Sand Deposits Research Articles

Lithofacies and Depositional Environments of the Garubathan Alluvial Fan, North Bengal, India

Abstract The sedimentology of the Garubathan alluvial fan of north Bengal foothills is a product of Himalayan neotectonics and monsoon climate. The active neo-tectonics of the Main Central Thrust (MCT), Ramgarh Thrust (RT) and Ghis Transverse Fault (GTF) produce a huge amount of angular clasts in the upper reaches of the river Chel and Mal. During the wet season, either sediment flow by gravity or turbulent stream flow or both, move the clasts to the downhill. The tectonic zone of Main Boundary Thrust (MBT) and Main Frontal Thrust (MFT) are relative passive thrusts than the MCT, RT and GTF in the study area. A very low angle slope is observed in the area of MBT and MFT of the study area. So, the downhill deposition occurred in MBT and MFT zones of the study area. The river Chel and Mal are perinial rivers. During dry periods (pre-monsoon and post-monsoon), in the absence of sediment flow by gravity or turbulent stream flow, the low stream competency deposit the fine sediments. To identify the depositional environments three, seven and six lithofacies varieties were identified in the upper, middle and lower fan surfaces, respectively. The non-cohesive sediment flows by gravity deposited large angular boulders, cobbles and pebbles in the upper fan area. These deposits are either chaotic, unsorted, un-imbricated or graded and imbricated. Deposition of sand is scanty. Both, sediment flow by gravity and fluvial processes deposited angular to round clasts with matrix in the middle fan area. In this area the deposits are reverse graded, reverse to normally graded, laminated and cross-bedded. The high facies diversity of this area indicates highly variable nature of the depositional environments. In the lower fan area, presence of both clast-supported chaotic and matrix-supported laminated or cross-bedded layers suggests a complex nature of the depositional environment of sediment flow by gravity and fluvial processes.

Constitutive modelling of fabric effect on sand liquefaction

Sand liquefaction under static and dynamic loading can cause failure of embankments, slopes, bridges and other important infrastructure. Sand liquefaction in the seabed can also cause submarine landslides and tsunamis. Fabric anisotropy related to the internal soil structure such as particle orientation, force network and void space is found to have profound influence on sand liquefaction. A constitutive model accounting for the effect of anisotropy on sand liquefaction is proposed. Evolution of fabric anisotropy during loading is considered according to the anisotropic critical state theory for sand. The model has been validated by extensive test results on Toyoura sand with different initial densities and stress states. The effect of sample preparation method on sand liquefaction is qualitatively analysed. The model has been used to investigate the response of a sand ground under earthquake loading. It is shown that sand with horizontal bedding plane has the highest resistance to liquefaction when the sand deposit is anisotropic, which is consistent with the centrifuge test results. The initial degree of fabric anisotropy has a more significant influence on the liquefaction resistance. Sand with more anisotropic fabric that can be caused by previous loading history or compaction methods has lower liquefaction resistance.

GEYSERNAYA RIVER ALLUVIUM (KAMCHATKA): COMPOSITION AND FEATURES OF FORMATION<a href="#FN2"><sup>2</sup></a>

A comprehensive compositional analysis of the alluvium from the river with active gas-hydrothermal manifestations was carried out for the first time. Geysernaya river alluvium is characterized by: poor roundness of boulders and pebbles (grades 1–2), poorly sorted fine-clastic component, abundance of rock fragments and intergrown minerals even in the fine sand fraction. All these indicate the sediment weak disintegration with significant amount of slope material in it, including redeposited by mudflows. The high content of smectite-zeolite and other newly formed (secondary) minerals aggregates (up to 70% of the light fraction 0.1–0.25 mm in size) and altered rock fragments (up to 70–80% in the pebble fraction of alluvium) indicate that a gas-hydrothermal activity significantly impact the bedrock and alluvium weathering within the thermal fields. The material accumulates predominant in the areas of: (1) active delivery of slope material (temporary dams), (2) the longitudinal profile flattening in dammed reservoirs, and (3) mudflow material removal. Formation of two dammed reservoirs over the past 15 years, as well as layers of fine sand found in the low terrace’s sediments, indicate that such short-lived basins form periodically in the Geysernaya river valley. The conditions of the fine sand deposition in sections of a single-branch channel and within dammed reservoirs are differ, which affects the heavy fraction leading minerals ratio. The well-rounded gravel and abundance of coarse sand, and their decrepit appearance indicates that, along with the processing of incoming slope and mudflow material large volumes the Geyzernaya river continues to cut in and erodes the ancient fluvial sediments.

