Applicability of CPT-based methods in predicting toe bearing capacities of driven piles in sand

This paper presents a study on applicability of predicting toe bearing capacities from cone penetration test (CPT) for PHC (pretensioned spun high-strength concrete) driven piles into deep sandy deposits in the Nakdong River deltaic area west of Busan City in South Korea. Using toe bearing capacities obtained from pile driving analyzer (PDA) tests as reference values, which were reliably calibrated by on-site O-cell tests, the applicability of the CPT-based methods was evaluated using a statistical rank index (RI). A total of 82 piezocone penetration test soundings and 190 PDA test piles were used for reliability analysis in this study. Three correction steps were applied to obtain reliable PDA and CPT data sets before ranking is carried out. The RI index is combined from four criteria: (1) the best-fit line, (2) the arithmetic mean and standard deviation, (3) the cumulative probabilities, and (4) the log-normal and histogram distributions. Based on these criteria the performance of some SPT-based methods in the literature is evaluated.     

Numerical modeling of ground borehole expansion induced by application of pulse discharge technology

Pulse discharge technology (PDT) is an innovative technique that can be used to enhance bearing capacity of piles and resisting capacity of anchors. It enlarges the section area and compacts the surrounding soil by high-powered shock wave pressure induced by an underwater electrical discharge. This study aims to establish a suitable numerical model for the simulation and prediction of ground borehole expansion induced by PDT. In order to examine the relationship between electricity and the characteristics of shockwaves generated by PDT, laboratory pulse discharge tests were performed using PDT equipment used in current practice. Then, based on the underwater explosion (UNDEX) model and a coupled acoustic–structural analysis scheme, the results of laboratory PDT tests were analyzed and numerically benchmarked to determine the equivalent UNDEX model parameters for providing shock loading input in a ground borehole expansion simulation. A series of expansion simulations for undrained clayey and sandy soils were performed, and the predicted borehole expansion behaviors were compared with the test results. Moreover, a parametric study was conducted to examine the effects of soil properties on the expansion behavior. The results of the numerical work in this study appeared to be consistent with field test results published in the literature and showed that the soil characteristics related with packing, state of stresses, and degree of saturation were important when analyzing borehole expansion behavior.     

Genetic Implications of Two Different Ultramafic Rocks from Hongseong Area in the Southwestern Gyeonggi Massif, South Korea

Two distinct ultramafic bodies occur in Baekdong and Bibong in the Hongseong area within Gyeonggi massif of South Korea. The Hongseong area is now extensively documented as an extension of the Dabie-Sulu collision belt in China. The Baekdong ultramafic body has a NWW elongation direction. This elongation trend is similar to the general trend of the Dabie-Sulu collision belt. The Bibong ultramafic body is elongated in a NNE direction and runs parallel to the direction of the main fault in the study area. The Baekdong ultramafic bodies show porphyroclastic and mylonitic textures while those at Bibong exhibit a mosaic texture. Both were grouped into peridotite and serpentinite based on their modal abundance of serpentine. In the olivine (Fo) vs. spinel [Cr# = Cr/ (Cr+Al)] diagram, both ultramafic rocks fall with in olivine spinel mantle array. The compositions of olivine, orthopyroxene and spinel indicate that the Baekdong ultramafic rock formed in deeper parts of the upper-mantle under passive margin tectonic setting. The SREE content of Baekdong ultramafic rock vary from 0.19 to 5.7, exhibits a flat REE pattern in the chondrite-normalized diagram, and underwent 5% partial melting. Conversely, large variation in SREE (0.5 21.53) was observed for Bibong ultramafic rocks with an enrichment of LREE with a negative slope and underwent 17 24% partial melting. The Baekdong ultramafic rocks experienced three stages of metamorphism after a high pressure residual mantle stage. The first stage of metamorphism occurred under the eclogite-granulite transitional facies (1123 911°C, >16.3 kb) the second under the granulite facies (825 740°C, 16.3 11.8 kb) and the third is the retrogressive metamorphism under amphibolite facies (782 718°C, 8.2 8.7 kb) metamorphism. The Baekdong ultramafic rocks had undergone high-P/T metamorphism during subduction of the South China Block, and experienced a fast isothermal uplift, and finally cooled down isobarically. Evidences for metamorphism were not identified in Bibong ultramafic rocks. Hence, the Baekdong ultramafic rocks with in the Hongseong area may indicate a link on the Korean counterpart of Dabie-Sulu collision belt between North and South China Blocks.     

