Experimental Investigation on the Pressure Distribution Law and Calculation Method of Muddy Water with High Silt Content

The pressure distribution law of muddy water with high silt content has great influence on the stress and strain calculation of the dam body. Currently, there is a few research studies referring to the calculation method of high silt content muddy water pressure, which leads to no reliable theoretical basis for muddy water pressure calculation in dam design. In this paper, muddy water with high silt content was prepared and the imitation tests and model tests were carried out to investigate the pressure distribution law. Based on the test result analysis, it is indicated that the muddy water with high silt content is also in a flowable and viscous state, which is consistent with the law of fluid behavior; the horizontal pressure is equal to the vertical pressure at the same position, and this relationship is generally time independent; through the test result analysis, a pressure formula for muddy water with high silt content is proposed; through comparison between the pressure formula-calculated results and monitoring data, it is indicated that the proposed pressure formula is applicable in the calculation of muddy water pressure. The formula can be a useful tool in the dam safety and design calculation.

Strength and Microstructural Assessment of Reconstituted and Stabilised Soft Soils with Varying Silt Contents

The study of the strength of reconstituted and stabilised soft soils is very important in geotechnical engineering. The soil particles, such as clay, sand, and silt play important roles in determining the behaviour of soils. The behaviour of clay and sand particles are unique; however, the behaviour of silt particles lie in a transitional form between sand and clay. Therefore, this paper seeks to investigate (a) the effect of silt contents on the strength of soft soils; (b) the effect of silt content on the strength of cement-stabilised soft soils; and (c) the microstructure of the soft soil specimens stabilised by cement with varying particle size distribution. A series of tests consisting in consolidated, isotropic undrained (CIU) triaxial tests, unconfined compressive strength (UCS) tests, and scanning electron microscope (SEM) images were conducted in this study to achieve these objectives. In conclusion, the relationship between the silt content and critical state behaviour of soft soils (both clay and silt particles) are proposed. For the cement-stabilised specimens, the unconfined compressive strength increases with the increase in silt content when the cement content is 10%. However, the UCS decreases with the increase in silt content when cement content is 30%. With cement content ranging from 15–25%, the UCS increases at first with the increase of silt content but decreases once the silt content reaches a ‘saturation’ point.

Sediment mobilization by bottom trawls: a model approach applied to the Dutch North Sea beam trawl fishery

Bottom trawls impact the seafloor and benthic ecosystem. One of the direct physical impacts is the mobilization of sediment in the wake of trawl gear components that are in contact with or are close to the seabed. The quantity of sediment mobilized is related to the hydrodynamic drag of the gear components and the type of sediment over which they are trawled. Here we present a methodology to estimate the sediment mobilization from hydrodynamic drag. The hydrodynamic drag of individual gear components is estimated using empirical measurements of similarly shaped objects, including cylinders, cubes, and nets. The method is applied to beam trawls used in the Dutch North Sea flatfish fishery and validated using measurements of beam trawl drag from the literature. Netting contributes most to the hydrodynamic drag of pulse trawls, while the tickler chains and chain mat comprise most of the hydrodynamic drag of conventional beam trawls. Taking account of the silt content of the areas trawled and the number of different beam trawl types used by the fleet, sediment mobilization is estimated as 9.2 and 5.3 kg m−2 for conventional 12 m beam and pulse trawls, respectively, and 4.2 and 4.3 kg m−2 for conventional 4.5 m beam and pulse trawls.

Geology and geotechnical investigations of part of the Anambra Basin, Southeastern Nigeria: implication for gully erosion hazards

Background Geologic and geotechnical conditions of soils where Nanka and Ajali Formations outcropped in Anambra Basin, Southeastern Nigeria were investigated and accessed. This was done using detailed mapping and mechanical soil laboratory tests to unravel the genesis and continued expansion of gully erosion in the study areas. Results Field study revealed that gully erosions are more pronounced in the study area with poor vegetation cover and a high degree of slope steepness. Grain size analysis revealed that the soils of the Nanka Formation have an average sand content value of 90.90% (sandy) and silt content value of 3.0% (low fine portions). The plasticity index of the fine portions indicates that the soils are weak plastic, with a mean value of 5.29%. The soils have an average cohesion value of 0.30 kg/cm2 indicating a very weak cohesion. The soils are highly permeable; with an average value of 2.67 × 10–3 cm/s. The compaction test further revealed that the soils are loosely compacted. The soils for the Ajali Formation have an average sand content value of 95.10% (sandy) and silt content value of 1.43% (low fine portions). The plasticity index of the fine portions indicates that the soils are weak plastic, with a mean value of 2.70%. The soils have an average cohesion value of 0.30 kg/cm2 indicating a very weak cohesion. The soils are highly permeable; with an average value of 2.70 × 10–3 cm/s. The compaction test revealed that the soils are loosely compacted. Conclusion After field surveys and laboratory analyses, it was found that the gully erosions have been developing respectively on steep slopes and non-vegetated areas, and their genesis facilitated by the cohesionless and very permeable nature of the sandy formations. Following those key findings, it was proposed many practices (agronomic and engineering mainly) that can help mitigate the formations as well as the expansion of this very damaging hazard type. The potential implications of these gully erosion include damaging of buildings, residential houses, bridges, and roads, loss of farmland and vegetation, isolation of villages and towns, increased migration of inhabitants as well as degradation of agricultural fertile land.

