Hazard and risk assessment for sinkhole formation on dolomite land in South Africa

 A method is proposed to assess the risk for sinkhole formation in dolomitic areas where changes in land use are envisaged. Data from geotechnical site investigations are used for the zoning and characterization of sites in terms of the hazard (maximum size of sinkhole that can form), while the inherent risk for this hazard to occur is assessed by assuming that the site may be developed or treated incorrectly (abused). By considering both the hazard and the inherent risk, it is possible to select appropriate types of development and precautionary measures to reduce the final (development) risk to an acceptable level. Received: 15 September 1996 · Accepted: 12 May 1998     

Poroelastic analysis of cover-collapse sinkhole formation by piezometric surface drawdown

Where the water table is above the soil-rock contact in karst regions, cover-collapse sinkholes in the soil and soft sediment above the rock commonly occur as a result of drawdown of the piezometric surface in the karst aquifer. Transient stresses and pore pressures around soil voids at the soil-rock contact can cause hydraulic fracturing of the soil near the wall of the void. After the first such fracture, successive sloughing of soil propagates the soil void rapidly to the surface, resulting in a cover-collapse sinkhole. Sinkhole formation by this mechanism should be strongly a function of rate and magnitude of piezometric surface drawdown, permeability and tensile strength of the soil, and the size, depth, and geometry of the initial soil void. Large soil voids and those with walls that are partly planar or of low curvature are most susceptible to hydraulic fracture and the resulting progression to sinkhole formation.     

Occurrence and consequences of acid sulphate soils and methods of site remediation

The oxidation of sulphides in acid sulphate soils (ASS) causes the acidification of many Australian coastal river systems. The acidity negatively impacts upon coastal ecosystems, aquaculture, agriculture and concrete and steel infrastructure. In the low-lying floodplains, relatively deep surface drains fitted with one-way floodgates lower the watertable, thereby exposing the sulphidic minerals to oxidation. On the Broughton Creek floodplain in SE Australia, four distinct remediation strategies have been developed to tackle the issue of acidification by ASS: (i) simple V-notch weirs that raise the level of the watertable surrounding the drains thereby submerging the pyrite and preventing the further formation of acidity; (ii) modified two-way floodgates that allow the inflow of tidal water into the drains, thereby buffering the acidity within the drain before it enters the river and raising the level of the watertable surrounding the drain; (iii) lateral impermeable lime barriers that both prevent oxidation of pyrite by stopping the downward movement of oxygen into the soil and neutralise the acidity in the groundwater; and (iv) permeable reactive barriers (PRB) that passively intercept the groundwater flow and neutralise the acidity. Each remediation strategy has a distinct role to suit the different terrain and groundwater conditions.     

Sediment consolidation and archaeological site formation

Consolidation is the reduction in sediment volume that occurs in response to natural overburden loading. As void space is reduced, solid particles within the consolidating sediment undergo rearrangement, including downward displacement and reduction in inclination angle. Buried artifacts are also subject to this rearrangement. An experiment was designed to simulate consolidation of artifact‐bearing sediments and document the extent of artifact rearrangement caused by varying degrees of consolidation. Results indicate that artifacts will generally follow the downward movement of the sediment regardless of individual artifact attributes, and that significant reductions in artifact inclination angle can occur. © 2006 Wiley Periodicals, Inc.     

Conceptual models in exploration geochemistry: Norden 1975

This compilation and summary of geochemical exploration conditions in Norden is the second in a series of special issues on exploration geochemistry. The first issue dealt with the Canadian Cordillera and Canadian Shield. The conceptual models from the Canadian Shield form an integral part of the present volume. These studies are an attempt to pull together very extensive exploration geochemical information and define it in terms of a limited number of conceptual models.A total of 45 case histories are presented in this volume which cover various aspects of collection, analysis and interpretation of data from glacial till, stratified drift, organic deposits, stream sediments and water. These data are described in a relationship to the conceptual models outlined by Bradshaw (1975). An overall summary is given with respect to these models and also a summary is given of the relative importance of frost heave, transport by glaciation, transport by water and wind, multiple glacial transport, ion and molecular dispersion, groundwater transport, transport by capillary water, electrochemical transport and mixed dispersion.The final section contains 13 short articles dealing with methods of geochemical exploration which are presently used in the different countries of Norden.     

