Treatment of Collapsibility of Gypseous Soils by Dynamic Compaction     

Mohammed Y. Fattah  Hawraa H. M. al-Musawi  Firas A. Salman 《Geotechnical and Geological Engineering》2012,30(6):1369-1387

Gypseous soils are distributed in vast areas and various regions of Iraq and other countries. Many foundation failure problems that occur in these soils are associated with percolation of water and dissolution of gypsum. Many attempts were made by several researchers to treat and improve the properties of gypseous soils to decrease the dissolution of gypsum and collapse potential of these soils. The purpose of the present work is to investigate the effect of dynamic compaction process on the behaviour of gypseous soils. Extensive laboratory tests are carried out to study the geotechnical properties and the behaviour of three gypseous soils of different gypsum contents; 60.5, 41.1 and 27?%. The tests included compaction characteristics, compressibility, and collapsibility tests for samples tested before and after treatment by dynamic compaction process under different number of blows, falling weights and heights of falling of the weights. Three weights are used to compact the samples, namely; 2, 3 and 5?kg. The number of blows is varied between 20 and 40, while three heights of drop are tried (35, 50 and 65) cm. The results showed that the best improvement in compressibility is achieved when the sample is compacted by 20 blows; above this number a negligible decrease in the compression index C_C is obtained. As the gypsum content increases, the dynamic compaction has greater effect on improvement of compressibility of the soil, while as the height of drop increases, the compression index C_C decreases.  相似文献   

Relative Sea Level Changes in Maldives and Vulnerability of Land Due to Abnormal Coastal Inundation   总被引：1，自引：0，他引：1  

Tariq Masood Ali Khan  Dewan Abdul Quadir  T. S. Murty  Anwarul Kabir  Fahmida Aktar  Majajul Alam Sarker 《Marine Geodesy》2013,36(1-2):133-143

Oceanic Islands in the Pacific and Indian Oceans have extremely small land areas, usually less than 500 km2, with maximum height about 4 m above sea level. The Republic of Maldives is an independent island nation in the Indian Ocean south of Sri Lanka which stretches vertically in the Indian Ocean from 07° 06'N - 0° 42'S. The land area of this island country is about 300 km2, and none of Maldives' 1190 islands has an elevation more than 3 m above sea level. In fact the Maldives has the distinction of being the flattest country on earth, making it extremely vulnerable to the effects of global warming. Of the south Asian countries, the Maldives is the most vulnerable nation, facing severe consequences as a result of global warming and sea level rise (SLR). Because of their obvious vulnerability to SLR, the Government of Maldives is very much concerned about climate change. As global warming and the related SLR is an important integrated environmental issue, the need of the hour is to monitor and assess these changes. The present article deals mainly with the analysis of the tidal and Sea Surface Temperature (SST) data observed at Male and Gan stations along the Maldives coast in the northern and southern hemispheres, respectively. The objective of the analysis is to study the trends of these parameters. Trend analysis is also performed on the corresponding air temperature data of both stations. The results show that Maldives coastal sea level is rising in the same way (rising trend) as the global sea level. The mean tidal level at Male has shown an increasing trend of about 4.1 mm/year.Similarly at Gan, near the equator,it has registered a positive trend of about 3.9 mm/year.Sea level variations are the manifestations of various changes that are taking place in the Ocean-Atmosphere system. Therefore, the variations in SST and air temperature are intimately linked to sea level rise. It is found that SST and air temperature have also registered an increasing trend at both stations. The evidence of rising trends suggest that careful future monitoring of these parameters is very much required. Tropical cyclones normally do not affect the Maldives coast. However, due to its isolated location, the long fetches in association with swells generated by storms, that originated in the far south have resulted in flooding. Thus the rising rate of sea level with high waves and flat topography have increased the risk of flooding and increased the rate of erosion and alteration of beaches.  相似文献   

The use of vertical electrical sounding resistivity method for the location of low salinity groundwater for irrigation in Chaj and Rachna Doabs     