Geology and Geotechnical Investigations of the Anambra Basin, Southeastern Nigeria: Implication for Gully Erosion Hazards

BackgroundGeologic and geotechnical conditions of soils where Nanka and Ajali Formations outcropped in Anambra Basin, Southeastern Nigeria were investigated and accessed. This was done using detailed mapping and mechanical soil laboratory tests to unravel the genesis and continued expansion of gully erosion in the study areas. ResultsField study revealed that gully erosions are more pronounced in the study area with poor vegetation cover and a high degree of slope steepness. Grain size analysis revealed that the soils of the Nanka Formation have an average sand content value of 90.90% (sandy) and silt content value of 3.0% (low fine portions). The plasticity index of the fine portions indicates that the soils are weak plastic, with a mean value of 5.29%. The soils have an average cohesion value of 0.30kg/cm2 indicating a very weak cohesion. The soils are highly permeable; with an average value of 2.67x10-3 cm/sec. The compaction test further revealed that the soils are loosely compacted. The soils for the Ajali Formation have an average sand content value of 95.10% (sandy) and silt content value of 1.43% (low fine portions). The plasticity index of the fine portions indicates that the soils are weak plastic, with a mean value of 2.70%. The soils have an average cohesion value of 0.30kg/cm2 indicating a very weak cohesion. The soils are highly permeable; with an average value of 2.70x10-3 cm/sec. The compaction test revealed that the soils are loosely compacted.ConclusionsAfter field surveys and laboratory analyses, it was found that the gully erosions have been developing respectively on steep slopes and non-vegetated areas, and their genesis facilitated by the cohesionless and very permeable nature of the sandy formations. Following those key findings, it was proposed many practices (agronomic and engineering mainly) that can help mitigate the formations as well as the expansion of this very damaging hazard type. The potential implications of these gully erosion include damaging of buildings, residential houses, bridges and roads, loss of farmland and vegetation, isolation of villages and towns, increased migration of inhabitants as well as degradation of agricultural fertile land.

Threshold silt content dependency on particle morphology (shape and size) of granular materials: review with new evidence

The threshold silt content is well known as a key parameter affecting the mechanical response of binary granular assemblies considering particle characteristics (size and shape). In this context, the threshold silt content (TSC) is determined from different laboratory tests based on packing density response (emax and emin versus silt content «Sc») and theoretical approaches proposed by several researchers in the specialized published literature using the characteristics of host sand and silt [emax(sand), emin(sand) , emax(silt) , emin(silt) , Gs , Gf and x]. The analysis of the recorded data indicates that the TSC derived from the (emax) curve appears more reliable than that obtained from the (emin) one. Moreover, it is found that the proposed analytical methods are suitable to quantify the threshold silt content (TSC) than that determined experimentally using the packing density (emax and emin). In addition, the test results show that the new introduced ratios [(D50s×As)/(D50f×Af)] and [(Cus×As)/(Cuf×Af)] determined based on particle characteristics (shape and size) appear as appropriate parameters for predicting the threshold silt content (TSC) of sand-silt mixture of the compiled data from the published literature as well as that of the present research related to Chlef sand, Fontainebleau sand and Hostun sand mixed with Chlef silt.

Study on Effect of Different Compaction Methods of Aeolian Sand in Taklimakan Desert by Content of Powder Clay

The wind-blown sand in Taklimakan Desert was mixed with powder and clay particles to carry out heavy compaction and surface vibration compaction tests. The results show that the surface vibration compaction effect of aeolian sand is better when the water content is extremely low or saturated, but the effect is worse when the water content is about 2% ~ 4%, but it is still better than heavy compaction. With the increase of silt content, the surface vibration compaction effect decreases little in a wide range, but at and near the boundary where the dry compaction effect changes from obvious to inconspicuous, the surface vibration compaction effect decreases rapidly, which is soon lower than that of heavy compaction. In addition, with the increase of silt content, the reduction degree of surface vibration compaction effect is also affected by water content: the reduction is smaller when the water content is extremely low, followed by the reduction when saturated or optimal water content, and the reduction is the largest when the water content is about 2% ~ 4%. The research results are beneficial to the popularization and application of surface vibration compaction, especially in the dry compaction technology of aeolian sand subgrade.