Showing papers in "Journal of Geotechnical and Geoenvironmental Engineering in 2015"

Stress-Strain Behavior of Sands Cemented by Microbially Induced Calcite Precipitation

Abstract: Microbial induced calcite precipitation (MICP) is a novel biomediated ground improvement method that can be used to increase the shear strength and stiffness of soil. The evolution of the shear strength and stiffness of sand subjected to undrained and drained shearing is evaluated using triaxial tests. MICP treated sands with cementation levels ranging from young, uncemented sand to a highly cemented sandstonelike condition are subjected to undrained shear. A transition from strain hardening to strain softening behavior and a corresponding transition of global to localized failure as cementation is increased is observed. Moderately cemented specimens are subjected to various stress paths, which result in a change to the shear strength and volumetric behavior. Shear wave velocity is used to nondestructively monitor the change in small-strain stiffness during shearing, which provides an indication of cementation degradation as a function of strain level. Because shear wave velocity is influenced by ...

Efficient System Reliability Analysis of Slope Stability in Spatially Variable Soils Using Monte Carlo Simulation

Abstract: Monte Carlo simulation (MCS) provides a conceptually simple and robust method to evaluate the system reliability of slope stability, particularly in spatially variable soils. However, it suffers from a lack of efficiency at small probability levels, which are of great interest in geotechnical design practice. To address this problem, this paper develops a MCS-based approach for efficient evaluation of the system failure probability P f , s of slope stability in spatially variable soils. The proposed approach allows explicit modeling of the inherent spatial variability of soil properties in a system reliability analysis of slope stability. It facilitates the slope system reliability analysis using representative slip surfaces (i.e., dominating slope failure modes) and multiple stochastic response surfaces. Based on the stochastic response surfaces, the values of P f , s are efficiently calculated using MCS with negligible computational effort. For illustration, the proposed MCS-based system reliab...

Mechanisms for Soil-Water Retention and Hysteresis at High Suction Range

Abstract: Conventional conceptual mechanisms for the hysteresis of soil-water retention are the ink-bottle pore neck and the solid–liquid–air-contact angle. However, these mechanisms fail to explain hydraulic hysteresis for matric suction greater than 10 MPa. A conceptual model, based on hydration-water retention, is provided in this paper. Two hydration mechanisms, namely, particle-surface hydration and crystalline cation hydration, are distinguished to explain hydraulic hysteresis. The former is mainly involved in water retention by anions of oxygen and/or hydroxyls on particle surface, leading to reversible water adsorption and desorption. By contrast, cation hydration is controlled by both exchangeable cations and the intermolecular forces such as Coulomb attraction and London dispersion, leading to hysteretic water-retention behavior. Based on this hysteresis model, the highest total suction for any soil can be identified. From the isotherms of various soils at 25°C, it is found that the highest total ...

Behavior of Geocell-Reinforced Subballast Subjected to Cyclic Loading in Plane-Strain Condition

Abstract: Large-scale cubical triaxial tests were conducted to investigate the behavior of reinforced and unreinforced subballast under cyclic load. Granular material with an average particle size (D50) of 3.3 mm and geocell with a depth of 150 mm and nominal area of 46×103 mm2 were used in this study. The laboratory results proved that subballast stabilization was influenced by the number of cycles (N), the confining pressure (σ3′), and the frequency of train-caused vibration (f). The experimental results also confirmed that the geocells influenced the subballast behavior under cyclic loading, particularly at low confining pressure and high frequency. The additional confining pressure induced by the geocell reduced its vertical and volumetric strains. The optimum confining pressure required to reduce excessive volumetric dilation also was identified in this study. An empirical model using a mechanistic approach is proposed to determine the additional confinement induced by the geocells, as well as the prac...

Closed-Form Equation for Thermal Conductivity of Unsaturated Soils at Room Temperature

Abstract: Thermal conductivity is a fundamental physical property governing heat transfer in soil. It depends on soil types, pore structure, temperature, and moisture content, and can vary over an order of magnitude. Some theories have been established to address the effect of temperature on thermal conductivity. Other theoretical works focus on the effect of moisture content on thermal conductivity of different sandy and loamy soils. This work addresses the effect of all soil types and moisture content on thermal conductivity for ambient temperatures from 20 to 25°C. Thermal conductivity varies little within the hydration and capillary regimes, varies moderately within the funicular regime, and varies greatly within the pendular regime. A closed-form equation is proposed and validated by explicitly considering the soil-water retention regimes. Results taken from the literature for 25 soils and from the current study for two clay soils show that the closed-form equation can accurately predict thermal conduc...

