Silty Clay Layer Research Articles

Assessment of ground condition for a mass rail transit system in Singapore

Subsurface ground conditions will have a large influence on the design of underground structures such as tunnelling and deep excavation works. Adequate site investigation information is very useful in understanding the ground conditions. For the on-going mass rail transit system Circle Line Stage 2 - Contract 823 project, close to 90 exploratory boreholes were sunk to investigate the ground condition. The project involves the construction of three underground MRT stations and twin bored tunnels of approximately 2.5 km long. The objectives of the site investigation were to obtain a better appreciation of the ground subsurface profile along the route of the project and to ascertain design parameters. The results obtained from the site investigation are summarised in this paper. In this mass rapid transit project, the geological conditions of the site can be generalised as three main types: Fill, Kallang Formation and Old Alluvium Formation. Part of the geological profile of the site is shown in the figure. In this paper, the characteristics and engineering properties of Kallang Formation, especially Marine Clay Layer and Old alluvium Formation are discussed in detail. The Kallang Formation at the site consists of the following strata: (a) Marine clay layer, (b) Estuarine layer, (c) Silty/clayey sand layer (Fluvial sand F1); (d) Silty clay layer (Fluvial clay F2). The Marine Clay layer is the predominant layer within this formation found at the site with a maximum thickness of about 30 m. The silty clay (F2) is encountered mainly as an intermediate layer between the Upper and Lower Marine Clay layers as well as sub-layers found in ''buried valleys''. The estuarine layer and clayey sand (F1) are only encountered in a few boreholes and they are generally discontinuous laterally over the site. One of the most interesting findings from the site investigation were evidence of possible occurrence of some previous earthslips of Old Alluvium hillocks (shown as dotted area in figure) that had taken place during the initial stage of the Holocene period, i.e. before the deposition of the Lower Marine Clay layer, and are now buried between Kallang Formation soils. These earthslips had caused huge volume of soils displaced into adjacent valleys. Some of these ''buried valleys'' are now filled with intact Old Alluvium soils, which have undergone moderate degree of weathering albeit the soil fabric of the parent material remains relatively undisturbed. These earthslip layers are unusually much denser or stiffer than the Fluvial F1 and F2 soils that are commonly encountered within the Kallang Formation, as the measured SPT N-values could be greater than 30 blows. (A). Reprinted with permission from Elsevier. For the covering abstract see ITRD E124500.

Coupled scattering and reflection measurements in shallow water

The characteristics of shallow-water reverberation are often controlled by scattering from the seabed. While scattering mechanisms are understood in general, the state-of-the-art falls far short of predicting the correct angular and frequency dependence of scattering in a given region. A series of acoustic and supporting geoacoustic measurements were conducted over a large area in the Straits of Sicily in order to study seabed scattering in a complex littoral environment. The hypothesis was that exploiting direct path reflection coefficient measurements, in conjunction with the scattering measurements, could help illuminate the underlying scattering mechanisms. The sediment at the seabed interface was found to be a fine silty clay with nearly uniform properties across the area. Notwithstanding this spatial homogeneity, 1-6-kHz reflection and scattering measurements showed significant spatial variability. The coupled reflection-scattering approach resolved this apparent discrepancy, revealing that the reflection and scattering processes are largely controlled by the sediment properties below, rather than at, the water sediment interface. Measurements at 3600 Hz show that site-to-site variability is in part controlled by the thickness of the silty-clay layer. Layers up to 10 m below the water sediment interface contribute to the scattering at 3600 Hz.

Varves, turbidites and cycles in upper Holocene sediments (Makran slope, northern Arabian Sea)