Models and mechanisms of drilling-induced sinkhole in China

The present paper distinguishes the four general types of collapsed sinkholes induced by drilling in regions where non-indurated sediments (clay, silt, and sand) overlie unknown caves or open voids in underlying lithified karst rocks. These sinkhole models are classified into balance arch, hourglass, vibration, and subjacent drilling-induced erosion forms. A mechanical model was built for each type to assess the collapse probability. Drilling operations using boreholes facilitate rapid, turbulent, and erosive flow. These activities resulted in the 26 sinkholes that have been attributed to constructions in China in the last several years. Awareness of potential collapse conditions should allow construction projects to avoid high-risk settings that result in economic losses, environmental concerns, and life-threatening accidents caused by such rapid collapse of the land surface. Awareness and close monitoring of high-risk conditions during borehole monitoring should minimize the hazard.     

Electrokinetic remediation of an electroplating site: design and scale-up for an in-situ application in the unsaturated zone

In-situ electrokinetic remediation of contaminated soils requires integrated approaches and adequately engineered setups to control relevant mass fluxes. Based on laboratory findings, this study presents the design of a pilot-scale remediation at an operating electroplating site. The fine-textured soil developed from Jurassic limestone exhibits a chromium, copper, nickel, and zinc contamination down to depths of more than 4 m. The feasibility of an electrokinetic remediation in the unsaturated zone was tested in a lab-scale experiment with subsoil material sampled at the site. The electrodes were placed in water-impermeable, ion-selective membrane wells. This construction allows the necessary watering of the electrodes, maintains unsaturated conditions in the soil compartment, and enables the transfer of contaminant ions into the wells. In addition, the soil is protected from pH changes caused by water electrolysis at the electrodes. The setup includes a watering and drainage system to compensate the electroosmotic water flux and impede desiccation of the anodic region. With a direct current of 70 V and an electric field strength of 2.2 V cm⁻¹, contaminant removal rates amounted up to 27% and 66% (w/w) of the initial zinc/copper and chromium/nickel concentrations. Copper, nickel, and zinc accumulated in the cathode well, while chromate species were enriched in the anode well. Given the successful lab-scale remediation, the pilot plant was designed for the in-situ treatment of a soil volume of 12 m³ below a production hall. A power of 500 V DC at a maximum current of 30 A is supplied by a transformer rectifier. This yields an electric field strength comparable to the lab-scale experiment and thereby similar contaminant transport velocities. A vacuum distillation unit is employed for process water reuse and to control electrolyte conductivity. To cope with chlorine gas generation at the anodes a gas absorber unit is employed. According to the lab-scale results, about 2, 9, 9, and 15 kg zinc, chromium, copper, and nickel, respectively, are expected to be removed from the field plot during an operation time of 10 months.     

Comparison of surrogate models with different methods in groundwater remediation process

Surrogate modelling is an effective tool for reducing computational burden of simulation optimization. In this article, polynomial regression (PR), radial basis function artificial neural network (RBFANN), and kriging methods were compared for building surrogate models of a multiphase flow simulation model in a simplified nitrobenzene contaminated aquifer remediation problem. In the model accuracy analysis process, a 10-fold cross validation method was adopted to evaluate the approximation accuracy of the three surrogate models. The results demonstrated that: RBFANN surrogate model and kriging surrogate model had acceptable approximation accuracy, and further that kriging model’s approximation accuracy was slightly higher than RBFANN model. However, the PR model demonstrated unacceptably poor approximation accuracy. Therefore, the RBFANN and kriging surrogates were selected and used in the optimization process to identify the most cost-effective remediation strategy at a nitrobenzene-contaminated site. The optimal remediation costs obtained with the two surrogate-based optimization models were similar, and had similar computational burden. These two surrogate-based optimization models are efficient tools for optimal groundwater remediation strategy identification.     