Active Earth Pressures for Unsaturated Retaining Structures

Abstract: Although commonly ignored in classical earth pressure methods, precipitation-induced failures in retaining structures highlight a need for explicit consideration of negative pore pressures or matric suction. Changes in the degree of saturation in the backfill can significantly affect active earth pressures. This paper presents an analytical framework for calculating the thrust of active earth pressures under unsaturated steady flow conditions. The proposed method addresses limitations associated with the collapse mechanism and effective stress representation in alternative analytical methods. The formulation was derived by implementing an analytical solution for one-dimensional (1D) steady flow into a limit equilibrium–based effective stress analysis. A closed-form solution for the thrust was obtained by employing a log spiral surface, considering the effect of tension cracks, backslope inclination, and batter for c′-ϕ′ soils with variable backfill saturation. A unified effective stress representa...

Behavior of Geotextile-Encased Granular Columns Supporting Test Embankment on Soft Deposit

Abstract: A 5.35 m high test embankment was constructed on a soft foundation improved by geotextile-encased granular columns (GECs). The embankment construction was performed in four stages over 65 days, resulting in a total applied stress of around 150 kPa. The soft soil and the encased columns were instrumented to measure surface settlements, excess pore pressure, surface vertical stresses, and radial deformation of the geotextile encasement. Stress concentration and the difference in settlement between the top of the encased columns and the soft soil were studied. Results showed that the differential settlement increased as the embankment height increased and when the excess pore pressure was being dissipated. Due to soil arching, the vertical stress supported by the encased column was over two times greater than the stress transmitted to the soft soil. Also, vertical stress on the encased column increased as consolidation progressed, whereas it did not vary significantly on the soft soil.

Tensile Strength of Compacted Clayey Soil

Abstract: Tensile strength of soil plays an important role in controlling the cracking and tensile failure of many earth structures. In this investigation, a direct tensile test apparatus was developed to determine the tensile strength of compacted clayey soil over a broad range of water contents (4.3–28.5%) and with different dry densities (1.5–1.7 Mg/m3). The results show that the tensile strength of compacted clayey soil significantly depends on water content. The tensile strength characteristic curve (TSCC) exhibits one peak value occurring at the critical water content wc around 11.5%. With increasing water content, the tensile strength increases at the dry side of wc and then decreases at the wet side of it. Generally, with the increase of dry density, the tensile strength also increases. Moreover, a modified model is proposed to describe the tensile strength characteristics of compacted clayey soil, and it is validated by the obtained test data.

Improved Simplified Method for Prediction of Loads in Reinforced Soil Walls

Abstract: The Simplified Method as reported in AASHTO and Federal Highway Administration (FHWA) manuals has been demonstrated to give poor predictions of unfactored reinforcement loads and strains, especially for geosynthetic reinforced soil walls. The writers have proposed the K-stiffness Method to improve the load prediction accuracy for walls under working stress (operational) conditions. However, it has also been recognized in recent publications by the writers and others that further improvements to the K-stiffness Method are needed. Furthermore, acceptance of the K-stiffness Method has been hindered due to its perceived complexity and the use of the plane strain friction angle to quantify the strength of the reinforced soil. This paper takes a fresh look at both methods and uses lessons learned from the K-stiffness Method development to improve the accuracy of the AASHTO/FHWA Simplified Method. Key parameters introduced during the development of the K-stiffness Method are applied to the Simplified Met...

Shake Table Test of Large-Scale Bridge Columns Supported on Rocking Shallow Foundations

Abstract: This paper presents the results of a series of shake table tests of two 460-mm-diameter columns supported on 1.5-meter-square shallow rocking foundations. The tests were conducted using the Large Outdoor High-Performance Shake Table of the Network for Earthquake Engineering Simulation at the University of California at San Diego. The first specimen was aligned with the uniaxial direction of shaking, and the second was positioned in a skew configuration. The specimens were placed inside a soil-confining box 10.1 m long and 4.6 m wide with a 3.4-m height of clean sand compacted at 90% relative density. Three series of tests were performed; each had different groundwater and backfill conditions. The test protocols included up to six historical ground motions and resulted in peak drift ratios up to 13.8%. For peak drift ratios up to 6.9%, the rocking foundations performed very well, with residual drift ratios between 0.5 and 0.9% depending on the backfill conditions and with minimal settlements and no...