Abstract We have analysed two Late Holocene records, each about 5 ka long, consisting of varved sediments deposited in the oxygen minimum zone off Pakistan (upper continental slope off Ormara and west of Karachi). Varve counting was checked by accelerator mass spectrometry (AMS) 14 C dating. Detailed lithofacies analysis, ultra-high-resolution X-ray fluorescence scanning, flux rates from sediment traps and the lamina-by-lamina-analysis of a 5 year record (1993–1998) support our interpretation of the annual character of the laminae. Although the pelagic material is deposited throughout the year, most of it is apparently laid down during the high-productivity period of the late summer monsoon. During the winter (mainly mid-December to February-March) mainly light-coloured detrital material (siliciclastic material and reworked carbonate flour) is deposited, probably by river flood events. Event deposits include turbid-plume or suspensate deposits (light grey homogeneous to graded silty clay layers), which are being laid down at decadal or shorter intervals; they are explained by episodically strong river floods after heavy rains transporting mud-charged waters to the narrow shelf and onto the steep continental slope. Medium grey or reddish grey, graded and laminated silt turbidites originated from less frequent, unchannelized, low-density turbidity currents. In general, periods with thin varves (generally correlated with rare turbidites) are correlated with minima of detrital element ratios (TiO 2 /Al 2 O 3 , Zr/Al 2 O 3 , K 2 O/Al 2 O 3 ), especially in Period I ( c. 5600-4700 a bp), suggesting a climate with reduced precipitation and river runoff (possibly winter monsoon dominated). Period II (4700-2600 a bp) is characterized by comparatively thick varves documenting a generally wet period (with possibly summer monsoon domination). During Period III (2600-1000 a bp) a gradual thinning of varves and a decrease of turbidite abundance (thickness) per century is interpreted as a gradual decline of precipitation and river runoff leading finally to dry conditions from 1600 to 1000 a bp. The sequence of cycles detected by autocorrelation and standard Fourier analysis seems to contain a large proportion of multiples of the lunar perigee cycle (4.425 a, 8.85 a) and the lunar (half) nodal cycle (9.3 a, 18.6 a). Our test for cyclicity in the series of varve thickness (varve cycles) and of abundance of turbidites (turbidite cycles) detected prominent high-frequency cycles. Some cycles of varve thickness match the cyclicity of turbidite frequency. We also detected the presence of a 1470 a cycle, previously reported from the glacial-age Greenland ice record.

Forming conditions of the Graikas lignite, N. Peloponnese

In Northern Péloponnèse (southern Greece) several lignite seams occur, many of which were exploited in the past decades. In the small Graikas basin, in the upland Aigialia, a 2.5-m-thick lignite seam outcrops within the Pliocene/ Pleistocene sediments. The pre-Neogene margins and the basement of the basin consist of radiolarites, pelagic limestones, and flysch of the Pindos isopic zone. The sediments filling the basin include marly, sandy and clay layers, which deposited under marine, brackish and lacustrine conditions, during the rifting of the Corinth graben (Late Pliocene-Early Pleistocene). The seam consists of lignite and clay-rich lignite layers, of matrix lithotype, with total thickness of 1.4 m, intercalating with thin marly, silty, clay and humic clay layers. Fourteen lignite samples were obtained for proximate and ultimate analyses and coal-petrography studies. The ash contents of the Graikas lignite range up to 46.2% on dry base revealing intense inorganic input. The total sulphur contents are also high up to 4%. The fixed carbon and volatile matter contents (33.2-46% and 53.9-66.8% on daf, respectively), as well as the H/C and O/C atomic ratios and the reflectance of Eu-ulminite Β (Rm 0.26-0.30%), indicate a low rank (soft brown coal, Weichbraunkohle). Micropetrographic studies revealed a Huminite content >73%, Liptinite <23%, and Inertinite <12%. Attrinite and Densinite are the most prevailing macérais, while Texto-ulminite A and Eu-ulminite A show moderate values. Inertodetrinite and Semi-fusinite dominate within the Inertinite macerai group. Cutinite and Liptodetrinite are the most abundant macérais of the Liptinite group. Mainly clay and carbonate minerals constitute the inorganic matter (7-30%). However, pyrite content is also significantly high, up to 10%, revealing anoxic marine influence. Factor analysis suggests that peat accumulation started under anoxic conditions and intense bacterial activity. The peat-forming vegetation was mostly herbaceous with minor contribution of arboreal vegetation. Moreover, negative correlation is revealed between the gelification degree and the inorganic input. Coal-facies diagrammes suggest low preservation of the organic tissues and highly scattered gelificationindeces. The peat in the Graikas basin started accumulating in a lagoonal environment under brackish conditions behind a barrier. Progressively, sea regraded and the conditions became limnic to limnotelmatic

Vacuum preloading consolidation of Yaoqiang Airport runway

Yaoqiang Airport is an international airport serving the city of Jinan, China. The soil on the site consists of alternate layers of silty sand, silty clay, silt and clay. An under-consolidated soft clay layer approximately 4 m thick is located at between 7·5 m and 11·5 m depth above a silty clay layer. Soil improvement was proposed to consolidate the site prior to the construction of a runway to eliminate excessive settlement under static and dynamic loads on the runway. The results from field pilot tests for both surcharge preloading and vacuum preloading under the same consolidation pressure of 80 kPa are presented. Soil settlement in the range 20–30 cm was achieved in 80–90 days. For the vacuum treatment, in-situ deep mixing slurry cut-off walls were installed to control vacuum loss in a shallow silty sand layer. Data from the successful full-scale vacuum treatment of the site are also presented

