Modeling the Undrained Shear Strength with Soil Index Properties for Niger Delta Soft Clays

The aim of this study was to model the Undrained Shear Strength (USS) of soil found in the coastal region of the Niger Delta in Nigeria with some soil properties. The undrained shear strength (USS) is a key parameter needed for most geotechnical/structural designs. Accurate determination of the USS of soft clays can be challenging to obtain in the laboratory due to the difficulty in remoulding the clay to its in-situ conditions before testing and more accurate test such as Cone Penetration test (CPT) can be quite expensive. This study was carried out at Escravos site which is located in Delta state, Nigeria. Three Boreholes were drilled and soil samples were collected at 0.75 m intervals up to a depth of 45 m. Laboratory tests were used to obtain the moisture content, bulk unit weight, liquid and plastic limit, while CPT was used in obtaining the undrained shear strength. Classification of the soil samples was done by adopting the Unified Soil Classification System and various models relating the USS with the soil properties were developed. The result showed that most of the soils at Escravos site were predominately inorganic clay of high plasticity which are problematic due to the expansion and shrinking nature of this type of soil. The model developed showed that the soil properties that gave the best fit with the USS were the moisture content and effective stress of the soil. The coefficient of determination (R2) and the root mean square error (RMSE) obtained for this model were 0.805 and 6.37 KN/m2, respectively.

Shear strength model of the reinforced concrete beams with embedded through-section strengthening bars

In this study,finite element(FE)analysis is utilized to investigate the shear capacity of reinforced concrete(RC)beams strengthened with embedded through-section(ETS)bars.Effects of critical variables on the beam shear strength,including the compressive strength of concrete,stiffness ratio between ETS bars and steel stirrups,and use of ETS strengthening system alone,are parametrically investigated.A promising method based on the bond mechanism between ETS strengthening and concrete is then proposed for predicting the shear resistance forces of the strengthened beams.An expression for the maximum bond stress of the ETS bars to concrete is developed.This new expression eliminates the difficulty in the search and selection of appropriate bond parameters from adhesion tests.The results obtained from the FE models and analytical models are validated by comparison with those measured from the experiments.Consequently,the model proposed in this study demonstrates better performance and more accuracy for prediction of the beam shear-carrying capacity than those of existing models.The results obtained from this study can also serve researchers and engineers in selection of the proper shear strength models for design of ETS-strengthened RC beams.

A new model for evaluating the dynamic shear strength of rocks based on laboratory test data for earthquake-resistant design

The dynamic shear strength of rocks is required for the earthquake-resistant design of nuclear power plants in Japan.This research aims to propose a mathematical model for estimating the dynamic strength and to validate the model.Two different types of specimens were prepared for the model validation,and the monotonic and cyclic loading tests were conducted to obtain the mathematical model parameters.Subsequently,multistep cyclic loading tests were performed,followed by simulations using the mathematical model.The test results demonstrated that the dynamic shear strength exceeded the static shear strength,which agreed with previous researches.Furthermore,the dynamic shear strength calculated using the mathematical model was generally consistent with that obtained from the experimental data.

Bilateral shear strength of rectangular frame column based on simplified space truss-arch model

To investigate the bilateral shear strength of rectangular frame column subjected to oblique horizontal load, we presented a simplified space truss-arch model developed from unilateral truss-arch model. Main parameters in the new model were the cross-sectional area, transverse reinforcement raito, axial load, and material strength of the column. The reduction coefficient of concrete sterength owing to the severe cracking of column was also introduced in the model. Finally, 14 specimens under oblique horizontal load were tested to verified the feasibility and applicability of the space truss-arch model.

A New Modification to Shear Lag Model as Applied to Stiffness and Yield Strength of Short Fiber Reinforced Metal Matrix Composites

A new modification for the shear lag model is given and the expressions for the stiffness and yield Strength of short fiber metal matri×composite are derived. These expressions are then compared with our experimental data in a SiCw/Al-Li T6 composite and the published experimental data on different SiCw/Al T6 composites and also compared with the previous shear lag models and the other theoretical models.

