Pore water pressure

About: Pore water pressure is a research topic. Over the lifetime, 11455 publications have been published within this topic receiving 247670 citations. The topic is also known as: pwp.

Differences in soluble organic carbon chemistry in pore waters sampled from different pore size domains

Abstract: Spatial isolation of soil organic carbon (SOC) in different sized pores may be a mechanism by which otherwise labile carbon (C) could be protected in soils. When soil water content increases, the hydrologic connectivity of soil pores also increases, allowing greater transport of SOC and other resources from protected locations, to microbially colonized locations more favorable to decomposition. The heterogeneous distribution of specialized decomposers, C, and other resources throughout the soil indicates that the metabolism or persistence of soil C compounds is highly dependent on short-distance transport processes. The objective of this research was to characterize the complexity of C in pore waters held at weak and strong water tensions (effectively soil solution held behind coarse- and fine-pore throats, respectively) and evaluate the microbial decomposability of these pore waters. We saturated intact soil cores and extracted pore waters with increasing suction pressures to sequentially sample pore waters from increasingly fine pore domains. Ultrahigh resolution mass spectrometry of the SOC was used to profile the major biochemical classes (i.e., lipids, proteins, lignin, carbohydrates, and condensed aromatics) of compounds present in the pore waters; some of these samples were then used as substrates for growth of Cellvibrio japonicus (DSMZ 16018), Streptomyces cellulosae (ATCC ® 25439™), and Trichoderma reseei (QM6a) in 7 day incubations. The soluble C in finer pores was more complex than the soluble C in coarser pores, and the incubations revealed that the more complex C in these fine pores is not recalcitrant. The decomposition of this complex C led to greater losses of C through respiration than the simpler C from coarser pore waters. Our research suggests that soils that experience repeated cycles of drying and wetting may be accompanied by repeated cycles of increased CO 2 fluxes that are driven by i) the transport of C from protected pools into active, ii) the chemical quality of the potentially soluble C, and iii) the type of microorganisms most likely to metabolize this C.

In situ measurement of PCB pore water concentration profiles in activated carbon-amended sediment using passive samplers.

Abstract: Vertical pore water profiles of in situ PCBs were determined in a contaminated mudflat in San Francisco Bay, CA, 30 months after treatment using an activated carbon amendment in the upper layer of the sediment. Pore water concentrations were derived from concentrations of PCBs measured in two passive samplers; polyethylene (PE, 51 μm thick) and polyoxymethylene (POM, 17 μm thick) at different sediment depths. To calculate pore water concentrations from PCB contents in the passive samplers, an equilibrium approach and a first-order uptake model were applied, using five performance reference compounds to estimate pore water sampling rates. Vertical pore water profiles showed good agreement among the measurement and calculation methods with variations within a factor of 2, which seems reasonable for in situ measurements. The close agreements of pore water estimates for the two sampler materials (PE and POM) and the two methods used to translate uptake in samplers to pore water concentrations demonstrate the ...

Centrifugal modeling of seismic behavior of large-diameter pipe in liquefiable soil

Abstract: This study focused on the behavior of a large-diameter burial pipe with special reference to its stability against flotation subject to soil liquefaction. Centrifugal modeling technique was used where the results are presented for a total of eight shaking table tests conducted on the burial pipe in a laminar box under 30g gravitational field. The ground was prepared with Nevada sand at a relative density of 38% and shaken with a sinusoidal wave at an amplitude of 0.5g. The use of a viscous fluid in a saturated soil deposit satisfied the time scaling relationships of both dynamic and dissipation phenomena. The centrifugal modeling technique simulated flotation of pipeline as the soil liquefied. A technique that used gravels and geosynthetic material was used to mitigate flotation. The response of the soil deposit, in terms of acceleration and excess pore pressure, was investigated. The uplifting of the pipe, earth pressure response and ground surface deformation were also presented. Based on the test results, a design procedure was proposed for the burial pipe in resisting flotation due to soil liquefaction. The deadweight and stiffness of the gravel unit, which was confined by geosynthetic, were important items in design.

SELFRAC: Experiments and conclusions on fracturing, self-healing and self-sealing processes in clays

Abstract: In assessing the performance of a deep HLW repository, the evolution of the excavated damaged zone with time is a key issue. In the framework of SELFRAC fracturing, self-sealing and self-healing processes of Opalinus and Boom clay were studied in laboratory and in situ experiments. Definitions for the terms excavation damaged zone (EDZ), excavation disturbed zone (EdZ), sealing and healing are presented. It is shown that sealing and partial healing occur and the consequences of the results for performance assessment of HLW disposal in argillaceous rocks are discussed. The results of several in situ experiments and observations at the HADES underground research facility are detailed. The origin and extent of excavation induced fractures are discussed and sealing and (partial) healing of these fractures is demonstrated. In the description of the hydraulic features of the EdZ, the anisotropic pore pressure distribution around HADES and its evolution with time are discussed. Pore pressure is influenced several tens of metres into the host rock and its evolution is influenced by the anisotropic in situ stress state and the anisotropic hydraulic conductivity of Boom clay. Around the connecting gallery, an increase of hydraulic conductivity is measured up to about 6–8 m into the host rock, outside this influenced zone values between 4 × 10 −12 m/s and 6 × 10 −12 m/s were obtained. The highest value measured (close to the gallery) was of the order of magnitude of 10 −11 m/s. The observed increase is caused by lower effective stress levels close to the gallery rather than by excavation induced fractures. Self-boring pressuremeter tests show that total stress is influenced up to 6–8 m into the host rock and material parameters such as undrained shear strength and shear modulus are influenced up to 2–3 m into the host rock. In situ seismic transmission measurements showed that the closure of a borehole influences the seismic parameters of the surrounding host rock: a decrease in seismic velocity is measured and higher frequencies disappear from the transmitted signals. After closure of the borehole, sealing of the damaged zone around it occurs, this is observed by the recovery of seismic velocity and the reappearance of higher frequencies. Fracture sealing is also demonstrated by seismic and hydraulic measurements on a reinstalled fractured clay core.