Posttemperature Effects on Shaft Capacity of a Full-Scale Geothermal Energy Pile

Abstract: Shallow geothermal heat exchangers integrated in structural pile foundations have the capability of being an efficient and cost-effective solution to cater for the energy demand for heating and cooling of built structures. However, limited information is available on the effects of temperature on the geothermal energy pile load capacity. This paper discusses a field pile test aimed at assessing the impact of thermomechanical loads on the shaft capacity of a geothermal energy pile. The full-scale in situ geothermal energy pile equipped with ground loops for heating/cooling and multilevel Osterberg cells for static load testing was installed at Monash University, Melbourne, Australia in a sandy profile. Strain gauges, thermistors, and displacement transducers were also installed to study the behavior of the energy pile during the thermal and mechanical loading periods. It has been found that the pile shaft capacity increased after the pile was heated and returned to the initial capacity (i.e., initi...

Failure Mechanism and Bearing Capacity of Footings Buried at Various Depths in Spatially Random Soil

Abstract: The objective of this paper is to demonstrate how the spatial variability of random soil affects the failure mechanism and the ultimate bearing capacity of foundations buried at various depths. A nonlinear finite-element analysis combined with random field theory is employed to explore the vertical capacity of foundations embedded at different depths in random soil. Different possibilities of shear failures resulting from spatial patterns of soil are demonstrated and are used to explain the significant discrepancy between the bearing capacity of the random soil and that of uniform soil. The effect of the spatial pattern of the soil on the development of shear planes is also investigated, with the coefficients of variation for the bearing capacity demonstrated to be closely related to the shear plane length. The results of the statistical variation in the bearing capacity are provided for different embedment depths, and these are also reported as the failure probability of the footing compared wit...

Centrifuge Modeling of End-Restraint Effects in Energy Foundations

Abstract: This study presents the results from physical modeling experiments on centrifuge-scale energy foundations in dry sand and unsaturated silt layers. These experiments were performed to characterize end restraint effects on soil-structure interaction for energy foundations in different soils and include tests on foundations with semifloating and end-bearing toe boundary conditions and free-expansion and restrained-expansion head boundary conditions. Two scale-model energy foundations having different lengths were constructed from reinforced concrete to simulate end-bearing and semifloating conditions in soil layers having the same thickness. The foundations include embedded thermocouples and strain gauges, which were calibrated under applied mechanical loads and nonisothermal conditions before testing. The variables measured during the experiments include axial strain and temperature distributions in the foundation, temperature, and volumetric water content measurements in the soil, vertical displace...

Biopolymer Stabilization of Mine Tailings for Dust Control

Abstract: Mine tailings, or mill tailings (MTs), are highly susceptible to wind erosion (dust) and have brought about different environmental and safety concerns. Many efforts have been attempted to stabilize MTs for dust control, but all have drawbacks. The current study investigates the feasibility of using two natural and renewable biopolymers, xanthan gum and guar gum, to stabilize MTs for dust control. Moisture retention and wind tunnel tests were performed to evaluate, respectively, the enhancement of water retention capacity and the improvement of resistance to wind dispersal after MTs were treated with biopolymer solutions of different concentrations. Because the resistance to the formation of dust is closely related to how easy the particles can be detached from the surface, a flat-ended cylindrical penetrometer was manufactured and used to evaluate the surface strength (maximum penetration force) of dry MT specimens treated with biopolymer solutions of different concentrations. Scanning electron ...

Thermal-Hydro-Mechanical Analysis of Frost Heave and Thaw Settlement

Abstract: Frost heave and thaw settlement are the cause of substantial damage to infrastructure in regions of seasonal freezing as well as seasonal thawing (permafrost). While frost heaving of soils has been researched for decades, less attention has been paid to quantitative estimates of settlement and loss of strength of soils due to thawing. A constitutive model is developed, capable of simulating freezing and thawing of soils, and associated changes in the soil strength. While the porosity growth parameters describing frost heaving have been calibrated and validated for a specific soil, the description of the thawing phase has not been validated due to a lack of experimental data. The yielding of the frozen soil is described using the critical state concept, with the pore ice content being an important parameter affecting the yield function. The model was calibrated using available laboratory test data and used in the simulation of a freezing–thawing cycle in the soil with embedded footing.

