Calcareous Silt Research Articles

Pliocene–Pleistocene sedimentary and geomorphologic development of the Vasilikos river catchment, S Cyprus, in relation to uplift of the Troodos ophiolite and climate-related changes

AbstractThe Pleistocene development of the Vasilikos River exemplifies the interaction of focused, tectonically induced surface uplift and climate-influenced changes. The resulting sediments are well exposed in Vasilikos Quarry and in the main river catchment further east. An important erosional surface incises the highest-level (oldest) fluvial conglomerates, down into Late Pliocene – Early Pleistocene open-marine mudrocks (Nicosia Formation), allowing integration with the circum-Cyprus sedimentary–geomorphic development (F1–F4 stages). To determine where the quarry deposits lie in relation to the Vasilikos river catchment, the fluvial deposits were mapped and valley profiles were constructed, revealing four main episodes, each associated with incision and distinctive fluvial deposition. Source lithology strongly influenced channel morphology, infill and adjacent slope-sediment (colluvium) composition. Palaeosols, particularly red-brown terra rossa, developed on abandoned fluvial terraces and adjacent hillslopes, especially overlying F3 surfaces. The combined evidence allows close correlation of the Vasilikos river and quarry deposits. Relatively coarse (chalky conglomerate/breccia) and fine-grained colluvium (calcareous silt – Cyprus harvara) developed especially on lower hillslopes following incision (mainly above F2 and F3 surfaces). Based on regional comparisons, overall sediment aggregation ended during the Early Pleistocene. The F1–F2 surfaces and deposits are inferred to be Middle Pleistocene, the F3 ones later Middle Pleistocene and the F4 ones near the Middle–Late Pleistocene boundary. Geomorphology and deposition were tectonically forced during strong, focused Early–Middle Pleistocene surface uplift. Coarse clastic ruff-off and palaeosol development (terra rossa) and related sediment aggradation are inferred to have increased during warm, humid periods. Late Pleistocene geomorphology and deposition were more influenced by climatic change, with semi-perennial streamflow, rapid sediment aggradation and palaeosol (terra rossa) development during warm, humid periods (interglacials). Cooler (glacial) periods enhanced fluvial-incision, sediment-bypassing and hillslope colluvial processes (e.g. frost shattering, downslope creep and mass flow) when sediment transport (bypassing) exceeded sediment supply. Neotectonic faulting affected the catchment but did not greatly affect geomorphology or sediment supply. Although climate / climate change (and eustatic sea-level change) had an important influence, tectonics is interpreted as the fundamental driver of geomorphological development and fluvial sedimentation, with implications for other areas, regionally to globally.

Penetrometer testing in a calcareous silt to explore changes in soil strength

This paper describes a centrifuge study using a range of penetrometer tests (T-bar, piezocone and free-fall piezocone) to explore strength changes in a reconstituted, normally consolidated, natural calcareous silt. Various penetrometer test procedures were applied to measure the penetration resistances including monotonic, cyclic and twitch-type movements as well as pauses for pore pressure dissipation. These mobilised combinations of partial or full remoulding, strain softening, consolidation and viscous rate effects. The penetrometer resistance – representing a proxy for strength – reduced by a factor of 4·1 from drained to undrained conditions (at the lowest fully undrained penetration rate). In undrained conditions, viscous enhancement of the penetration resistance raised the tip and shaft resistance in free-fall piezocone tests by ∼2·8 and ∼3·6 times, respectively. The ‘restart’ resistance immediately after the dissipation tests was ∼2·5 times higher than the resistance prior to dissipation, giving an indication of consolidation-induced strength gain. The ‘twitch’ test (using sequential steps decreasing the velocity) captured drainage and viscous rate effects, and also gave a ‘restart’ resistance that showed even greater consolidation effects than from a dissipation test. Overall, the different penetrometer test types and procedures measured resistances in the same soil sample that varied by a factor exceeding 20 from highest to lowest, resulting from different penetration rates and history, due to strain rate, strain level (or remoulding) and consolidation. An expression for the monotonic penetration resistance combining drainage and viscous rate effects was fitted to the response of all tests, spanning >7 orders of magnitude in strain rate.

