Reconnaissance of the July 10, 2000, Payatas Landfill Failure

Following ten days of extremely heavy rains from two typhoons, a fast moving slope failure of municipal solid waste was triggered at the Payatas Landfill, Quezon City, Philippines. The wasteslide buried more than 330 persons. Only 58 persons were rescued while, after weeks of recovery efforts, 278 bodies were recovered. This paper documents the events and circumstances that led to the failure. Beyond stating the known facts leading up to the failure, only a brief discussion of the suspected reasons for the failure is presented in this paper.     

Translational Failure Analysis of Landfills

The scope of this paper is to develop a new approach to the two-part wedge method for translational failure analysis of landfills. The upper and lower bound solutions for the landfill stability, i.e., FSmax and FSmin, can be readily determined using this method. Using an average factor of safety, FSave, to replace the true factor of safety, FStrue, the differences between FSave and FStrue are within 5% for most considered cases. The solutions from the new method ensure that the waste strength is not exceeded anywhere within the waste mass. The calculated results agreed well with the results computed from the computer code PCSTABL6. The ability of the new method to calculate the translational failure of waste mass with a predetermined sliding failure face is demonstrated. Also, a waste filling sequence to keep the factor of safety above a stipulated value during the operation phase of the landfilling process can be generated.     

Case Study of the Failure of a Cross Vault: Church of Holyrood Abbey

The church of Holyrood Abbey, in Edinburgh, collapsed in 1768 after an inappropriate intervention in the nave vaults. This resulted in excessive lateral thrusts, which could not be contained by the existing buttressing systems, causing progressive instability of the lateral walls. This effect was studied on a lateral cross vault of the church. A replica in 1:4 scale was built and tested initially under service loads and subsequently until collapse due to movement of the two front abutments. Analysis of the model was carried out with the finite-element program ABAQUS. The resulting behavior demonstrated the significant load-bearing capacity of the structure under service conditions and its high sensitivity to imposed changes of the geometry. Although the tensile stresses exceeded the flexural strength at the vertices and the abutments, the collapse was dominated by the membrane tensile failure at the groins, hence both the geometry and condition of this area are critical for the safety of the vault. The results of this study can improve the assessment and thus help in the preservation of many important Gothic and neo-Gothic churches.     

Composition and Characteristics of Excavated Materials from a New Jersey Landfill

The composition of material excavated from the Burlington County landfill in New Jersey was determined, and the major reclaimed fractions characterized. Based on a waste age map, 98 samples (80?kg each) collected from 13 gas extraction well borings were handsorted into 14 fractions and fines (<2.54?cm) that fell through the screen were collected. At least 50%, by weight, of the material was fines. The most abundant oversize materials (overs) fractions, by weight, were miscellaneous items, wood, other plastics [not polyethylene terephthalate or high density polyethylene containers], and paper. Less paper was found in the oldest (7.5–11.5?years) section of the landfill (P<0.10), most likely due to microbial degradation. Several of the characteristics of the materials excavated from the landfill, such as temperature, particle size, bulk density, volatile solids, and contamination were correlated with the age of the deposits made. High levels of adherent soil will likely prove to be an insurmountable obstacle to recycling most excavated waste fractions other than fines unless further processing is pursued.     

Leaching Behavior of Metals Released from Cement-Stabilized/Solidified Refinery Oily Sludge by Means of Sequential Toxicity Characteristic Leaching Procedure

In this study, stabilization/solidification (S/S) of refinery oily sludge was applied using two types of cement (I and II), in cement-to-waste ratio from 0.1 to 0.7. The leaching behavior of heavy metals was investigated, by means of a five-point sequential toxicity characteristic leaching procedure (TCLP) test. Sequential TCLP was used to provide an improved assessment of long-term contaminant potential leachability, because the acidic leachant is renewed, whereas in the single TCLP, contaminant leachability is limited by the pH neutralization of the alkaline binder. Cement-based S/S of real refinery oily sludge resulted in very low leachability of heavy metals. Pb and Cd were not detected in any TCLP leachate. The maximum leachability of Fe, Zn, and Ni occurred in the pH range between 5.5 and 6.5. The leachability of Cu and Cr increased with increasing pH. Maximum cumulative percentage of Fe, Ni, and Zn leaching after five consecutive TCLP extractions (for worst case conditions, i.e., 10% II42.5) were 0.01, 22, and 1.2%, respectively, on the basis of metal content of each solidified sample. Further, the leaching behavior of Zn and Ni was modeled using the chemical equilibrium program Visual MINTEQ. Using several combinations of suspected solid phases of Zn and Ni hydroxides, carbonates and sulfides, and surface complexation onto ferrihydrite the diffuse double layer model did not accurately describe the leaching behavior of Zn and Ni.     