Shear strength criteria for rock,rock joints,rockfill and rock masses:Problems and some solutions

Although many intact rock types can be very strong,a critical confining pressure can eventually be reached in triaxial testing,such that the Mohr shear strength envelope becomes horizontal.This critical state has recently been better defined,and correct curvature or correct deviation from linear Mohr-Coulomb(MC) has finally been found.Standard shear testing procedures for rock joints,using multiple testing of the same sample,in case of insufficient samples,can be shown to exaggerate apparent cohesion.Even rough joints do not have any cohesion,but instead have very high friction angles at low stress,due to strong dilation.Rock masses,implying problems of large-scale interaction with engineering structures,may have both cohesive and frictional strength components.However,it is not correct to add these,following linear M-C or nonlinear Hoek-Brown(H-B) standard routines.Cohesion is broken at small strain,while friction is mobilized at larger strain and remains to the end of the shear deformation.The criterion 'c then σn tan φ' should replace 'c plus σn tan φ' for improved fit to reality.Transformation of principal stresses to a shear plane seems to ignore mobilized dilation,and caused great experimental difficulties until understood.There seems to be plenty of room for continued research,so that errors of judgement of the last 50 years can be corrected.

非饱和黏性土的广义有效应力三剪弹塑性本构模型

将非饱和土广义有效应力原理与三剪强度准则相结合,提出了非饱和土广义有效应力三剪强度准则。将所提准则作为破坏准则,分别采用等量代换法和坐标平移法推导出新的破坏应力比,并将其与非饱和土修正剑桥模型相结合得到了新的屈服函数。相比于原来修正剑桥模型中的破坏应力比为定值,新的屈服函数可以更好地反应土体全应力状态、中间主应力效应和拉压不等效应。在弹塑性理论的框架下,建立了非饱和土的广义有效应力三剪弹塑性本构模型。以江西正常固结非饱和重塑红黏土作为试验研究对象,进行室内土工试验、土水特征曲线试验、压缩回弹试验、非饱和土常规三轴固结排水试验。将该本构模型计算结果与非饱和土三轴固结排水试验结果进行对比验证。结果表明:数值模拟结果与试验结果吻合较好,验证了该本构模型的正确性。在轴向应变较小时,等量代换法和坐标平移法模拟结果比较接近,随着轴向应变增大直至偏应力达到平稳状态的过程中,等量代换法计算结果要大于坐标平移法计算结果,且更接近于试验值。真三轴计算预测结果表明:在固结排水条件下,初始压实度、净围压、基质吸力相同,中间主应力影响系数越大,则剪应力和体应变越大。b值相同的情况下,轴向应变较小时,等量代换法计算结果和坐标平移法计算结果比较接近,随着轴向应变的增大,二者之间的差值也越来越大。

不同饱和度下膨胀土原位孔内剪切试验及强度响应特征

膨胀土强度随饱和度变化显著,非饱和膨胀土的抗剪强度一直是研究膨胀土工程问题的关键。选取南阳市某高速路沿线边坡膨胀土为研究对象,进行了天然条件下处于不同饱和度状态的膨胀土原位孔内剪切试验,获得了自然条件下膨胀土的抗剪强度随饱和度的变化特征。膨胀土的抗剪强度、黏聚力、内摩擦角随着膨胀土饱和度的增大而逐渐减小。结合现场试验数据和土-水特征曲线,提出了以法向应力、饱和度为变量和以法向应力、基质吸力为变量的两种非饱和膨胀土的抗剪强度计算模型,并结合试验数据对计算模型的适用性进行了验证。与之前常用的非饱和土抗剪强度计算模型相比较,提出的两种计算模型所需的拟合参数少,适用于更宽吸力范围、不同法向应力条件下非饱和膨胀土抗剪强度的计算,且结果更为准确。

