Mechanisms to explain soil liquefaction triggering,development,and persistence during an earthquake

Mechanisms have been proposed to explain the triggering,development,and persistence of soil liquefaction.The mechanism explaining the horizontal failure plane(triggering)and its depth below the phreatic surface is governed by the flux properties and effective stress at that plane.At the failure plane,the pore water pressure was higher than the effective stress,and the volume change was the highest.The pore water pressure is a function of the soil profile features(particularly the phreatic zone width)and bedrock motion(horizontal acceleration).The volume change at the failure plane is a function of the intrinsic permeability of the soil and bedrock displacement.The failure plane was predicted to occur during the oscillation with the highest amplitude,disregarding further bedrock motion,which was consistent with low seismic energy densities.Two mechanisms were proposed to explain the persistence of soil liquefaction.The first is the existence of low-permeability layers in the depth range in which the failure planes are predicted to occur.The other allows for the persistence and development of soil liquefaction;it is consistent with homogeneous soils and requires water inflow from bedrock water springs.The latter explains many of the features of soil liquefaction observed during earthquakes,namely,surficial effects,“instant”liquefaction,and the occurrence of short-and long-term changes in the level of the phreatic surfaces.This model(hypothesis),the relationship between the flux characteristics and loss of soil shear strength,provides self-consistent constraints on the depth below the phreatic surfaces where the failure planes are observed(expected to occur).It requires further experimental and observational evidence.Similar reasoning can be used to explain other saturated soil phenomena.

Relationships Between Permeability and Erodibility of Cultivated Acrisols and Cambisols in Subtropical China

The relationships between soil erodibility factor （K） and soil saturated permeability （gfs） for cultivated Acrisols derived from Quaternary red clay and Cambisols derived from red sandstone were studied and quantified using a rainfall simulator and Guelph permeameter in a hilly area of subtropical China. A negative correlation existed between Kfs of the topsoil （0-5 cm） and K. The empirical expression K ≈ α × Kfs^-b＋c, where a, b and c are the structural coefficients related to soil properties, such as soil type, soil parent material, organic matter, pH and mechanical composition, best described the relationship between soil saturated permeability and soil erodibility.

Geochemical Assessment for Morendat East Geothermal Prospect, Using Radon and Carbondioxide Concentration from Soil, Kenya

Geochemical assessment was carried out at the Morendat East geothermal prospect by characterizing radon （22~Rn） and Carbondioxide （CO2） concentration levels from soil-gas survey. The primary aim was to locate permeable zones and infer the presence of possible heat source linked to an active geothermal system. The secondary aim was to rank the prospect and facilitate its development by the private sector. This study focused on the distribution of Radon and Carbon dioxide concentration levels in the soil cover within Morendat East area located in Nakuru County. The area was considered as having potential for geothermal resource hence earmarked for study in the financial Year 2014/2015 by the Ministry of Energy and Petroleum. The location is characterized by scarcity of surface geothermal manifestations hence soil gas survey was considered appropriate for the study. Random sampling method was used and resulted in sampling 100 points in an area of about 90 km^2. CO2 concentration measurements were done using an Orsat gas sampling apparatus whereas ^220Rn gas concentrations were measured using a portable radon detector. The CO2 values ranged from 0-5.4% while the ^220Rn ranged from 0-2,834 counts per minute （cpm）. Possible faults were inferred north of the prospect area due to the anomalously high levels of CO2 and ^220Rn recorded.

Study on the subgrade deformation under high-speed train loading and water–soil interaction

It is important to study the subgrade characteristics of high-speed railways in consideration of the water–soil coupling dynamic problem,especially when high-speed trains operate in rainy regions.This study develops a nonlinear water–soil interaction dynamic model of slab track coupling with subgrade under high-speed train loading based on vehicle–track coupling dynamics.By using this model,the basic dynamic characteristics,including water–soil interaction and without water induced by the high-speed train loading,are studied.The main factors-the permeability coefficien and the porosity-influencin the subgrade deformation are investigated.The developed model can characterize the soil dynamic behaviour more realistically,especially when considering the influenc of water-rich soil.

Some Classical Terzaghi Primary Consolidation Differential Equation Mathematical Added Variabilities in Order to Get Better Field Monitoring Data Match Results

In this paper is illustrated a mathematical added variability of the classical Terzaghi primary consolidation equation(1923)considering independently as variables the Consolidation Coefficient Cv and as well the Height Hi of the consolidating Laboratory Consolidation Test soil sample in order to finally grasp the low permeability layer time behaviour.It is easy to show that,when the Cv variation is positive,each of these two added variabilities differentiations has as maximum a factor 2 related to the laboratory evaluated coefficient of consolidation,for a certain incremental load of reference in a Laboratory Consolidation Test.At this scope,it is analysed the overall behaviour of a typical clayey material,from the mineralogical point of view,namely especially either composed by lean clay with main kaolinite mineralogical content or fat namely with Illite mineralogical content or even very dilatant namely principally constituted by Montmorillonite.The Montmorillonite variability with Cv is negative,and consequently the differentiation enhancement factor can become naught.As it is known so far,in normal conditions of a soft clay,a difference in Construction Values of the Coefficient of Consolidation is up to 23 times greater than laboratory evaluated results,and this according to the author’s experience,may be also mainly explained not starting from Laboratory Consolidation Test Data,but through a more general macroscopic behaviour of the soil underneath the newly loaded area,putting aside the case of temperature-induced changes.In conclusion,it is suggested how to model the analytical problem of the so modified Terzaghi Primary Consolidation differential equation in order to better manage the construction unknowns of the phenomenon.

