbed to different levels. Then, the specimens with different extents of sample disturbance were trimmed for both oedometer tests and unconfined compression tests. The degree of sample disturbance SD is obtained from the oedometer test data. The relationship between the unconfined compressive strength q u and SD is studied for investigating the effect of sample disturbance on q u. It is found that the value of q u decreases linearly with the increase in SD. Then, a simple method of correcting q u for sample disturbance is proposed. Its validity is also verified through analysis of the existing published data.

Artificial intelligence model for studying unconfined compressive performance of fiber-reinforced cemented paste backfill

To reduce the difficulty of obtaining the unconfined compressive strength(UCS) value of fiber-reinforced cemented paste backfill(CPB) and analyze the comprehensive impact of conventional and fiber variables on the compressive property, a new artificial intelligence model was proposed by combining a newly invented meta-heuristics algorithm(salp swarm algorithm, SSA) and extreme learning machine(ELM) technology. Aiming to test the reliability of that model, 720 UCS tests with different cement-to-tailing mass ratio, solid mass concentration, fiber content, fiber length, and curing time were carried out, and a strength evaluation database was collected. The obtained results show that the optimized SSA-ELM model can accurately predict the uniaxial compressive strength of the fiber-reinforced CPB, and the model performance of SSA-ELM model is better than ANN, SVR and ELM models. Variable sensitivity analysis indicates that fiber content and fiber length have a significant effect on the UCS of fiber-reinforced CPB.

The compressive strength experimental study of cemented soil under H2SO4 corrosive in earlier period

In order to simulate and study the erosion effect process such as the changes of corrosive depth and unconfined compression strength of cemented soil sample in earlier period from 0 day to 60 days, a series of tests including unconfined compressive tests, measuring the blocks＇ sizes, and taking photos, are conducted on the cemented soil blocks which were cured in different concentrations of H2SO4 solutions. The results of tests show that the corrosive depth is increasing and the unconfined compression strength is decreasing with the increase of H2SO4 solution concentration at the same erosion time, and the corrosive degree is increasing with the corrosive time. In the earlier state, the corrosive effect is serious, but the effect becomes slow in the later state in the same concentrated H2SO4 solution. After take statistics the date, a coefficient a is put forward to predict the reduction of the compressive strength of cemented soil in various concentration of H2SO4 solution, which could be used in practical design.

Unconfined compressive strength prediction of soils stabilized using artificial neural networks and support vector machines

This study aims to improve the unconfined compressive strength of soils using additives as well as by predicting the strength behavior of stabilized soils using two artificial-intelligence-based models.The soils used in this study are stabilized using various combinations of cement,lime,and rice husk ash.To predict the results of unconfined compressive strength tests conducted on soils,a comprehensive laboratory dataset comprising 137 soil specimens treated with different combinations of cement,lime,and rice husk ash is used.Two artificial-intelligence-based models including artificial neural networks and support vector machines are used comparatively to predict the strength characteristics of soils treated with cement,lime,and rice husk ash under different conditions.The suggested models predicted the unconfined compressive strength of soils accurately and can be introduced as reliable predictive models in geotechnical engineering.This study demonstrates the better performance of support vector machines in predicting the strength of the investigated soils compared with artificial neural networks.The type of kernel function used in support vector machine models contributed positively to the performance of the proposed models.Moreover,based on sensitivity analysis results,it is discovered that cement and lime contents impose more prominent effects on the unconfined compressive strength values of the investigated soils compared with the other parameters.

Modeling of unconfined compressive strength of soil-RAP blend stabilized with Portland cement using multivariate adaptive regression spline

The recycled layer in full-depth reclamation (FDR) method is a mixture of coarse aggregates and reclaimed asphalt pavement (RAP) which is stabilized by a stabilizer agent. For design and quality control of the final product in FDR method, the unconfined compressive strength of stabilized material should be known. This paper aims to develop a mathematical model for predicting the unconfined compressive strength (UCS) of soil-RAP blend stabilized with Portland cement based on multivariate adaptive regression spline (MARS). To this end, two different aggregate materials were mixed with different percentages of RAP and then stabilized by different percentages of Portland cement. For training and testing of MARS model, total of 64 experimental UCS data were employed. Predictors or independent variables in the developed model are percentage of RAP, percentage of cement, optimum moisture content, percent passing of #200 sieve, and curing time. The results demonstrate that MARS has a great ability for prediction of the UCS in case of soil-RAP blend stabilized with Portland cement (R2 is more than 0.97). Sensitivity analysis of the proposed model showed that the cement, optimum moisture content, and percent passing of #200 sieve are the most influential parameters on the UCS of FDR layer.

