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Bashar Tarawneh 《地学前缘(英文版)》2017,8(1):199-204
Standard Penetration Test(SPT) and Cone Penetration Test(CPT) are the most frequently used field tests to estimate soil parameters for geotechnical analysis and design.Numerous soil parameters are related to the SPT N-value.In contrast,CPT is becoming more popular for site investigation and geotechnical design.Correlation of CPT data with SPT N-value is very beneficial since most of the field parameters are related to SPT N-values.A back-propagation artificial neural network(ANN) model was developed to predict the N6o-value from CPT data.Data used in this study consisted of 109 CPT-SPT pairs for sand,sandy silt,and silty sand soils.The ANN model input variables are:CPT tip resistance(q_c),effective vertical stress(σ'_v),and CPT sleeve friction(f_s).A different set of SPT-CPT data was used to check the reliability of the developed ANN model.It was shown that ANN model either under-predicted the N_(60)-value by 7-16%or over-predicted it by 7-20%.It is concluded that back-propagation neural networks is a good tool to predict N_(60)-value from CPT data with acceptable accuracy. 相似文献
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Current techniques for liquefaction screening, ground modification for liquefaction mitigation, and post-improvement verification rely on knowledge gained from extensive research on clean sands, field observations of liquefied ground, and judicial correlation of normalized penetration resistance [(N1)60,qc1N] or shear wave velocity (vs1) data with field liquefaction observations. Uncertainties prevail on the direct extrapolation of such techniques for silty soil sites. This paper examines laboratory data on liquefaction resistance, strength, and vs1 of sands and silty soils using grain contact density as the basis. Effect of silt content on cyclic resistance, strength, mv, and cv is examined in this light. Rational insights on effects of silt content on the current screening techniques based on (N1)60, qc1N, and vs1 to silty soils are offered. Recent advances and modifications to the traditional densification, drainage, and permeation grouting techniques to make them viable for silty soils are discussed. 相似文献
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The effect of repeated freezing and thawing cycles on an experimentally-produced laminated silt loam was studied with the purpose of obtaining more insight into the genesis of macro- and microstructures observed in the loessic formations of Northwestern Europe. The laminated silt loam was subsequently subjected to 18 cycles of alternate freezing and thawing. The minimum temperature recorded after 11 days of frost was ? 7°C at a depth of 5 cm and ? 4°C at 29 cm. The underlying sediments, compact loam (except its upper part) and sand, always remained unfrozen. The experiment reproduced a seasonal superficially frozen ground. New structures and microfabrics in the form of vesicles, platy structures, shear planes, and micro-undulations were created by ice segregation and thawing, mechanical stress and subsequent frost-creep. The impact of the freezing and thawing cycles is very strong, all the laminae being deformed or broken. Judging by the abundance and the diversity of the structures created, freezing is a more important process than simple drying without frost. As is evidenced by the range in temperature chosen for the experiment and the low number of cycles, these structures do not necessarily require severe climatic conditions to develop, unlike frost cracks or ice wedge casts. They could develop in winter conditions similar to those present today in the French Southern Alps. 相似文献
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Janet S. Wright 《Sedimentary Geology》2007,202(3):337-351
Quartz silt is a widespread detrital sediment with large aeolian (loess) and alluvial silt deposits forming important components of many contemporary landscapes. Despite research findings which indicate that a range of opportunities exist for the comminution of quartz into silt particles within a wide variety of geomorphic environments (e.g. glacial grinding, fluvial comminution, aeolian abrasion, frost weathering, salt weathering, insolation weathering and deep weathering), the ‘glacial-aeolian’ hypothesis has traditionally been favoured as the most likely explanation for loess formation and loess is seen as primarily a Quaternary phenomenon. As a consequence there has been a tendency to underestimate sediment inputs into loess systems by geomorphological processes operating within pre-Quaternary environments. In particular, earth scientists may have considerably underestimated the role of weathering in global silt generation, as there are now many references to the existence of a patchy but widespread distribution of pre-Quaternary weathering profiles across the glacial and periglacial landscapes of the Northern Hemisphere (e.g. North America, British Isles, north and central Europe), landscapes within which many of the classical loess deposits are located. These observations suggest that weathering profiles may have covered large tracts of the Northern Hemisphere land surface prior to the Quaternary glaciations. This, in turn, may have important implications for quartz silt generation as: (1) experimental studies indicate that many weathering processes are capable of generating significant quantities of silt-sized debris, and (2) particle characteristics displayed by saprolitic material that has developed on quartz rich crystalline source rocks often include significant quantities of either silt-sized material, or quartz grains that are weakened by weathering derived microfractures. Thus, weathering profiles may represent ‘mines’ of actual and potential quartz silt, available for release into sedimentary systems when these profiles are subsequently reworked by geomorphological processes such as glacial, fluvial and aeolian erosion. 相似文献
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