Liquefaction Resistance of Soils from Shear-Wave Velocity

A simplified procedure using shear-wave velocity measurements for evaluating the liquefaction resistance of soils is presented. The procedure was developed in cooperation with industry, researchers, and practitioners and evolved from workshops in 1996 and 1998. It follows the general format of the Seed-Idriss simplified procedure based on standard penetration test blow count and was developed using case history data from 26 earthquakes and >70 measurement sites in soils ranging from fine sand to sandy gravel with cobbles to profiles including silty clay layers. Liquefaction resistance curves were established by applying a modified relationship between the shear-wave velocity and cyclic stress ratio for the constant average cyclic shear strain suggested by R. Dobry. These curves correctly predicted moderate to high liquefaction potential for >95% of the liquefaction case histories and are shown to be consistent with the standard penetration test based curves in sandy soils. A case study is provided to illustrate application of the procedure. Additional data are needed, particularly from denser soil deposits shaken by stronger ground motions, to further validate the simplified procedure.

Evidence for Mediaeval soil erosion in the South Hams region of Devon, UK

A major theme of research into the causes of past and present soil erosion has been to determine the relative importance of climate and land-use change in influencing Holocene erosion rates. Previous work suggests that land-use change, especially the conversion of woodlands into agricultural land, is the main factor influencing long-term increases in soil erosion. A study of an extensive minerogenic sediment deposit in a wetland at Slapton Ley in Devon suggests that agricultural intensification occurred before the onset of sedimentation (a silty-clay layer c. 40 cm thick) in the valley-bottom wetland of the Slapton Sewage Works marsh. The base of the silty-clay layer lies at an altitude of between 2.2 and 2.6 m AOD and has been radiocarbon dated at two locations. Conventional radiocarbon ages (± 2 σ) were 910 ± 160 yr and 960 ± 140 yr BP. Successful radiocarbon dating of the upper surface of this minerogenic layer at one location yielded a conventional radiocarbon age of 730 ± 120 yr BP. Within the errors associated with radiocarbon dating, the onset of sedimentation appears to be associated with a period of climatic deterioration towards the end of the Mediaeval Climatic Optimum. While agriculture plays an important role in exposing unprotected soil at certain times of the year, an increase in the magnitude and frequency of wet and severe winters may have led to a substantial increase in the risk of erosion. Contemporary analogues serve to illustrate the complex relationships which may exist between agricultural practices, climate and weather conditions and to explain why erosion is often localized and episodic in nature.

The submarine delta of the Ganges–Brahmaputra: cyclone-dominated sedimentation patterns

The Ganges–Brahmaputra belongs to the world's largest rivers in terms of sediment discharge, but little is known yet about the processes controlling sediment distribution on the shelf and the documentation of these processes in large- and small-scale sedimentary structures. For this study the submarine delta of the river system was investigated by high-resolution seismic reflection profiles, and piston and gravity coring. Logged physical properties of the cores were combined with visual core description, grain-size analysis, and radiography. Sedimentation rates were estimated by 210Pb and 137Cs gamma spectrometry and cross-checked with evaluation of seismic profiles. The data reveal that the broad delta topset (<20 m waterdepth) is formed by a thick layer of sand + silt. Highest sedimentation rates (about 10 cm a −1) occur at the centre of clinoform delta foreset beds where about 20% of the total riverine sediment load is deposited and thus cause an annual progradation of the subaqueous delta front by about 15 m. The foreset beds consist of graded sand + silt layers which are thought to be deposited by sediment-laden flows generated during the surge of tropical cyclones (tempestites) interbedded with silty clay layers. The head of a canyon, the Swatch of No Ground, that deeply incises into the shelf, forms a sediment trap along the westward cyclonic transport path where sedimentation rate increases to about 50 cm a −1. Episodically earthquakes or storms destabilize especially the rapidly accumulated foreset beds in the eastern delta creating up to 8 m thick mass flows. On the outer shelf in water depth beyond 80 m no Holocene sediment is deposited.