Development of Sand Deposits in the Southern Part of the Curonian Spit

Development of Sand Deposits in the Southern Part of the Curonian Spit

Study on the physical, mechanical and mineralogical properties of dredged marine sand as a partial replacement for fine aggregate in concrete

Dredged Marine sand are the excess sediment deposits removed periodically from the beds of artificially constructed ports and harbors to maintain the design depth and to facilitate waterway. Due to this phenomenon, large quantum of dredged marine sand pile near the estuary by routine dredging activities which has initiated several environmental and public issues. To alleviate the issues, in the recent, several studies have been conducted for the effective utilization of dredged marine sand as construction material. Moreover, the dredged marine sand sediments have considerable economic and environmental advantages when employed as a substitute material for natural fine aggregates in concrete production. This study emphasis on the physical, mechanical and mineralogical characteristics of concrete replaced with dredged marine sand as fine aggregate. For the study, the dredged marine sand samples were collected from the dredging site of the Ariyankuppam estuary close to the artificially created fishing harbor of the Puducherry coast. The collected samples were used in concrete after screening with preliminary treatment to remove shells, organic substances, and other contaminants. The investigation conducted on the mineralogical properties of dredged marine sand showed that silicon oxides (quartz), calcite (CaCo3), calcium sulfate (CaSo4), sodium sulfate (Na2So4), and other minerals were present. The presence of calcite, calcium improves the durability and strength of the concrete while, silicon oxides acts as a filler material. The dredged marine sand's physical characteristics indicated that the samples are finer and matches with the properties of conventional materials. The chemical characteristics evidenced the presence of heavy metals like iron (Fe), lead (Pb), and zinc (Zn), which are found in chemical properties, serve to accelerate the reaction in concrete and improve its qualities. For a comparative study, both treated and untreated dredged marine sand partially and completely replaced with M−sand were used in concrete for the investigation. From the analysis of the test results pertaining to the mechanical properties of dredged marine sand concrete which performed better than conventional concrete, a cost-effective way to improve the characteristics of concrete both at its fresh and hardened state.

Improvement of methods for combat with sand in production wells

Today, a large number of methods are used to combat the flow of sand along with the reservoir fluid, which must be divided into the following groups: improving the operating conditions of wells, under which sand rises along with the fluid from the well; creation of technology and equipment that allow retaining sand in the annulus. Methods that are used according to the first group are rarely used due to the fact that conditions arise for hydroabrasive wear of all equipment that comes into contact with sand, disturbance of the formation structure in the bottomhole formation zone, sand deposits in surface equipment and in the well sump when wells are shut down. The most promising method of combating these manifestations are technologies and equipment used according to the second group: injection of cement, foam-cement and cement-sand mixtures into the annulus of the well bottom zone; downhole filter application; injection of sand with a large fraction of grains and gravel into the bottomhole zone of wells; injection of synthetic resins into the annulus of the bottomhole zone of the well; combined methods, including the above. Titanium screens and gravel packs are the most effective means of preventing formation failure. Keywords: downhole reservoir; sand plug; well; steam-thermal impact.

