Clay Strata Research Articles

Electro-osmotic chemical treatment of clay with interbedded sand

Electro-osmotic chemical treatment is a ground improvement method that injects chemical solutions into the soil during electro-osmosis to increase soil strength. However, previous studies have shown that the electro-osmotic chemical treatment method is inadequate when applied to clay with interbedded sand. The reason was that the injected chemical solutions may leak from the interbedded sand during electro-osmosis, resulting in poor improvement of the clay. In this study, a small-scale test cell (0·23 m wide, 0·44 m long, 0·32 m deep) with a pair of electrodes were designed to develop an appropriate electro-osmotic chemical treatment process for clay strata with sand layers. A clay stratum overlying a sand layer was used to make the conductivity of the sand layer relatively high. The results show that the permeability coefficient of the interbedded sand could be effectively reduced to 10−5–10−6 m/s by first injecting sodium silicate into the sand by pressure, followed by injecting calcium chloride by electro-osmosis. The calcium chloride could therefore effectively be flowed in the clay during electro-osmosis after decreasing the permeability coefficient of the interbedded sand, resulting in strength improvement of the clay. The strength of the clay was increased by up to 20 times the original strength near the cathode region.

A Parametric Study on Stability of Open Excavations in Alluvial Soils of Lahore District, Pakistan

Rapid urbanization and expansion of metropolitans in the developing world is pressing the need of tall structures with multiple basements. In several such projects, open land is available around excavation site and unsupported deep excavations by maintaining appropriate side slopes offer economical solution. In this research, subsoil stratigraphy of Lahore district was established to be comprising of a top clay stratum 1.5–8 m thick, followed by a sand layer. Considering subsoil data from several geotechnical investigation reports, the effect of four key parameters viz., cohesion of clay layer, friction angle of sand layer, thickness of clay layer at the top and slope inclination of underlying sand layer on safety factor of open excavations was studied. Six hundred twenty-five slope stability analyses were conducted by considering different geometries and soil properties. Based on the results of these analyses, a regression model was suggested to estimate safety factor of open excavations in similar stratigraphy which would be useful in feasibility studies and preliminary design of deep excavations. It was established that the clay layer cohesion was the most dominant contributor to safety factor.

Streambed nitrogen cycling beyond the hyporheic zone: Flow controls on horizontal patterns and depth distribution of nitrate and dissolved oxygen in the upwelling groundwater of a lowland river

Biogeochemical turnover in hyporheic zones is known to have the potential to affect the chemical signature of surface water cycling through shallow streambed sediments. This study investigates the impact of streambed physical properties on the fate of nitrate and dissolved oxygen in groundwater upwelling through the streambed of a lowland river. For analyzing depth‐dependent patterns and zonation of nitrogen concentrations, diffuse gel probes in shallow (top 15 cm) streambed sediments have been deployed in a nested setup together with multilevel minipiezometers for streambed sediments of 15–150 cm. Spatial heterogeneity of groundwater upwelling was controlled by patterns of low‐conductivity peat and clay strata that caused locally confined conditions, suggesting increased streambed residence times. Nitrate concentrations in the upwelling groundwater changed by up to 68.06 mg L−1 within the top 15 cm of streambed sediments and by up to 107.47 mg L−1 at depths of 15–150 cm, indicating that significant nitrogen turnover was not restricted to shallow streambed sediments. Intensive reduction of nitrate concentrations was found, in particular, in vicinity of low‐conductivity streambed strata. The coincidence of confined groundwater upwelling and reduced oxygen concentrations at these locations suggests that increased residence times and associated depletion of dissolved oxygen create conditions favorable for nitrate reduction. Our results highlight that increased nitrogen turnover at aquifer‐river interfaces is not necessarily limited to shallow streambed zones, where surface water is mixing with groundwater, but can affect upwelling groundwater in reactive hot spots that extend to greater streambed depths and beyond hyporheic mixing zones.