Biochar, Manure, and Sawdust Alter Long‐Term Water Retention Dynamics in Degraded Soil

Core Ideas Biochar's long‐term water retention effects on soil are poorly understood. The temporal effects of biochar, manure, and sawdust on water differed. Biochar and nonpyrolized organics all had long‐lasting effects on water. Water retention dynamics were influenced by the repellency and particle size of the material. Water retention in the first or second years may not reflect the material's long‐term potential. Biochars are porous but more recalcitrant than nonpyrolyzed organic materials, possibly causing more persistent alterations to soil water dynamics. In this 6‐yr outdoor study, we amended an irrigated calcareous silt loam with a single 1 or 2% dry weight application of hardwood biochar, manure, sawdust, or acidified sawdust; 1% biochar + 2% manure; or a control. Soil water retention and plant‐available water (PAW, g H2O per g dry soil) were measured in spring. Across all years, 1% biochar + 2% manure produced the greatest PAW (0.262), with PAW in the order: 1% biochar + 2% manure > 2% rates > 1% rates > control (0.222). In most years, the 2% treatments increased PAW relative to the control. The PAW ratios (treatment PAW/mean annual control PAW) for the 2% rates varied with amendment and year (P < 0.0001): 2% manure peaked in Year 1, declining to a minimum in Year 3; the other 2% treatments were least in Year 1 and peaked between Years 3 and 5; 1% biochar + 2% manure consistently had a ratio near the maximum. Amendment effects on soil water retention were immediate but the peak benefits were delayed because of the differing hydrophobicity of the original materials and their particle sizes, where greater sizes slowed the removal of hydrophobic surface coatings. Biochar's effects on PAW were no more persistent than those of nonpyrolyzed amendments; however, adding biochar and manure had a mutually stabilizing effect, producing a large, more consistent retention increase over time.

Sedimentary characteristics and genesis of the salt lake with the upper member of the Lower Ganchaigou Formation from Yingxi sag, Qaidam basin

Abstract The Oligocene Lower Ganchaigou Formation (E32) was deposited in the salinized lake, which developed in the western Qaidam Basin in the Oligocene. The sediments are dominated by micritic dolomites and organic-rich calcareous mudstones, forming the high-quality reservoirs and source rocks. Intersalt and subsalt hydrocarbon-bearing system developed. Extensive geological and geochemical data from the Yingxi Sag and its surrounding areas have been analyzed to identify major rock types, determining petrological characteristics, interpreting depositional environments and establishing models for the evolution of the Basin. Four major lithologies formed in the lake, lacustrine carbonates, mudstones, evaporates and clastic rocks. The main minerals encountered in these sediments are dolomites and calcites (31.2%), clay minerals (28%), quartz and feldspar (25.6%), anhydride (6.3%), halite (5.6%), pyrites (3.3%) and glauberites (2.2%). Eight lithofacies are distinguished; Micritic dolomite facies; Calcareous sandstone facies; Granular Limestone facies; Packstone facies; Biomicrite facies; Laminated calcareous siltstone facies; Calcareous mudstone facies and Evaporite facies. These are divided into the basin marginal environments and the intrabasinal environments, which are further grouped into five zones: the bench slope zone, the gentle slope zone, the steep slope zone, the underwater ridge zone and the semi-deep to deep lake zone. The facies sequence developed through the early, middle and late sedimentary and evolutionary stages, which corresponded to brackish lake (carbonates and calcareous silts), saline lake (anhydrite-rich carbonates and mudstones) and hypersaline lake (thick-layer halite and thin-layer carbonates). These changes resulted from the chemical, biological and physical sedimentary controls that resulted from variations of climatic, geomorphological and tectonic influences over time. An important result of this history is that both intersalt and subsalt hydrocarbon-bearing system are developed in these rocks.

Cyclic Capacity and Diving Potential of Novel Fish Anchor in Calcareous Silt

AbstractThis paper reports the performance of a novel dynamically installed fish anchor under cyclic operational loading in calcareous silt. The investigation was carried out through a series of ce...

Performance of a Novel Dynamically Installed Fish Anchor in Calcareous Silt

AbstractDiving upon pullout of an installed anchor leads to an increase in embedment depth and, hence, capacity under operational loadings. It is particularly critical for dynamically installed anc...

