Excess Pore Water Research Articles

Analysis of historical cases of liquefaction (sand boils) case study: Kelapa Gading Residence, Sigi Regency, Central Sulawesi Province

The Palu earthquake on September 28th, 2018, caused liquefaction in several locations in Central Sulawesi. According to The National Disaster Management Authority of Indonesia data, five prominent areas with massive impacts experienced liquefaction in flow liquefaction: Balaroa, Petobo, Jono Oge, Lolu, and Sibalaya. Meanwhile, the locations that experienced liquefaction in the form of sand boils needed to be recorded optimally. This research aims to see the parameters of soil layer behavior in areas that experience liquefaction in the form of sand boils. The study was conducted in Kelapa Gading housing, Sigi Regency, Central Sulawesi. Based on the initial survey, this location experienced sand boils in several areas. The research used the CPT-based liquefaction triggering procedure method and soil behavior index method. The result showed that the liquefaction potential was found at a depth of 2.5-3.3 meters for PGA 0.34 and -2.5-(-3.5) for PGA 0.68. When receiving cyclic load, the soil layer with an Ic value > 2.60 with a thickness of 1.6 m at the upper layer can withstand liquefaction with a thickness of 0.8 meters in the form of quicksand on the surface and only causes sand boils. Sand boils would not happen in the Kelapa Gading area if the excess pore water were redirected to discharge wells.

The Stability of Sidoarjo Mud Volcano Embankment Induced By The Excess Pore Water And Mud Pressure Based On Numerical Simulation

Sidoarjo mud volcano is a geology phenomenon which is the worst in terms of disaster to the people and environment. This is partly due to the overpressure at depth and as well as the cracks and fracture existence. Furthermore, the overpressurization impacts the increasing of pore water pressure and causing the reduction of effective stress. The complexity of the subsurface’s physical condition causes the instability of the embankment. This paper presents the evaluation of the stability of the embankment under the ideal and the presence of subsurface pressure conditions. The numerical simulation using Plaxis 2D has been conducted to determine the change of pore water pressure due to subsurface pressure and the safety factor of an embankment. The results show the subsurface pressure impact the increasing of pore water pressure around 208 kPa consequently. It reduces the safety factor around 4-30% from the ideal condition. The safety factor of embankment in the existing condition is still less than the minimum requirement which is 1,5 in both modeling conditions. The embankment collapse was caused by the landslide that leads upstream of the embankment as the effect of the tendency of upstream side landslides that is greater than the downstream side.

One-Dimensional Consolidation Analysis of Unsaturated Soils under Cyclic Loadings

This paper presents analytical solutions to Fredlund and Hasan’s one-dimensional consolidation equations for unsaturated soils subjected to various cyclic loadings. Two new variables are introduced so that the governing equations for excess pore air and water pressures can be transformed to a set of conventional diffusion equations. Based on the general solutions for two introduced variables, the analytical solutions are derived for one-dimensional consolidation of unsaturated soils under trapezoidal, rectangular, triangular, and haversine cyclic loadings. It shows through the degeneration into the existing solutions for unsaturated and saturated soils that the proposed solutions are more general ones for one-dimensional consolidation of soils from unsaturated to saturated states. A comprehensive parametric study is conducted to investigate the effects of different parameters on one-dimensional consolidation of unsaturated soils under various cyclic loadings. The proposed solutions can be effectively utilized in the analysis of consolidation of unsaturated soils subjected to various cyclic loadings.

Two‐Dimensional Parametric Study of an Embankment on Clay Improved by an Artificial Crust Composite Foundation

In order to reduce the foundation settlement, conserve resources, and be environmental‐friendly while increasing the use of soil resources, an artificial crust layer formed by in situ stabilization is proposed to combine with prestressed pipe piles over soft ground in road construction. In this study, a centrifuge test and two‐dimensional coupled‐consolidation finite‐element analyses are conducted to simulate the construction of an embankment. And a two‐dimensional parametric study is conducted to study the performance indicated by maximum long‐term settlement, excess pore water, and tensile stress under various conditions. The results of the centrifuge test clearly show that the measured settlement, excess pore water, and tensile stress are in good agreement with the calculated results. In addition, the key factors of pile spacing and thickness and strength of the crust have an influence on the maximum settlement, stress of the foundation, and tensile stress of the crust using the two‐dimensional coupled‐consolidation finite‐element analyses. And the stress transfer regular of the foundation is analyzed under various conditions. Moreover, the failure of the crust contained tensile cracking and shearing failure and the thickness of the pile that pierced the crust are also affected by the key factors.

Compaction of diagenetically altered mudstones – Part 1: Mechanical and chemical contributions

At low temperatures, siliciclastic mudstones compact mechanically. Above 70 °C, where the smectite-to-illite transformation dominates clay diagenesis, they also compact chemically, provided that excess pore water can escape. There are two prevailing conceptual models for the compaction of siliciclastic mudstones at higher temperatures, above ∼100 °C. One holds that precipitation of minerals during diagenesis cements the mudstones such that mechanical compaction no longer occurs even if the mudstones can drain freely. According to the other model, diagenetically altered mudstones continue to compact mechanically in response to increasing effective stress. We found that wireline-log and pressure data from Cretaceous mudstones at Haltenbanken are consistent with ongoing mechanical compaction accompanying chemical compaction up to at least 130 °C. We suggest that mechanical compaction continues because grain contacts in siliciclastic mudstones following smectite-to-illite transformation are still mostly between clay grains.