Evaluation of the Foundation Beds Liquidation by Using Soil Modeling for El-Burullus Power Plant Area, Kafr El-Sheikh, Egypt

In this study, the soil has been numerically modeled as the Mohr-Columb model because it is simple to capture essential features of soil behavior. Plaxis 2D software program has been used for modeling. The dynamic analyses depend on some data, such as grain size gradation for materials, stiffness and water level. This data has been used in the calculation process. Simple applications have been chosen to calculate the relations. The program computes entered data automatically. Earthquakes result in dynamic loading on soil which has a significant effect on the soil properties. The model is formed of five soil layers. Sands and mud deposits covered the area and Delta also. Some of the study results can be estimated by using the modeling method. The applied load value is 100 kN/m2. The amplification factor (S %) to the soil in the study area is 108 % when soil is without the foundation load and 150 % when soil with foundation load. Thus, the soil is classified as type – D (Moderate) and no liquefaction is expected in the results, but subduction or landslide, so piling foundations are recommended within the area of study. As well, numerical modeling is recommended in several locations in Egypt to obtain suitable areas for the foundation constructions.

Dynamic installation of torpedo anchors in slightly overconsolidated clay-overlaying-sand deposit

Torpedo anchor installation involves uncertain design and construction parameters, especially in layered soil deposits. Large deformation finite element and coupled Eulerian–Lagrangian (LDFE/CEL) analyses are performed in this study to elucidate the dynamic installation of torpedo anchors in an over consolidated clay-overlaying-sand deposit. The parametric analysis is conducted after model verification to explore the effect of upper clay layer thickness, anchor impact velocity, anchor submerged weight, soil properties and anchor geometric dimensions. The soil failure patterns and dynamic installation behaviour in the clay-overlaying-sand soil deposit are found to differ substantially from those in single-layer clay and sand deposits, which exhibit a squeezing flow pattern at the clay-sand soil layer interface. As the demarcation of the two velocity phases during the anchor penetration process (acceleration and deceleration phases) falls below the interface of two soil layers, the contribution of the internal friction angle of sand to the anchor final penetration depth exceeds that of the clay undrained shear strength. Based on intensive modelling data, an empirical method for predicting the anchor penetration depth in single and layered soil deposits is derived for engineering applications.

New seismic monitoring center in South America to assess the liquefaction risk posed by subduction earthquakes

The east of Cali is composed of loose sand deposits with high water table levels. This condition and the high seismic hazard of the city make cyclic liquefaction one of the main hazards in the city, which may affect more than 600,000 citizens and important infrastructures such as the city’s main drinking water treatment plants. Therefore, it was decided to design and implement a seismic monitoring center to study the behavior of liquefiable soils under local seismogenic conditions, in which subduction earthquakes predominate. First, more than 130 earthquakes from two seismic monitoring centers with liquefiable layers in the USA were studied to determine the requirements for the adequate design of the monitoring center. Then, a robust geotechnical and seismic characterization of the study area including SPT, CPTu, and seismic and ambient noise tests were carried out. From this information, the specifications and location of the instruments and, in general, the characteristics of the monitoring center were defined. The monitoring center has been planned to be established in two stages, and the first one has already been built and commissioned. The implementation of the first stage allowed to adequately record 35 earthquakes from different seismogenic sources, most of them from subduction earthquakes, and to verify that the potentially liquefiable layer remains saturated throughout the year. Subsequent ground motion sensors will allow to deeply study and understand large shear strains and excess pore pressures generation in the soil deposit, as well as their relationships with different intensity measures. The experience shared herein can benefit the design, construction, and operation of other seismic monitoring centers across the world.

Sand, wind, paleosols, war: Late Quaternary aeolian dynamics in the Selima Sand Sheet Region, Darb el Arba'in Desert, Southern Egypt