Numerical investigation of novel dynamic installed fish anchors in clay and calcareous silt

This paper reports the results from three-dimensional dynamic finite element analysis undertaken to provide insight into the behaviour of a novel dynamically installed anchor (DIA), termed as fish DIA, during dynamic installation and monotonic pullout in non-homogeneous clay and calcareous silt. The fish DIA has an elliptic-shaped shaft, which reduces hydrodynamic drag resistance. The shaft is shaped to be thicker near the head to lower the mass centroid, and increase its diving potential with a specialised padeye position. A series of large deformation finite element analyses have been carried out considering the relevant range of parameters in terms of soil undrained shear strength; impact velocity, padeye offset ratio and pullout angle. Considering the difference in soil undrained shear strength, and DIA dimensions and mass; overall anchor tip embedment depths of the fish DIA lied in the range of that of the OMNI-Max DIA. The tracked anchor trajectory confirmed that, compared to the OMNI-Max DIA, the fish DIA dove deeper and earlier for a wide range of padeye offset ratio. These are more critical and beneficial for calcareous silt where the achieved embedment depths are generally lower compared to those in clay.

A middle Holocene steppe bison and paleoenvironments from the Versleuce Meadows, Whitehorse, Yukon, Canada

A partial skeleton of a bison was recovered during residential house construction in Whitehorse, Yukon, Canada. The specimen represents a young (estimated 6 year old) bison individual that died, was partially scavenged by carnivores, and subsequently buried by calcareous silt sediment in a pond or small lake during the middle Holocene, ∼5400 years ago. Palaeoenvironmental data, including molluscs, pollen, vascular plant, and bryophyte macrofossils demonstrate that the small waterbody was surrounded by white spruce dominated boreal forest. Morphometric analysis of the skeleton reveals that its taxonomic affinity is ambiguous, likely owing to it representing an ontogenetically young individual, though it does share some cranial and horn core characteristics of named species such as Bison occidentalis or Bison priscus. Mitochondrial genomic data confirm that this bison belongs to Clade 2A (northern clade), which represents Pleistocene steppe bison (B. cf. priscus) in Beringia through the Holocene and is not represented in living bison species. These data further demonstrate that northern steppe bison population survived the late Pleistocene extinction event, persisted locally in southern Yukon into the Holocene, and are best characterized as a species with a high degree of morphological variability and ecological flexibility.

Inorganic Fertilization Effects on the Structure of a Calcareous Silt Loam Soil

Core Ideas Long‐term inorganic fertilization decreased aggregate stability. Long‐term inorganic fertilization decreased soil macroporosity. Long‐term inorganic fertilization did not change soil organic C content. Soil water‐holding capacity was not affected by inorganic fertilization. Swine manure combined with inorganic fertilizers improved soil structure. Inorganic fertilizers have been intensely used in the North China Plain (NCP) to maintain or increase crop yields, but their effects on soil physical properties, especially soil structure, are unclear. The objective of this study was to evaluate the effects of 12 yr of successive application of inorganic fertilization on soil aggregate stability, pore structure, and hydraulic properties of a calcareous silt loam soil. A long‐term field experiment (2001–2013) was established at Luancheng Ecosystem Station, NCP. The experiment included three fertilization treatments: (i) inorganic fertilizer, NPK; (ii) inorganic fertilizer and organic manure, NPKOM; and (iii) a control treatment with no fertilizer, CK. Results showed plots receiving long‐term NPK and NPKOM had significantly greater wheat (Triticum aestivum L.) (275 and 307%, respectively) and maize (Zea mays L.) yields (59 and 107%, respectively) than the control. However, the application of inorganic fertilizer significantly decreased aggregate stability and macroporosity, by 55.3 and 36.1%, respectively, relative to the control. No differences in soil organic carbon (SOC), bulk density (BD), saturated conductivity (Ks), and water‐holding capacity were found between the NPK and the CK treatments. On the other hand, the addition of organic manure with inorganic fertilizers increased SOC, total porosity, and saturated conductivity by 38.5, 5.2, and 75%, respectively, compared with the CK treatment. This study indicated inorganic fertilization alone could not improve soil structure of the calcareous silt loam, although it maintained high yields. Use of organic amendments along with inorganic fertilizers can improve soil structure and crop yields.

