Abstract

The engineering economics of an integrated coal-to-methanol conversion system and coal-in-methanol transportation system are examined, under the circumstances of the western coalfields, i.e., long distances from major markets and scarcity of water in the vicinity of the mines. The transportation economics are attractive, indicating tariffs of approximately 40 cents per million Btu per thousand miles for the coal-methanol pipeline vs 60 cents via coal-water pipelines and upwards of a dollar via rail. Energy consumption is also less in the coal-methanol pipeline than in the coal-water pipeline, and about equal to rail. It is also concluded that, by a proper marriage of the synthetic fuel (methanolization) plant to the slurrification plant, most, and in some cases all, of the water required by the synthetic fuel process can be supplied by the natural moisture of the coal itself. Thus, the only technology which presently exists and by which synthetic fuel from western coal can displace petroleum in the automotive fuel market is the integrated methanol conversion and tranportation system. The key element is the ability of the methanol slurry pipeline to accept and to deliver dry (1 to 5% moisture) coal, allowing the natural coal moisture to be used as synthesis feedstockmore » in satisfaction of the large water requirement of any synthetic fuel plant. By virtue of these unique properties, this integrated system is seen as the only means in the foreseeable future whereby western coal can be converted to synthetic fuel and moved to distant markets.« le Document type: Report

Abstract

This paper discusses two ratios involving penetration resistance and shear-wave velocity (VS) that have been proposed for quantifying the influence of microstructure in aged and cemented soils for liquefaction assessment. The first ratio is the small-strain shear modulus (Gmax) divided by the cone penetration test tip resistance (qc). Because Gmax/qc is dimensionless, it can be expressed as a ratio of measured VS divided by a function of qc with velocity units. The second ratio is the measured VS divided by an estimated VS from penetration resistance-VS relationships for relatively young sand deposits (MEVR). The advantages and limitations of both ratios are discussed. The influence of various fines content (𝐹𝐹𝐹𝐹) corrections on 𝑉𝑉𝑆𝑆, penetration resistance-𝑉𝑉𝑆𝑆 relationships, and a relationship between MEVR and the liquefaction cyclic resistance ratio correction factor for microstructure (𝐾𝐾𝐷𝐷𝐷𝐷) is evaluated using two published datasets. The results show the 𝐹 𝐹𝐹𝐹 correction to 𝑉𝑉𝑆𝑆 is minimal in the range for which the correction was derived. The 𝐹𝐹𝐹𝐹 corrections to qc and standard penetration test blow count are significant for silty soils, having a net effect of lowering the penetration resistance-𝑉𝑉𝑆𝑆 relationships and increasing the slope of the 𝑀𝑀𝑀𝑀𝑉𝑉𝑀𝑀-𝐾𝐾𝐷𝐷𝐷𝐷 predictive relationship

Abstract

The influence of soil crushability on the strength parameters of aragonite sand under cyclic undrained conditions is investigated in this study. The investigation used aragonite sand, which is known for being susceptible to crushing under normal loading conditions. A series of cyclic simple shear tests were carried out at different normal loads of 100kPa, 150kPa, 200kPa, and 250kPa under a constant confining pressure. To maintain consistency in particle crushing, sieving tests were used to assess the level of particle breaking, with testing stopping after a predetermined number of cycles. The results show that particle crushing increased the fines content of the soil, even when the effective stress was low during the undrained shear phase. The liquefaction resistance of aragonite sands increased as normal load increased. These findings show the major influence of soil crushability on the engineering behavior of aragonite sand, implying that conventional assumptions about the link between normal load and liquefaction resistance may not be true for crushable soils.