磷石膏/木质素固化铅污染土的无侧限抗压强度

采用工业固体废弃物磷石膏、木质素对人工配制铅污染土进行固化处理,通过无侧限抗压强度(UCS)试验探究固化剂掺量、养护龄期对不同程度铅污染土固化后应力-应变曲线、破坏形态及无侧限抗压强度的影响规律,对比分析两种固化剂的固化效果,并采用扫描电镜(SEM)试验分析土样固化前后的微观特性。试验结果表明,磷石膏、木质素均能增大固化土的无侧限抗压强度,减小破坏应变;固化土的无侧限抗压强度随磷石膏掺量增加呈持续上升趋势,随木质素掺量增加呈先上升后下降趋势;延长养护时间能有效提高固化土无侧限抗压强度。随固化剂掺量和养护龄期的增加,土体内部胶结水平提高,土样破坏形态从局部张裂逐渐转变为剪切破坏,呈现脆性破坏特征。两种固化剂固化土效果各有优劣,木质素对高浓度铅污染土的固化效果优于磷石膏,抵抗变形能力更好,而磷石膏短期内提升强度能力及对铅的固定效果更好。扫描电镜试验表明,固化剂可起到填充孔隙、胶结土颗粒的作用,水化产物在土体内形成致密结构,宏观表现为强度增强。

固废材料复合固化盐渍土的力学性能

【目的】解决宁夏回族自治区盐渍土地基在盐-冻胀和盐腐蚀作用下存在的强度劣化问题。【方法】采用水泥、粉煤灰、硅灰和砖粉作为固化剂,基于正交试验方案开展无侧限抗压强度试验和三轴剪切试验;通过X射线衍射和扫描电子显微镜等微观表征手段,研究不同固化剂用量对盐渍土无侧限抗压强度和抗剪强度的影响规律,确定较优的盐渍土固化组合。【结果】水泥和硅灰会大幅提高固化盐渍土的无侧限抗压强度,粉煤灰用量的增加会使固化盐渍土的强度呈现先增后减的变化趋势,砖粉的潜在火山灰活性较难激发,需要水泥的水化反应为其提供碱性环境;4种固化剂影响固化盐渍土强度的主次顺序为水泥、粉煤灰、硅灰、砖粉;水泥、粉煤灰、硅灰和砖粉质量分数分别为3%、5%、5%和6%时固化效果最佳;固化盐渍土强度主要受水化硅酸钙、水化铝酸钙、钙矾石等晶体的相互作用,导致土颗粒中晶体和胶凝物的分布从单个和细小的团簇转变为更复杂的三维网络结构,增强土颗粒、盐分和胶凝物之间的结合力。【结论】利用固废材料替代部分水泥固化盐渍土,提高固废资源利用率的同时大幅改善盐渍土地基的抗压和抗剪性能。

Determination and Evaluation of Strength Characteristics of Dry Jet Mixing

Dry jet mixing (DJM) for soft soil stabilization has been widely used since 1980s. The quality and strength of stabilized columns are fundamental parameters to evaluate the stabilization work. This paper presents the standard penetration test (SPT) method and its test results on cement columns. It is shown that SPT is an effective and simple method for inspecting and evaluating cement columns. The strength characteristics along the length of the column, a good correction between SPT blow count and the unconfined compressive strength are achieved.

铝离子絮凝剂对微生物加固砂土效果的影响试验研究

灌注次数过多制约了微生物诱导碳酸钙沉积(MICP)在实际工程中的应用。为了减少灌注次数、提高胶结效率,提出一种MICP加固强化方法,即在胶结液中添加铝离子絮凝剂,以提高MICP加固速率和增强加固效果。开展MICP砂柱试验,在胶结液中加入不同浓度AlCl3·6H2O进行灌注试验,然后测试加固砂柱碳酸钙含量及无侧限抗压强度(UCS)。在水溶液试验中,观察不同溶液条件下沉积物生成情况及溶液的pH值变化,并通过XRD、SEM试验研究铝离子絮凝剂对沉积碳酸钙的成分及形态的影响。结果表明:与常规方法的对照组比较,胶结液中加入适量铝离子絮凝剂,灌注3次后砂柱即可形成有强度的固结体,灌注5次后砂柱无侧限抗压强度可达到1.7MPa,而常规对照组达到相同的强度需要灌注9次。铝离子絮凝剂的掺入有效减少了MICP灌注处理次数,对实际应用有重要意义。

基于离散元法的水泥稳定碎石微裂细观机理研究

为探究水泥稳定碎石微裂细观演化机理,构建了细观非均质水泥稳定碎石数值模型,结合室内无侧限抗压强度试验和单轴压缩数值试验反演出模型细观参数,引入微裂隙网络研究不同裂隙参数对微裂程度的影响,分析不同裂隙数目下系统能量演化规律。结果表明:数值模拟与室内试验结果基本吻合,构建的水泥稳定碎石离散元模型可较为准确地表征材料细观破坏特征;微裂损伤是二次振动加载后裂隙宽度增大和裂隙数目增多共同作用的结果,裂隙密度对水泥稳定碎石微裂程度起决定性作用;裂隙密度增加,材料储存弹性应变能的能力减弱,峰值点水泥稳定碎石材料的输入总能量降低。验证了早期微裂对于降低收缩应力的积极作用,揭示了水泥稳定碎石材料微裂力学特征和细观机理。

Strength and deformation characteristics of carbonated reactive magnesia treated silt soil

