Gradation affects basic mechanical characteristics of Chinese calcareous sand as airport subgrade of reefs

Abstract

Construction of the reefs in the South China Sea is a significant foundation to the secure stability and economic development of China. The construction of an airport runway is necessary for this realization. The calcareous sand is the main primary material in the runway construction. A certain type of calcareous sand near a certain reef of the South China Sea was studied in this paper. To investigate this specific calcareous sand, quartz sand was used as a reference for comparison. Microscopic 3-D imaging, compression and triaxial tests were conducted to test the micro, squeezing and shear properties. The effect mechanism of gradation on the calcareous sand’s compressibility and shear characteristics are discussed from a mesoscopic viewpoint using 3-D morphology. Calcareous sand particles are multiangular and flatter in comparison with quartz sand. The larger the particle sizes are, the more different the two sands’ morphologies are. The compressibility of calcareous sand is greater, and the effect of the coarse fraction (5–1?mm) content in the gradation plays the most significant role in this feature. When the coarse particles’ content is less than 25% and the mass ratio of the middle and fine particles (M) is constant, there is the worst coarse fraction content causing the calcareous sand to be most likely compressed. The worst coarse fraction content decreases with the increase in M, and an empirical formula is proposed. When the gradation, relative density and confining pressure are the same, the peak shear stress and strain of calcareous sand are all at a high level. The effect of confining pressure is manifested in calcareous sand. The shear strength and dilation of calcareous sand are also most affected by the medium coarse fraction (5–0.25?mm) content.     

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生物胺对锯缘青蟹大颚器发育的调节作用

雌性锯缘青蟹(Scylla serrata)于实验的第1天、第5天、第10天，分别注射100μL剂量为1μg／g体质量的5-HT，OA和DA，第15天解剖。结果表明，5-HT对锯缘青蟹大颚器发育具有显的促进作用，OA和DA的作用不明显。经免疫细胞化学检测，大颚器内存在5-HT免疫阳性细胞，免疫阳性细胞多数为卵圆形，少数具有很长的胞突，该结果首次为5-HT参与大颚器的生理活动提供了形态学证据。     

石盐的36Cl断代法

讨论了~936)Cl的成因、~(36)Cl断代法的原理及测试方法。自1987年以来,应用该方法测得柴达木盆地尕斯库勒湖和大浪滩湖石盐的沉积年龄,并与~(14)C,~(230)Th和古地磁测年法所测得的年龄数据进行对比,结果均在误差(1δ)范围内相吻合,表明石盐的~(36)Cl断代法是可行的,获得的年龄数据是可靠的。     

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针对当前从事钙质超微化石定量研究使用的不同制样方法，简要介绍了适用于光学显微镜（LM）和扫描电子显微镜（SEM）的传统涂片法、小珠校准法、随机沉淀法和过滤法的主要流程和设备要求，同时对不同方法的优缺点进行了评述。     

厦门海沧海岸地区采石废弃地生态恢复研究

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Studies on Genus Cryptomonas from China seas

ＩＮＴＲＯＤＵＣＴＩＯＮＣｒｙｐｔｏｍｏｎａｓｉｓｕｎｉｃｅｌｌｕｌａｒｂｉｆｌａｇｅｌｌａｔｅｗｈｉｃｈｉｓａｃｏｍｍｏｎｇｅｎｕｓｏｆＣｒｙｐｔｏｐｈｙｔａ .Ｔｈｅｃｅｌｌｓａｒｅｕｓｕａｌｌｙｓｔｒｏｎｇｌｙｃｏｍｐｒｅｓｓｅｄｌａｔｅｒａｌｌｙ .ＴｈｅｒｅａｒｅｏｎｅｏｒｔｗｏｌａｒｇｅＣｈｌｏｒｏｐｌａｓｔｓｔｈａｔｃｏｎｔａｉｎｃｈｌｏｒｏｐｈｙｌｌａ ,ｃ ,ｓｏｍｅｃｈａｒａｃｔｅｒｉｓｔｉｃｃａｒｏｔｅｎｏｉｄｓａｎｄｐｈｙｃｏｂｉｌｉｎｐｉｇｍｅｎｔｓ (Ｈｕｅｔａｌ.,1 997;Ｗｅｉ…     

长牡蛎四倍体诱导的研究

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Longshore drift estimation using fluorescent tracers: New insights from an experiment at Comporta Beach, Portugal

A fluorescent sand-tracer experiment was performed at Comporta Beach (Portugal) with the aim of acquiring longshore sediment transport data on a reflective beach, the optimization of field and laboratory tracer procedures and the improvement of the conceptual model used to support tracer data interpretation.

The field experiment was performed on a mesotidal reflective beach face in low energetic conditions (significant wave height between 0.4 and 0.5 m). Two different colour tracers (orange and blue) were injected at low tide and sampled in the two subsequent low tides using a high resolution 3D grid extending 450 m alongshore and 30 m cross-shore. Marked sand was detected using an automatic digital image processing system developed in the scope of the present experiment.

Results for the two colour tracers show a remarkable coherence, with high recovery rates attesting data validity. Sand tracer displayed a high advection velocity, but with distinct vertical distribution patterns in the two tides: in the first tide there was a clear decrease in tracer advection velocity with depth while in the second tide, the tracer exhibited an almost uniform vertical velocity distribution. This differing behaviour suggests that, in the first tide, the tracer had not reached equilibrium within the transport system, pointing to a considerable time lag between injection and complete mixing. This issue has important implications for the interpretation of tracer data, indicating that short term tracer experiments tend to overestimate transport rates. In this work, therefore, longshore estimates were based on tracer results obtained during the second tide.

The estimated total longshore transport rate at Comporta Beach was 2 × 10^− 3 m³/s, more than four times larger than predicted using standard empirical longshore formulas. This discrepancy, which results from the unusually large active moving layer observed during the experiment, confirms the idea that most common longshore transport equations under-estimate total sediment transport in plunging/surging waves.