Abstract

Chile is the third country with most tailing dams worldwide (764, of which 15% active, 62% inactive, and 23% abandoned). Today, one of the main challenges of the mining industry is to ensure environmental sustainability. To achieve this, it is not only necessary to have regulations guaranteeing correct design, maintenance, closure stages, but also supervision and suitable technology enabling rapid, reliable, and cost-effective diagnosis of the overall tailings dam stability. For the last 20 years, French instrumented dynamic cone penetrometer, P.A.N.D.A®, has been used for in-depth quality control of tailings deposits, mainly due to its rapidity, portability, easy-to-use, cost-effective, and environmentally friendly testing which is based on standardized methods and able to produce immediate results. The last few years, different studies have been carried out to characterize tailings dams from a geotechnical perspective as well as to assess their spatial and temporal variability. This article presents a summary of the 20 years of Chilean experience in compaction quality control and geotechnical characterization of mine waste facilities using P.A.N.D.A® to assess the overall stability, slope analysis stability, liquefaction triggering, spatial variability of material properties and evaluation of some geotechnical parameters. Indeed, given the scale of the problem these structures represent for the community and the environment, it seemed necessary to bring together most of the work carried out in Chile to propose an innovative alternative to the rest of the mining community.

Abstract

The state of the practice to evaluate the dynamic liquefaction potential of a soil column entails the use of simplified methods that compares the cyclic stress ratio with the cyclic resistance ratio. One of the most used methods is the Boulanger & Idriss 2014, which relies on cone penetration test data to estimate in-situ cyclic resistance ratio and cyclic stress ratio distributions, considering corrections factors for soils with fine contents. Saye, Olson and Franke in 2021 presented a novel method to assess liquefaction susceptibility using cone penetration test data on soils ranging from non-sensitive clays to clean sands. The procedure was developed using +400 documented case records of liquefaction and non-liquefaction in clean sands, silty sands, sandy silts, and low plasticity fine grained soils. Although promising, this method is not widely used in the industry yet. This paper presents a comparison between both methods for tailings. It uses cone penetration test soundings performed in tailings with a wide range of mineralogy and fine contents, combined with variations in peak ground accelerations and magnitudes. This analysis shows that Saye, Olson and Franke’s method is generally more robust, particularly for the analysis of fine tailings, as Boulanger & Idriss’ method relies on site specific data or the engineer’s judgement to define an Ic cut-off value that screens out clay-like soils from the liquefaction analysis.

Abstract

Major challenges are encountered in characterizing and performing liquefaction assessment of gravelly soils since performing traditional in-situ tests, such as the Cone Penetration Test (CPT), in gravelly soils can be challenging, and since gravelly soils are not well-represented in existing case history databases used to develop semi-empirical methods for liquefaction assessment. This has been the primary reason for the ongoing efforts to develop methods based on other invasive tests, such as shear-wave velocity (Vs), and penetration tests with larger probes and greater energy delivered to the rod, such as the Dynamic Cone Penetration Test (DPT). While CPT-based liquefaction analyses have been comprehensively studied, limited research has been conducted comparatively evaluating the performance of the other two methods. This paper performs liquefaction triggering assessment of gravelly reclamations using data from the welldocumented case history of the port of Wellington (New Zealand) using CPT, DPT, and Vs measurements. Results show that while the Vs measurements overestimate liquefaction resistance, the DPT and CPT agreed relatively well with observations from past earthquakes due to the greater sensitivity of these test methods to soil density and stratigraphy

Abstract

Simplified methods for seismic liquefaction assessment based on the flat dilatometer test (DMT), in which the liquefaction triggering curve is defined based on the horizontal stress index (KD), have been proposed over the years. One major drawback of the existing methods, valid for clean sand, is the lack of a correction factor for the fines content. An updating of the empirical relationship CRR-KD proposed by Chiaradonna and Monaco (2022) to incorporate the effects of the fines content is currently under development and validation. This paper illustrates the results obtained from application of the new method at the site of San Carlo – Terre del Reno (Ferrara) located in the Emilia-Romagna plain (Italy), where widespread liquefaction occurred in the 2012 seismic sequence. A comprehensive site characterization from previous insitu and laboratory tests carried out by various research groups is available for the sand, silty sand and sandy silt deposits in the San Carlo area. The performance of the new CRR-KD curve accounting for the fines content effect is compared with that obtained by adopting the “clean sand” curves proposed by Chiaradonna and Monaco (2022), as well as with that obtained by using the CPT-based method by Boulanger and Idriss (2014). Even though verified only for specific Italian soils in this area and requiring further field validation, the proposed approach appears as promising to improve the DMTbased liquefaction assessment in silty sands.