长大纵坡路段沥青混合料设计研究

车辙损坏是长大纵坡路段沥青路面常见的损坏类型,这对沥青混合料的高温稳定性提出了更高的要求。依托多哥壹号公路改建工程,对长大纵坡路段基于抗剪性能的沥青混合料设计进行了研究。首先根据现场调研情况,对同济大学车辙预估模型进行标定,使之适用于多哥壹号公路工程,进而结合路面容许车辙深度,给出沥青层混合料所需的抗剪强度要求。以此为依据,设计了AC13-1、AC13-2、Sup13-1、Sup13-2和SAC13五种级配。通过单轴贯入抗剪强度试验和车辙试验,优选出高温性能较优的级配,并检验其他路用性能。试验结果表明,基于工程所用原材料,Sup13-2级配的抗剪强度最高,其他路用性能也均满足要求,可作为壹号公路的施工级配。

干湿循环作用下吹填固化轻质土蠕变特性研究

采用新型固化技术对高含水率吹填土进行固化处理,通过三轴流变仪,考虑干湿循环次数、围压和初始静偏应力等因素研究其对吹填固化轻质土蠕变变形和抗剪强度指标的影响规律。试验结果表明:吹填固化轻质土具有密度小、质量轻及强度高等优点。在一定程度上,增大围压可有效缓解吹填固化轻质土的蠕变变形,而初始静偏应力对其影响较小,前7次干湿循环对土体破坏应力的影响最大,而后基本保持不变。抗剪强度指标c、φ值均随初始静偏应力的增加而逐渐降低,随干湿循环次数的增加呈现出先减小而后逐渐稳定的趋势,且前7次干湿循环,二者均呈指数函数降低;7次以后,变化均较小并逐渐稳定。基于c、φ值与时间关系曲线,分别构建了不同偏应力作用下吹填固化轻质土c、φ值的预测公式。根据蠕变曲线发展态势,通过回归分析,引入围压、初始静偏应力和干湿循环次数等因素,建立了吹填固化轻质土蠕变变形预测模型,并验证了其可行性。研究结果可为实际工程场地提供理论依据。

屋面材料对雪层持水量及积雪滑落的影响

为揭示屋面材料对屋面积雪滑落的影响规律,考虑混凝土、钢、膜与玻璃等常用屋面材料,对不同材料屋面上雪层的最大持水量及屋面-雪层剪切强度展开试验研究,并引入度日模型,建立屋面积雪滑落的判定方法,分析了屋面材料对屋面积雪滑落的影响。结果表明屋面积雪的最大持水量随屋面材料粗糙度的增大而增大;除玻璃外,屋面积雪滑落的临界温度也随屋面材料粗糙度的增大而增大。研究的结果为进一步探索屋面积雪滑落的机理提供重要参考依据。

Discrete modeling of rock joints with a smooth-joint contact model

Structural defects such as joints or faults are inherent to almost any rock mass.In many situations those defects have a major impact on slope stability as they can control the possible failure mechanisms.Having a good estimate of their strength then becomes crucial.The roughness of a structure is a major contributor to its strength through two different aspects,i.e.the morphology of the surface(or the shape)and the strength of the asperities(related to the strength of the rock).In the current state of practice,roughness is assessed through idealized descriptions(Patton strength criterion)or through empirical parameters(Barton JRC).In both cases,the multi-dimensionality of the roughness is ignored.In this study,we propose to take advantage of the latest developments in numerical techniques.With3D photogrammetry and/or laser mapping,practitioners have access to the real morphology of an exposed structure.The derived triangulated surface was introduced into the DEM(discrete element method)code PFC3D to create a synthetic rock joint.The interaction between particles on either side of the discontinuity was described by a smooth-joint model(SJM),hence suppressing the artificial roughness introduced by the particle discretization.Shear tests were then performed on the synthetic rock joint.A good correspondence between strengths predicted by the model and strengths derived from well-established techniques was obtained for thefirst time.Amongst the benefits of the methodology is the possibility offered by the model to be used in a quantitative way for shear strength estimates,to reproduce the progressive degradation of the asperities upon shearing and to analyze structures of different scales without introducing any empirical relation.