Mineralogy and Geochemistry of Geophagic Clays from Share Area,Northern Bida Sedimentary Basin,Nigeria

The Share area occurs within the northern Bida Sedimentary Basin in Nigeria. The focus is on the geological settings, mineralogical and chemical compositions of Share geophagic clays with the aim of inferring their depositional environments, provenance and possible human health implications. The field method include collection of representative samples at appropriate clay stratum and the samples of the geophagic clays were subjected to petrographic, X-Ray fluorescence and X-Ray diffraction analyses. XRD revealed that Geophagic clays are polymineralic and the main reflections of the clay minerals identified were kaolinite, nacrite, gibbsite and dickite. The peaks of other traces are hematite, quartz and pyrite. Geochemical data indicated that geophagic clays composed of SiO2 content ranging from 64.40% to 46.30%, Al2O3 values varies from 36.54% to 20.54%, Fe2O3 values varies from 4.71% to 1.42%, MgO content varies from 0.08% to 0.06%, CaO ranges between 1.30% and 0.03%, TiO2 values varies from 9.17% to 0.20%, and MnO content ranges from 0.631%. to 0.09%. These values indicate that the geophagic clays are essentially siliceous aluminosilicates. The presence of sedimentary structures typical of tidal sedimentation, low abundance of MgO and K2O indicate lack of expandable clays, and the presence of ironstones further attests to abundant oxygen due to sub aerial exposure resulting to the oxidation of Fe2+ to Fe3+. The presence of basal conglomerate, rootlets structures, iron capping, fining upward sequence and abundances of kaolinite indicate a fluvial (continental) sedimentation. Geophagic clays may introduce metals like Fe, Zn, Cu, Ni, Ti, and Zr to the gastro-intestinal system of consumers, causing adverse effects like increase in the gastro-intestinal pH, and the binding of plant toxins and pathogens which create a surfacial coating on the stomach with inferred pharmaceutical implications. Negative impact of ingesting geophagic clays may lead to electrolyte disturbance, intestinal obstruction, constipation, hypertension, peritonitis, eclampsia, iron deficiency, anemia, microbiological infections, helminthiasis and heavy metal poisoning while coarse sandy quartz particles in the clays could affect dental enamel and also lead to the possible rupturing of the Sigmoid colon due to the abrasive nature of the particles.

A Space-Time-Dependant Design Method and the Stability of Ice Wall for Deep Shafts

The mechanical properties of artificial frozen soils are the key for application of artificial ground freezing, (AGF) especially the creep characteristics of artificial frozen clay when a deep shaft is sunk by using AGF. Many catastrophic accidents took place in clay strata in deep freezing shafts past because of freezing tube breaking and flooding through ice wall caused by large creep deformation of ice wall. A new creep constitutive equation with separated variables for artificial frozen clay, after C. C. Vialov, is presented on base of testing data of most kinds of artificial frozen clay under the condition of drained system. On base of the new equation, a space-time- dependant design method, a modified C. C. Vialov’s, is proposed and has been successfully used for ice wall of deep shafts all over China since 1996. Finally, the stability of ice wall for deep shafts can economically and efficiently be controlled by adjusting the variables of temperature T, un-supported height h and time elapsed t according to their sensitivity or influence.

Reconstruction of Late Neogene paleoenvironmental changes in the area of Pannonhalma (Western Hungary) using granulometric methods

A generalized section of the Pannonhalma Hills has been compiled and analysed. The stratigraphic column of the section represents the paleoenvironmental and paleoclimatic changes of the last ca. 7–8 million years. The elevated old strata also comprise the deposits of the Lake Pannon, overlain by Plio-Pleistocene terrestrial sediments. The generalized section consists of shallow freshwater, fl uvial sediments and Pleistocene eolian loess deposits. These strata can be correlated with Austrian outcrops (e.g. at Gollersdorf), situated at the northern margin of the Little Hungarian Plain. The black freshwater clay strata differ markedly from other clay horizons, and can be considered and applied as marker horizons in correlative studies. This black clay is the product of fi rst appearance of rivers in the region. A detailed granulometric analysis has been performed to refi ne the results of paleoenvironmental reconstructions for Transdanubia.

