Effect of slaking on direct shear behaviour of crushed mudstones

This study investigates the effects of wetting and drying cycles, known as slaking, on the strength-displacement characteristics of crushed mudstone. A series of direct shear tests was conducted by simulating cyclic wetting and drying under different stress conditions using a modified direct shear apparatus. The effects of the stress ratio, the density of specimen, the initial water content before wetting, the slaking index, and the number of wetting and drying cycles on the test results was investigated. Experiments were also performed on less-slakable materials, including crushed sand stone, silica sand and glass beads, to compare the results with the crushed mudstone. Considerable creep displacement on the crushed mudstones was observed during both drying and wetting phases under the constant shear stress conditions. The creep displacement during the drying was more significant than during the wetting phase. The creep displacement accumulated with progressive wetting and drying cycles. The drying-induced displacement was observed when the water content became smaller than the amount of water absorption of the mudstone specimens. Correspondingly, a gradual decrease of the peak stress ratio was observed with the number of wetting and drying cycles. In contrast to the mudstones, the influence of cyclic wetting and drying on the crushed sand stone, silica sand and glass beads is almost negligible. A higher slaking index, a lower water content before wetting, and lower initial density accelerate the slaking of mudstones.     

Analysis of TerraSAR-X data sensitivity to bare soil moisture, roughness, composition and soil crust

Soils play a key role in shaping the environment and in risk assessment. We characterized the soils of bare agricultural plots using TerraSAR-X (9.5 GHz) data acquired in 2009 and 2010. We analyzed the behavior of the TerraSAR-X signal for two configurations, HH-25° and HH-50°, with regard to several soil conditions: moisture content, surface roughness, soil composition and soil-surface structure (slaking crust).The TerraSAR-X signal was more sensitive to soil moisture at a low (25°) incidence angle than at a high incidence angle (50°). For high soil moisture (> 25%), the TerraSAR-X signal was more sensitive to soil roughness at a high incidence angle (50°) than at a low incidence angle (25°).The high spatial resolution of the TerraSAR-X data (1 m) enabled the soil composition and slaking crust to be analyzed at the within-plot scale based on the radar signal. The two loamy-soil categories that composed our training plots did not differ sufficiently in their percentages of sand and clay to be discriminated by the X-band radar signal.However, the spatial distribution of slaking crust could be detected when soil moisture variation is observed between soil crusted and soil without crust. Indeed, areas covered by slaking crust could have greater soil moisture and consequently a greater backscattering signal than soils without crust.     

精制糖结块问题与熟化仓技术的探讨

针对精制糖易结块的问题,选取公司自产精制糖和其他2个不同精制糖厂家的同质量产品作试验比较,找出影响精制糖结块的原因,制定措施,同时介绍了熟化仓技术,为解决精制糖结块问题提供参考,促进糖业生产技术的发展。     

高填方地基填筑方案的选择与设计

巫山县新城污水处理厂高填方地基的最大填方高度为75m,填筑方量约56.7万m3.当三峡水库蓄水至175m时,填筑体绝大部分处于库水位以下,设计中必须考虑填方体的整体稳定性和湿化变形引起高填方不均匀沉降对直径为70m的氧化沟的不利影响.在污水处理厂厂区建(构)筑物基础设计中,采用短刚性桩复合地基将部分荷载由桩传递到深部强夯层面上去,减少氧化沟边缘与中心点的不均匀沉降,并有效地减少总沉降.本文通过巫山县新城污水处理厂高填方地基工程实例,详尽地介绍了高填方工程填筑方案的选择与设计.     

Effect of initial water content and shear stress on immersion-induced creep deformation and strength characteristics of gravelly mudstone

Soft sedimentary rocks undergo deterioration due to weathering induced by dry–wet cycles in a process known as slaking. To investigate the effect of the initial water content and shear stress on the immersion-induced creep deformation and strength characteristics of gravelly mudstone (slaking index = 1 and 2), creep tests were conducted using a modified direct-shear-test apparatus under different creep-stress ratios. Crushed mudstone with different degrees of compaction and initial water content was subjected to immersion under the creep-shear-stress conditions. After the creep shear and vertical displacements stabilized, a monotonic shear loading was applied. During creep immersion, the increment in the creep-shear displacement increases as the creep-stress ratio increases and the initial water content and/or degree of compaction decrease. Retaining a high initial water content in crushed mudstone is recommended to maintain its shear-stress stability. Under the same density, the peak shear strength decreased with an increase in the increment of the creep-shear displacement during creep immersion. The results indicate that the occurrence of immersion-induced creep deformation in addition to slaking can result in the deterioration of slope stability.     

Preparation of slaking resistant CaO aggregate from lightweight CaCO3 with oxide addition

CaO aggregate was sintered from reagent-grade lightweight CaCO₃ powder by the addition of 0-20% (molar ratio) MgO and ZrO₂, respectively. The results showed that the CaO derived from lightweight CaCO₃ was highly sinterable and compact CaO aggregate with relative density above 96% was obtained after sintering at 1400 °C for 2 h, but further increase of compactness was restrained due to the occurrence of abnormal grain growth. The densification of the aggregate was promoted due to the behavior of oxide addition on restraining the grain growth of CaO. With increasing the amount of oxide addition, the microstructure of CaO aggregate underwent a restructuration process. Homogeneous microstructure, with well growing MgO grains occupying most of the boundary triple points of CaO grain, formed by the addition of 20% MgO. Especially when 20% ZrO₂ was added, CaZrO₃ layer formed around CaO grains. The slaking resistance of the aggregate was appreciably improved due to the promotion of densification, the formation of CaO solid solution (while MgO added) and the modification of microstructure.     

Effects of slaking and degree of compaction on the mechanical properties of mudstones with varying slaking properties

An earthquake in Suruga Bay off Shizuoka Prefecture in 2009 caused an embankment near the Makinohara Service Area of the Tomei Expressway to fail. One of the causes of this failure was the slaking progression of the Neogene Period mudstone in the lower portion of the embankment.The objective of this study is to understand how the degree of slaking affects the compressive and shearing behaviors of crushed mudstone aggregates. A drying-immersion cycle test is proposed; it illuminates how the number of repeated drying and immersion cycles affects the slaking of fine-grained material. Unconfined compression, triaxial compression, and one-dimensional consolidation tests were carried out on crushed mudstone aggregate specimens created by compaction.Consequently, the unconfined compressive strength and maximum deviator stress in the triaxial compression tests on the crushed mudstone aggregates dropped as the grains became finer due to slaking even if the initial density was the same. The compressibility increased and the consolidation yield stress decreased as the grains became finer particles. The degree to which slaking had progressed affected these characteristics as well.