A study of the strength characteristics of marine sediments utilizing a submersible: A. L. Inderbitzen and F. SimpsonASTM Spec. Techn. Publ. No. STP 501, 204–215 (1972)

One of the tasks of the Lockheed Missiles and Space Company's submersible Deep Quest has been to obtain detailed information on the strength characteristics of the sea floor. Continuing projects, carried out with a corer and a vane shear machine mounted on the submersible, are a comparison of in-place and laboratory vane shear strength values and an investigation of the lateral and vertical variability of in-place shear strength. The area being investigated for these projects is approximately 13 nautical miles southwest of San Diego, Calif., on the floor of the San Diego Trough at a depth of 4050 ft. Because the projects are still incomplete, no definitive conclusions can be made. However, initial results indicate inconsistencies in the difference between in-place and laboratory vane shear strength values. Lateral variability between in-place vane shear strength measurements does not appear to be related to distance test locations. Vertical variability in in-place vane shear strength values appears to decrease with depth into the sediment.     

扁铲侧胀试验计算地基承载力

简单介绍扁铲侧胀试验,首次提出用扁铲侧胀试验计算地基承载力的方法。利用上海地区部分重大工程中的扁铲 侧胀试验数据,在与室内土工试验、静力触探试验及十字板剪切试验的试验参数相关分析的基础上,经数理统计后给出了上 海地区用扁铲侧胀试验计算地基承载力的经验公式,并对其计算精度进行了评价。     

Cone penetration resistance equation as a function of the clay ratio, soil moisture content and specific weight

The cone penetrometer is a simple versatile device which is widely used to monitor the strength of a soil in terms of its resistance to the penetration of a standard cone. The soil penetration resistance is a function of soil moisture content, soil specific weight and soil type. The soil type is characterised by means of a clay ratio which is the ratio of the clay content of the soil to the content of silt and sand.Based on the classical bearing capacity theories for strip foundations, a general cone penetration resistance equation is developed to represent the variability of cohesion and friction angle by means of soil type and moisture content. The empirical relationship is shown to give an accurate prediction of the cone penetration resistance for a wide range of soils from a loamy sand to a heavy clay (clay ratios 0.10–1.60) and over a wide spectrum of soil moisture contents from 10 to 65% w/w.     

Soil response to track and wheel tractor traffic

Experiments were conducted on a Eudora silt loam to determine the effect of tracked and wheeled tractor traffic on cone penetration resistance and soil bulk density at three different soil-water content levels. Treatment plots were ripped to a depth of 0.45 m and irrigated 5 days prior to the experiment. Significant differences in penetration resistance and bulk density were observed between the treatments within the plowing depth (0.30 m). After the tractor passes, the average penetration resistance recorded was about 7.5% higher and the soil bulk density was about 3% higher in the wheel treatment plots. However, at the soil-water content level close to Proctor optimum (15% w/w), no significant difference was observed in the average penetration resistance of the two treatments.     

FFP在黏土中贯入过程的CFD模拟

圆锥静力触探法(Cone penetration test, CPT)广泛应用于土的抗剪强度测试中。在此基础上发展的自由落体式贯入仪(Free fall penetrometer, FFP),依靠自由下落获得的动能和自身重力势能贯入土中,不需要借助外部加载装置,提高其使用的便捷性。但在动力贯入过程中FFP与土的相互作用更为复杂,涉及到土体的率效应和拖曳阻力等的影响。因此,对FFP各项受力和相关参数的准确分析有助于提高其实用性以及测量的准确性。作者采用基于计算流体动力学(computational fluid dynamics, CFD)的分析软件ANSYS CFX 17.0模拟FFP在均质黏土中的贯入过程,借助动网格的大变形分析方法来模拟FFP贯入过程中的运动边界问题。提出了薄层单元法模拟FFP与土体的界面摩擦接触行为。在CFD模拟中,土体材料采用非牛顿流体来模拟,其剪切强度受土体切应变率的影响(即土体的率效应)。通过模拟贯入仪在黏土中以不同的速度贯入的过程,研究FFP的端部阻力和侧壁阻力与贯入速率、土体强度和密度、界面摩擦系数以及率效应参数之间的关系,建立了端部承载力系数、端部和侧壁率效应参数及拖曳系数的表达式,并提出了土体不排水抗剪强度的预测方法,为FFP测试数据的解析提供依据。      