Consolidation Behavior of Soils Subjected to Asymmetric Initial Excess Pore Pressure Distributions with One-Way Drainage

A consolidating clay layer can be singly or doubly drained. The degree of consolidation is a function of the initial excess pore pressure distribution and the drainage conditions. Traditional geotechnical engineering practice assumes a uniform initial excess pore pressure distribution, for which the singly drained and doubly drained solutions to Terzaghi's one-dimensional consolidation theory are available in most textbooks. In this paper, several symmetric and asymmetric initial excess pore pressure distributions are studied using a series solution method. Excess pore pressure isochrones and average degree of consolidation plots are generated for all cases, assuming an impervious boundary at the base of the clay stratum. These plots enable users to determine the average degree of consolidation and pore pressure at a specific depth for a variety of loading scenarios. Pore pressure redistribution is also clearly more prevalent in singly drained clays, where pore-water pressures at certain depths increase at certain times, a phenomenon not generally expected during consolidation.

New Progress on Rectorite/Polymer Nanocomposites

Rectorite is a kind of layered silicate originated from Hubei province; it has unique structure character- istic albeit with the structure and characteristic much like those of montmorillonite. Rectorite is a regularly inter- stratified clay mineral with alternate pairs of dioctahedral mica-like layer (nonexpansible) and dioctahedral mont- morillonite-like layer (expansible) in 1:1 ratio. In recent years, rectorite has been widely used in the preparation of polymer/layered silicate nanocomposite. This paper introduced the structure and surface modification of rectorite and the structure and preparation method of rectorite/polymer nanocomposite. In particular, the new results of chitosan- based rectorite nanocomposite were summarized. The researchers prepared a series of chitosan-based rectorite nanocomposites via simple solution intercalation, although the rectorite content in these studies was higher than that of other reports, rectorite still dispersed well in the chitosan matrix, there were hydrogen-bonding and electrostatic interactions between rectorite and chitosan. Moreover, the researchers studied antimicrobial activity and mechanism, adsorption capacity, drug-controlled release behavior, gene transfection capacity and structure-property relationship of chitosan-based rectorite nanocomposites. In addition, the films, microsphere and nanoparticles of chitosan-based rectorite nanocomposites were prepared and their properties such as mechanical property, barrier ability, antiultra- violet capacity, thermal stability were studied. At last, the future research of rectorite/polymer nanocomposite was expected.

Recent Developments in the Swelling Model of Expansive Clays for Pavement-Heave Calculations

Abstract The prediction of pavement heave necessitates knowledge of the swelling-pressure characteristic (the swelling model) of the clay stratum under consideration, data that are usually obtained from laboratory tests on undisturbed clay specimens. It is demonstrated that a general swelling model equation should be employed that predicts the percentage of swell under a given vertical pressure exerted on clay characterized by the following parameters: (a) the liquid limit, (b) the ratio between the in situ moisture content and the plasticity limit, and (c) the in situ dry density. The development of this general equation is described by applying the Excel-solver analysis to 352 local test results, yielding preferable results to those stemming from a previous analysis that utilized the multiple linear regression method. Together with employing the general swelling model, an adjustment for any specific given condition is performed by conducting linear regressions (a simple one and a zero-intercept one) with the local test results and the general swelling model. Finally, the paper outlines guidelines for choosing the most relevant of the three calculated models.