First scientifically documented by the British explorer and soldier Ralph Alger Bagnold, the Selima Sand Sheet is an extensive low-relief area located within the modern hyperarid core of the Eastern Sahara. Field survey and trenching reveal a surface mantle of near ‘pinstripe” laminated aeolian sands that comprise active chevron (or zibar) bedforms, which are apparent on satellite datasets. These active sands cover Quaternary paleosols with morphostratigraphic characteristics that reflect differing degrees of soil development over time as a function of in situ weathering of quartz parent materials, addition of silts and clays via illuviation and eluviation processes, the precipitation of carbonates, rubification, and bioturbation by plants and insects. A relative chronostratigraphy is inferred from the associated archaeological (Neolithic) and historical materials (Late Historic to World War II), and absolute ages for these deposits are provided by optical dates using single aliquot regeneration techniques (SAR). Constraining the timing of aeolian sedimentation provides a basis for reconstructing paleoenvironmental changes and pedogenesis over Late Quaternary timescales in this region of northeast Africa. Accretion of the sand sheet was episodic and occurred during time periods of enhanced aeolian activity at ∼20–14 and ∼5–3 ka years ago. Late Pleistocene deposition of the sand sheet was out-of-phase with the widely recognized period of rainwater-fed “pluvial” playa lake formation and wadi river drainage alluviation documented in the Sahara, which resulted from enhanced monsoonal rains associated with the orbitally-forced precessional insolation maximum in the Northern Hemisphere. Enhanced bioturbation processes associated with wet phases during the Holocene have completely obliterated most primary sedimentary structures in the Pleistocene-aged sand sheet, resulting in the development of a cohesive, coarse sand and granule-dominated deposit exhibiting incipient prismatic soil structural development. The younger sand sheets dating to the Late Holocene (∼4–3 ka years ago) preserve primary sedimentary structures (e.g. planar laminations), and increasing amounts of cohesion and structure with age. Reconstructing the maximum estimated accumulation rates, and assuming approximately uniform rates of sedimentation across the Selima Sand Sheet area, sediment storage within the sand sheet may be on the order of ∼7 km3/1000 years during the time period that has elapsed since the mid-Holocene onset of arid conditions.

Modeling of sand transport and elbow erosion in horizontal two-phase slug flow

Horizontal wells play an important role in maximizing the recovery of hydrocarbons from oil and gas reservoirs. During production, if the rate of production of produced fluids with sand particles is low, the deposition of sand particles in horizontal flow lines can wreak havoc on production systems in such a way as to cause increased pressure loss and reduction or loss of production when the pipe is partially or completely blocked. On the other hand, if the production rate of fluids is high, the impact of sand particles on the wall of the pipe will erode the inner surface of the pipe fittings. In this case, erosion can be severe enough to cause a hazardous spill and complete shutdown of systems. Therefore, it is important to quantify the sand transport and erosivity of different flow regimes. Under moderate velocities, there exists a flow regime which is called slug flow which is characterized by the intermittent appearance of liquid slugs propagating through the pipe. Studying the sand deposition and erosion due to sand particles entrained in intermittent flows is extremely difficult since the solid particle velocity magnitudes are coupled with several multiphase flow parameters such as phase distribution and slippage between the phases. This work focuses on the improvement of mechanistic models for predicting critical deposition of sand particles in horizontal pipes and erosion in horizontal-horizontal elbows. In this investigation, a modified model is proposed to better predict the critical deposition velocity and the characteristic particle velocity as a function of the slug flow characteristics. The model predictions are compared with the sand transport and erosion data collected at the University of Tulsa and other research institutions. The results show that the new approach provides improved predictions for sand transport and maximum erosion in standard elbows when compared with existing models.