Parametric modeling and estimation of acoustic sediment properties using a system identification approach

The acoustic properties of marine sediments are measured to obtain an acoustic signature of their mechanical characteristics. The proposed 1-D wave propagation model accounts for absorption and dispersion. Use is made of an inverse procedure based on a maximum likelihood estimator for obtaining a parametric identification of the sediments. Measurements are performed in the laboratory, in reflection and transmission modes, on prepared samples of natural sediments, at normal incidence, and using a controlled measurement environment in the frequency range of 300 to 700 kHz. The model validation is performed for a water layer, an ideal medium with little absorption and dispersion, and for a silty-clay layer. A comparison between the estimated and measured amplitude and phase characteristics for these two media indicates that the parametric identification of the silty-clay is successful. For both media, comparable differences, of 0.3 dB maximum for the amplitude and three degrees for the phase, are observed.

Geology of Cairo, Egypt

Research Article| May 01, 1988 Geology of Cairo, Egypt ABDU A. SHATA ABDU A. SHATA Professor Emeritus Department of Hydrogeology, Desert Research Institute, Malaria, Cairo, Egypt Search for other works by this author on: GSW Google Scholar Environmental & Engineering Geoscience (1988) xxv (2): 149–183. https://doi.org/10.2113/gseegeosci.xxv.2.149 Article history first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation ABDU A. SHATA; Geology of Cairo, Egypt. Environmental & Engineering Geoscience 1988;; xxv (2): 149–183. doi: https://doi.org/10.2113/gseegeosci.xxv.2.149 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyEnvironmental & Engineering Geoscience Search Advanced Search Abstract The engineering geology of Cairo, Egypt, is essentially influenced by the Quaternary alluvial deposits of the River Nile and the adjacent desert dry streams, as well as by the Tertiary shallow marine carbonates of the ancient Mediterranean Sea and the terrestrial quartzitic sandstone. The alluvial deposits, developed mainly into a top silty clay layer and a lower sandy and gravel layer, have a thickness of about 300 m. The white Tertiary carbonates and the red quartzitic sandstone dominate the elevated plateau and the disconnected buttes and mesas in the area east of the Nile and have a thickness of about 500 m. These are locally overlain by gypsiferous clay deposits having a thickness of about 50 m. Buildings and other structures in the lower Nilotic Cairo are dominantly supported by drilled pier piles and/or continuous mat foundations, but in the elevated or hilly portions of Cairo the structures are supported by raft foundations and/or isolated footings. Cairo is located on the southern side of the “mobile folded belt” on the edge of the “Mediterranean Geosyncline.” That belt is oriented NE-SW and is dominantly crossed, in the northwest-southeast direction, by a belt of normal faults. The intersection of the two geological structural belts has a bearing upon the seismicity of Cairo. Ecological constraints in Cairo comprise the shifting sand and dust, particularly in spring time, the continuous rising of the ground-water surface and the air pollution. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Dolomitization of Fossiliferous Siliciclastic Sediments in Salisbury Embayment: ABSTRACT

Bioclastic, medium-grained sand beds in the Chesapeake Group formations (Miocene) of Maryland and Virginia, contain abundant intergranular dolomite and calcite cement. The sand beds are dominated by fairly well-sorted subrounded quartz grains (mean grain size approximately 250 µm), molluscan-shell debris, and variable amounts of mud and iron oxides that coat many of the grains. The surfaces of the quartz grains surrounded by carbonate cement are etched and pitted, indicating high pH conditions within the diagenetic environment. Initially abundant primary porosity and permeability may be completely filled with diagenetic equant calcite spar and/or rhombic dolomite. However, shell material may be completely dissolved by this process, creating a conspicuous secondary po osity. Dolomitization appears to be stratigraphically controlled by impermeable silty clay layers, above and below the sandy beds, which confine the diagenetic fluids to these zones. Though calcitization appears to be more variable, it also seems to be stratigraphically controlled. Preliminary 13C and 18O results indicate that the dolomite and calcite cements are in isotopic equilibrium, and a 14C-age determination suggests that dolomitization began less than 30,000 yr ago. The abundant presence of limpid dolomite suggests a fresh or brackish water origin for these cements, and the presence of ferroan dolomite may indicate an organic influence in the dolomitization process. The confinement of diagenetic fluids in thin (1-2 m) permeable sand layers may induce the concentration of the necessary available cations to initiate dolomitization. End_of_Article - Last_Page 302------------