Pervaiz Sikandar  Allah Bakhsh  Muhammad Arshad  Tariq Rana 《Environmental Earth Sciences》2010,60(5):1113-1129

A geoelectrical resistivity survey using vertical electrical sounding (VES) was conducted at Chaj Doab (land between rivers Jhelum and Chenab, Pakistan) and Rachna Doab (land between rivers Chenab and Ravi, Pakistan), with the objective of investigating groundwater conditions. A total of 90 sites were selected with 43 sites in Chaj and 47 sites in Rachna Doabs. The resistivity meter (ABEM Terrameter SAS 4000, Sweden) was used to collect the VES data by employing a Schlumberger electrode configuration, with half current electrode spacings (AB/2) ranging from 2 to 180 m and the potential electrode (MN) from 1 to 40 m. The field data were interpreted using the Interpex IX1D computer software and the resistivity versus depth models for each location was estimated. The outputs of subsurface layers with resistivities and thickness presented in contour maps and 3-D views by using SURFER software were created. A total of 102 groundwater samples from nearby hydrowells at different depths were collected to develop a correlation between the aquifer resistivity of VES and the electrical conductivity (EC) of the groundwater and to confirm the resulted geophysical resistivity models. From the correlation developed, it was observed that the groundwater salinity in the aquifer may be considered low and so safe for irrigation if resistivity >45 Ω m, and marginally fit for irrigation having resistivity between 25 and 45 Ω m. The study area has resistivities from 3.9 to 2,222 Ω m at the top of the unsaturated layer, between 1.21 and 171 Ω m, in the shallow aquifers, and 0.14–152 Ω m in the deep aquifers of the study area. The results indicate that the quality of groundwater is better near the rivers and in the shallow layers compared to the deep layers.  相似文献   

Recent Sea Level and Sea Surface Temperature Trends Along the Bangladesh Coast in Relation to the Frequency of Intense Cyclones     

Tariq Masood Ali Khan  O. P. Singh  Md. Sazedur Rahman 《Marine Geodesy》2000,23(2):103-116

Bangladesh, one of the most densely populated countries in the world, is a victim of frequent natural calamities like tropical cyclones, tornadoes, floods, storm surges and droughts. Now the sea level rise (SLR) has also been included in these natural calamities. The SLR is likely to have greater impact on that part of Bangladesh having low topography and a wide flood plain. Since 21% of the population lives in the low coastal belt, any increase in sea level will be a problem of ominous proportion for Bangladesh. Since the cyclogenesis enhances over the Bay of Bengal during May and November, the sea level and sea surface temperature (SST) trends of these two months have been analyzed and calculated. The results of the selected stations one in the eastern coast and another in the western coast of Bangladesh show that Bangladesh coastal sea level is rising in the same way as the global sea level, but the magnitude is quite different. The difference in the behavior of sea level rise along the Bangladesh coast and the global trend may be due to the tectonic activity such as subsidence of the land. The mean tide level at Hiron Point (in Sunderbans) has shown an increasing trend of about 2.5 mm/year in May and 8.5 mm/year in November. Similarly near Cox?s Bazar (in the eastern coast of Bangladesh) it has registered a positive trend of about 4.3 mm/year in May and 10.9 mm/year in November. Thus the increment in the sea level along the Bangladesh coast during cyclone months is much more pronounced. In coastal waters near Hiron Point the SST has registered an increasing trend of about 1°C in May and 0.5°C in November during the 14-year period from 1985?1998. Near Cox?s Bazar, SST has shown a rising trend of about 0.8°C in May and about 0.4°C in November during the same 14-year period. The magnitude of SST trend is slightly more along the west coast. Any change in the frequency and intensity of tropical cyclones will have far reaching implications in the South Asian region. The rise in SST in the cyclone months seems to be correlated with the frequency and intensity of tropical cyclones. During these months, an increasing trend in the frequency and intensity of severe cyclones has been observed.  相似文献   