Taphonomy and site formation on California's Channel Islands

Inhabited by humans for over 12,000 calendar years, California's Channel Islands contain thousands of archaeological sites, ranging from dense shell middens and villages to small lithic scatters and camps. Similar to many islands around the world, the Channel Islands have a dearth of burrowing animals and limited historical development leading to generally good preservation of archaeological constituents and relatively high stratigraphic integrity. Despite these favorable preservation conditions, numerous natural and cultural processes have impacted the island's archaeological record. Channel Islands archaeologists, however, have given relatively limited attention to the effects of taphonomic and formation processes. The authors provide an overview of taphonomic and formation processes affecting Channel Islands archaeology, illustrating the importance of regional taphonomic syntheses in the management, preservation, and interpretation of archaeological sites. These data also demonstrate the significance of detailing formation processes in islands and other areas where burrowing rodents and other disturbances are thought to be absent or limited. © 2006 Wiley Periodicals, Inc.     

地下水位变化对透—阻型岩溶塌陷影响的分析

文章从一维地下水运动和渗透力学的角度,分析比较潜水位上升与承压水位下降对岩溶地区透—阻型盖层中阻水层渗透稳定性的影响,重点讨论了承压水位下降速度(降速)与下降深度（降深）对阻水层中渗透坡降的影响,结果表明:地下水位变化（潜水位上升或承压水位下降）产生的非稳定渗流不利于岩溶洞穴开口上方阻水层的稳定,承压水位的下降对岩溶开口附近处阻水层中渗透力的影响远大于潜水位的变化;在承压层水位最大降深确定的条件下,承压水位下降速度愈快,岩溶开口附近处阻水层中向下渗透力愈大。因此,在覆盖型岩溶地区抽取地下水时,为了减缓或避免覆盖型塌陷的发生,应同时控制好最大降深和最大开采速度。      

岩溶塌陷研究现状及趋势分析

为全面掌握当前国际岩溶塌陷研究动态,促进岩溶塌陷综合防治水平提升,重点从成因机制、识别评价和监测预警三个方面总结了当前国内外岩溶塌陷研究现状,以此为基础,综合运用文献和项目数据对国内外岩溶塌陷研究趋势进行了分析。结果显示:人类工程活动与岩溶环境相互作用关系是当前国际岩溶塌陷研究的热点;成因机理定量化、隐患识别快速化、监测预警精细化和风险防控时效化将是未来的重点攻关方向。      

Conceptual models in exploration geochemistry: The Canadian Cordillera and Canadian Shield

This volume summarizes the exploration geochemical conditions in the secondary environment, in the Canadian Cordillera and the Canadian Shield. This is achieved by a number of conceptual models which describe the principles and mechanisms of formation of anomalies, which govern the use of exploration geochemistry. These models have been constructed by drawing together information already existing in the literature plus 38 individual case histories contained in this volume.The formation of anomalies is described for: (1) residual overburden, (2) overburden of local origin (e.g. till), and (3) transported overburden of remote origin (e.g. stratified glacial drift and alluvium). Within each of these categories the effect of element mobility, seepage zones, bogs, variation in overburden thickness, rock type change and soil type change are also described.An attempt has been made, not only to summarize both these conditions where geochemistry can be used as a reliable exploration tool, but also to identify areas where the use of geochemistry is unreliable.A summary is also given of the length of anomalous dispersion and contrast in both soil and sediments for all the case histories quoted, both in this volume and in the literature. This summary is divided according to the type of deposit, i.e. porphyry copper, massive sulphide, etc., and provides a guide for planning the optimum sampling interval.     

Logistic regression model for sinkhole susceptibility due to damaged sewer pipes

The occurrence of anthropogenic sinkholes in urban areas can lead to severe socioeconomic losses. A damaged underground sewer pipe is regarded as one of the primary causes of such a phenomenon. This study adopted the best subsets regression method to produce a logistic regression model that evaluates the susceptibility for sinkholes induced by damaged sewer pipes. The model was developed by analyzing the sewer pipe network as well as cases of sinkholes in Seoul, South Korea. Among numerous sewer pipe characteristics tested as explanatory variables, the length, age, elevation, burial depth, size, slope, and materials of the sewer pipe were found to influence the occurrence of sinkhole. The proposed model reasonably estimated the sinkhole susceptibility in the area studied, with an area value under the receiver-operating characteristics curve of 0.753. The proposed methodology will serve as a useful tool that can help local governments to choose a cavity inspection regime, and to prevent sinkholes induced by damaged sewer pipes.     