Bearing Capacity of Footings Placed Adjacent to c′-ϕ′ Slopes

Abstract: Conventional bearing capacity analyses for shallow foundations placed on slopes use a modified set of bearing capacity factors based on soil properties, footing geometry, and slope configuration, but are restricted to purely cohesionless or purely cohesive soils. This approach is adequate for establishing bearing capacity on engineered fills with controlled foundation properties, yet does not adequately address design for bearing capacity on soils that have both cohesion and internal frictional resistance—a common scenario for native soils. This role becomes increasingly important in design for mechanically stabilized earth walls, which are often placed on slopes of native c′-ϕ′ soils in which the bearing capacity can often be the critical design constraint. Prior approaches to bearing capacity on horizontal ground for c′-ϕ′ soils utilize principles of limited state plasticity in their formulation, yet the most commonly applied bearing capacity approaches on slopes use semiempirical formulations t...

Evaluation of one-dimensional site response techniques using borehole arrays

Abstract: Numerical techniques commonly used to compute the dynamic response of soil deposits under earthquake shaking are investigated by analyzing data from instrumented borehole arrays. Eleven instrumented vertical arrays are investigated using over 650 recorded ground motions that span a range of shaking intensities. Based on data from the selected borehole arrays, site response predictions using one-dimensional equivalent linear (EQL) analysis, equivalent linear analysis with frequency-dependent soil properties (EQL-FD), and fully nonlinear (NL) analysis are compared with the borehole observations. The results across all sites indicate that at peak shear strains less than about 0.1%, all three site response techniques predict, on average, site amplification within ±20% of observed. At peak shear strains larger than 0.1% and at periods less than about 0.4 s, EQL and NL analyses underpredict site amplification and EQL-FD analyses overpredict site amplification. The underprediction for the EQL and NL tech...

Numerical Evaluation of the Behavior of GRS Walls with Segmental Block Facing under Working Stress Conditions

Abstract: This study numerically evaluated the combined effects of different controlling factors (i.e., wall height, stresses induced during backfill compaction, reinforcement stiffness, toe conditions, and facing stiffness) on the behavior of geosynthetic-reinforced soil (GRS) walls under working stress conditions. The results were compared with values predicted by different currently used methods. It was shown that toe resistance has a major effect on the prediction capability of those design methods. Parametric analyses have shown that the amount of tension in the reinforcement varies with restraint at the base of the block facing. For free-base conditions with a constant value for reinforcement stiffness, the tension in the reinforcements was the same irrespective of the facing stiffness and the wall height. For the fixed-base conditions, the amount of tension in the reinforcements and horizontal toe load varied as a function of the facing stiffness. Comparing individual measurements of reinforcement te...

Geometrical Method for Evaluating the Internal Instability of Granular Filters Based on Constriction Size Distribution

Abstract: Internal instability occurs when the finer fraction from a well-graded granular soil escapes with the infiltrates, rendering a filter ineffective Thus far, numerous particle size as well as constriction size distribution–based geometrical methods have been proposed to assess potential internal instability This paper reports the results from hydraulic tests performed on six granular soils (five well-graded sand-gravel mixtures and medium sand) at different uniformity coefficients and compacted at varying relative density The study facilitated an objective evaluation of some of the well known published methods, leading to a more realistic interpretation of filtration data based on a revised technique, which accurately demarcates the boundary between internally stable and unstable granular soils A large body of published data and the current laboratory results were used to validate the proposed criterion for the assessment of internal instability, which is also sensitive to the relative density o

Experimental Studies on Behavior of Single Pile under Combined Uplift and Lateral Loading

Abstract: 1-g model experiments were carried out in the laboratory to investigate the behavior of a single pile in sand under combined uplift and lateral load. Dimensions of the model pile were ascertained using physical scaling laws, based on adopted material properties of model and prototype pile foundations. The model pile is made up of aluminum and has outer and inner diameters of 25.4 and 19.0 mm, respectively. Different length-to-diameter ratios of 18, 28, and 38 are considered by varying the pile length to simulate behavior of both stiff and flexible piles. The test tank dimensions were chosen such that boundary effects are minimized. The size of the model steel tank is 1.0×1.0×1.2 m (depth). Experiments were performed on single piles embedded in sandy soil under independent uplift and lateral loading, and combined lateral and uplift loading. Results indicate that the load-deflection behavior is nonlinear for independent uplift and lateral load tests, as well as in the case of combined loading. It i...

