Occasional Gravel Research Articles

Subsurface Integrity Assessments of a Proposed Plaza Building at Oniru Lekki, Lagos, South-western Nigeria, Using Geoelectrical and Geotechnical Methods of Investigations

Subsurface integrity assessment for building foundation using geophysical and geotechnical methods was carried out at Oniru, Eti- Osa, Lagos State. A total of twenty-five Vertical Electrical Sounding (VES), five 2-D Resistivity Imaging Survey traverses and two borings with Standard Penetration Test (SPT) were carried out at the study site. The acquired data were processed quantitatively using partial curve matching and computer iteration technique to generate the geoelectric sections, the 2-D model and the SPT logs. The VES results revealed five to six geologic units corresponding to topsoil, clayey sand, sandy clay, clay/peat, and sand while the 2-D resistivity structure corresponds with the VES result. The borehole log reveals sand layers having an N-value of 22-30 which is indicative of medium-dense, brown (medium to fine) sand with occasional gravels from depth 1.50 - 7.50m. The borehole log information correlates well with the VES/2-D result. For the sand layer which connotes dense, grey (medium to fine) sand with occasional gravels from a depth 7.50 – 15.75m with N-value ranging from 26–30m. The study analysis shows that the proposed building could be placed on the dense sand at depth 7.50 – 15.75m, this, however, should depend on the proposed load, length, and breadth of the proposed building. This study has provided useful information about the subsurface condition for engineering structure and zone suitable for the proposed foundation.

Lubrication performance of pipejacking in soft alluvial deposits

Pipejacking technologies has been extensively chosen by many mega cities worldwide to construct their sewer pipelines. Lubrication has been deemed to be the key factor in manipulating the performance of pipejacking works. Inadequate lubrication during pipejacking can lead exaggerated jacking force causing damages to the jacked pipe string and adjoining properties. Due to limited studies, a consensus has not yet reached. This study gives an access of evaluating the lubrication performance via the reduction in the frictional coefficient μ and investigates the impacts of injection type, soil and lubrication natures, and misalignment on the lubrication performance for a pipejacking project in alluvial soil deposits. The effect of misalignment, while ramming through the 8–21 m section of gravel at Drive C, gears up the frictional stress τld to 12.5 kPa (compared to 0.4 kPa of the 2–8 m section of the same gravel) and reduces the reduction to 71%. While traversing through the 24–31 m section of clayey gravel at Drive D, the occasional gravel not being long enough to develop lower face resistance leads the misleading reduction of 60%. These factors have greater influences on the lubrication performance than the injection type. The presented results would be helpful in managing the lubrication performance while pipe ramming for upcoming pipejacking project.

Technological Interventions in Delineation of Palaeochannels for Groundwater Development in Sangrur District in Punjab

Indo-Gangetic plains are categorized as over stressed due to intense agricultural practices specifically dependent on ground water extraction. The exploitation of all resources in general and groundwater resources in particular are posing a serious threat to sustenance of flora and fauna. In the present study an effort has been made to demarcate the palaeochannels of Sangrur district, Punjab (29 40’ and 30 38’N, 75 16’and 76 10’E) with the help of sophisticated tools like GIS and satellite remote sensing which provides synoptic, multi-spectral and multi-temporal coverage. Neotectonic movements in the Late Quaternary lead to change in the direction of the flow of various drainage systems. The migration and later on abandonment of these drainage systems have given rise to number of dry Palaeochannels which are seen as great potential source of groundwater in the study area where groundwater levels are steeply declining. Inference of drilling data proposes that vertical thickness of palaeochannels ranges between 70 to 140 meters, constituted of alternating layers of fine to medium sands with occasional gravels. Groundwater quality along these palaeochannels are of good quality hence makes it a future target area for groundwater exploitation. Technological interventions are need of the hour to develop our resources on sustainable approach as it will help us to demarcate and quantify these resources for sustainable development and this study is an attempt in this direction.