Diagenesis of oxyanions (V, U, Re, and Mo) in pore waters and sediments from a continental margin

This research tests the hypothesis that trace metals respond to the extent of reducing conditions in a predictable way. We describe pore water and sediment measurements of iron (Fe), manganese (Mn), vanadium (V), uranium (U), rhenium (Re), and molybdenum (Mo) along a transect off Washington State (USA). Sediments become less reducing away from the continent, and the stations have a range of oxygen penetration depths (depth to unmeasurable O₂ concentration) varying from a few millimeters to five centimeters. When oxygen penetrates ∼1 cm or less, Fe is reduced in the pore waters but reoxidized near the sediment-water interface, preventing a flux of Fe²⁺ to overlying waters, whereas Mn oxides are reduced and Mn²⁺ diffuses to overlying waters. Both Re and U authigenically accumulate in sediments. Only at the most reducing location, where the oxygen penetrates 0.3 cm below the sediment-water interface, does the surface 30 cm of sediments become reducing enough to authigenically accumulate Mo.Stations in close proximity to the Juan de Fuca Ridge crest are enriched in Mn and Fe from hydrothermal plume processes. Both V and Mo clearly associate with Mn cycling, whereas U may be associating with either Mn oxides and/or Fe oxyhydroxides. Rhenium is uncomplicated by adsorption to Mn oxides and/or Fe oxyhydroxides, and Re accumulation in sediments appears to be due solely to the extent of reducing conditions. Therefore, authigenic sediment Re enrichment appears to be the best indicator for intermediate reducing conditions, where oxygen penetrates less than ∼1 cm below the sediment-water interface, when coupled with negligible authigenic Mo enrichment.     

Serpentine Jade (Bowenite) in Korea

INTRODUCTIONA new gem- quality serpentine deposit was discovered in1995 in Booyo area,about 2 5 0 km southwest of Seoul,Korea(Fig.1) and is being mined by the Booyo Nokok (meaninggreen jade) Mining Company.After the Booyo material isfashioned into rings,beads,cabochons,pendants and ear-rings,they are traded on the domestic market under the nameof “Booyo precious serpentine”.The green Booyo bowenite(serpentine jade) has gained high reputation in the countryand a much higher value tha…     

Three-dimensional analysis of bearing behavior of piled raft on soft clay

The piled raft has proved to be an economical foundation type compared to conventional pile foundations. However, there is a reluctance to consider the use of piled rafts on soft clay because of concerns about excessive settlement and insufficient bearing capacity. Despite these reasons, applications of piled rafts on soft clay have been increased recently. Current analysis methods for piled rafts on soft clay, however, are insufficient, especially for calculating the overall bearing capacity of the piled raft. This study describes the three-dimensional behavior of a piled raft on soft clay based on a numerical study using a 3D finite element method. The analysis includes a pile–soil slip interface model. A series of numerical analyses was performed for various pile lengths and pile configurations for a square raft subjected to vertical loading. Relatively stiff soil properties and different loading types were also used for estimating the bearing behavior of the piled raft. Based on the results, the effect of pile–soil slip on the bearing behavior of a piled raft was investigated. Furthermore, the proportion of load sharing of the raft and piles at the ultimate state and the relationship between the settlement and overall factor of safety was evaluated. The results show that the use of a limited number of piles, strategically located, might improve both bearing capacity and the settlement performance of the raft.     

A finite difference method for earthquake sequences in poroelastic solids

Induced seismicity (earthquakes caused by injection or extraction of fluids in Earth’s subsurface) is a major, new hazard in the USA, the Netherlands, and other countries, with vast economic consequences if not properly managed. Addressing this problem requires development of predictive simulations of how fluid-saturated solids containing frictional faults respond to fluid injection/extraction. Here, we present a finite difference method for 2D linear poroelasticity with rate-and-state friction faults, accounting for spatially variable properties. Semi-discrete stability and accuracy are proven using the summation-by-parts, simultaneous-approximation-term (SBP-SAT) framework for discretization and boundary condition enforcement. Convergence rates are verified using the method of manufactured solutions and comparison to the analytical solution to Mandel’s problem. The method is then applied to study fault slip triggered by fluid injection and diffusion through high-permeability fault damage zones. We demonstrate that in response to the same, gradual forcing, fault slip can occur in either an unstable manner, as short-duration earthquakes that radiate seismic waves, or as stable, aseismic, slow slip that accumulates over much longer time scales. Finally, we use these simulation results to discuss the role of frictional and elastic properties in determining the stability and nature of slip.     