The contribution of frictional contacts to the shear strength of coarse glass bead powders and slurries

This paper investigates the use of the shear vane technique as a means of determining frictional and cohesive interparticle force contributions to the shear strength of coarse glass bead powders and slurries. To this end, the shear strength of 203-μm glass beads in air and slurried in water and kaolinite suspensions was determined as a function of vane immersion depth, vane geometry, and container size. Both vane immersion depth and container diameter are found to significantly impact the shear strength measured using the vane technique. An equation describing interparticle frictional and cohesive contributions to shear vane measurements was derived in an effort to describe the experimental results. A Janssen stress distribution model for granular materials forms the basis for this equation and appears to explain the behavior of shear strength measurements at varying immersion depths. The presence of the Janssen stress distribution can affect the interpretation of shear vane results. Rather than shear strength being a material property, as is the case with flocculated colloid slurries and polymer solutions, shear strength becomes a process property where vane depth, container size, and container material can result in significant measurement variations. Such parameters should be considered before using the shear vane results on applications involving granular material components.US Department of Energy Environmental Management Science Program project no. 90162.     

静力触探锥头阻力的近似理论与实验研究进展

锥头阻力在静力触探试验中扮演着十分重要的角色.从不同角度,对触探中锥头阻力的研究进行简要阐述,对承载力理论、空洞膨胀理论、应变路径法及运动点位错法等几种理论分析方法进行了回顾.另外,对数值分析和实验研究的进展情况进行了叙述.并对各种方法的适用性进行了比较.承载力理论虽然简单,但忽略了土的压缩性和探杆周围初始应力的增加,所以不能精确地模拟锥头的深层贯入.空洞膨胀理论提供了一个分析锥头阻力的简单而较精确的方法,它考虑了土的压缩性(或膨胀性)和锥头贯入过程中锥杆周围应力增加的影响.但这种方法是将锥头贯入与空洞膨胀之间做了一个等效模拟,所以不同的模拟方法,得到的结果差别较大.应变路径法能够有效解决饱和粘土中的不排水贯入,但不适用于砂土.运动点位错法因为考虑了部分排水,所以能较好地预测固结系数,但采用了线弹性分析,故位错法在其他方面的应用还需要大量的试验验证.有限元法在处理锥头贯入这类慢侵彻问题时缺乏一种很好的处理技术,导致它在进行破坏荷载计算时有显著的误差和数值计算困难.标定槽试验将在验证和建立锥头阻力与土的性能关系方面继续起到一个重要作用,但其结果需经过校正后才可应用到现场.最后对该领域的研究趋势进行了讨论.      

An empirical model to predict soil bulk density profiles in field conditions using penetration resistance, moisture content and soil depth

Cylindrical soil probes measuring 300 mm in diameter by 300 mm in height were prepared in the laboratory using samples extracted from a well drained loamy soil (FAO classification: Vertic Luvisol). These probes were compacted at different moisture contents [3, 6, 9, 12, 15 and 18 (% w/w)] and using different compaction energies (9.81, 49.05, 98.1 and 981 J). The soil penetration resistance was determined by means of the ASAE 129 mm² base area cone and seven other different cones with base sizes of 175, 144, 124, 98, 74, 39 and 26 mm². The variability of the penetration resistance measurements increased as the size of the cone decreased. Nevertheless, the penetration resistance values proved to be independent of the cone used, as long as the size of the latter was equal to or greater than 98 mm². This confirms the possibility of using cones with areas smaller than the ASAE standard when measurements are to be carried out in dry soils with high levels of mechanical resistance. The experimental data were used to develop an empirical model, a linear additive model on a log–log plane, capable of estimating soil bulk density depending on soil penetration resistance, soil moisture content and depth. This model has provided good results under field conditions and has allowed soil bulk density profiles and accumulated water profiles to be accurately estimated.     