Deep Excavation Supported by Diaphragm Wall: A Case Study

Space scarcity and demand for us to build skyscrapers as well as deeper basements are increasing in the present scenario. Excavations are commonly carried out in congested areas to increase underground usable spaces. Hence a case study is made on shoring system for excavation depth of 14.2 m for an office block located in Noida. The office blocks which consist of 14 stories with 3 levels of combined basement are surrounded by existing structures and service lines. Subsoil of the study area mainly consists of two strata, silty sand with occasional gravel and sand with traces of silt at deeper depth. Diaphragm wall is supported by soil anchors during excavation and after basement construction is over, the diaphragm wall will derive horizontal support from the floor slabs and the basement raft. Hence analyses of diaphragm wall are divided into two phases and are carried out using PLAXIS 2D and STAAD Pro software. Inclinometers are used to monitor the diaphragm wall deflection and a similar trend of displacement pattern is observed between the predicted and the measured lateral deflection of the wall. Cross-hole sonic logging and Koden test were also carried out to check the quality of concrete and verticality of the drilled hole respectively.

Extensive Quaternary aeolian deposits in the Drakensberg foothills, Rooiberge, South Africa

Deposits of aeolian sand are known to have accumulated in periglacial environments during the cold phases of the late Quaternary. In many instances, however, they form low-relief topographic units which may not be readily identified without detailed field survey. This study aims to use a multidisciplinary approach, combining remotely sensed data analysis and field survey, to investigate the extent and palaeoenvironmental significance of sand ramps in the Drakensberg/Rooiberge foothills of South Africa. Analysis of Google Earth™ imagery has demonstrated that gully systems are a common component of the landscape, and heterogeneously distributed across the landscape. Field investigation confirmed the hypothesis that the gullies are mainly eroding into sand ramps of fine sands and very coarse silts which mantle many of the lower hillslopes of the region. These sand units include palaeosols and occasional gravel lags, but are otherwise remarkable for their homogenous composition, cross-bedding and the complete absence of clasts. Much of the sediment is thus interpreted as aeolian in origin.The deposits are sufficiently similar in many respects to the Masotcheni Formation, a late Quaternary colluvium which outcrops abundantly in the Drakensberg, to propose an assignation to this unit. However, an aeolian component in the Masotcheni has not previously been described. The distribution of aeolian accumulation in the region is consistent with southward transport during late Quaternary cold phases from a source on the Highveld to the north of the study area. The low relief and complex fluvial network in this region would concentrate sediment eroded from the Drakensberg/Rooiberge, which would subsequently be available for deflation when the balance between fluvial flow regime, seasonally frozen ground and north-westerly trade winds were optimal for aeolian entrainment. Deposition is primarily topographically controlled, and is in places sufficiently extensive that it may be better described as a discontinuous coversand. This study suggests that aeolian deposits may be overlooked in other environments subject to past periglacial landscape development, and develops a potential methodology by which this problem may be overcome.

Evolution of an advancing gravel front: observations from Vedder Canal, British Columbia

Channelization of the lowermost part of Vedder River in 1922 initiated a natural experiment relevant to the unresolved question of how abrupt gravel–sand transitions develop along rivers. The new channel (Vedder Canal) had a fine bed and a much lower slope than the gravel-bed river immediately upstream. Changes in morphology and sedimentology as gravel advanced into and along the Canal are documented using air photos, historical surveys, and fieldwork. The channel aggraded and steepened until stabilized by occasional gravel extraction in recent decades. The deposited material fines progressively along the Canal but the gravel front has retained an abrupt appearance because it has advanced by the sequential development of discrete gravel tops on initially sandy alternate bars. Near the gravel front the bed is highly bimodal and there is a sharper drop in the extent of gravel-framework surface facies than in bulk gravel content. Ahead of the front, gravel is restricted to thin ribbons which often become buried by migrating sand. Calculations show that even though the gravel bed at the head of the Canal is almost unimodal, size-selective transport during floods can account for the strong bimodality farther downstream.

