Muniram Budhu

Earth Fissure Formation from the Mechanics of Groundwater Pumping

This paper presents the formulation of the mechanics governing the changes in stress state from groundwater pumping. A 2-layer alluvium consisting of a cemented alluvium layer on top of an unconfined aquifer alluvium layer is considered. It is shown that the stress state in the aquifer alluvium consists of compression, simple shear, and couple stresses. The shear stresses on the vertical planes and horizontal planes are not equal. Consequently, a Cosserat rather than the conventionally used Cauchy continuum better simulates the stresses in the aquifer alluvium. Land subsidence from groundwater level decline consists of vertical compression (consolidation), shear displacement, and macrorotation. The latter occurs when conditions are favorable for the microrotation imposed by asymmetric stresses to become macrorotation. Earth fissures are formed in aquifer alluvium from groundwater pumping by simple shear on vertical planes and rotation and not by tension as commonly suggested. Earth fissures are formed in the upper cemented alluvium by simple shear strains and rotations. Highly cemented alluviums are more prone to earth fissure formation than weakly cemented alluviums. It is shown that there is a critical characteristic length of √2 times the aquifer alluvium thickness below which earth fissures would, theoretically, not develop. The distances from the well face at which earth fissures will form depend not on the total drop in groundwater level but on the gradient of the groundwater profile. The slope of the subsidence bowl, which consists of simple shear strain and rotation, is established as an indicator for the initiation of earth fissures.

Biopolymer Stabilization of Mine Tailings

AbstractA feasibility study was performed on using xanthan gum and guar gum, two biopolymers that are naturally occurring and inexpensive, to stabilize mine tailings (MT). The simple fall cone method was adopted to evaluate the liquid limit and undrained shear strength of sun-dried MT mixed with xanthan gum or guar gum solutions at different concentrations. Environmental scanning electron microscopy (ESEM) imaging was also conducted to study the microstructure of the biopolymer-MT system. The results indicate that the inclusion of xanthan gum or guar gum increases both the liquid limit and the undrained shear strength of the MT, higher biopolymer concentrations leading to greater increases. The increase of the liquid limit and undrained shear strength of the MT mixed with a biopolymer solution is mainly attributable to the high viscosity of the biopolymer pore fluid and the bonding between the biopolymer and the MT particles. Guar gum is more effective than xanthan gum in increasing the liquid limit and u...

The Influence of Clay Zones on Land Subsidence from Groundwater Pumping

The objective of this article is to analyze the influence of clay zones on subsidence from groundwater pumping. Finite element analyses were conducted on a sand-only aquifer and a sand aquifer with two clay zones located at different distances from the well face. A model that accounts for recoverable and nonrecoverable strains was used to simulate the sand and clay. This model couples the groundwater flow with the stress-deformation response of the aquifer materials. Each aquifer was pumped from a single well for a period of 6 months, and then the groundwater level was lowered gradually to an elevation below the elevation of the clay zones and kept there for 10 years. The groundwater level was then raised gradually back to the original elevation over a period of 10 years. The results of the analyses show that the ground surface subsidence profile is strongly influenced by the presence of the clays zones. The ground surface sags where these clay zones are present resulting in a wavy ground surface profile. Subsidence continued when pumping is stopped, albeit at a much slower rate than during pumping, and when the groundwater level is below the elevation of the clay zones. Clay zones further away from the well face lag the subsidence of clay zones nearer the well face because of lower changes in hydrostatic head. Sags in ground surface subsidence profile from groundwater pumping are indicators of the presence of low hydraulic conductive geological materials.

Earth fissure formation from groundwater pumping and the influence of a stiff upper cemented layer

Typical soil profiles in arid and semi-arid regions where groundwater is pumped consist of geological materials that vary from uncemented soils to rock. A finite-element analysis using a 20 m thick stiff cemented top layer over a 400 m thick aquifer is used to study how the cemented layer affects earth fissure initiation. This paper presents the results of this study on the key parameters influencing earth fissure formation in a soil profile with a top cemented layer. Three scenarios, each representing three cementation strength parameters, are investigated. A method based on the gradient of the slope of the subsidence bowl is proposed to determine earth fissure initiation. It is shown that earth fissures will not form for gradients below 8 × 10−5. The gradient at which an earth fissure would form depends on the cementation strength and tensile strength of the upper cemented alluvium layer. A highly cemented upper alluvium layer is more prone to earth fissure formation than an uncemented one. However, if the top layer is stiff enough to be classified as a ‘rock’, it will be less prone to earth fissure initiation when the cementation increases.