Poroelastic Theory of Consolidation in Unsaturated Soils

The theory of poroelastic behavior in a deformable porous medium containing two immiscible, viscous, compressible fluids was applied to the three‐dimensional consolidation of unsaturated soils. Three coupled partial differential equations were developed that feature the displacement vector of the solid phase and the excess pore water and air pressures as dependent variables. These equations generalize the classic Biot consolidation model, which applies to saturated soils, with effective stress emerging naturally from a pure compliance formulation of the relation between stress and strain. Under uniaxial strain and constant total compaction stress, the equations simplify to two coupled diffusion equations for the excess pore water and air pressures. Analytical solutions describing the response to instantaneous compression under both permeable and semipermeable boundary drainage conditions were obtained using the Laplace transform. Numerical calculations of pore water pressure, effective stress, and total settlement were made for a soil with clay texture as a representative example. The results show that excess pore water pressure dissipates faster at higher initial water content, leading to higher effective stress. The loading efficiency also was found to be highly sensitive to initial water saturation.

Using in situ pore water concentrations to estimate the phytotoxicity of nicosulfuron in soils to corn (Zea mays L.)

The phytotoxicity of an herbicide in soil is typically dependent on the soil characteristics. To obtain a comparable value of the concentration that inhibits growth by 50% (IC50), 0.01 M CaCl(2) , excess pore water (EPW) and in situ pore water (IPW) were used to extract the bioavailable fraction of nicosulfuron from five different soils to estimate the nicosulfuron phytotoxicity to corn (Zea mays L.). The results indicated that the phytotoxicity of nicosulfuron in soils to corn depended on the soil type, and the IC50 values calculated based on the amended concentration of nicosulfuron ranged from 0.77 to 9.77 mg/kg among the five tested soils. The range of variation in IC50 values for nicosulfuron was smaller when the concentrations of nicosulfuron extracted with 0.01 M CaCl(2) and EPW were used instead of the amended concentration. No significant difference was observed among the IC50 values calculated from the IPW concentrations of nicosulfuron in the five tested soils, suggesting that the concentration of nicosulfuron in IPW could be used to estimate the phytotoxicity of residual nicosulfuron in soils.

Linking ecological impact to metal concentrations and speciation: A microcosm experiment using a salt marsh meiofaunal community

Microcosm experiments addressed the impact of a mixture of Cu, Cr, Cd, Pb, and Hg at three concentrations after 36 h, 12 d, and 30 d on a meiofauna-dominated salt marsh community. In addition to analyzing effects on meiofaunal abundances, the study quantified the sediment metal concentrations of all five metals and pore-water concentrations, speciation, and ligand complexation of Cu. Abundances of deposit feeders such as the polychaete Streblospio benedicti, gastropods, and bivalves were impacted at lower metal concentrations than the mainly algal-feeding copepods, ostracods, and nematodes. We suggest that this might be due to bulk ingestion of metal-contaminated sediments resulting in relatively higher metal exposure in the deposit feeders than in the other, nondeposit feeding taxa. Copepod and ostracod abundances decreased only in the highest metal treatment, where levels of inorganic Cu ([Cu']) in pore waters were similar to levels associated with both acute and subacute toxicity in published in vivo toxicity studies of marine copepods. The higher metal treatments yielded disproportionately higher pore-water [Cu] compared with sediment [Cu], suggesting saturation of sediment-associated ligands with increased additions of Cu. Similarly, the higher metal treatments appeared to reach saturation of the organic Cu ligands, with the excess pore-water [Cu] present in the more toxic, inorganic species of Cu. Acid-volatile sulfide (AVS) concentrations at sediment horizons inhabited by meiofauna were low and AVS was not considered a significant metal ligand at these depths. Since meiofauna are predominantly associated with oxic surface sediments, it is doubtful that AVS is a major factor controlling availability of free metal for exposure to these taxa.

Field Studies of Well-Instrumented Barrette in Hong Kong

Over the last 15 years, barette foundations have become increasingly popular in parts of Asia, such as Hong Kong and Malaysia, for many civil engineering structures and tall buildings. A large excavated rectangular pile (barette) with lateral earth pressure and pore-water pressure cells was successfully constructed and tested in a sequence of marine, alluvial, and weathered granite soils. A soft base formed beneath the bottom of the barette permitted over 100 mm of vertical settlement, completely mobilizing the shaft friction at the barette-soil interface. During the vertical load tests, an unusual and complex response of pore-water pressures and earth pressures at the barrette-soil interface was measured. During each vertical loading cycle (except the last one) and before interface slippage of the barrette occurred, excess positive pore-water pressures were recorded in all soil layers. Upon the initiation of slip at the barrette-soil interface, a sudden drop in the measured pore pressures as well as a substantial drop in lateral earth pressures generally resulted. Subsequent loading and unloading slippage events did not show the same dramatic behavior unless a period of consolidation/recovery was allowed first. This implies that caution must be used in design of barrettes relying heavily on skin friction when shearing induces contractive soil behavior. The current test results indicated that the empirical uncorrected N-value measured by Standard Penetration Tests (SPT-N approach) and the deduced shaft friction coefficient (beta) value based on the effective stress principle (effective stress beta-method) were inconsistent.

Mechanics of mudflow mobilization in low-angled clay slopes

The Bagnold theoretical method of grain flow is used to explain the mobilization of mudflows formed in clay slopes on low angled surfaces. The reported texture of these mudflows consists of hard pieces of clay or rock in a soft clayey matrix (mud) which can be regarded as a mass of concentrated grains that are dispersed in a fluid medium as assumed by the Bagnold approach. The values of the slope angle at which four cases of mudflow of the reported texture are mobilized in the field, and those obtained using the Bagnold method, are closely in agreement. The Bagnold method provides an alternative to the ‘undrained loading’ and the ‘excess pore water or artesian pressure’ effects which are used to explain mudflow mobilization on flat surfaces but are reported to not be sufficiently comprehensive to explain all cases.