Cone resistance in sand by incremental method

A new method has been developed for the determination of cone resistance under drained conditions. Numerical methods are used for the solution of the differential equations of plasticity theory for soils and for the determination of the stress states in the soil produced by the penetration of the cone. It is assumed that the stresses produced by the penetration of the cone remain ‘locked in’ the soil and constitute boundary conditions for further penetration. The computation starts with the cone base at the surface and is continued by successively incrementing the depth by a small amount. Charts are given for the computation of cone resistance in sands for various friction angles. The importance of the effect of the shear stresses generated at the surface of the cone and characterized by the interface friction angle, δ, is discussed in detail.     

装甲钢/UHPC复合靶体抗侵彻性能试验与数值模拟研究

装甲钢/超高性能混凝土（UHPC）复合防护结构在重点工程中抵抗弹体的高速侵彻作用具有广泛的应用前景。为评估该复合结构的抗侵彻性能,对两种复合靶体开展侵彻试验与数值模拟研究。首先,开展了12发30 mm口径30CrMnSiNi2A弹体372~646 m/s速度侵彻复合靶试验。随后通过一系列静动态力学性能试验标定装甲钢材料的本构模型参数,并建立三维有限元模型对上述试验开展数值模拟分析。通过对比试验和数值模拟得到的弹体侵彻深度、残余弹体长度和装甲钢板的失效模式,验证了装甲钢本构模型参数的可靠性。进一步基于弹道效益系数对复合靶抗侵彻性能进行了定量评估。最后,确定了不同装甲钢板厚度复合靶体的临界贯穿速度,并对弹体侵彻复合靶的弹、靶失效模式进行了讨论。     

刚性平头弹正侵彻钢筋混凝土靶的阻力模型

本文基于素混凝土侵彻理论,将钢筋混凝土中钢筋的失效模式简化为弯曲剪切失效后,建立了刚性平头弹侵彻钢筋混凝土靶的阻力模型,侵彻深度的计算结果与Young公式吻合良好,表明本文提出的理论模型可较为合理地预测侵彻深度。进一步分析了不同着靶点的位置对弹体侵彻的影响,结果表明:当弹体直径与钢筋网眼尺寸的比值小于1时,弹体撞击到网眼中心处侵彻深度最大;当弹体直径与网眼尺寸的比值大于1时,最不利着靶点位置视其比值而定。最后,基于防护角度的最不利工况,建立了侵彻深度的工程计算公式。     

Evaluation of penetrometers for measuring soil strength

Cone index, as determined by a cone penetrometer, is frequently used as a measure of soil strength. The index is a compound parameter involving components of shear, compressive and tensile strength and soil metal friction. In order to assess the effect of soil type and condition on the relative contributions of these components to penetration resistance, the forces required to push blunt and sharp probes into two soils under a range of moisture contents and bulk densities were investigated. The maximum penetration force in homogeneous soil was not uniquely related to dry bulk density or cohesion, but varied with soil moisture content.At high and low moisture contents, the soil tended to interact with the shaft of the penetrometer thus increasing the resistance to penetration. At low moisture content, bodies of compressed soil formed in front of the probe, effectively changing the probe geometry.It was concluded that interpretation of cone index in typical layered field soils is difficult. Even in homogeneous soils, the proportion of shear, compressive and tensile components that the cone index reflects varies with soil condition.     