Groundwater potential zoning of a peri-urban wetland of south Bengal Basin, India

Demand for groundwater for drinking, agricultural, and industrial purposes has increased due to rapid increase in population. Therefore, it is imperative to assess the groundwater potential of different areas, especially in a fragile wetland ecosystem to select appropriate sites for developing well fields to minimize adverse environmental impacts of groundwater development. This study considers East Calcutta Wetlands (ECW)--a freshwater peri-urban inland wetland ecosystem located at the lower part of the deltaic alluvial plain of South Bengal Basin and east of Kolkata city. This wetland is well known over the world for its resource recovery systems developed by local people through ages, using wastewater of the city. The subsurface geology is completely blanketed by the Quaternary sediments comprising a succession of silty clay, sand of various grades, and sand mixed with occasional gravels and thin intercalations of silty clay. Groundwater occurs mostly under confined condition except in those places where the top aquitard has been obliterated due to scouring action of past channels. The groundwater in the study area is being over-extracted at the rate of 65 × 10(3) m(3)/day. Overlay analysis in Geographic Information System platform using multiple criteria such as water quality index, hydraulic conductivity, groundwater velocity, and depth to piezometric surface reveals that in and around ECW, there are five groundwater potential zones. About 74% of the aquifer of this area shows very poor to medium groundwater potential. Management options such as minimization of groundwater abstraction by introducing the treated surface water supply system and the implementation of rainwater harvesting and artificial recharge in high-rise buildings and industries are suggested for different potential zones.

Understanding wetland sub-surface hydrology using geologic and isotopic signatures

Abstract. This paper attempts to utilize hydrogeology and isotope composition of groundwater to understand the present hydrological processes prevalent in a freshwater wetland, source of wetland groundwater, surface water/groundwater interaction and mixing of groundwater of various depth zones in the aquifer. This study considers East Calcutta Wetlands (ECW) – a freshwater peri-urban inland wetland ecosystem located at the lower part of the deltaic alluvial plain of South Bengal Basin and east of Kolkata city. This wetland is well known over the world for its resource recovery systems, developed by local people through ages, using wastewater of the city. Geological investigations reveal that the sub-surface geology is completely blanketed by the Quaternary sediments comprising a succession of silty clay, sand of various grades and sand mixed with occasional gravels and thin intercalations of silty clay. At few places the top silty clay layer is absent due to scouring action of past channels. In these areas sand is present throughout the geological column and the areas are vulnerable to groundwater pollution. Groundwater mainly flows from east to west and is being over-extracted to the tune of 65×103 m3/day. δ18O and δD values of shallow and deep groundwater are similar indicating resemblance in hydrostratigraphy and climate of the recharge areas. Groundwater originates mainly from monsoonal rain with some evaporation prior to or during infiltration and partly from bottom of ponds, canals and infiltration of groundwater withdrawn for irrigation. Relatively high tritium content of the shallow groundwater indicates local recharge, while the deep groundwater with very low tritium is recharged mainly from distant areas. At places the deep aquifer has relatively high tritium, indicating mixing of groundwater of shallow and deep aquifers. Metals such as copper, lead, arsenic, cadmium, aluminium, nickel and chromium are also present in groundwater of various depths. Therefore, aquifers of wetland and surrounding urban areas which are heavily dependent on groundwater are vulnerable to pollution. In the area south of ECW isotope data indicates no interaction between shallow and deep aquifer and hence this area may be a better location to treat sewage water than within ECW. To reduce the threat of pollution in ECW's aquifer, surface water-groundwater interaction should be minimized by regulating tubewell operation time, introducing treated surface water supply system and artificial recharging of the aquifer.