A series of unconfined compression tests(UCTs) were conducted to investigate the effects of content of reactive magnesia(Mg O) and carbonation time on the engineering properties including apparent characteristics, stress-strain relation, and deformation and strength characteristics of reactive Mg O treated silt soils. The soils treated with reactive Mg O at various contents were subjected to accelerated carbonation for different periods of time and later, UCTs were performed on them. The results demonstrate that the reactive Mg O content and carbonation time have remarkable influences on the aforementioned engineering properties of the soils. It is found that with the increase in reactive Mg O content, the unconfined compressive strength(qu) increases at a given carbonation time(<10 h), whereas the water content and amounts of crack of the soils decrease. A threshold content of reactive Mg O exists at approximately 25% and a critical carbonation time exists at about 10 h for the development of qu. A simple yet practical strength-prediction model, by taking into account two variables of reactive Mg O content and carbonation time, is proposed to estimate qu of carbonated reactive Mg O treated soils. A comparison of the predicated values of qu with the measured ones indicates that the proposed model has satisfactory accuracy.

Key parameters controlling electrical resistivity and strength of cement treated soils

The improvement of question soils with cement shows great technical, economic and environmental advantages. And interest in introducing electrical resistivity measurement to assess the quality of cement treated soils has increased markedly recently due to its economical, non-destructive, and relatively non-invasive advantages. This work aims to quantify the effect of cement content （aw）, porosity （nt）, and curing time（T） on the electrical resistivity （p） and unconfined compression strength （UCS） of cement treated soil. A series of electrical resistivity tests and UCS tests of cement treated soil specimen after various curing periods were carried out. A modified Archie empirical law was proposed taking into account the effect of cement content and curing period on the electrical resistivity of cement treated soil. The results show that nt/（aw·T） and nt/（aw·T^1/2） ratio are appropriate parameters to assess electrical resistivity and UCS of cement treated soil, respectively. Finally, the relationship between UCS and electrical resistivity was also established.

Strength properties of xanthan gum and guar gum treated kaolin at different water contents

Nowadays,using biopolymer as a ground improvement method has become very popular.However,since biopolymers are organic and degradable,their long-term effect is not fully known.In this study,the effects of biopolymers on the mechanical behavior of kaolin clay were investigated through a comprehensive program of experiments.Two types of biopolymer,i.e.xanthan gum and guar gum were chosen to investigate the effect of biopolymer type.For this purpose,specimens were prepared using standard Proctor energy at four different water contents(25%,30%35%and 40%)with 0.5%,1%,1.5%and 2%biopolymer inclusions.The specimens were cured for 1 d,7 d,28 d and 90 d.Moreover,some of the specimens were kept in the curing room for 3 years to observe the long-term effect of the biopolymers.At the end of the curing periods,the specimens were subjected to unconfined compression test,and scanning electron microscopy(SEM)analysis was performed to observe the mechanism of strength improvement.The results revealed that the unconfined compressive strength(UCS)of the specimens treated with biopolymers increased in all biopolymer inclusion levels and water contents up to a 90-d curing period.For specimens containing xanthan gum,the maximum strength increase was observed at 25%water content and 2%xanthan gum with 90-d curing.The strength increased 5.23 times induced by xanthan gum addition when compared to the pure clay.Moreover,the increase in strength reached 8.53 times in specimens treated with guar gum.Besides,increasing water content caused more ductile behavior,thus increasing the axial deformation.

Evaluation of the mechanical degradation of carbonate aggregate by rock strength tests

Aggregate degradation(AD) is one of the major reasons accounting for failure of aggregate materials, and the mechanical degradation of aggregate materials can be determined by different test methods. This process basically requires many aggregate samples and special instruments, and thus is time-consuming.The main purpose of this research is to evaluate the possibility of estimating the AD characteristics using rock strength tests and to investigate the relationships between AD properties and rock strength tests.For understanding the relationships, two common rock strength tests are employed, i.e. unconfined compressive strength(UCS) and point load index(PLI) tests. In the tests, the AD properties of 40 kinds of carbonate aggregates sampled from Iran were studied. The AD properties were determined by Los Angeles abrasion value(LAAV), aggregate impact value(AIV) and aggregate crushing value(ACV). Also,the samples are classified according to the strength and rock types, and the effect of this classification is investigated based on the relationship between rock strengths and AD properties. The results indicate that the PLI is better than UCS for evaluation of AD properties. Among rock strength tests, PLI has a closer relationship with AIV(R^2 = 0.832). Also, UCS has relative larger effects on the ACV(R^2 = 0.812) under the same loading condition. The weakest correlation occurs between LAAV and UCS(R^2 = 0.679). In view of the rational AD properties in the predictive procedure, it is possible to predict AD properties based on the strength tests and rock types. The results also show that the prediction of AD properties using rock strength test based on rock types yields better correlations than that using unclassified samples. The classification based on rock types can extrapolate the different relationships of AD prediction from rock strength tests. The results in this context could be used for preliminarily selecting proper rock aggregates with a limit of allowable AD tests for practical applications by PLI.