A State-Dependent Hypoplastic Bounding Surface Model for Gassy Sand

As a kind of partially saturated soil often containing dissolved gas with a high degree of saturation (S > 85%), gassy sand sediment widely exists in the marine environment all over the world. Due to the effect of gas dissolution and exsolution on the pore fluid compressibility, its stress–strain and pore pressure responses are quite different from those of common saturated and unsaturated soils when subjected to undrained loading. Since almost all the gas bubbles are occluded in the pore water of offshore gassy sand, the matric suction may be neglected, and an undrained constitutive model for gassy sand is developed based on the existing hypoplastic bounding surface model for saturated sand. Both Boyle’s and Henry’s laws are employed in the model to characterize the equilibrium behavior of the gas compressibility and solubility, and then the equivalent compressibility coefficient of the pore fluid is obtained. To avoid unrealistic volumetric expansion, the concepts of the critical state and state-dependent dilatancy stress ratio are incorporated to describe its ultimate shear strength and dilatancy characteristics, respectively. Finally, the triaxial undrained test results on gas-charged sand from Hangzhou Bay are analyzed at three initial saturation degrees of 85%, 90%, and 100%, and two effective confining pressures of 50 kPa and 200 kPa. Moreover, carbon dioxide (CO2) was selected in the test, and the samples were loose with a relative density of 30%. It is noted that a good agreement is achieved between the simulation results and the experimental data, including the influence of gas content and confining pressure on the shear dilatancy and the mean effective stress increase at the beginning of the effective stress path, among others.

Paleogene sand injectites of the Uljanovsk-Syzran Volga region (eastern Russian platform)

Relevance of the work. The Paleogene quartz sandstones of the Sosnov Formation that occurred in the UlyanovskSyzran Volga region are known as a valuable source of glass raw materials being considered a scarce raw material of federal significance. But, predicting new deposits based on ideas of the coastal-marine origin of the Sosnov sands exhausted possibilities. The purpose of the work. The main aim of the work is to consider the Sosnov Formation is a complex of sand intrusions. The second one is to determine the possibility of improving the accuracy of forecasting new objects of sand raw materials. Methods. 35 sand samples from the Sosnov and the Bathonian Lukojanov Formation are analyzed using the inductively coupled plasma mass spectrometry and X-ray fluorescence analysis. The 3D-model of the Sosnov strata is constructed. Results. The Sosnov Formation is shown as a complex of sand injectites. The element geochemical study of the Sosnov and the Bathonian Lukojanov sands reveals a high possibility of their genetic similarity. The tectonic trigger of injectite formation is determined. The 3D-model of the Sosnov Formation constructed demonstrates the lateral and vertical variability of the sand deposit morphology. Conclusions. The geochemical study of the Sosnov and Lukojanov sands reveals the latter could be considered a possible source layer due to the genetic similarity of both strata. The tectonic trigger for the formation of sand intrusions was, most likely, the Late Paleocene activation of the Zhigulevskii fault. 3D-modeling of a particular sand deposit could improve the accuracy of predictive constructions.

The use of fine fractions of waste from stone quarries in Azerbaijan as sand in the preparation of concrete

Relevance. In recent years, the enterprises of the construction industry of the republic are experiencing an acute need for inert materials, especially for fine aggregates. The sand deposits available in Absheron are very insignificant and, moreover, in some cases do not meet the requirements of regulatory documents. As a result, it is necessary to use imported sands, which are also not always of satisfactory quality due to their significant fine grain and high content of clay and silt particles. In addition, the use of imported sands significantly affects the cost of finished products. Therefore, the study of the possibility of using fine fractions of stone quarry waste instead of sand in the preparation of heavy concrete is very timely and of undoubted interest. In the article, the characteristics of the materials used for the preparation of concrete are considered in sufficient detail, the main properties of limestone sand with different content of dust particles are investigated, the influence of the properties of limestone sand on the strength characteristics of concrete and their resistance to various temperature and humidity influences is studied. For the purpose of comparison, samples were simultaneously made using river sand from the Mingechevir deposit. The obtained results show that in concrete on gravel and crushed stone when using limestone sand, in comparison with concrete on natural sand, the consumption of cement per 1m3 of concrete slightly increases. The purpose of the research. The article deals with the problem of using fine fractions of stone quarry waste as sand in the preparation of concrete. Research methodology. A simple technique was used to determine the volume increment upon swelling. The physical and mechanical tests of sand have been conducted, the study of the particle size modulus when mixed with gravel and crushed stone and the ability to increase volume during swelling are shown. Results. The use of cheap local wastes of shell limestones as small and large aggregates of concrete will make it possible to somewhat cover the need of the construction industry of the republic for aggregates, especially for fine aggregates. Conclusions. Limestone sands obtained by sawing the shell limestones of the Apsheron Peninsula are a suitable fine aggregate for the preparation of concrete.