Hydrochemical framework of the aquifer in and around East Kolkata Wetlands, West Bengal, India

The area lies between Hugli river in the northwest and Bidyadhari river in the east and includes the East Kolkata Wetlands. The East Kolkata Wetlands is included in the List of Wetlands of International Importance (“Ramsar List”), as per the Convention on Wetlands signed in Ramsar, Iran, in 1971. This wetland has been declared as a Ramsar site on the 19th August 2002 (Ramsar site no. 1208) and therefore has acquired an international status. The area is a part of the lower deltaic plain of the Bhagirathi–Ganga river system and is generally flat in nature. The sub-surface geology of the area is completely blanketed by the Quaternary fluviatile sediments comprising a succession of clay, silty clay, sand and sand mixed with occasional gravel. The Quaternary aquifer is sandwiched between two clay sequences. The confined aquifer is made up of moderately well sorted sand and reflects fluviatile environment of deposition. The regional groundwater flow direction is from east to west. Detailed geochemical investigations of 40 groundwater samples along with statistical analysis (for example, correlation and principal component analysis) on these chemical data reveal: (i) four types of groundwater quality, for example, good, poor, very poor and water unsuitable for drinking purpose, (ii) four hydrochemical facies which may be assigned to three broad types such as “fresh”, “blended”, and “brackish” waters, (iii) the evolution of the “blended” water is possibly due to hydraulic mixing of “fresh” and “brackish” waters within the aquifer matrix and/or in well mixing, and (iv) absence of Na–Cl facies indicates continuous flushing of the aquifer.

Classification of the Alaskan Beaufort Sea Coast and estimation of carbon and sediment inputs from coastal erosion

A regional classification of shoreline segments along the Alaskan Beaufort Sea Coast was developed as the basis for quantifying coastal morphology, lithology, and carbon and mineral sediment fluxes. We delineated 48 mainland segments totaling 1,957 km, as well as 1,334 km of spits and islands. Mainland coasts were grouped into five broad classes: exposed bluffs (313 km), bays and inlets (235 km), lagoons with barrier islands (546 km), tapped basins (171 km) and deltas (691 km). Sediments are mostly silts and sands, with occasional gravel, and bank heights generally are low (2–4 m), especially for deltas (<1 m). Mean annual erosion rates (MAER) by coastline type vary from 0.7 m/year (maximum 10.4 m/year) for lagoons to 2.4 m/year for exposed bluffs (maximum 16.7 m/year). MAERs are much higher in silty soils (3.2 m/year) than in sandy (1.2 m/year) to gravelly (−0.3 m/year) soils. Soil organic carbon along eroding shorelines (deltas excluded) range from 12 to 153 kg/m2 of bank surface down to the water line. We assume carbon flux out from depositional delta sediments is negligible. Across the entire Alaskan Beaufort Sea Coast, estimated annual carbon input from eroding shorelines ranges from –47 to 818 Mg/km/year (Metric tones/km/year) across the 48 segments, average 149 Mg/km/year (for 34 nondeltaic segments), and total 1.8×105 Mg/year. Annual mineral input from eroding shorelines ranges from −1,863 (accreting) to 15,752 Mg/km/year, average 2,743 Mg/km/year, and totals 3.3 ×106 Mg/year.

An analysis of artificial riffles and enhancement of benthic community diversity by physical habitat simulation (PHABSIM) and direct observation

