Paul M. Santi

Predicting the unconfined compressive strength of the Breathitt shale using slake durability, Shore hardness and rock structural properties

Abstract Compressive strength is the most widely used design parameter in the construction industry and in rock engineering. For example, Bieniawski [Bieniawski, Z. T., Estimating the strength of rock materials, Is. J. S. Afr. Inst. Min. Metall., 1974, 74, 312–320.] reported that mining engineers request the uniaxial compressive strength (UCS) more often than any other rock property. However, standards set for specimen preparation are very demanding. Therefore it is quite difficult and sometimes impossible to fulfill these requirements using weak rocks and especially shales. This paper evaluates the use of the slake durability and Shore hardness tests to estimate UCS, based on laboratory correlations performed for this study and others and based on analysis of structural and physical material properties affecting both strength and durability.

Debris flows and their toll on human life: a global analysis of debris-flow fatalities from 1950 to 2011

Abstract Debris flows cause significant damage and fatalities throughout the world. This study addresses the overall impacts of debris flows on a global scale from 1950 to 2011. Two hundred and thirteen events with 77,779 fatalities have been recorded from academic publications, newspapers, and personal correspondence. Spatial, temporal, and physical characteristics have been documented and evaluated. In addition, multiple socioeconomic indicators have been reviewed and statistically analyzed to evaluate whether vulnerable populations are disproportionately affected by debris flows. This research provides evidence that higher levels of fatalities tend to occur in developing countries, characterized by significant poverty, more corrupt governments, and weaker healthcare systems. The median number of fatalities per recorded deadly debris flow in developing countries is 23, while in advanced countries, this value is only 6 fatalities per flow. The analysis also indicates that the most common trigger for fatal events is extreme precipitation, particularly in the form of large seasonal storms such as cyclones and monsoon storms. Rainfall caused or triggered 143 of the 213 fatal debris flows within the database. However, it is the more uncommon and catastrophic triggers, such as earthquakes and landslide dam bursts, that tend to create debris flows with the highest number of fatalities. These events have a median fatality count >500, while rainfall-induced debris flows have a median fatality rate of only 9 per event.

Field Methods for Characterizing Weak Rock for Engineering

Many classification and testing methods for shale, slaking rock, weak rock, and weathered rock have been developed. However, few of these methods are suitable for field use or are applicable to a wide range of material types. The purpose of this paper is to present a summary of recent research and analysis evaluating classification and testing methods. This summary will assist the practitioner in properly identifying problem shale and weak rock units, in adequately describing their characteristics in the field, and in selecting and performing field tests to quantify their behavior. For identification of shale and weak rock units, three increasingly site-specific tools are presented. First is a map showing occurrences of weak rock units in the United States. Second is a detailed list of suspect rock types that may appear on regional or local geologic maps. Third is a summary of engineering properties that describe weak rock units, based on a review of technical literature. Some of these properties are compressive strengths between 1 and 20 MPa, slake durability less than 90 percent, clay content greater than 15 percent, poor induration, a significant amount (50 to 75 percent) of matrix between hard blocks, or high moisture content. Methods of field description were chosen based on a review of existing methods to assess their ease of application, breadth of application, and the usefulness of the engineering properties indicated by each system. Two modified methods are presented to indicate proportion and nature of corestones and matrix, strength, influence of discontinuities, and reactivity to water. Finally, field-testing methods that estimate strength, permeability, durability, and reaction to water are identified. These include point load index, Norwegian Geotechnical Institute Rock Mass Classification, jar slake, and hammer rebound classification. Predictive equations to estimate unconfined compressive strength, slake durability, and slake index are given.

Experimental investigation on the breakage of hard rock by the PDC cutters with combined action modes

Abstract To verify the feasibility and efficiency of rotary-percussive drilling assisted by waterjets in very hard rocks, experiments on the performance of polycrystalline diamond compact (PDC) cutters resisting different combined loads of static thrust, impact, cutting and waterjets on Missouri red granite and Halston limestone were investigated. The experiments were conducted by means of a drop hammer and linear cutting-impact table. The effects of static thrust (WOB), impact energy, impact spacing and waterjets on the rate of penetration in hard rocks are described and the results are analyzed by measuring the depth of the craters or cuts penetrated by PDC cutters. Results from the study confirmed that the combined mode of cutting-impact is very effective in very hard rocks.

Methods for Predicting Shale Durability in the Field

Durability of shales and other weak rock is an important parameter describing the materials susceptibility to breakdown upon exposure to water or during construction work. While laboratory methods have been developed to measure durability, no correlations between laboratory results and simple field tests have been determined. The results of this study show that certain field parameters can predict slake durability with acceptable accuracy. The recommended field tests, in order of desirability, are slake index, jar slake, hammer rebound, and NGI “Q” value. Single variable and multiple variable linear regression equations are given, including equations conservatively modified so that 95% of the slake durability values are underpredicted.