Effect of multiple passes of tractor with varying normal load on subsoil compaction

A field experiment was conducted on alluvial soil with sandy loam texture, in a complete randomized design, to determine the compaction of sub-soil layers due to different passes of a test tractor with varying normal loads. The selected normal loads were 4.40, 6.40 and 8.40 kN and the number of passes 1, 6, 11 and 16. The bulk density and cone penetration resistance were measured to determine the compaction at 10 equal intervals of 5 cm down the surface. The observations were used to validate a simulation model on sub-soil compaction due to multiple passes of tractor in controlled conditions. The bulk density and penetration resistance in 0–15 cm depth zone continuously increased up to 16 passes of the test tractor, and more at higher normal loads. The compaction was less in different sub-soil layers at lower levels of loads. The impact of higher loads and larger number of passes on compaction was more effective in the soil depth less than 30 cm; for example the normal load of 8.40 kN caused the maximum bulk density of 1.53 Mg/m³ after 16 passes. In 30–45 cm depth layer also, the penetration resistance increased with the increase in loads and number of passes but to a lesser extent which further decreased in the subsoil layers below 45 cm. Overall, the study variables viz. normal load on tractor and number of passes influenced the bulk density and soil penetration resistance in soil depth in the range of 0–45 cm at 1% level of significance. However, beyond 45 cm soil depth, the influence was not significant. The R² calculated from observed and predicted values with respect to regression equations for bulk density and penetration resistance were 0.7038 and 0.76, respectively.     

A tyre option for sugarcane haulout trucks to minimise soil compaction

Change in soil cone resistance was used as an indicator of soil compaction after the passage of haulout trucks running dual tyres or super single tyres. Cone resistance was measured to a depth of 0.6 m in the inter-row and in transects from the middle of one crop row to the middle of the adjacent row. Treatments consisted of one, two, three and four passes by both dual tyres and super single tyres and one and two passes of reduced pressure and standard pressure super single tyres aligned down the inter-row. Soil cone resistance increased with an increasing number of passes under the dual tyres. There was less change in soil cone resistance after the passage of super single tyres. A small reduction in soil cone resistance resulted when low tyre pressure was used compared with the standard tyre pressure in the super single tyres. Soil cone resistance was greater in the row after passage of the dual tyres compared with low-pressure super single tyres. There is an advantage in using super single tyres on haulout trucks compared with conventional dual tyres to minimise soil compaction.     

刚性弹丸侵彻钢筋混凝土的实验和简化分析模型

通过Φ57mm半穿甲弹对钢筋混凝土的垂直侵彻实验,得到了弹丸的撞靶速度、成坑深度、最大侵彻深度以及过载时程曲线等实验数据.对实验后钢筋的断裂特征进行分析,得到钢筋的典型破坏模式.将钢筋的破坏简化为弯曲+剪切断裂和弯曲+拉伸断裂这两种模式.根据混凝土侵彻模型和梁断裂失效理论,建立了刚性弹丸垂直侵彻钢筋混凝土的简化分析模型.将理论计算得到的侵彻深度、速度与过载时间历程分别与实验数据进行对比,结果表明两者吻合较好.研究表明,钢筋只对弹体侵彻过程产生局部影响,混凝土的抗侵彻阻力仍是钢筋混凝土抗侵彻阻力的主要组成部分.     

三维双连续铜/石墨自润滑复合材料的构筑及其摩擦磨损性能研究

以聚氨酯海绵为三维连续网络结构模板,采用浸渍法在聚氨酯海绵骨架表面均匀涂敷石墨浆料构筑具有三维连续网络结构的石墨骨架,然后在石墨骨架中填充铜合金粉,经排胶-热压烧结工艺制备石墨相和金属铜呈三维双连续复合型结构的铜/石墨自润滑复合材料.研究考察了三维双连续复合结构对材料承载能力和抗冲击破坏能力的影响,并探究了材料在重载作用下的摩擦磨损行为.结果表明：通过三维双连续结构设计,能够有效改变石墨相的富集状态和分布形式,并借助连续金属铜基体的高承载作用,显著提升材料在重载作用下的减摩抗磨性能.在180 N载荷下与轴承钢相对摩擦时,块体663铜合金和均相铜/石墨复合材料均出现急剧磨损并与摩擦配副发生“卡咬”现象,其中块体663铜合金与配副由于“卡咬”严重而停止试验,均相铜/石墨复合材料的磨痕深度达1.38 mm.然而,具有三维双连续结构的铜/石墨复合材料的摩擦系数可保持约在0.12左右,磨痕深度为0.16 mm,展现出优异的长时间耐磨损性能,磨损率约为5.3×10-6 mm3/(N·m).同时,该结构设计能够大幅减少石墨相与金属铜间的弱界面数量,并有效利用连续石墨相对裂纹传播路径的“歧化”引导和金...     