钢纤维混凝土压-剪复合性能及损伤本构关系

为研究钢纤维混凝土的压-剪复合受力性能及损伤模型,以钢纤维体积率、压应力比为参数,完成了60个钢纤维混凝土试件的直剪和压-剪试验,分析了各参数对剪切强度和峰值剪切位移的影响,推导了钢纤维混凝土在压-剪复合受力下的损伤全曲线模型,分析了损伤演化规律,提出了压-剪强度计算式。结果表明:剪切强度和峰值剪切位移均随压应力比的增大而增大。随着钢纤维体积率的增加,剪切强度呈现先增后减的趋势,峰值剪切位移规律不明显。压应力比的增大显著减缓了损伤发展;提出的损伤本构模型和压-剪强度公式计算结果与试验值吻合较好。

水动力-溶蚀作用下灰岩结构面剪切力学特性

中国西南地区溶蚀岩体分布广泛。岩溶作用下,结构面强度持续劣化是影响岩体稳定性的重要因素之一。为探究溶蚀作用下结构面的演化特征,揭示岩溶作用对灰岩结构面剪切力学特性的影响,以武隆鸡尾山溶蚀岩质坡体为例,采用室内结构面渗流溶蚀试验和结构面直接剪切试验,并结合三维形貌光学扫描技术,阐明了水动力-溶蚀作用灰岩结构面的表观演化模式和剪切力学特性演化规律,揭示了水动力-溶蚀作用下结构面劣化机理。结果表明:灰岩结构面在化学溶蚀和物理冲蚀双重作用下,先后经历“点式选择性溶蚀—细槽线式稳定渗流溶蚀—优势管道流强烈溶蚀—壁面缓慢溶蚀”4个阶段;溶蚀过程中,灰岩结构面表面粗糙度指数和溶蚀率指标随时长增大而增大,并呈收敛趋势;直剪过程中,溶蚀结构面表现出初期锁固、后期剪摩阻滑的两阶段特征,且时间越长、应力水平越高,剪切硬化特征越显著;随溶蚀时间增长,结构面主要抗滑结构由刚性稳定微凸体发展为细微溶槽并最终演变为深大岩溶管道,其极限抗剪强度呈现出“先减小,后增大”的趋势;基于Barton公式建立了灰岩溶蚀结构面抗剪强度预测模型。

风化锯齿形结构面抗剪强度特性及估算模型

为研究风化程度对不同起伏角锯齿形结构面剪切强度、剪切变形等抗剪强度特性的影响规律,制作了起伏角分别为15°、25°、35°、45°的4种不同的灰岩规则锯齿形结构面,通过开展室内风化模拟试验制备不同风化程度的锯齿形结构面岩样,进行不同法向应力下的室内锯齿形结构面直剪试验,探究风化灰岩锯齿形结构面抗剪强度及其参数的变化规律。试验结果表明:锯齿形结构面剪切应力-剪切位移曲线表现为峰值剪断型,呈现先近似线性增加,达到峰值剪切应力后跌落,最后基本趋于稳定,保持一定的残余抗剪强度的趋势;随着风化程度的增加,灰岩锯齿形结构面抗剪强度呈现减小的趋势,其抗剪强度参数发生不同程度的劣化,黏聚力的劣化程度大于摩擦角,而结构面起伏角大小与抗剪强度之间呈现正相关;基于模型试验结果,建立了风化锯齿形结构面抗剪强度估算模型,揭示结构面抗剪强度与风化程度及起伏角的定量化关系。

Analysis of complete plasticity assumption for solid circular shaft under pure torsion and calculation of shear stress

The distribution of shear stress on the cross-section of plastic metal solid circular shaft under pure torsion yielding,the applicability of complete plastic model assumption and the shear stress formula were researched.Based on the shear stress formula of circular shaft under pure torsion in elastic stage,the formula of torque in elastic stage and the definition of yield,it is obtained that the yielding stage of plastic metal shaft under pure torsion is only a surface phenomenon of torque-torsion angle relationship,and the distribution of shear stress is essentially different from that of tensile stress when yielding under uniaxial tension.The pure torsion platform-torsion angle and the shape of torque-torsion angle curve cannot change the distribution of shear stress on the shaft cross-section.The distribution of shear stress is still linear with the maximum shear stress τs.The complete plasticity model assumption is not in accordance with the actual situation of shaft under torsion.The experimental strength data of nine plastic metals are consistent with the calculated results of the new limiting strain energy strength theory(LSEST).The traditional yield stress formula for plastic shaft under torsion is reasonable.The shear stress formula based on the plane assumption in material mechanics is applicable for all loaded stages of torsion shaft.