Shear Viscosity of Clays in the Fall Cone Test

Although viscometers are commonly used to determine the viscosity of clay soils, they are suitable only for determining the viscosity of soils for water contents greater than the liquid limit. Because soil flow can take place within the plastic range, the viscosity has to be determined through other methods. This paper investigates the use of a fall cone test to determine the viscosity of clay soils with a liquidity index of less than one. Eight soils, including kaolin and 6 natural clay soils, were thoroughly investigated using the fall cone test. The results of the study show that the fall cone test is suitable to determine the shear viscosity of clay soils. Excellent correlations were found between the liquidity index and the viscosity. A relationship exists between the dynamic equilibrium depth and the final penetration depth such that it is unnecessary to measure the rate of fall of the cone to determine the soil viscosity.

Feasibility Study of Compressed Air Energy Storage using Steel Pipe Piles

Because of the intermittent nature of renewable energy such as solar and wind energy, an energy storage system is needed to maximize the utilization efficiency of renewable energy. Of the different methods for energy storage, compressed air energy storage (CAES) is a promising one for storage of renewable energy. CAES can be divided into two general categories: large scale storage and small scale storage. The large scale storage includes salt caverns, hard rock caverns and deep aquifers, which require special geological formations that may not be available at a desired location. The small scale storage includes flexible bags under water, steel tanks above or below ground surface and pipelines above or below ground surface, which are flexible and can be used at different locations. In this paper, we briefly reviewed the different methods for CAES and studied the feasibility of using steel pipe piles for small scale CAES of renewable energy. The results indicate that steel pipe piles are a viable means for small scale CAES.

A lattice type model for particulate media

In this paper, a lattice-type model to simulate the micro-mechanical behaviour of particulate/granular media is presented. In this numerical model, a particulate assembly is simulated as a lattice/truss. Nodes located at contacts between a particle and its neighbours are linked by bars to each other. Each particle is represented by a lattice within its microstructure and particle interact through load transfer at the nodes. Constraints are prescribed at the nodes to describe active, deactivated and reactivated contacts. When a particulate assembly develops into a mechanism (deformation with zero incremental load), further deformation is simulated through a framework that describes the kinematics of the particles (sliding, rolling and rotation of particles). This framework is formed by introducing nodes at the particle centroids and linking them with bars. Bars-linking particles with a non-sliding contact are assigned large stiffnesses relative to bars linking particles with a sliding contact. Numerical tests are conducted on two-dimensional assemblies of disks, arranged as very loose and very dense packing under simple shear loading conditions. The results concord with the results of numerical tests conducted using the discrete element method and with photoelastic experiments. Additionally, the model is applied to study the effects of initial imperfections caused by particles with low elastic modulus.

Modelling groundwater changes due to fluctuating dam discharge

Abstract In this contribution, two numerical methods are used to predict the free surface changes in a sand bar due to fluctuations in river stage. One is a fixed-mesh, finite-element seepage formulation including Biots consolidation theory, and the other is a boundary element method solution of the Laplace equation. Both models give overall predictions that are in good agreement with field data recorded at an instrumented sand bar in the Colorado River subjected to stage fluctuations from operation of the Glen Canyon Dam. The boundary element method appears to offer significant advantage in data preparation and computational times over the finite-element method for the problem studied in this paper.

Ground Movements from Aquifer Recharge and Recovery

AbstractThis paper deals with ground response to surface water infiltration from an aquifer storage and recovery facility in Arizona. It presents a coupled groundwater flow–soil deformation model to investigate the role of low-hydraulic conductive materials (LHCMs), such as clays and silts, on the spatial and temporal flow and ground response. Finite element analyses were conducted that simulated the flow from surface injection ponds into the ground with and without LHCMs. The results showed that the presence of LHCMs significantly influences the flow path and the ground surface deformation profile.