Ground Investigations for Changi East Reclamation Projects

Geotechnical ground investigation is important in all construction works particularly, land reclamation projects. The Changi East reclamation project is a mega project that involves creation of land space as large as 3,000 hectares in multiple phases between 1991 and 2005. Ground investigation plays a critical role in the Changi project which involved substantial amount of ground improvement works after reclamation by sand filling. One important aspect of the investigation was to evaluate the geotechnical characteristics of the underlying compressible soils beneath the original seabed for the selection of suitable methods of ground improvement. The other important aspect of the investigation was to characterize and verify the compactness of the reclaimed sand fill. Many types of in situ tests were extensively used in the project. The field vane shear test provides correlations between the undrained shear strength and depth for the upper and the lower marine clay strata in the Northern part and the Southern Part of the reclaimed site. Combined with laboratory undrained shear strength tests, the field vane strength profiles allow the derivation of the undrained shear strength over effective stress ratios for the upper and the lower marine clays. In addition, results from three other in situ tests, the piezocone cone penetration test, the flat dilatometer test, and the self boring pressuremeter test provided useful verification of these correlations. A field-performance based method of assessing degree of consolidation in the underlying clay was developed by combining field monitoring, laboratory testing and conventional as well as specialized in situ testing. An effective use of in situ testing methods for assessment, the outcome of ground improvement and for fill quality control in the densification of granular soils is illustrated with field observation data collected at the project site.

Measuring the load–deformation response of rockfill columns by a full-scale field test on a natural riverbank

A full-scale field test loading of a riverbank stabilized with rockfill columns was used to measure the load–deformation characteristics of the reinforced slope. The test site is located on the natural banks of the Red River in the city of Winnipeg. Rockfill column technology has evolved from granular shear key methods for stabilizing slopes. The relatively weak lacustrine clays are stabilized with compacted columns of limestone rockfill. The columns typically extend through the clay stratum and are anchored in the underlying till. The project involved an extensive site investigation, and soils characterization program in preparation for the field test. Eleven 2.1 m diameter columns were tested by loading the bank with 1920 t of fill. The deformations were measured with standard and in-place inclinometers. The pore-water pressure response of the in situ soils was continuously monitored with vibrating wire piezometers. The results have shown that shear stresses are mobilized along the entire length of the column when subjected to loading, and that complete densification is important in minimizing deformations. This paper discusses the design and construction of the field test and presents the results of the monitoring programs.

Controlled installation of spudcan foundations on loose sand overlying weak clay

Offshore jack-up rigs are often used for site exploration and oil well drilling. The footings of jack-up rigs are known as spudcan foundations. The risk of rapid uncontrolled penetration of spudcan in seabed (“punch-through”) exposes jack-ups to significant risk during installation in strong over weak layered seabeds. An example for this is a thin loose sand layer overlying a weaker stratum of clay. To prevent spudcans from “punch-through”, an in-situ measurement concept is suggested in this paper to control the installation process of spudcan foundations. First, three-dimensional finite element studies using a Coupled Eulerian–Lagrangian method are carried out to simulate the penetration process. The numerical results have been validated with existing analytical solutions and centrifuge model test data. Furthermore, parametric studies are carried out to quantify the influences of the sand thickness and shear strength of the clay on the bearing capacity of spudcans. Based on the numerical studies an idea for the development of an in-situ measurement concept is suggested to control the spudcan penetration process in-situ.

A Critical Reappraisal of the Average Degree of Consolidation

Since its development in 1925, Terzaghi’s expression for the average degree of consolidation has been extensively used in teaching, research and consulting to determine the consolidation settlement that has taken place at a specific time in a geotechnical problem. Recent research by the authors has revealed that the term degree of consolidation is not very meaningful when the initial pore pressure distribution is highly skewed. In view of these findings, a review of all aspects of Terzaghi’s consolidation theory is required, particularly when considering asymmetric initial pore pressure distributions. An exact method for estimating the consolidation settlement of a clay stratum using the mass flux per unit area out of the drainage boundaries is proposed. Graphical representations of both exact and traditional methods reveal identical average degree of consolidation curves. In light of this, Terzaghi’s expression for the average degree of consolidation was re-examined. Upon application of the original governing one-dimensional consolidation equation, it was found that the traditional and exact methods for calculating the average degree of consolidation are identical. Thus, the widespread proclivity for geotechnical engineers to use Terzaghi’s average degree of consolidation equation to estimate the consolidation settlement of a clay stratum has been validated.