碳化复合桩内外芯界面剪切特性试验研究

为了探究碳化复合桩内外芯界面的剪切特性,采用直剪试验研究不同法向应力条件下碳化黏土-透水混凝土界面的摩擦特性,得到不同参数对界面剪切特性的影响规律,并建立了基于无侧限抗压强度的界面剪切强度预测模型.结果表明:界面剪切强度、黏聚力、内摩擦角和界面摩擦角等指标先随碳化时间、氧化镁掺量和初始含水率的增加而增大,随后减小或趋于平稳;碳化黏土-透水混凝土界面剪切强度最高达399 kPa;界面剪切应力-剪切位移曲线有双曲线型和软化型2种类型,同时界面剪切强度与无侧限抗压强度呈线性关系,界面剪切强度约为碳化黏土无侧抗压强度的0.17~0.30倍.

风化花岗片麻岩砂类土抗剪强度参数预估模型

【目的】分析风化花岗片麻岩砂类土非饱和抗剪强度随含水率和压实度的变化规律。【方法】以皖西大别山区典型风化花岗片麻岩砂土填料为研究对象,采用静压成型法制备该砂类土20种不同含水率和压实度组合状态的非饱和试样,通过室内大型直剪试验分析含水率和压实度对其抗剪强度参数的影响,回归建立相应的综合关系模型,并验证其预估精度。【结果】在相同压实度下,土样黏聚力和内摩擦角分别与含水率比值(含水率与最佳含水率之比)成显著的单峰左偏态高斯型函数关系和幂函数负相关性;在相同含水率下,黏聚力和内摩擦角均与压实度成显著的对数函数正相关关系;所建立的抗剪强度参数与含水率、压实度之间的综合关系模型具有较高的预估精度。【结论】预估模型可用于预测该砂类土的似黏聚力强度特性,并可供同类土体强度参数建模参考。

酸雨环境下低矮RC剪力墙抗震性能试验研究与抗剪强度预测

为揭示酸雨环境中低矮RC剪力墙的抗震性能变化规律,在人工气候实验室中模拟酸雨环境,对5榀低矮RC剪力墙进行加速腐蚀,在达到预期腐蚀目标后对其进行拟静力加载试验。以此研究酸雨腐蚀程度相同情况下,不同设计参数对剪力墙试件承载力、变形等指标的影响。试验结果表明:酸雨环境下,H^(+)、SO_(4)^(2-)、NO_(3)^(-)等多种侵蚀离子将导致试件混凝土强度损失、钢筋锈蚀、保护层锈胀开裂与脱落;随轴压比的增加,墙体的开裂、屈服和峰值荷载增大,裂缝发展速度变慢,但其破坏时更突然;水平分布筋的增大对承载力提升不大,但可以约束剪力墙腹板混凝土,限制裂缝发展从而提升试件延性。在试验研究基础上,基于拉压杆模型提出了针对酸雨腐蚀的RC剪力墙抗剪强度预测公式,并验证了其准确性。所提模型可为酸雨侵蚀环境下RC剪力墙全寿命周期内的抗震性能评估提供理论支撑。

基于神经网络模型的预拌流态土剪切特性研究

为充分利用工程弃土,将其与固化剂和水充分拌和,制备一种回填后无需压实且工程性质良好的新型填筑材料。依托南京某基坑肥槽回填工程,对不同配比的预拌流态土进行直剪试验,研究预拌流态土的剪切特性,基于神经网络模型开展了预拌流态土剪应力-剪切位移预测研究。结果表明:预拌流态土剪应力-剪切位移曲线类型受水泥配合比、养护龄期和垂直压力影响;预拌流态土的抗剪强度和粘聚力受水灰比、垂直压力、养护龄期、水泥配合比影响;预拌流态土剪应力-剪切位移神经网络预测模型对抗剪强度的预测具有较高的精度。