Robust geotechnical design of earth slopes using fuzzy sets

Abstract: This paper presents a fuzzy set–based robust geotechnical design (RGD) approach for the design of earth slopes in which uncertain soil parameters are represented as fuzzy sets. For a slope with fuzzy sets as inputs, the stability (factor of safety) of the slope is also a fuzzy set. The failure probability of the slope can readily be determined based on the obtained fuzzy factor of safety; further, the design robustness in terms of the signal-to-noise ratio (SNR) can also be evaluated. The purpose of the RGD is to derive a design that is robust against the uncertainty in the input parameters, with an explicit consideration on safety and cost. Therefore, a multiobjective optimization is performed and a three-dimensional or two-dimensional Pareto front showing a trade-off between objectives can be obtained, which allows for an informed design decision. The effectiveness of the proposed fuzzy set–based RGD approach is demonstrated through an illustrative example.

Discussion of “Kinematic Bending of Fixed-Head Piles in Nonhomogeneous Soil” by Raffaele Di Laora and Emmanouil Rovithis

Abstract: Kinematic bending of elastic single fixed-head piles in continuously inhomogeneous soil is explored in both static and dynamic regime. A generalized parabolic function is employed to describe the variable shear modulus in the inhomogeneous stratum, which can simulate both cohesive and cohesionless soil deposits. The problem is treated numerically by means of rigorous elastodynamic finite-element analyses and simplified beam-on-dynamic-Winkler-foundation (BDWF) formulations. A novel expression is proposed for the active length of a pile in inhomogeneous soil, by means of kinematic interaction considerations. This allows an alternative interpretation of kinematic soil-pile interaction along an effective depth, contrary to existing definitions in which soil response is evaluated at a specific location. Following this interpretation, a design formula for kinematic pile-head moments is derived for both static and dynamic loading. A new dimensionless parameter is identified to govern dynamic pile bendin...

Cyclic Shear Strain Needed for Liquefaction Triggering and Assessment of Overburden Pressure Factor Kσ

Abstract: This paper has two objectives. The first is to evaluate the cyclic shear strain needed to trigger liquefaction, γcl, in clean and silty sands in the field during earthquakes as an alternative to the currently used cyclic resistance ratio (CRR). The second objective is to explore the effect of a high effective overburden pressure, σv0′, on the value of CRR. The first objective is accomplished mainly by using an equation relating γcl and CRR valid for shear wave velocity–based liquefaction charts. This equation is supplemented with laboratory results from undrained cyclic strain-controlled tests as well as large-scale and centrifuge model shaking experiments. It is shown that for recent uncompacted clean and silty sand deposits and earthquake magnitude Mw=7.5, γcl≈0.03%, with this value increasing to γcl≈0.3% (in some cases to 0.6%) in denser and overconsolidated, preshaken, and compacted sands. These small values of γcl in the field are controlled by two factors: excess pore pressure buildup in the...

Vibration Reduction of Plane Waves Using Periodic In-Filled Pile Barriers

Abstract: The frequency dispersion characteristics of pile barriers are receiving more attention due to their effectiveness and a better understanding of their behavior at attenuating middle and lower frequency ground vibrations. Based on a comprehensive study, this paper proposes a two-dimensional periodic pile barrier system, which can produce low-frequency or middle-frequency attenuation zones (AZs). Periodic pile barriers are composed of periodically arranged hollow piles filled with either soft or hard in-fill materials. Finite element method and plane wave expansion method are first used to study dispersion curves, AZs, and corresponding wave dispersion mechanisms. Influencing factors of the periodic pile barrier on the AZs are then identified based on a parametric study. To further illustrate the effectiveness of the vibration attenuation, a three-dimensional pile–soil finite element model with combined periodic pile barriers is analyzed, and the frequency ranges of vibration reduction are found to b...

Characterization of Model Uncertainty for Cantilever Deflections in Undrained Clay

Abstract: This work presents a critical evaluation of the model factor for the mobilized strength design (MSD) method for cantilever deflection in undrained soft to medium-stiff clay. The model factor is characterized in two parts. A correction factor η is first defined as the ratio between the wall-top deflection computed from the FEM and its corresponding value computed from the MSD. The hardening soil with a small-strain model is used in FEM. The statistics of η are evaluated using 82 numerical simulations. Because η is not random, and therefore cannot be modeled directly as a random variable, it is decomposed as a product of a systematic part (f) and a random part (η∗). The random part is modeled as a lognormal random variable with a mean of 1.01 and a coefficient of variation (COV) of 0.18. The model factor for FEM (eFEM) is next defined as the ratio between the measured wall-top deflection and the corresponding FEM result. The statistics of eFEM are evaluated using 45 field cases. The ratio eFEM is ra...