Demonstration Projects Using Wick Drains to Stabilize Landslides

A new method has been developed to stabilize slopes and landslides using driven, geotextile wick drains rather than drilled polyvinyl chloride or steel drains. Compared to drilled horizontal drains, wick drains can be significantly deformed without rupturing. They resist clogging, and they can be installed quickly and economically by workers with no previous training. Since 1998, more than 170 drains, totaling more than 2,600 m (8,600 ft) in length, have been installed at eight sites in Missouri, Colorado, and Indiana. At three of the sites, drains were installed at a density and layout considered to be appropriate for full-scale stabilization: 27 to 44 drains were driven at each site, averaging 15 to 20 m (50–70 ft) in length. A method was developed to accurately estimate the groundwater-table profile after drain installation, and computer slope-stability analysis using this method showed significant increases (10–40 percent) in factors of safety after drain installation. The limitations of the methodology should be recognized: it may be applied in specific situations requiring relatively short (<30–45 m, or <100–150 ft) drains in materials ranging from soft to very stiff (up to 30 blows/ft in standard penetration tests). The potential effectiveness of drainage as a mitigation option should be verified through analysis of site geology and hydrogeology before drain installation.

Relationships between size and velocity for particles within debris flows

Estimation of the impact forces from boulders within a debris flow is important for the design of structural mitigation elements. Boulder impact force equations are most sensitive to the inputs of particle size and particle velocity. Current guidelines recommend that a design boulder should have a size equal to the depth of flow and a velocity equal to that of the flow. This study used video analysis software to investigate the velocities of different sized particles within debris flows. Particle velocity generally decreased with increasing particle size, but the rate of decrease was found to be dependent on the abilities of particles to rearrange within debris flows.

Water Table Profiles in the Vicinity of Horizontal Drains

One of the most common and effective means of slope stabilization is lowering the water level within a soil mass. Frequently, horizontal drains are installed for this purpose. Computer-aided slope stability analyses are then used to evaluate the increase in factor of safety produced by drain installation. Critical to these analyses is the location and shape of the water table surface above the drain field. However, evaluation of the water table surface is complicated by its complex corrugated shape, with troughs corresponding to drain locations and ridges at the midpoints between drains. The objective of this research was to accurately describe the water table surface within a drain field using easily measured field and laboratory parameters. To accomplish this, physical and computer modeling of the water table along and between drains was conducted. The results of these analyses were compared to an analytical solution of the water table profile between drains that was derived by modifying groundwater equations developed for agricultural engineering applications. Based on these comparisons, a method was developed to describe the water table surface using the analytical solution and an experimentally derived correction factor. The method was confirmed by comparisons to field data. As a result of this research, water table surface heights can be approximated along and between drains. Additionally, an average water table surface height may be calculated and used in stability analyses, allowing accurate substitution of two-dimensional analyses for more complex three-dimensional situations.

Predicting locations of post-fire debris-flow erosion in the San Gabriel Mountains of southern California

Timely hazard assessments are needed to assess post-fire debris flows that may impact communities located within and adjacent to recently burned areas. Implementing existing models for debris-flow probability and magnitude can be time-consuming because the geographic extent for applying the models is manually defined. In this study, a model is presented for predicting locations of post-fire debris-flow erosion. This model is further calibrated to identify the geographic extent for applying post-fire hazard assessment models. Aerial photographs were used to map locations of post-fire debris-flow erosion and deposition in the San Gabriel Mountains. Terrain, burn severity, and soil characteristics expected to influence debris-flow erosion and deposition were calculated for each mapped location using 10-m resolution DEMs, GIS data for burn severity, and soil surveys. Multiple logistic regression was used to develop a model that predicts the probability of erosion as a function of channel slope, planform curvature, and the length of the longest upstream flow path. The model was validated using an independent database of mapped locations of debris-flow erosion and deposition and found to make accurate and precise predictions. The model was further calibrated by identifying the average percentage of the drainage network classified as erosion for mapped locations where debris flows transitioned from eroding to depositing material. The calibrated model provides critical information for consistent and timely application of post-fire debris-flow hazard assessment models and the ability to identify locations of post-fire debris-flow erosion.

Optimizing Faculty Use of Writing as a Learning Tool in Geoscience Education

As geoscience educators, we focus on helping students understand technical content and learn to think like geoscientists. Although research substantiates writing as a tool for teaching technical content and disciplinary thinking, geoscience educators often do not integrate writing in geoscience education because of the frustrations and exigencies involved. To address these issues, this paper describes the literature on using writing as a learning tool in both cross-disciplinary and geoscience teaching contexts. Further, we describe our Less is More approach, designed so faculty can spend less time grading student writing and still yield more learning benefits from incorporating writing. This approach involves five strategies, including explicitly integrating assignments with course objectives, designing effective assignments, incorporating process writing, evaluating writing effectively and efficiently, and consulting appropriate campus resources. Results of an initial assessment using this approach with a geoscience course suggest gains in student learning.