RESEARCH PHYSICAL AND MECHANICAL PROPERTIES OF SAND AND CEMENT FOR FOAM CONCRETE PRODUCTION

The article presents the results of experimental studies of the properties of sand and cement. A comparative study of cements from different manufacturers for physical and mechanical characteristics, as well as analyzed the mining sites of quarry sand in Akmola region and their characteristics on the physical and mechanical properties. Evaluation of the physical and mechanical characteristics of Portland cement was made for the three types. The main evaluation parameters were: setting time, compressive and flexural strength. Performed studies have shown that the sand deposits «Eltok» (Type 1) on the physical and mechanical properties can be used for building purposes in the production of foamed concrete. A comparative analysis of the data setting time and strength properties of Portland cement shows that the most positive effect on the kinetics of concrete strength has «Kokshe-Cement» (Type 3). Based on the parameters, as well as taking into account their effectiveness on the physical and mechanical properties of concrete for further studies, the composition of Type 3 was chosen. As a result of the study of properties it is shown that the sands and cements are suitable for use in the foam concrete production.

Effect of the molecular weight of sacrificial agents on superplasticizer interaction with clays on cement-based materials

The high affinity among polycarboxylate-based superplasticizer admixtures (PCEs) and aggregates containing trace amounts of clay has been considered one of the challenges in concrete production in recent years because of its impact on water and chemical admixtures demand as well as its effects on concrete performance. Two types of clays were identified as impurities in a natural sand deposit; therefore, two pure clays were selected, kaolinite (KGa-2) and illite–smectite (ISCz-1), with a cation exchange capacity (CEC) of 2.75 meq/100 g and 27.50 meq/100 g, respectively. As the main results, the adsorption isotherms with PCE using total organic carbon (TOC) showed 99 % adsorption of the admixture on ISCz-1 clay, increasing the interplanar distance from 10.68 Å to 11.54 Å, and decreasing the specific surface area, suggesting intercalation and physical adsorption between the admixture and the clay. For KGa-2 clay, PCE adsorption was about 79 %, with no measured changes in interplanar d-spacing and the specific surface area decreased slightly due to the kaolinite stability.A mitigation strategy based on two quaternary ammonium compounds as sacrificial agents with different molecular weights was tested: hexadecyltrimethylammonium bromide (HTB) and tetraethylammonium bromide (TTB), and their proportions were varied based on multiple of the cation exchange capacity of the clay (0.5,1.0,1.5,2.0,2.5 and 3.0 CEC). Surface changes on functionalized ISCz-1 showed a 76 % reduction in surface area for 1.0 CEC HTB and 21 % for 1.5 CEC TTB. Both molecules exhibited an increase in d-spacing, but in different patterns due to molecular weight and molecule structure. The results of mini-slump tests and rheological measurements indicate that a synergistic effect occurs with the PCE at higher molecular weight (HTB), which increases the flowability of the mortar and causes a decrease in yield stress.

Effects of sand sedimentation and wind erosion around sand barrier: Numerical simulation and wind tunnel test studies

Effects of sand sedimentation and wind erosion around sand barrier: Numerical simulation and wind tunnel test studies

Liquefaction behavior evaluation of a multi-layered site with fines-dominated soils