Geologic constraints on rain-fed Qocha reservoir agricultural infrastructure, northern lake Titicaca Basin, Peru

This paper reports new data on qocha ponds from the Rio Pucara–Azángaro interfluvial zone, northern Lake Titicaca Basin, Peru. Qocha are a little known form of Andean agriculture that developed around 800–500 B.C. and remain in use today. Prior estimates suggested that in the study area, there were more than 25,000 qocha. While most Andean sunken beds are excavated to reach groundwater, qocha are rain-fed ponds. How these rain-fed ponds functioned has been an open question, but one that is answered in part by research presented in this paper. We suggest that a thick impermeable stratum of clay that was possibly deposited by paleolake “Minchin” created a perched water table that makes rain-fed qocha reservoir agriculture possible. Field geology shows that within the study area, this stratum only exists under Terrace E. Based on this model, we hypothesized that persistently used qocha should only be found on Terrace E. To test this hypothesis we used remotely sensed data to inventory qocha and to determine their distribution by each terrace present. We identified 11,737 qocha. By area 93.77% and by count 94.33% of the qocha are located on Terrace E. These results strongly supported our hypothesis. This case study illustrates that the long term viability of this form of agriculture is made possible by a physical context that is beyond human control.

Strata consolidation subsidence induced by metro tunneling in saturated soft clay strata

To choose the optimum construction method of metro tunneling, we conducted research with numerical simulation on strata consolidation subsidence by dewatering, dynamic dewatering, and non-dewatering construction method, taking the integrated effects of fluid-solid coupling and tunneling mechanics into account. We obtained the curved surfaces of ground surface subsidence and strata consolidation subsidence. The results show that the quantity of ground surface subsidence is 31 mm for the non-dewatering method, 39 mm for the dynamic dewatering method, and 105 mm for the dewatering method. Their ratio is 1:1.3:3.4; and the percentages of strata consolidation subsidence to whole ground surface subsidence of each construction method is 27% (no-dewatering), 50% (dynamic dewatering), and 79% (dewatering). It is obvious that the non-dewatering construction method is the most effective method to control the strata consolidation subsidence induced by metro tunneling in saturated soft clay strata, and it has been successfully applied to the construction of the Shenzhen metro line 1.

A Stress Path Method for Settlement Computation of Normally Consolidated Clays

A stress path method for computing the settlement of normally consolidated clays is presented. The proposed method introduces the characterization of the stress-strain behavior that eliminates unnecessary experimental cost due to uncertainty in the design stress path. For arbitrary control of the effective stress during consolidation, a technique of back-pressure equalization, which enforces the immediate drained condition on the soil specimen without change of the effective stress state, was used. To account for nonlinear anisotropic response in computing the consolidation strains, the iteration procedure was designed. For the proposed method, the stress path experiments on the normally consolidated kaolin were conducted. An example illustrating the feasibility of proposed method in precisely calculating the settlement is shown for a circular footing on the clay stratum.

Pleistocene Eider Duck (Somateria cf. mollissima) from Champlain Sea Deposits near Shawinigan, Québec

Most of a pelvic bone of a large eider duck (Somateria cf. mollissima) was collected in place in a unit of stratified clay and sandy silt near Shawinigan, Québec. The fossil is important because it is the first bird specimen from Champlain Sea deposits to be identified to the generic level. Evidently the duck died and was deposited near the northern shore of the Champlain Sea a few hundred years before the sea drained. A sample from a bed of large, marine mollusc shells (Mya arenaria) found in place just above the eider duck fossil yielded a radiocarbon date of 10 300 ± 100 years BP.

Fossil frogs from the Clarendonian (late Miocene) of Oklahoma, U.S.A.