Evaluation,repair and stabilization of the boling sinkhole

Abrupt ground subsidence occurred along FM 442, approximately 3 miles east of Boling, in Wharton County, Texas, in August 1983 The subsidence created a depression of approximately 250 feet in diameter with a maximum depth of about 25 feet. Roadway collapse, pavement breakage, and inundation of the sinkhole by subsurface waters forced the closure of FM 442 to thru-traffic The vicinity of the sinkhole is underlain, by alluvial deposits of the Colorado River drainage basin and unconsolidated Miocene, Pliocene, and Pleistocene sediments to a depth of about 500 feet. The sediments consist largely of sand, silts, clays, and gravels. The Boling Salt Dome and its associated caprock occur directly beneath the section of unconsolidated sediments Major and minor axes of the dome are about 5 miles and 35 miles, respectively, and the sinkhole occurred approximately 1 mile east-northeast of the dome's center An investigation was conducted in the immediate area of the sinkhole to determine the cause of the subsidence and also to determine the feasibility of dewatering the sinkhole Four monitoring wells were installed around the perimeter to evaluate the potential recharge from shallow sand units Two 300-foot holes were drilled and geophysically logged to determine the stratigraphy adjacent to the sinkhole, and two slope indicators were installed in order to evaluate further earth movements A total of six million gallons of saline water were removed and disposed of from the sinkhole Based on information provided by the geologic and dewatering investigation, the Texas State Department of Highways and Public Transportation elected to fill the existing sinkhole and reconstruct the roadway A total of 3,500 cubic yards of rock borrow and 26,000 cubic yards of soil borrow were placed in the depression Construction began in February 1984, and the roadway was completed in May A monitoring program to evaluate subsequent earth movements will continue into 1985     

Geoenvironmental protocol for site and waste characterization of former manufactured gas plants; worldwide remediation challenge in semi-volatile organic wastes

The most common and difficult of all hazardous waste sites are those that historically produced artificial (manufactured) gas; for gas-making was international in scope and at the very core of the industrial revolution. With former manufactured gas plants (FMGPs), virtually no geologic region in the industrialized or urbanized world or its trade centers and ports escaped the gas industry. These plants applied pyrolysis of organic matter (roasting to drive off volatiles in the form of useful gases) to illuminate the world and to fuel all manner of progress.

Gas was and is the universal fuel. Its prominence stemmed from the omnipresence of organic matter and the universal process for the extraction of its volatile contents to manufacture useful gas. Furthermore, for most of the century and a half-long history of manufactured gas, natural gas was unavailable to slow or daunt the production of man-made gas and the universal creation of its toxic tar residues and other harmful waste residuals.

Today we face the presence of toxic organic gas manufacturing residuals as a unique threat to both the health and welfare of contemporary society, as well as being a long-term threat to the environment that is dominantly geologic in character. Most of these tar residuals are highly resistant to natural degradation or attenuation in the environment and their lives, therefore, they are measured in geologic time. Given its environmental persistence, potential problems associated with tar may exist centuries to thousands of years.

Engineering geologists and geological engineers are, by training and experience, particularly well equipped to plan, manage and conduct site and waste characterization efforts for FMGPs and related coal-tar sites.     

Mechanism of sinkhole formation during groundwater-level recovery in karst mining area,Dachengqiao, Hunan province,China

The Meitanba Coal Mine area in Hunan province, China, had been impacted by severe cover collapse sinkholes since 1982 due to mine dewatering. After the coal mine was closed in February 2015, the groundwater level has increased significantly. A series of sinkholes were recorded in the study area during groundwater-level recovery. Analysis of monitoring results and in-situ investigation indicated that 13 sinkhole collapses were more likely induced by abrupt change of groundwater–air pressure in response to heavy rainfall from March 2015 to July 2016 when the groundwater level increased by as much as 76 m. When the karst conduit was flooded, a relatively sealed environment was formed between saturated sediments and flooded karst conduit. Implosion of entrapped air might have caused the cave roof to collapse followed by surface collapses in a short time. On the other hand, four sinkholes occurred in November 2016 when the groundwater levels were near the soil–bedrock interface at elevations between 52.5 and 58.9 m amsl and the groundwater-level increase was at slower paces. Field measurements indicate that the groundwater-level fluctuation at the soil–bedrock interface could enlarge the soil cavity and accelerate the subsoil erosion process.