Performance of Historic Downstream Canal Control Algorithms on ASCE Test Canal 1

Researchers have developed several algorithms to automatically control water levels in irrigation canals. Proportional-integral (PI) control logic has been used for downstream water-level control, but its performance has not always been satisfactory. Heuristic downstream water-level controllers (e.g., canal automation for rapid demand deliveries, or CARDD) have also been proposed but not rigorously tested. The ASCE Task Committee on Canal Automation Algorithms developed a series of test cases to evaluate the performance of canal control algorithms. In this paper, simulation tests were performed on the ASCE Test Canal 1 using three downstream control algorithms: (1) The standard PI control logic; (2) The PI control logic with hydraulic decouplers; and (3) The heuristic CARDD control logic. These controllers were tuned manually using trial-and-error techniques. Performance of the PI control logic improved with the addition of hydraulic decouplers. CARDD did not perform as well as the PI controllers under the conditions imposed on ASCE Test Canal 1. Robustness of these controllers depends on the aggressiveness of the controller as well as the initial flow rate.     

Compaction Characteristics of Municipal Solid Waste

Compaction characteristics of municipal solid waste (MSW) were determined in the laboratory and in the field as a function of moisture content, compactive effort, and seasonal effects. Laboratory tests were conducted on manufactured wastes using modified and 4X modified efforts. Field tests were conducted at a MSW landfill in Michigan on incoming wastes without modifications to size, shape, or composition, using typical operational compaction equipment and procedures. Field tests generally included higher efforts and resulted in higher unit weights at higher water contents than the laboratory tests. Moisture addition to wastes in the field was more effective in winter than in summer due to dry initial conditions and potential thawing and softening of wastes. The measured parameters in the laboratory were γdmax-mod = 5.2?kN/m3, wopt-mod = 65%, γdmax-4×mod = 6.0?kN/m3, and wopt-4×mod = 56%; in the field with effort were γdmax-low = 5.7?kN/m3, wopt-low = 70%; γdmax-high = 8.2?kN/m3, and wopt-high = 73%; and in the field with season were γdmax-cold = 8.2?kN/m3, wcold = 79.5%, γdmax-warm = 6.1?kN/m3, and wwarm = 70.5%. Soil compaction theory was reasonably applicable to wastes with the exception that the Gs of waste solids increased with compactive effort resulting in steep degree of saturation curves and low change in wopt between efforts. Moisture addition to wastes during compaction increased the workability, the unit weight, and the amount of incoming wastes disposed, and reduced the compaction time. The combined effects have significant environmental and economic implications for landfill operations.     

Parameter Evaluation and Performance Comparison of MSW Settlement Prediction Models in Various Landfill Types

Estimation of settlement for municipal solid waste (MSW) landfills is critical to the successful site operation and maintenance as well as to the future development of the sites. In this paper, the six existing settlement prediction models are analyzed according to the three landfill types. 15 MSW landfill sites are classified into three categories, Types I, II, and III depending on their settlement activity levels and fill age. Measured settlement data of each landfill site are plotted as a strain curve on a logarithmic time scale, and the slope of the curve is used to determine a settlement activity level. First, the parameters of each prediction model are evaluated to determine their typical values for each type of the landfills. The results will serve as a basis for engineers to determine if their calculated model parameters are within the typical ranges. Second, each model’s performance of predicting settlement for the landfill sites is analyzed against the measured settlement data to compare the model’s applicability according to the landfill types. The results recommend specific prediction models to be used in a certain landfill type(s).     

Spatial and Temporal Temperature Distributions in Municipal Solid Waste Landfills