Abstract

The presence of a non-liquefiable crust overlying a liquefiable layer plays a significant role in determining the occurrence of liquefaction damage, as originally formulated by Ishihara in 1985. Following the 2010-2011 Canterbury seismic sequence (New Zealand), almost no foundation deformation occurred in areas characterized by soils susceptible to liquefaction overlaid by at least 3 m-thick intact crust. In contrast, the 2012 Emilia-Romagna earthquake (Italy) provided evidence of liquefaction in silty-sandy layers below 3 to 9 m-thick crusts. Therefore, Ishihara’s approach and the variety of liquefaction severity indices need to be further tested to assess to what extent they can be considered reliable predictors of performance. This study aims at better understanding the role of non-liquefiable crusts in preventing damage to buildings and infrastructures. In this respect, in situ and laboratory tests were conducted at selected sites in EmiliaRomagna. The results of two case studies in Mirandola (Modena, Italy), which share similar soil profiles but exhibited different liquefaction evidences following the 2012 seismic sequence, are presented. Comprehensive geotechnical and geophysical surveys were performed at both the sites, by means of piezocone tests, seismic dilatometer tests, boreholes, laboratory tests, electrical resistivity tomography and multichannel analysis of surface waves. These surveys document the geotechnical and geophysical properties of the 5 m-thick non-liquefied (or potentially non-liquefiable) crust and of the liquefied (or potentially liquefiable) silty-sandy deposits. This effort is aimed at understanding how the surface layer properties contributed to the different behavior observed at the two sites during the earthquake events.

Abstract

In the simplified methods for estimating the cyclic resistance ratio (CRR) based on the flat dilatometer test (DMT), the liquefaction triggering curve is defined as a function of the horizontal stress index. A DMT-based calibration of a simplified pore water pressure model for effective stress analyses has been also recently proposed by Chiaradonna et al. (2023), even though limited to an ideal clean sand. This paper aims to explore the effects of the fines content on the seismic response of a liquefiable site where the cyclic strength of the soils is estimated by dilatometer tests. This evaluation is firstly performed on an ideal one-dimensional soil column, where the percentage of fines content is parametrically changed. Then, the study is verified on a real case, by considering a well-investigated site located in the Emilia-Romagna plain (Italy), where widespread liquefaction occurred in the 2012 seismic sequence. Indeed, a comprehensive site characterization from previous in-situ and laboratory tests carried out by various research groups is available for sand, silty sand, and sandy silt deposits encountered in that area. The nonlinear dynamic analyses accounting for the fines content effect are compared with that obtained by adopting the calibration procedure based on laboratory tests. Guidelines and limitations of the proposed approach obtained from this study are useful in providing awareness to practitioners about the calibration strategies for dynamic analysis based on DMT-tests.

Abstract

On March 18, 2023, a Mw6.6 earthquake hit the South Guayas coastal region (Ecuador), resulting in human fatalities and extensive structural damage. The event triggered widespread soil liquefaction evidences by significant volume of ejected material, which persisted several weeks following the event, marking the epicentral area prone to liquefaction. To assess the susceptibility to seismic-induced soil liquefaction, we performed one seismic dilatometer test (SDMT) in an area where the phenomenon clearly manifested. This study aims to evaluate and compare various established SDMT methods for predicting soil liquefaction potential under the specific 2023 seismic event. The findings are expected to enhance the understanding of liquefaction and contribute to improve seismic hazard assessment in areas along the Ecuadorian coast, which are often interested by earthquakes, as well as to the development of mitigation strategies in this earthquake prone coastal region.