Delta River Swampy Areas Earth Fill Embankments Primary Consolidation Management Issues

It is well known that soft silty clayey and even peaty soils especially existing in Great River Deltas Swampy Areas,under important Earth Fill Embankment Construction experience huge and hardly bearable primary consolidations settlements along with the minor but not negligible consequent secondary consolidation effects.In order to properly manage these particular huge settlements environments,it is very important to follow up the settlements monitoring data,by a macroscopic soil volume interpretation along with some amendments namely some mathematical added variabilities of the classic Terzaghi Primary Consolidation Equation,which are examined in a companion paper recently published in this Journal.In this paper some indications are given about how to face the macroscopic soil volume primary consolidation settlements,and especially it is suggested how to interpret the misleading laboratory consolidation test values of the coefficient of consolidation.Moreover,some design alternative solutions are examined to grasp both the potential technical and economic benefits along with their consequent disadvantages.Finally,this paper underlined the primary role of the supervision engineer to get a good estimate in the settlements forecasting and his related ability to understand the meaning of anomalous monitoring data and to timely make and match the primary consolidation settlements forecasting calculation adjustments.

Seismic isolation effect of lined circular tunnels with damping treatments

The Havriliak-Negami model for dynamic viscoelastic material behavior and Biot＇s theory of poroelasticity are employed to develop an exact solution for three-dimensional scattering effect of harmonic plane P-SV waves from a circular cavity lined with a multilayered fluid-filled shell of infinite length containing viscoelastic damping materials and embedded within a fluid-saturated permeable surrounding soil medium. The analytical results are illustrated with numerical examples where the effects of liner/coating structural arrangement, viscoelastic material properties, liner-soil interface bonding condition, seismic excitation frequency, and angle of incidence on the induced dynamic stress concentrations are evaluated and discussed to obtain representative values of the parameters that characterize the system. It is demonstrated that incorporating viscoelastic damping materials with a low shear modulus in the constrained layer configuration is an efficient means of enhancing the overall seismic isolation performance, especially for near-normally incident seismic shear waves where the amplitudes of induced dynamic stresses may be reduced by up to one-third of those without isolation in a relatively wide frequency range. Some additional cases are considered and good agreements with solutions available in the literature are obtained.

Active earth pressure acting on retaining wall considering anisotropic seepage effect

This paper presents a general solution for active earth pressure acting on a vertical retaining wall with a drainage system along the soil-structure interface. The backfill has a horizontal surface and is composed of cohesionless and fully saturated sand with anisotropic permeability along the vertical and horizontal directions. The extremely unfavourable seepage flow on the back of the retaining wall due to heavy rainfall or other causes will dramatically increase the active earth pressure acting on the retaining walls, increasing the probability of instability. In this paper, an analytical solution to the Laplace differential governing equation is presented for seepage problems considering anisotropic permeability based on Fourier series expansion method. A good correlation is observed between this and the seepage forces along a planar surface generated via finite element analysis. The active earth pressure is calculated using Coulomb's earth pressure theory based on the calculated pore water pressures. The obtained solutions can be degenerated into Coulomb's formula when no seepage exists in the backfill. A parametric study on the influence of the degree of anisotropy in seepage flow on the distribution of active earth pressure behind the wall is conducted by varying ratios of permeability coefficients in the vertical and horizontal directions,showing that anisotropic seepage flow has a prominent impact on active earth pressure distribution. Other factors such as effective internal friction angle of soils and soil/wall friction conditions are also considered.

Modeling Runoff from Semi-Arid Agricultural Lands in Northwest Iran

Transformation of rainfall into runoff over an area is a very complex process which exhibits both temporal and spatial variability;runoff in a defined area can be affected by factors such as topography, vegetation, rainfall characteristics and soil properties. This study was conducted to develop an empirical model using the rainfall characteristics and soil properties for predicting runoff from dry-farming lands in a semi-arid agricultural area in Hashtroud, Northwest Iran. Runoff plots(1.83 m × 22.1 m) in triplicate were installed in thirty-six sloped dry-farming lands in the study area. Runoff under natural rainfalls was measured in each plot during a2-year period. The results showed that runoff for 41 runoff-producing rainstorm events with duration longer than 30 min was largely associated with a rainfall index obtained by multiplying the positive square root of rainfall depth(h0.5) by the logarithm of the maximum 30-minute intensity(LogI30)(R2= 0.81). Runoff significantly varied among the plots(P < 0.001), which was considerably related to the effective soil properties(R2= 0.74), i.e., soil permeability(Per) and aggregate stability(AS). A multiple linear regression model was developed between runoff and the rainfall index(h0.5logI30) and the effective soil properties(AS and Per). Evaluation of the model using 34 runoff-producing rainstorm events that occurred during the next two years resulted in high values of the efficiency coefficient and R2(0.88 and 0.91, respectively), which revealed that the model developed in this study could be used in predicting runoff from the dry-farming lands in the semi-arid regions.