Observational evidence for stellar mass black holes     

Tariq Shahbaz 《Journal of Astrophysics and Astronomy》1999,20(3-4):197-210

I review the evidence for stellar mass black holes in the Galaxy. The unique properties of the soft X-ray transient (SXTs) have provided the first opportunity for detailed studies of the mass-losing star in low-mass X-ray binaries. The large mass functions of these systems imply that the compact object has a mass greater than the maximum mass of a neutron star, strengthening the case that they contain black holes. The results and techniques used are discussed. I also review the recent study of a comparison of the luminosities of black hole and neutron star systems which has yielded compelling evidence for the existence of event horizons.  相似文献   

Anisotropy parameter inversion in vertical axis of symmetry media using diffractions          下载免费PDF全文

Umair bin Waheed  Alexey Stovas  Tariq Alkhalifah 《Geophysical Prospecting》2017,65(1):194-203

Diffractions play a vital role in seismic processing as they can be utilized for high‐resolution imaging applications and analysis of subsurface medium properties like velocity. They are particularly valuable for anisotropic media as they inherently possess a wide range of dips necessary to resolve the angular dependence of velocity. However, until recently, the focus of diffraction imaging or inversion algorithms have been only on the isotropic approximation of the subsurface. Using diffracted waves, we develop a framework to invert for the effective η model. This effective model is obtained through scanning over possible effective η values and selecting the one that best fits the observed moveout curve for each diffractor location. The obtained effective η model is then converted to an interval η model using a Dix‐type inversion formula. The inversion methodology holds the potential to reconstruct the true η model with sufficiently high accuracy and resolution properties. However, it relies on an accurate estimation of diffractor locations, which in turn requires good knowledge of the background velocity model. We test the effectiveness and applicability of our method on the vertical transverse isotropic Marmousi model. The inversion results yield a reasonable match even for the complex Marmousi model.  相似文献   

Analysis of the traveltime sensitivity kernels for an acoustic transversely isotropic medium with a vertical axis of symmetry          下载免费PDF全文

Ramzi Djebbi  René‐Édouard Plessix  Tariq Alkhalifah 《Geophysical Prospecting》2017,65(1):22-34

In anisotropic media, several parameters govern the propagation of the compressional waves. To correctly invert surface recorded seismic data in anisotropic media, a multi‐parameter inversion is required. However, a tradeoff between parameters exists because several models can explain the same dataset. To understand these tradeoffs, diffraction/reflection and transmission‐type sensitivity‐kernels analyses are carried out. Such analyses can help us to choose the appropriate parameterization for inversion. In tomography, the sensitivity kernels represent the effect of a parameter along the wave path between a source and a receiver. At a given illumination angle, similarities between sensitivity kernels highlight the tradeoff between the parameters. To discuss the parameterization choice in the context of finite‐frequency tomography, we compute the sensitivity kernels of the instantaneous traveltimes derived from the seismic data traces. We consider the transmission case with no encounter of an interface between a source and a receiver; with surface seismic data, this corresponds to a diving wave path. We also consider the diffraction/reflection case when the wave path is formed by two parts: one from the source to a sub‐surface point and the other from the sub‐surface point to the receiver. We illustrate the different parameter sensitivities for an acoustic transversely isotropic medium with a vertical axis of symmetry. The sensitivity kernels depend on the parameterization choice. By comparing different parameterizations, we explain why the parameterization with the normal moveout velocity, the anellipitic parameter η, and the δ parameter is attractive when we invert diving and reflected events recorded in an active surface seismic experiment.  相似文献   

Geotechnical assessment of cut slopes in the landslide-prone Himalayas: rock mass characterization and simulation approach     

Siddique  Tariq  Mondal  M. E. A.  Pradhan  S. P.  Salman  M.  Sohel  M. 《Natural Hazards》2020,104(1):413-435

Natural Hazards - The roadway networks serve as arteries for the ongoing socio-economic activities within the Himalayan region. The perilous conditions of geologically active and fragile terrain...  相似文献