Stability of Embankment on Clay

The paper describes the failure of an embankment on clay and the investigation sponsored by the Ohio DOT and the Federal Highway Administration, carried out to determine the mechanism of the failure. The slip surface passed through a thin layer of soft silty clay. Measured deformations and pore-water pressures are summarized. The shear strength of the silty clay was measured by unconfined compression tests, triaxial tests, and simple shear tests. Stability analyses using the undrained shear strength measured by the unconfined compression test and the simple shear test give safety factors between 1.1 and 1.4. The consolidated-undrained triaxial test was found to overestimate the undrained shear strength by a considerable amount. Stability analyses using effective stress and measured by triaxial and simple shear tests also overestimate the safety factor. Probability analysis was used to evaluate the effect of the various uncertainties on the computer safety factors. /HRIS/

Strudel Scour: A Unique Arctic Marine Geologic Phenomenon

ABSTRACT Northward-flowing rivers of Alaska inundate extensive areas of sea ice during spring breakup. Drainage of large volumes of fresh water through the ice at holes and cracks (strudel) causes scour depressions more than 4 m deep and as much as 20 m or more across in the sea floor below. These modern strudel scours and their filled counterparts were studied by side-scan sonar, echosounder, high-resolution seismic gear, diving observations, and sediment sampling. Strudel scours occur within 30 km of river mouths. Their shapes and distribution patterns correspond to those of strudel seen in the ice canopy. The scours are most numerous in the inner areas of overflow, as many as 25 per kilometer of ship's track. Strudel scours also occur outside of the 1970-72 overflow areas; these must be relatively old. One strudel scour investigated by diving was surrounded by a ridge, had vertical walls exposing a tundra horizon, and terminated at a gravel layer 4 m below a lagoon floor. Another one terminated at a semiconsolidated layer of silty clay. Both the gravel and silty clay are pre-Holocene deposits. From highly irregular bedding in seismic records it is apparent that virtually all of the Holocene deposits and significant parts of underlying older sediments around river mouths have been reworked by strudel scour. This mixing of sediments by vertical strudel flow causes sediment types to vary greatly over small areas. These new observations add further complicating factors to be considered in the interpretation of shallow-water deposits of cold climates.

Behavior of a Soil Mass Under Dynamic Loading

For the initial stages of a major research project concerned with the distribution of stress and strain in multi-layered pavement systems subjected to dynamic surface loading the work described was limited to direct loading of a single layer of silty clay contained in a pit 8 ft sq by 5 ft deep, in which were buried instruments capable of measuring stress, strain and deflection under dynamic conditions. The basis for design of the instruments used in this work is outlined and a novel strain cell is described. To carry out this work under dynamic conditions it was necessary to design a loading system that was capable of delivering a single pulse of up to 5 tons with a variable duration; details are given of the pneumatic system that was developed. The initial layout of instruments to enable principal stresses and strains to be obtained is described. Tests were designed to determine stress and strain patterns set up for a variety of uniform surface contact pressures and rates of loading and the results obtained are compared with existing theories for stress distribution and surface deflection in a linear isotropic elastic half space. In addition, the relationship between apparent in situ soil modulus and applied stress is compared with results obtained from cyclical laboratory compression tests.

STRATIGRAPHY OF THE MACKENZIE RIVER DELTA, NORTHWEST TERRITORIES, CANADA

An investigation was carried out in April 1961 to determine the distribution of permafrost under and adjacent to a small lake in the Mackenzie River delta near the new townsite of Inuvik, Northwest Territories, Canada. Using drilling methods, deposits were sampled to bedrock at a depth of about 230 feet, and it is believed that this is the first study in which a complete section of the deltaic deposits has been obtained. Perennially frozen ground was not found in the hole bored under the center of the lake but was found in the total thickness of deposits in each of three holes drilled adjacent (within 500 feet) to the lake. About 180 feet of stratified silts, fine sand, and organic material overlie 50 feet of dense silty clay deposited on bedrock. Results of laboratory tests on the sediments sampled suggest that the lower portion of the dense silty-clay layer, which contains pebbles, is probably till deposited by the ice sheet that covered the area during the Wisconsin. The upper portion of the silty-clay layer, containing no pebbles, was possibly deposited under glaciomarine or estuarine conditions. The sediments overlying the clay layer are of deltaic origin and were deposited by the present Mackenzie River and its postglacial predecessors.