Fossil frogs of North America have been reviewed by Holman (2003), and records from the middle and late Miocene of North America are relatively numerous. Nonetheless, frog fossils from the late Miocene Clarendonian North American Land Mammal Age time period (ca. 12.5-9 Ma) are rare and biogeographically poorly represented. There is a single record of a bufonid from the Clarendonian Land Mammal Age (LMA) of South Dakota (Holman, 1973), but most of our knowledge of Clarendonian LMA frogs comes from a single local fauna, the Wakeeney Lo cal Fauna (L.F.) of Kansas (Wilson, 1968; Holman, 1975, 2003). In this report we describe an important collection of middle to late Clarendonian (ca. 11-9 Ma; time scale of Woodburne, 2004) frog fossils recovered from the Whisenhunt Quarry fossil site of Beaver County, Oklahoma. The mammals of the Whisenhunt Quarry fossil site have been discussed previously by Dalquest et al. (1996) and, to a lesser degree, by Smith (2005). The Whisen hunt Quarry frogs represent the first lower vertebrates reported from the local fauna, but more importantly they provide new and noteworthy information that improves our knowledge about the diversity and distribution of North American midcontinental frogs from this time period. Fossil Locality?The Whisenhunt Quarry fossil site is located approximately 10 km south of Gate, Beaver County, Oklahoma, in the Laverne Formation at T3N, R28E, Sec. 9, SE 1/4, NW 1/4 (Dalquest et al., 1996; see Fig. 4 for the general location of the site). Late Miocene mammals from this Great Plains formation have been known to science since at least the late 19th century (see discussion in Tedford et al, 2004). Fossils from the Whisen hunt Quarry site were obtained by Dalquest et al. (1996) by pro cessing matrix collected at the quarry in the early 1990s. The ma terial was derived from a stratum of sand and diatomaceous clay, which they (Dalquest et al., 1996:133) believed represented an ancient still-water pool or lake in a marsh or swamp. No ra diometric date (numerical date) is available for the Whisenhunt Quarry, but on the basis of a detailed study of the Whisenhunt Quarry mammals, Dalquest et al. (1996) assigned the local fauna a biochronological age of middle to late Clarendonian LMA. They suggested that the Whisenhunt Quarry L.F. best correlated with the well-documented late Clarendonian Wakeeney L.F. of Kansas. On the basis of megaand micromammal components of the Whisenhunt Quarry and mammals from other nearby Lav erne Formation sites, Tedford et al. (2004) suggested a medial Clarendonian age for the local fauna.

Nachtigall: A continental sediment and pollen sequence of the Saalian Complex in NW-Germany and its relationship to the MIS-framework

The Nachtigall clay pit near Holzminden, northern Germany, is located in a subrosional basin filled with 43 m of interglacial, interstadial and stadial deposits adjacent to the Weser River. The succession separates the Older Middle Terrace from the Younger Middle Terrace of the Weser River. Nachtigall core KB1 (1998) mainly contains silt and clay with intercalated peat layers. The layers of fen peat and intercalated humic silt are between 36 and 22.5 m depth. According to palynological studies, the peat layers and some humic silts were deposited during interglacial and interstadial periods marked by forest vegetation, termed Nachtigall 1 and Nachtigall 2. They are subdivided by a stadial, termed Albaxen. The peat of Nachtigall 1 is interrupted twice by silt and clay strata (Allochthonous Unit I, II) which are reworked sediments of older glacial periods, possibly of late Elsterian or early Holsteinian age. The palynological sequences of Nachtigall and Göttingen/Ottostrasse show the same pattern. Moreover, the contemporaneous pollen profiles of Nachtigall and Göttingen/Ottostrasse can be compared with the Velay pollen sequence (France). The Nachtigall core section 36–26.02 m corresponds to Bouchet 2 – Bonnefond – Bouchet 3 in Velay. The profiles of Velay and Nachtigall are independently correlated to the MIS-timescale and correspond to MIS 7c, 7b, and 7a. TIMS 230Th/U-dating shows ages ranging from 227 + 9/−8 to 201 + 15/−13 ka, which are in good agreement with the inferred MIS 7 age.

Influence of clay properties on radon emanation

The emanation factor of clay strata was measured in a series of experiments. The clay emanation factor grows with increased dispersion and can reach values of up to 67%. This can be explained, in our view, by the increased number of nanodimensional particles with good emanation characteristics.