Numerical simulation of caisson installation and dissipation in kaolin clay and calcareous silt

Caissons are widely used to support fixed platforms in shallow water or moor floating platforms in deep water. Although the installation and pullout behaviours of caissons have been explored extensively, few studies are on the dissipation of excess pore pressures induced by installation of the caisson. The pull-out capacity or bearing capacity of the caisson under undrained conditions is enhanced by dissipation of excess pore pressure, given the caisson is installed in normally consolidated cohesive soil. This paper reports numerical simulations of caisson installation and the subsequent dissipation. The analyses were carried out using a coupled effective stress-pore pressure large deformation finite element (LDFE) approach incorporating the modified Cam-Clay model. The robustness of the LDFE model was validated by comparing the penetration resistance with centrifuge testing data and the guidelines. Caissons in two fine grained soils, kaolin clay and calcareous silt, were explored. The geometry of the caisson was varied to encompass the typical sizes of caissons. The dissipation responses at four locations near the caisson tip were interpreted. A normalised dissipation time around caissons is proposed, by modifying the conventional expression for a cone.

The formation placement and palaeoenvironment of the Middle Miocene Los Atajos Member, Trinidad

The age, palaeoenvironment and formation placement of the conglomeratic Los Atajos Member of central Trinidad have long been unclear. Seven samples (four from calcareous silts near the member's base exposed by building work at the Los Atajos Community Centre, and three from the underlying calcareous claystones of the Brasso Formation) were examined for calcareous microfossils. These indicate a conformable succession encompassing an overall regression. The oldest of the claystone samples, of uppermost early Middle Miocene Globorotalia fohsi fohsi Zone age (N11), contained an upper bathyal benthic foraminiferal assemblage, while the younger claystone samples yielded abundant, shallow neritic Hanzawaia carstensi. The recovery of the planktonic foraminifera Globorotalia mayeri but absence of Globigerinoides subquadratus suggest a Middle Miocene age (Globorotalia mayeri planktonic foraminiferal Zone; N14) for both the uppermost Brasso claystone sample and the Los Atajos Member. The benthic foraminiferal fauna in the Los Atajos is dominated by Rosalina subaraucana, with subdominant Cibicides ex gr. aknerianus and C. floridanus sensu Galloway and Heminway, and common Elphidium spp. This faunal succession has a close affinity with that of parts of the Lower to Middle Miocene Brasso Formation, especially the N10 Guaracara Limestone Member and the clays on which it sits. However, the Los Atajos Member assemblage differs markedly from that of the overlying Late Miocene San José Calcareous Silt Member of the Manzanilla Formation, from which the Los Atajos is separated by an unconformity of Globorotalia menardii (N15) Zone age. On these grounds, the Los Atajos Member is here placed within the Brasso Formation. The low diversity, high dominance benthic foraminiferal fauna and the associated ostracod assemblage in the Los Atajos are indicative of inner to shallower middle neritic palaeodepths in a carbonate-prone palaeoenvironment with marine vegetation and strong current action. It is concluded that the Los Atajos was deposited prior to the Late Miocene diversion of the palaeo-Orinoco River towards Trinidad, which is marked by the Manzanilla Formation.

Quaternary thermokarst and thermal erosion features in northern France: origin and palaeoenvironments

A thermokarst is a collapse feature resulting from the thawing of ice‐rich permafrost or of massive ice of various origins. Little attention has been paid to the sedimentary fabric resulting from this type of collapse, except for glaciotectonic features. In western Europe, two palaeo‐forms are commonly studied: lithalsas and ice‐wedge casts. Collapsed pingos are much rarer. Very few papers have compiled present‐day and fossil data. Here, field data collected from quarries in the eastern Paris Basin were analysed, providing useful records of thermokarst collapses in alluvial calcareous silts, sands, and gravels. These forms have a circular shape when viewed on satellite images. Permafrost is attested regionally by the recurrent occurrence of meter‐sized pattern grounds at the surface of the chalk and of ice‐wedge casts. Traces of segregation and reticulate ice are common. These features are primarily connected to a major interstadial, c. 150 ka BP, orbitally forced and commonly associated with a major glacial retreat. They occur both in drained and waterlogged situations, resulting in a specific pattern of deformation. They are controlled by the brittle and plastic behaviour of sediments and resemble passive glaciotectonism. Normal and reverse faults, with the offset decreasing downward, are common, and those with local shear are reported. Lithalsas, seasonal frost blisters, spring frost blisters and perhaps pingos seem to have formed. Most of these deformations correspond to thermokarst sinkholes bordered by gravitational collapse faults. The offset of these faults increases towards the surface, and the faults have been recurrently confused with neotectonism triggered by palaeo‐earthquakes. However, there are no faults beneath the observed deformation features, and the region lacks recorded seismic activity over the last century. Our data may be helpful in interpreting similar structures elsewhere.