Characterization of liquefaction response in terms of triggering and manifestation at sites with soils containing significant amounts of fines is critically important. Saturated fines-dominated soils, that are known as liquefaction-susceptible materials, would represent a range of extreme responses to earthquake excitations from cyclic mobility to cyclic liquefaction causing excessive displacements. In a multi-layered soil profile, the interaction of adjacent layers in porewater pressure redistribution along the site profile plays an important role in liquefaction response. In this study, an advanced Nonlinear Dynamic Analysis (NDA) procedure in predicting the liquefaction mechanism and manifestation at a site with multiple fines-dominated soil layers is presented. The procedure specifically aims at simulating the interactions in a multi-layered system containing both sand-like and clay-like materials. The liquefaction data recorded by Wildlife Liquefaction Array (WLA) in 1987 Superstition Hills Earthquake (M = 6.6) was deployed to validate the NDA procedure. WLA site consists of sandy silt, silty sand, clayey silt, silty clay, and silt deposits in its upper 20 m and has provided invaluable records of porewater pressure and ground motions. Two critical-state-based constitutive models, PM4Silt and PM4Sand, in a coupled dynamic-fluid finite difference platform were employed. Calibration of the constitutive models was conducted using Cyclic Direct Simple Shear (DSS) test single-element modeling. The simulated response of the site from the proposed approach was compared with those of other NDA procedures conducted on this case history in terms of liquefaction parameters such as excess porewater pressure ratio and maximum shear strain. These comparisons revealed that incorporating multi-layer effects in an advanced NDA procedure can enhance the liquefaction behavior predictions at sites with fines-dominated materials.

Seismic combined bearing capacity of strip footings on partially saturated soils using lower bound theorem of finite element limit analysis and second-order cone programming

The seismic bearing capacity of strip footings resting on unsaturated soils subjected to combined loading is investigated in this study using a combination of lower bound limit analysis and finite element discretization. Second-order cone programming (SOCP) is used in this instance to simulate the nonlinear form of the universal perfectly-plastic Mohr-Coulomb yield criterion during the stress field optimization process. Under no-flow and steady-state infiltration/evaporation flow conditions, the significant influence of matric suction induced below the surface footing is accounted for using the suction stress concept. The load eccentricity and inclination applied to the footing and pseudo-static forces exerted simultaneously to the footing (superstructure) and underlying soil are all incorporated into the equilibrium equations, resulting in combinations of limit moment (M), and vertical (V), and shear (H) forces, under the influence of seismic loading. The results demonstrate that the matric suction induced within the porous structure of the underlying soil stratum increases the capacity of the surface footing to withstand various combinations of eccentric and inclined loadings under seismic excitation. Moreover, at a given hydraulic condition, the failure envelopes of obliquely/eccentrically loaded shallow foundations shrink significantly with the increase in the seismic intensity; the process which is more highlighted in sand (no-suction and all flow conditions). As the flow state in the unsaturated clay changes from infiltration to evaporation, the failure envelopes are observed to enlarge. In addition, as the load inclination angle reaches the soil-footing interface friction angle, the ultimate horizontal bearing capacity of the foundation resting on sand (no-suction) drops to zero; however, there still exists a residual shear resistance in the underlying clay layer or unsaturated sand, posing non-zero horizontal bearing capacity even at extremely high angles of inclination. Last but not least, the influence of earthquake horizontal loading on the bearing capacity envelopes of a shallow footing resting on a sand deposit was corroborated to be more pronounced than on a cohesive soil deposit. Indeed, the intrinsic (residual) cohesion, normally found in cohesive soils, was realized to contribute significantly to suppress the detrimental effect of earthquake horizontal loading.

Influence of Different Particle Sizes of Sediments on the Lower Reaches of the Basin and its Significance in the Liao River Governance

Based on the sand volume and sedimentation volume data for different particle size (PS) groups, the relationship between the annual scouring and silting amount of the Juliu River-Liujianfang section and the yearly sediment volume entering the downstream river channel was established. The critical values of sediment storage and release for the downstream river channel were obtained. It was found to decrease with an increase in the sediment particle size. The correlation coefficient between the annual scouring and silting amount of the Juliu River-Liujianfang section and the annual sediment volume entering the downstream river channel increased with the coarsening of sediment PS. It indicated that the sediment size was proportional to the sediment amount (SA) entering the river channel. As the sediment size increased, the deposition amount increased due to the variation of unit sediment amount. Based on the treatment and achievement of source areas with sediment sizes larger than 0.05 mm, it is significant to concentrate on treatment areas with sediment sizes larger than 0.10 mm.