Evaluation of Pipe-Jacking Forces Based on Direct Shear Testing of Reconstituted Tunneling Rock Spoils

Abstract: The installation of underground trunk sewer lines in the Tuang formation of Kuching City, Malaysia, used trenchless technology in the form of the pipe-jacking method. The evaluation of pipe-jacking forces mainly involves empirical models developed for soils, with rather limited considerations for drives through weathered rock. Therefore, a novel approach is proposed to evaluate strength parameters by reconstituting and subsequently shearing scalped tunneling rock spoils in the direct shear apparatus. The direct shear results are then applied to a well-established pipe-jacking force model, which considers arching theory. The outcomes indicate that the backanalyzed frictional coefficients μavg are not only reliable but also related to their surrounding geologies because of soil-structure interaction. This study also highlights the significance of lubrication and effect of rock arching in assessing jacking forces. The successful characterization of reconstituted tunneling rock spoils in this paper ha...

Drained Monotonic Responses of Suffusional Cohesionless Soils

Abstract: Mechanical consequences of suffusion on the noncohesive soils with various initial fine contents under different initial effective confining pressures are presented in this paper. By using the modified triaxial permeameter, seepage tests and successive drained monotonic compression tests are performed. It is found that soil-drained strength decreases after suffusion and a temporary drop in stiffness at the initial stage of shearing with respect to the axial strain ranging from 0 to 1% is observed. The tests suggest that suffusion might create a distinct packing of soil grains, which might result from possible accumulation of fine grains at the spots where the constriction size—representing the size of pore channels in a soil—is smaller than that of fines. Those surviving fines after suffusion may function as reinforcement or jamming at the subsequent compression, resulting in a larger initial stiffness of the suffusional soils.

Bearing Capacity Factors for Ring Foundations

Abstract: Bearing capacity factors because of the components of cohesion, surcharge, and unit weight, respectively, have been computed for smooth and rough ring footings for different combinations of r(i)= r(o) and. by using lower and upper bound theorems of the limit analysis in conjunction with finite elements and linear optimization, where r(i) and r(o) refer to the inner and outer radii of the ring, respectively. It is observed that for a smooth footing with a given value of r(o), the magnitude of the collapse load decreases continuously with an increase in r(i). Conversely, for a rough base, for a given value of r(o), hardly any reduction occurs in the magnitude of the collapse load up to r(i)= r(o) approximate to 0.2, whereas for r(i)= r(o) > 0.2, the magnitude of the collapse load, similar to that of a smooth footing, decreases continuously with an increase in r(i)= r(o). The results from the analysis compare reasonably well with available theoretical and experimental data from the literature. (C) 2015 American Society of Civil Engineers.

Dike Failure Mechanisms and Breaching Parameters

Abstract: Dike risk management requires breaching parameters that can be estimated rapidly to support the prediction of inundation zones and decision making The objectives of this paper are to compile a database of dike breaching cases, study common dike failure mechanisms, and develop a set of empirical equations for estimating breaching length, depth, and peak discharge A database of over 1,000 dike failure cases was collected, with information on pre-breach dike geometry, materials, type of dike, failure mechanisms, breaching length, depth, and peak discharge A set of regression models are formulated using five control variables: dike height, width, material, type of dike, and failure mechanism The standard error is set as a selection criterion and the Akaike information criterion is used to optimize the proposed empirical models The new models are validated using independent cases and compared with available empirical equations for dikes and man-made dams

Dependence of Gas Collection Efficiency on Leachate Level at Wet Municipal Solid Waste Landfills and Its Improvement Methods in China

Abstract: Landfill gas (LFG) collection efficiency is low at many municipal solid waste (MSW) landfills in China. The relevant mechanism and potential solution for this problem are studied through laboratory gas permeability tests on MSW, field LFG extraction tests at a landfill subjected to leachate drawdown, numerical assessment of the LFG collection efficiency at the landfill with different leachate levels, and engineering application of the measures to improve LFG collection. The research work outcomes are as follows: High water content in the food-rich MSW is one of the major reasons causing the high leachate level at many Chinese landfills. High leachate mounds tend to result in a high degree of saturation in waste, and hence a low gas permeability of the waste. Therefore, the LFG collection efficiency at Chinese landfills with high leachate level is lower than expected. A drawdown of leachate level at a Chinese landfill by pumping resulted in a significant increase in the LFG collection rate and the ...