Installation and Monotonic Pullout of a Suction Caisson Anchor in Calcareous Silt

AbstractThis paper reports results from a series of model tests undertaken to provide insight into the behavior of a stiffened caisson anchor during installation and monotonic pullout in lightly overconsolidated calcareous silt. The tests were carried out in a beam centrifuge, varying the installation process (jacked in or jacked in followed by suction-assisted installation), and the consolidation period before anchor pullout. The mudline load inclination was also varied to encompass various mooring configurations. The centrifuge data were used to calibrate analytical installation and vertical pullout capacity models, based on conventional bearing and frictional resistance factors but with strain rate-dependent and strain-softened undrained shear strength for the soil. Piezocone-based direct design approaches were also proposed, deriving end-bearing and frictional resistance from cone tip resistance and sleeve friction, respectively. Holding capacity of suction caisson under inclined loading was presented...

Adjustment of Soil Saturated Paste Extract Electrical Conductivity and Sodium Adsorption Ratio for Excess Gypsum Dissolution Using Equilibrium Geochemical Modeling

Core Ideas In gypsum‐bearing soils, excess dissolution occurs in the soil saturated paste extract. EC and SAR may be adjusted for dissolution effects using geochemical modeling. Characterization of salinity and sodicity hazard is improved. Soil saturated paste extract (SPE) electrical conductivity (ECe) and sodium adsorption ratio (SARe) are widely used measures of soluble salts used to evaluate the salinity hazard to crop growth and the sodicity hazard to soil permeability. In gypsum‐bearing soils, sparingly soluble gypsum dissolves during preparation of the SPE as a result of soil water dilution. This produces a higher measured ECe and lower SARe than would be measured if only field‐soluble gypsum were present. As part of a soil remediation project, samples were collected from the location of a former oil and gas production facility with highly saline‐sodic, brine‐affected soils. The naturally calcareous silt loam soil with a smectitic clay fraction was previously amended with gypsum to mitigate elevated sodicity, of concern for sodic effects on soil permeability. The equilibrium geochemical modeling software program ExtractChem was used to model ECe and SARe in the absence of excess gypsum dissolution by first modeling EC and SAR at field water content and then modeling ECe and SARe at saturated paste water content while excluding gypsum from the modeled reaction. For samples with measured ECe <3 dS m−1, ECe modeled in the absence of excess gypsum dissolution was up to 52% lower than measured, and for samples with measured SARe <2, modeled SARe was up to 53% higher than measured. As remediation progressed, and ECe and SARe decreased toward target values, the magnitude of the excess gypsum effect was sufficient to affect the evaluation of remedial progress. Equilibrium geochemical modeling adjustment of ECe and SARe for gypsum dissolution that occurs as a result of SPE preparation is recommended to improve the evaluation of the progress of remediation of gypsum‐bearing, salt‐affected soil.

T-Bar to Spudcan Design Approach in Single-Layer Clays and Calcareous Silts

AbstractDifficulties in obtaining high-quality soil samples from offshore sites and heavy involvement of lab testing and engineering judgment have necessitated increasing reliance on in situ penetrometer tests, giving continuous penetration resistance profiles. This paper reports a framework for estimating spudcan penetration resistance directly from continuous resistance profile of a full-flow penetrometer (T-bar) test in single-layer clays and calcareous silts. The framework was validated chiefly against centrifuge test data, supplemented by some reported field data.

An exploratory Early and Middle Holocene sedimentary record with palynoforms and diatoms from Faiyum lake, Egypt

We report on the sedimentology, pollen and diatom records in a 26 m long core of Holocene sediments from the Tersa area, near the centre of the Faiyum Depression (Egypt). Two radiocarbon and one OSL dates have been obtained for the core, dates range from 9545 ± 60 Cal. BP to c. 4040 BP. These correspond respectively with the Terminal Palaeolithic (Qarunian) and Neolithic Faiyum A (Faiyumian) cultures. The core is subdivided into 3 sedimentological units: unit 1 (21–26 m) is very thinly laminated, calcareous silt deposited in a deep water lake; unit 2 (9.5–21 m) is finely laminated sand, silt and carbonates formed as a lacustrine fan delta; unit 3 (9.5 m to the core top), is formed of massive silt, sandy silt and very fine grained flood plain sands. Planktonic diatom taxa, mainly Cyclostephanos, Aulacoseira, Cyclotella and Stephanodiscus spp. were abundant in units 1 & 2-a, indicating deep, open lake conditions. Magnetic minerals increased from the base of unit 2 indicating an increasing contribution of Nile alluvium. Benthic taxa such as Fragilaria, Cocconeis, Amphora and Navicula tended to increase towards the core top, from unit 2-b; 3-a to 3-b, indicative of lake shallowing and periods of low Nile floods. Unit 3-c is barren of diatoms and is compatible with terrestrial flood plain conditions. Vegetation was mainly represented by herbaceous pollen throughout most of the core and in the topmost sediment, pollen was scarce but pteridophyte (Osmundaceae) spores increased. Arboreal vegetation had low percentages in most of the record but increased in the middle section of the core (unit 2). A depositional deltaic environment was indicated throughout most of the core (sub-units 2-a & 3-a), where high abundances of Poaceae, Cyperaceae, Chenopodiaceae, Amaranthaceae, Polypodiaceae and Osmundaceae were recorded, indicating high Nile floods and fluctuating rainfall.