Critical to river rehabilitation decisions is the prediction of the benefits of certain procedures. In low-order systems, planning should focus on flow requirements of lotic organisms, especially benthic species. We examined the value of placement of artificial riffles in Holly Fork, a low-order tributary of the West Sandy River (west Tennessee). The objective was to determine if the instream flow incremental methodology (IFIM) and its component computer model, PHABSIM, could adequately predict the habitat value of the riffles for benthic macroinvertebrates and if, after colonization, this ‘value’ was reflected by increased diversity of benthic macroinvertebrates. Holly Fork is a severely head-cut channel with 2 m high vertical embankments and a substrate dominated by sand and fines, with occasional gravel riffles. We chose to conduct the analysis of each stream reach using macroinvertebrate diversity as the ‘target’. Habitat suitability criteria, developed using data from adjacent watersheds, predicted a range of suitable physical conditions that supported highest benthic community diversity. A traditional IFIM analysis of a reach of the Holly Fork indicated that, below 0.2 m3/s (a flow exceeded 10% of the time), less than 5% of the wetted area contained adequate habitat for benthic macroinvertebrates. At optimum flows (0.4 m3/s and higher), only 15% of the wetted area, primarily across small gravel bars, was adequate to support high community diversity. Two artificial riffles, composed of large cobble and boulder keystones, with leading and trailing aprons of medium cobble and gravel, were placed at 35 m intervals in the test section. After hydrological stabilization and time for colonization by macroinvertebrates, the artificial riffles were re-analysed. The simulation predicted that this reach contained significantly higher amounts of available benthic habitat at low flows (more than tripled), and over 40% of the total wetted area should support high benthic community diversity at optimal flows. The presence of artificial riffles contributed most of this habitat enhancement. A plot of cell-by-cell composite habitat suitability and sample diversity from these cells revealed a significant correlation between PHABSIM predictions and actual community diversity. This technique can be an aid in demonstrating the value of certain restoration structures during the rehabilitation planning process. Our data suggest that benthic community diversity is an appropriate target for evaluation of instream flow values that sustain ecosystem integrity. © 1998 John Wiley & Sons, Ltd.

Holocene and late Last Glaciation pollen record from drillholes at Miramar and Lambton Harbour, Wellington, New Zealand

Abstract Pollen and spores obtained from condensed late Last Glaciation sequences of carbonaceous silts, with occasional gravel and peat horizons, from drillholes at Miramar and Lambton Harbour, Wellington, indicate a bleak, windswept, grassland/shrubland environment dominated by Poaceae. The dominant tree pollen type is Phyllocladus, probably P. alpinus. The 50.7 m thick Miramar sequence contains the Kawakawa Tephra at 24.5 m below ground level; this tephra was also identified in the field 16–17 m below ground level in two of the Lambton Harbour drillholes, the deepest of which went to 40 m. A disconformity exists between the late Last Glaciation sediments deposited immediately after deposition of the Kawakawa Tephra and the onset of Holocene sedimentation. This disconformity occurs in most sequences of this age in the Wellington area and is caused by unstable climatic and depositional conditions at the time. Recycling of spores, pollen, and dinoflagellates from Late Cretaceous and Cenozoic sediments occ...

The Pleistocene terrestrial carbonate mantle on the southeastern margin of the St Vincent Basin, South Australia

An extensive blanket of calcareous sediment and associated calcrete mantles Pleistocene non‐marine sediments in the St Vincent Basin. The nature of the carbonate mantle and its relationships with underlying sediments assigned to the Ngaltinga Formation have been studied in the Noarlunga and Willunga Embayments along the southeastern margin of the basin. The Ngaltinga Formation is comprised of clay‐rich sediments with channel sands and occasional gravels interpreted to be of fluvial origin. The clay‐rich sediments may represent flood‐basin or overbank deposits. Carbonate beds are present at intervals through the formation, especially within sands immediately below the carbonate mantle in the northern part of the Noarlunga Embayment. The form and mineralogical composition of these beds suggest they are the carbonate accumulation horizons of former soils or palaeosols. The carbonate mantle is interpreted as a complex sedimentary and pedogenic unit. The primary sediment contained both calcite and dolomite, wa...

Paleoenvironment and Depositional Environment of Miocene Olcese Sand, Bakersfield, California: ABSTRACT