Long-term spatial and temporal variations in temperatures have been investigated in covers, wastes, and liners at four municipal solid waste landfills located in different climatic regions: Alaska, British Columbia, Michigan, and New Mexico. Temperatures were measured in wastes with a broad range of ages from newly placed to old (up to 40 years). The characteristic shape of waste temperature versus depth relationships consisted of a convex temperature profile with maximum temperatures observed at central locations within the middle third fraction of the depth of the waste mass. Lower temperatures were observed above and below this central zone, with seasonal fluctuations occurring near the surface and steady and elevated values (above mean annual earth temperature) near the base of the landfills. Heat gain and long-term temperatures were directly affected by placement temperatures. Sustained concave temperature profiles were observed for winter waste placement. The highest heat gain and resulting high temperatures were observed in Michigan followed by British Columbia, New Mexico, and Alaska. The high heat gain in Michigan was attributed to coupled precipitation/moisture content and waste density. The time-averaged waste temperature ranges were 0.9–33.0, 14.4–49.2, 14.8–55.6, and 20.5–33.6°C in Alaska, British Columbia, Michigan, and New Mexico, respectively. Temperature increases occurred rapidly (over multiple years) in British Columbia and then dissipated for tens of years. Longer periods of temperature increase were observed at the other sites. Temperatures, temperature increases, and heat gain were higher during anaerobic decomposition of wastes than aerobic decomposition. A parametric study indicated that use of insulating materials over covers decreased temperature variations compared to uninsulated conditions for prevention of frost penetration or desiccation and for optimum methane oxidation. Overall, thermal regime of landfills is controlled by climatic and operational conditions.     

Municipal Solid Waste Landfill Settlement: Postclosure Perspectives

This paper presents settlement mechanisms and the methods for estimating settlements of municipal solid waste landfills, including bioreactor landfills. Based on results of field monitoring and data in published literature, coefficients of secondary compression for solid waste due to self-weight and external load are estimated. Special considerations are given to bioreactor landfills. Uses of these coefficients for long-term settlement estimation and their application to postclosure maintenance and development plans are discussed. Four case histories illustrating the use of these coefficients are presented. Methods of landfill treatment to reduce settlements are also presented.     

Stability Analysis When Using an Engineered Berm to Increase Landfill Space

The scope of this paper is to develop a new three-part wedge method to analyze translational failure when using an engineered berm to increase landfill space. The possible failure face may pass over the back slope of the berm or pass under the bottom of the berm. This depends on the geometric dimensions of the berm which in turn influences the amount of airspace gained. Each possible failure condition must be checked to make sure both the waste mass and berm remain stable. If the waste boundary is kept to be unchanged, FSover will increase and FSunder will decrease with increase of the back slope of the berm. The critical failure condition may be changed from passing over to passing under the berm by changing the back slope of the berm. If the location of the front toe of the berm is fixed, both FSover and FSunder increase with increased height of the berm, however, the critical failure condition will change from passing under the berm to passing over the berm.     

Automatic Tuning of PI Controllers for an Irrigation Canal Pool

This paper presents a method to automatically tune decentralized proportional integral (PI) controllers for an irrigation canal pool. The auto tune variation (ATV) method is based on a relay experiment, which generates small amplitude oscillations of the canal pool. The ATV procedure can be used to get the integrator delay model parameters of a canal pool, which in turn can be used to tune a PI controller using classic rules, or other rules such as the ones proposed by Litrico and Fromion. This method does not require advanced automatic control knowledge and is implemented in the SIC software developed by Cemagref, which also incorporates a supervisory control and data acquisition module for real-time control. The ATV method is evaluated by simulations and experiments on a real irrigation canal located in the South of France, for local upstream, local downstream, and distant downstream controller tuning.     

Evaluation of Decomposition Effect on Long-Term Settlement Prediction for Fresh Municipal Solid Waste Landfills

A considerable amount of settlement occurs due to the decomposition of municipal solid waste (MSW) in landfills over a period of years. Therefore, the effect of biological decomposition governs the long-term settlement characteristics of municipal solid waste landfills. In this study, we investigated the long-term settlement characteristics by applying a number of prediction methods to fresh MSW sites and predicting the settlement curves. Most proposed methods, excluding the power creep law, successfully predicted long-term settlement only if accelerated logarithmic compression due to decomposition of biodegradable MSW was included in the settlement prediction.     

Canal Seepage Reduction by Soil Compaction

Simple in situ vibratory soil compaction of earth lined canals was tested to determine the impact on seepage losses. Commercial equipment was used for vibratory compaction of long sections of five irrigation district earthen canals. Ponding tests were conducted before and after compaction. When the sides and bottoms of the canals were compacted, seepage reductions of about 90% were obtained; reductions of 16–31% were obtained when only sides were compacted.     

Can Hazardous Waste Sites be Breached as a Result of Future Climate Change?