Sequence architecture and heterogeneities of a field – Scale Vaca Muerta analog (Neuquén Basin, Argentina) – From outcrop to synthetic seismic

The Quintuco – Vaca Muerta System in the Neuquén Basin (Argentina) has received much attention due to its potential as a major unconventional play. This study combines field geology with satellite imagery interpretation to document the sequence architecture of the prograding mixed carbonate-siliciclastic system over several kilometers from the shelf to the basin. Detailed sections allow the allocation of bed-scale lithofacies changes within this sequence stratigraphic framework. Synthetic seismograms are constructed from the observed facies distribution and petrophysical properties in order to compare this architecture with subsurface seismic data.The field area, the Sierra de la Vaca Muerta, shows a prograding system along a 10 km long and 1 km thick cross section. The studied interval can be subdivided into eight depositional sequences based on the facies distribution, representing a very similar scale as the seven sequences documented in the global sea level chart in this time interval. This suggests a eustatic control on the system.The depositional sequences are dominated by calcareous shale and siliciclastics but have variable amounts of carbonates admixed both temporally and laterally, leading to different motifs of cyclicity and geometry. Shales and calcareous silt- and sandstones are the dominant facies. Pure carbonate or pure siliciclastic portions are very rare and restricted to sequence tops. Carbonate-rich portions are characterized by abrupt lateral facies transitions and breaks within their steep depositional profile, whereas siliciclastic-rich intervals show gently inclined profiles with no breaks and more gradual facies changes.In the temporal scale, heterogeneities occur both as cycles and events. Meter scale alternations of pure shale with calcareous shale are the typical cyclic expressions, which occur down-slope of carbonate-dominated systems. Mixed turbidites commonly follow just after carbonate sequences, triggered by the steeper depositional gradients. This distribution indicates that carbonate-rich intervals offer both more brittle volumes for fracturing (calc. shales and silty wackestones) and potential relatively permeable layers (turbidites) within the surrounding tight shale. These sweet spots follow the sequence stratigraphic framework and typically occur in close relation with tops of carbonate dominated cycles.These carbonate cycles prove to be easy to detect in the synthetic seismograms due to their strong acoustic impedance and geometrical expressions. These findings could offer a way to identify sweet spots for unconventional exploration in the basinal transition, since they are laterally related to carbonate sequence tops, which have a distinct seismic signature.

Dynamic installation and monotonic pullout of a torpedo anchor in calcareous silt

Challenges associated with dynamically installed anchors include prediction of the anchor embedment depth, which dictates the anchor's holding capacity. This is particularly true for calcareous sediments, as very little performance data exist for this anchor type in these soils. This paper reports results from a series of model tests undertaken to provide insight into the behaviour of a torpedo anchor during dynamic installation and monotonic pullout in lightly overconsolidated calcareous silt. The tests were carried out in a beam centrifuge, varying the drop height and consequently the impact velocity, and the consolidation period prior to anchor pullout. The mudline load inclination was also varied to encompass various mooring configurations. The centrifuge model test data were used to calibrate: (a) an analytical dynamic embedment model, based on conventional bearing and frictional resistance factors but with strain-rate-dependent undrained shear strength for the soil; and (b) an analytical quasi-static vertical pullout capacity model, accounting for reverse end bearing and frictional resistance. A total energy based expression, appropriate for calcareous silts, was proposed for predicting anchor embedment depth for a given anchor geometry, mass and impact velocity. For assessing anchor vertical holding capacity, a piezocone based direct design approach was also proposed, deriving anchor end bearing and frictional resistance from cone tip resistance and sleeve friction, respectively. Anchor capacity under inclined loading was presented as failure envelopes expressed in terms of dimensionless vertical and horizontal components of anchor net resistance, which agreed well with a finite-element based envelope developed for embedded foundations. The regain of anchor capacity was found to be in good agreement with predictions based on the cavity expansion framework.