The Olcese Sand near Bakersfield, California, contains evidence of a range of paleoenvironments including nonmarine, estuarine, and outer shelf depositional settings. Foraminifera from surface and subsurface samples place the Olcese in the Saucesian and Relizian of the California benthic stages. A pumice bed in the Olcese has been dated by fission track methods at 15.5 Ma. The Olcese Sand interfingers with the underlying Freeman Silt and the overlying Round Mountain Silt. In the type area, in Round Mountain oil field, the Olcese is 300-360 m thick. The Olcese is subdivided into three environmental facies. In the Knob Hill Quadrangle, the lower Olcese consists of (1) thinly bedded to blocky white tuffaceous silt and sand, or (2) planar cross-bedded fine to coarse-grained sand with pumice pebbles lining the bedding surfaces. Fossil mollusks and skate teeth indicate a shallow marine environment for the lower Olcese. Although the Olcese is predominantly a marine unit, the middle Olcese is nonmarine, with lenses of marine deposition. The middle Olcese is well exposed in the Knob Hill, Oil Center, and Rio Bravo Ranch Quadrangles, and is characterized by fine to coarse sand with occasional gravel lenses, strong cross-bedding, and a blue-gray color. The upper Olcese ismore » a very fine to medium-grained, marine sand that fines upward into a sandy siltstone southward toward the Kern River. Foraminifera and mollusks from outcrops in the Rio Bravo Ranch Quadrangle indicate outer shelf to estuarine environments for the upper Olcese. The varying environments in the Olcese Sand reflect slight but frequent fluctuations in water depth and can be used to interpret the basin-margin history.« less

Nearshore Bedform Patterns Along Rhode Island from Side-Scan Sonar Surveys

ABSTRACT Side-scan sonar was used to survey 24 km of nearshore zone adjacent to the southwestern Rhode Island beaches in April, June, September, and December, 1977. The seafloor generally consisted of zones of clustered boulders and broad sand areas with occasional gravel patches. Sand bedforms included ripples, megaripples, and sand waves. Fields of low amplitude sand waves, 10-15 m in wave length, were discovered lying parallel to the shoreline at depths to at least 8 m in all surveys but September. The shapes of these features were unresolved except for December when some of the forms were judged to be asymmetrical toward land. The mechanism responsible for their genesis was undetermined. Narrow bands of megaripples also were found trending perpendicular to the coast line. These bands transect or partially blanket the sand waves. At 300-400 m offshore the bands tended to merge and terminate. Within the bands, long-crested megaripples of unknown symmetry were oriented parallel to shore. Working hypotheses proposed for the development of these megaripple bands are: a) rip currents, b) rip currents and subsequent wave action, and c) storm-generated, along-shelf flows followed by wave activity.

Late Pleistocene plant macro-fossils from the Gokarna Formation of the Kathmandu Valley, Central Nepal

The Kathmandu Valley offers the best archive to study the Late Pleistocene climate in Nepal. The Gokarna Formation, constituting the middle part of the sedimentary sequence of the Kathmandu Valley comprises alternating layers of carbonaceous clay, silt, massive to parallel and large scale cross stratified, fine to coarse grained sands and occasional gravel layers, deposited at fluvio-deltaic and lacustrine environment. The organic rich layers of clay, silt, silty-sand and micaceous fine sand consists of abundant plant macro-fossils (fruit, seed and leaves). Plant macrofossils assemblage from the Gokarna Formation (thickness 28.5 m, Dhapasi section) in the northern part of the valley consists of 56 taxa from 35 families. Depending upon the available plant, seven macrofossil assemblages, DS-I to DS-VII in ascending order were established. The common tree and shrubs discovered from this section were Eurya, Ficus, Carpinus, Quercus, Alnus, Rubus, Pyracantha, Zizyphus, Carpinus, Boehmeria etc. Carex, Scirpus triqueter, Scirpus, Polygonum, Euphorbia, Oxalis, Mosla, Viola etc. were the common herbaceous taxa. The constant occurrence of subtropical and warm temperate taxa including Eurya, Ficus, Pyracantha and Zizyphus indicated that subtropical and warm temperate climate continued during the deposition of those macrofossil assemblages. However change in the constituents of those taxa and occurrence of taxa indicating cooler climatic condition like conifers and Betula may indicate minor fluctuation of climate during the deposition of the Gokarna Formation. doi: 10.3126/bdg.v12i0.2252 Bulletin of the Department of Geology, Vol. 12, 2009, pp. 75-88