The measurement of the yield stress of liquids

An analysis has been made of different methods of measuring the yield stress of liquids. In the experimental program, a comparison is made of measurements of the yield stress using an Instron 3250 Rheometer in several geometries (cone-plate, parallel plate and eccentric disk) in shear flow and stress relaxation, a laboratory vane and a cone penetrometer. Good agreement has been obtained between the shear flow data and the laboratory vane, while stress relaxation appears to underestimate the yield stress.     

PIV measurements in the bottom boundary layer of the coastal ocean

Turbulence measurements were recently performed in the bottom boundary layer of the coastal ocean using a submersible PIV system. The system consisted of two 2 KǶ K digital cameras, operating simultaneously. Optical fibers were used to transmit light from a surface mounted pulsed dye laser to the sample areas. The system was mounted on a seabed platform that allowed the sample areas to be aligned to the current, and measurements to be made up to 10 m above the bed. Sample profiles and time series of mean velocity as well as structure functions are presented. A method to calculate the Reynolds shear stress that is not contaminated by surface wave motion and instrument misalignment is also described.     

单钢板混凝土剪力墙抗爆性能研究

钢板混凝土剪力墙作为一种新型的抗侧力构件，具有良好的耗能能力和抗冲击性能，已逐渐应用于建筑工程结构的抗震和防护结构的抗爆设计。设计了3个试件，分别为普通钢筋混凝土板、单侧钢板混凝土板和夹心钢板混凝土板，开展了钢板混凝土剪力墙的接触爆炸试验，并通过非线性程序LS-DYNA建立了3个钢板混凝土剪力墙试件的数值模型，对比分析了不同试件在接触爆炸作用下的动态响应、破坏模式和抗爆性能。试验和数值分析结果表明:接触爆炸作用下，试验设计的3种试件呈现3种破坏模式；普通钢筋混凝土板中部发生混凝土贯穿破坏，钢筋发生较大弯曲变形；单侧钢板混凝土板由于栓钉拔出发生钢板和混凝土分离，丧失整体性和继续承载能力；夹心钢板混凝土板发生上层混凝土压碎，夹心钢板、上层和下层混凝土板连接性能较强，整体性较好，具有继续承载的能力，且夹心钢板混凝土板跨中挠度和混凝土碎块飞溅距离较小。单侧钢板混凝土板和夹心钢板混凝土板配置钢筋网可以显著增强混凝土层和钢板的连接性能，有效减小上下层混凝土的碎裂和剥落，增强其整体性和抗爆性能。     

Effect of wetting and drying on soil physical properties

Agricultural soils are subject to seasonal wetting and drying cycles. Effect of drying stress, as influenced by one cycle of wetting and drying, on physical properties of a clay–loam soil was investigated in the laboratory. The physical properties studied were soil bulk density, cone penetration resistance, shear strength, adhesion and aggregate size and stability. Three drying stress treatments were made by wetting air-dried soil of initial moisture content of 12% (on dry weight basis) to three different higher moisture contents, namely 27, 33 and 40%, and then drying each of them back to their original moisture content of 12%. Thus, the soil was subjected to three different degrees of drying stress. The results showed that the soil strength indicated by cone penetration resistance and cohesion, and soil aggregate size, increased with the degree of drying stress. However, the soil bulk density did not change significantly with the drying stress.