One of the most important design parameters for hazardous waste sites is the amount of precipitation that is predicted to fall on the unit throughout the duration of its life, usually decades to centuries. However, this design factor is complicated by strong evidence that climate change, whether from anthropogenic or natural causes, has increased the frequency and duration of strong storms throughout the world. This increase in precipitation can have serious consequences for the integrity of hazardous waste disposal facilities. Since the amount of precipitation falling on these units can accelerate the leaching of contaminants to the subsurface, any increase could cause premature failure. Historical records of rainfall are often used as a prediction of future precipitation in the design of hazardous waste management units. However, measurements made since the 1800s indicate that large-scale changes in precipitation have occurred over the Northern Hemisphere. Thus, the siting of hazardous waste disposal facilities should include an analysis of the effects of this possible increase in precipitation. Hazardous waste disposal facilities (especially landfills) also have the potential for failure due to design limitations. Increased precipitation can breach the cover system and cause either subsidence or leaching of contaminants into the subsurface. Little actual research exists that quantifies the effects of increased precipitation on the operation of abandoned or closed hazardous waste sites, so these effects need to be reviewed.     

Most Hydraulically Efficient Standard Lined Canal Sections

Cross-sectional dimensions of the most hydraulically efficient lined canals are evaluated based on an analysis of a generalized trapezoidal shape that reduces to two standard sections with rounded bottom vertices used in India, as well as to the commonly used trapezoidal section with sharp bottom vertices. The method of Lagrange multipliers is applied to find the dimensions of optimal sections when the only constraint imposed is that of uniform flow and normal depth and, in addition, when values of either channel side slope, bottom width, top width, or supply depth are specified as well. The analytic solutions obtained for the generalized trapezoidal section are shown to match known solutions for limiting cases including those for sections in the shape of sharp-cornered trapezoids, rectangles, triangles, and semicircles. Solutions presented will be useful for evaluating standard cross-sectional shapes used for lined canals in India, as well as other sections that can be obtained from the generalized trapezoid with rounded bottom vertices.     

Composite Compressibility Model for Municipal Solid Waste

Three important mechanisms that contribute to the compression of municipal solid waste are instantaneous compression in response to applied load, secondary mechanical creep, and time-dependent biological decomposition. A composite compressibility model that explicitly takes these mechanisms into account was developed and implemented in a computer program to calculate landfill settlements. The model performance was assessed using data from the Bandeirantes Landfill, which is a well-documented landfill located in Sao Paulo, Brazil, and upon which an instrumented test fill was constructed. Model parameter values were obtained by nonlinear regression analysis, and it was found that the composite model tracked observed patterns of landfill settlement very well. Furthermore, the average parameter values from nonlinear regression analyses for 20 instruments exhibited small deviations between calculated and observed settlements, indicating that a single set of parameter values can provide reasonably good representation of all the waste in the vicinity of the test fill. Recommendations for applying the model to other landfills are provided.     

Optimal Design of Parabolic Canal Section

Optimal design equations for a parabolic canal section are presented in this paper. The design equations for a minimum earthwork cost section and a minimum cost lined section are in explicit form and result in optimal dimensions of a canal in single step computations. These have been obtained after applying the Fibbonaci search method on a nonlinear unconstrained optimization problem. The study also addresses the bounds on the canal dimensions and the velocity of flow. A nondimensional parameter approach has been used to simplify the analysis, and a set of graphs for nondimensional parameters are presented as an alternative for design. Design procedures for different cases have been presented to demonstrate the simplicity of the method.     

Air Permeability of Waste in a Municipal Solid Waste Landfill

The permeability of compacted municipal solid waste in a landfill with respect to air (or gas) flow was estimated using a short-term air injection test. Air was added to 134 vertical wells installed at three different depths at flow rates in the range of 0.14?–1.4?m3?min?1 and the corresponding steady state pressures were recorded. The permeability of the waste with respect to airflow (described here as the air permeability) was estimated for different anisotropy ratios (kr/kz = 1, 10, and 100) using a steady state, two-dimensional, axisymmetric analytical fluid flow model in conjunction with the measured flow and pressure data. The air permeability of landfilled municipal solid waste modeled as an isotropic medium was found to range from 1.6×10?13 to 3.2×10?11?m2. The estimated air permeability results were on the low end of values previously applied to model landfill gas flow. Estimated air permeability decreased significantly with increasing waste depth. The lower permeability encountered in the deeper layers was primarily attributed to the lower porosity of the waste caused by higher overburden pressures and higher moisture content of waste in deeper layers of the landfill than in shallow layers. The results suggest that multiple wells screened at different depths provide greater control of air distribution within the landfill. Leachate recirculation was documented to impact the ability to add air. In addition to limitations posed by standing water in many of the deeper wells, waste exposed to leachate recirculation was found to be significantly less permeable to air when compared to original conditions.