Nutrient loads and sediment losses in sprinkler irrigation runoff affected by compost and manure

High water application rates beneath the outer spans of center pivot sprinkler systems can cause runoff, erosion, and nutrient losses, particularly from sloping fields. This field study determined runoff, sediment losses, and nutrient loads (dissolved organic carbon [C], nitrate-nitrogen [NO3-N], ammonium-nitrogen [NH4-N], total phosphorus [TP], ferric-oxide strip phosphorus [FeO P], dissolved reactive phosphorus [DRP], potassium [K], calcium [Ca], magnesium [Mg], and sodium [Na]) in sprinkler runoff for two years after a single application of either stockpiled or composted dairy manure. We studied five treatments, including a nonamended control, in each of six blocks, with each block situated under a different span of a low-pressure, moving-lateral sprinkler system. In October of 1999, we incorporated 29.1 Mg ha−1 (13 tn ac−1) or 71.7 Mg ha−1 (32 tn ac−1) of dry manure or 22.4 Mg ha−1 (10 tn ac−1) or 47 Mg ha−1 (21 tn ac−1) of dry compost into a calcareous silt loam soil on slopes from 0.8% to 4.4%. In the spring of 2000 and 2001, we collected surface soil (0 to 30 mm [0 to 1.2 in]) from furrows to determine soil test phosphorus (STP). We applied 21 to 46 mm (0.8 to 1.8 in) of water at an average application intensity of 28 mm h−1 (1.1 in hr−1; peak intensity of 40 mm h−1 [1.6 in hr−1]) to 6.4 × 36.6 m (21 × 120 ft) plots six times in 2000 and two times in 2001. Additional nonmonitored irrigations were made as needed to produce corn ( Zea mays L.) silage each year. At 15 to 30 minute intervals after runoff began, we measured runoff rates and collected runoff samples to determine sediment and constituent losses for each monitored irrigation. None of the amendment treatments significantly affected runoff, sediment losses, or loads of dissolved organic C, NO3-N, NH4-N, TP, FeO P, or Mg when averaged across irrigations. Without exception, runoff, sediment losses, and loads of every measured constituent varied among irrigations after accounting for differences in water applied. Treatments influenced DRP, K, and Ca runoff loads. Loads of Ca decreased, but Na increased with increasing manure application rates. Relative to the control, manure DRP loads were five to six times greater, whereas compost DRP loads were similar.

Experimental Investigation of Installation and Pullout of Dynamically Penetrating Anchors in Clay and Silt

This paper reports the results from a series of model tests undertaken to provide insight into the behavior of torpedo anchors during dynamic installation and pullout in lightly overconsolidated kaolin clay and calcareous silt. The tests were carried out in a drum centrifuge at 200g, varying the drop height (hence the impact velocity) and the time delay for consolidation before pullout. The pullout angle at the mudline was also varied to encompass various mooring systems, including catenary (0°), taut leg (45°), and tension leg (∼80°). Two geometries of torpedo anchors were explored, varying the fin and tip geometry. The results demonstrated that the anchor embedment depth increased as the drop height (and hence the impact velocity) increased and the soil undrained shear strength decreased. In stronger silt, the cavity above the installing anchor remained open, whereas in soft clay, it was fully backfilled and replenished. The corresponding anchor embedment depth was also about 0.63 times compared with that in clay. The anchor holding capacity was found to increase with increasing postinstallation consolidation time, depth of embedment, and soil undrained shear strength and with reducing pullout angle at the mudline. The anchor rotation during pullout, and hence the pullout distance for attaining the maximum capacity, reduced as the load inclination at the mudline increased. The fin geometry (rectangular or elliptical) and tip geometry (conical or ellipsoid) were shown to have remarkable influence on the holding capacity, with rectangular fins and conical tip proving to be more effective. The negligible adherence of silt along the anchor sides and the presence of semiliquid material around the extracting anchor resulted in a significantly (34–47%) lower holding capacity in the calcareous silt, with significantly higher intact undrained shear strength.