Evaluation of rock fracture patterns based on the element-free Galerkin method for stability assessment of a highly pressurized gas storage cavern

Reasonable failure paths are crucial in the stability assessment of a highly pressurized gas storage cavern in a rock mass using limit equilibrium analysis. In this study, the fracture patterns in the rock mass around a gas storage cavern are evaluated based on the element-free Galerkin (EFG) method with a cohesive crack model. The proposed analysis method was first validated through scaled-down model testing results before extending to a full-scale problem. Using the current approach, a parametric sensitivity analysis was performed by taking into account the influences of the stress ratio, the depth of the cavern, and the tensile strength of the rock mass. Based on the analysis results obtained, this research showed that the representative failure paths, in which the uplift evaluation is necessary, can be established from the EFG results with careful consideration of crack initiation and the propagation direction. The site having an in situ stress ratio greater than 1.2 is preferred for operation of underground gas storage caverns. By performing the limit equilibrium analyses for stability assessment of the rock mass above the pressurized cavern, we demonstrated that the factor of safety against uplift computed from the failure paths established in this study is higher than or equal to those obtained from analyses with the simplified models in previous studies without considering the influence parameters on the fracture patterns.     

Chemical and structural characterization of As immobilization by nanoparticles of mackinawite (FeSm)

The mobility and availability of arsenite, As(III), in anoxic environments is largely controlled by adsorption onto iron sulfides and/or precipitation of arsenic in solid phases. The interaction of As(III) with synthetic mackinawite (FeS_m) in pH 5 and 9 suspensions was investigated using high-angle annular dark field (HAADF) scanning transmission electron microscopy (STEM), STEM elemental mapping, high resolution TEM, and X-ray photoelectron spectroscopy (XPS). At pH 5, arsenic sulfide phases precipitate among the FeS_m particles as discrete particles that are an amorphous hydrous phase of arsenic sulfide. The oxidation state of As in the surface layers of the arsenic sulfide precipitates is ‘realgar-like’ based on XPS results showing that > 75% of the As 3d peak area is due to As with oxidation states between 0 and 2+. Discrete, arsenic sulfide precipitates are absent at pH 9, but elemental mapping in STEM-EDX mode shows that arsenic is uniformly distributed on the FeS_m, suggesting that uptake is caused by the sorption of As(III) oxyanions and/or the precipitation of highly dispersed arsenic sulfides on FeS_m. XPS also revealed that the FeS_m that equilibrated without As(III) has a more oxidized surface composition than the sample at pH 9, as indicated by the higher concentration of O ( three times greater than that at pH 9) and the larger fraction of Fe(III) species making up the total Fe (2p_3/2) peak. These findings provide a better understanding of redox processes and phase transitions upon As(III) adsorption on iron sulfide substrates.     

Simulations of energy balance components at snow-dominated montane watershed by land surface models

The quantification of energy interactions among land surface, atmosphere, and surface vegetation is significant to comprehend the hydrological cycle in montane watersheds. Moreover, elevation change is an essential in causing variations in energy fluxes. Thus, estimating the major components of energy interactions is essential for better understanding of the hydrological process. The advanced land surface models (LSMs); the common land model (CLM) and variables infiltration capacity (VIC) are used to estimate accurate hydrometeorological variables. These hydrometeorological variables such as net radiation and sensible, latent, and ground heat fluxes were estimated using CLM and VIC at upper and lower meteorological stations in Sierra Nevada Mountain, California, USA. The estimated fluxes were compared with observations at each site. The estimated daily and monthly net radiation and sensible heat flux from both models showed good agreement with the observations (R ≥ 0.84). The CLM-modeled estimates showed lower trends during the rainfall periods, which occurred mainly during winter at both sites. In comparison, the estimated daily and monthly latent heat flux from CLM at both sites showed better results with lower RMSE and bias than that from VIC, which underestimated latent heat flux. Both models overestimated ground heat flux, and the variation trend was similar to observation. For sensitivity analysis, according to elevation change, all the estimated energy fluxes had slightly different values at the upper and lower met stations. In future studies, parameterization for the LSMs will be conducted for more robust estimations of hydrometeorological variables in montane watersheds.