Additional Boreholes Research Articles

Uncertainty reduction strategies to enhance geotechnical site characterization: a case study of the red roof landslide in Wyoming

This study presents a method for identifying strategic locations to drill additional boreholes by quantifying and reducing subsurface uncertainties in geotechnical site investigations. The case study is the Red Roof landslide site located near milepost 140 on US Highway 26/89 in Teton County, Wyoming. A landslide remediation report had recommended additional boreholes before completion of the project. Two primary sources of uncertainty in geomaterials, namely geological and ground, are evaluated to determine the locations for these additional boreholes. The study aims to enhance site characterization and improve the accuracy of geotechnical assessments by strategically selecting and drilling additional boreholes that will reduce these subsurface uncertainties. The method involves reviewing and collecting the available site investigation data. An extensive geostatistical simulation is conducted based on the available data to identify spatial locations at the site that have uncertain subsurface conditions. Data from the additional boreholes could be utilized in these areas to reduce the uncertainty. This approach aligns with the current multi-phasing of site investigation in engineering practice, where a preliminary investigation is conducted before a detailed investigation. The results show that the locations of additional boreholes identified using this method differ from the ones earlier recommended, showcasing the effectiveness of the methodology in this application. This study also provides insights into effective strategies for reducing uncertainties through strategic borehole placement in similar geotechnical investigations. By quantifying geological and ground uncertainties, the method enables informed decision-making for slope stability analysis and risk assessment, with implications for infrastructure stability and geohazard mitigation.

Cyclicity of the Lower Buntsandstein in the eastern part of the Central European Basin: implications for Early Triassic palaeogeography and for geochronological calibration

Lower Buntsandstein small–scale cycles recognized in the Central European Basin (CEB) are readily used for astrochronological calibration of the Early Triassic time scales, although they are not well studied sedimentologically. Three borehole sections from the eastern part of the CEB, forming a south-north transect perpendicular to the basin axis, were studied in terms to better understand the depositional history of the Lower Buntsandstein developed as the Baltic Formation in the studied Polish part of the basin. Eleven sedimentary facies were recognized, based on lithological and sedimentological investigations of 655.7 m of drill cores from the Otyń IG 1, Gorzów Wielkopolski IG 1 and Kamień Pomorski IG 1 boreholes. The facies can be grouped according to a lithological criterion into facies of predominantly siliciclastic lithology (including 9 facies types) and facies of predominantly carbonate lithology (including 2 facies types). Facies analysis allowed to distinguish 8 facies associations of: 1) alluvial fan, 2) playa, 3) sandy-muddy coastal plain, 4) embayment and distal delta, 5) lagoon, 6) sand bars or shoals, 7) ooidal shoals or bars, and 8) offshore. Deepening-upward (DC) and shallowing-upward (SC) sedimentary cycles were recognized in parts of the Baltic Formation, with DCs dominating in the southernmost located Otyń IG 1, and SCs dominating in Gorzów Wielkopolski IG 1, located in the axial part of the basin. Symmetrical cycles are very rare. The statistical significance of the sedimentary cycles is relatively low according to Markov-chain analysis conducted with the phpSedistat software of Stanova et al. (2009). Analysis of small–scale cycles performed on well logs of investigated boreholes and additional boreholes in the vicinity of Otyń IG 1, implementing the earlier study of Becker (2005), showed that the correlation of well-log cycles (GR cycles) and sedimentary cycles is not obvious. GR cycles can be roughly correlated with lithological carbonate–siliciclastic cycles (c-s cycles), reflecting alternations of facies groups of predominantly carbonate and siliciclastic lithology. Calibration of GR cycles to earlier magnetostratigraphic results of Nawrocki (1997) and Becker and Nawrocki (2014) showed that neither the boundaries of GR cycles serve as reference horizons, nor the cycles document equal time periods. All existing depositional models of the Lower Buntsandstein were discussed, stressing the possible simultaneous interaction of allochthonous and autochthonous processes. Moreover, the tectonic overprint of the Central European Basin system during the Early Triassic should be taken into account. The presented results suggest that the Lower Buntsandstein cyclicity of the CEB cannot serve as a basis for astrochronological analysis.

Rapid warming and degradation of mountain permafrost in Norway and Iceland

Abstract. With the EU-funded PACE (Permafrost and Climate in Europe) project at the turn of this century, several deep boreholes (100 m+) were drilled in European mountain sites, including in mainland Norway, Svalbard and Sweden. During other projects from 2004 and the International Polar Year (IPY) period in 2006–2007, several additional boreholes were drilled in different sites in both Norway and Iceland, measuring temperatures along both altitudinal and latitudinal gradients. At most sites, multi-temporal geophysical soundings are available using electrical resistivity tomography (ERT). Here, we study the development of permafrost and ground temperatures in mainland Norway and Iceland based on these data sets. We document that permafrost in Norway and Iceland is warming at a high rate, including the development of taliks in both Norway and Iceland in response to global climate change during the last 20 years. At most sites, ground surface temperature (GST) is apparently increasing more strongly than surface air temperature (SAT). Changing snow conditions appear to be the most important factor for the higher GST rates. Modelling exercises also indicate that the talik development can be explained by both higher air temperatures and increasing snow depth.

Tracking of horizontal alignment of the long and large diameter uncharged hole in NATM tunnel

The long and large diameter uncharged hole boring (LLB) method is a cut blasting method that minimizes blast-induced vibrations by creating long and large diameter uncharged holes at the excavation face of tunnels prior to tunnel excavation. Drilling in this method typically uses a 50 m long with a 382 mm diameter hammer bit in the horizontal direction at the tunnel face. However, the significant weight and uni-directional rotation of the rod head, as well as variables such as geological characteristics, machine conditions, and inexperienced operators result in significant deviation from the target borehole alignment that hinders the vibration-dampening effect of the uncharged holes. Furthermore, since there is no method to verify the alignment of the boreholes until main tunnel construction, borehole misalignment is often not discovered until weeks after construction, which requires tunnel construction to cease until the equipment can be remobilized and an additional borehole be created, causing significant delays and increased costs for the entire tunnel project. In this study, the borehole alignment tracking and ground exploration system (BGS) is developed to predict and monitor the quality and alignment of boreholes for cut blasting methods such as the LLB methods immediately after boring. The BGS was subsequently tested at a subway construction site to evaluate its performance in the field. The measurements yielded by the BGS were compared with manually measured boring positions at every 5 m along the borehole. Although the BGS showed a maximum deviation of approximately 12% at a local point where the hole surface was relatively rough, the accuracy for the final boring position was approximately 97%, demonstrating excellent precision of the alignment tracking system. The BGS demonstrates excellent performance in predicting ground conditions and the boring quality of a cut hole immediately after drilling, and shows promise in various other applications for monitoring borehole alignment.

A Multi-Objective Approach for Optimizing the Layout of Additional Boreholes in Mineral Exploration

Accurate subsurface exploration requires an optimal network of boreholes. This paper proposes a multi-objective approach to optimize the layout of additional exploratory boreholes. In order to illustrate this approach, geochemical analyses of core samples at the eastern part of the Kahang copper deposit, Central Iran, were used. A measure of the grade uncertainty (kriging standard deviation) and a confidence measure on the ore/waste classification were first calculated by implementing ordinary and indicator kriging. An ore value function was then determined to measure the total value of each block by considering the grades of all the effective variables and their ore membership degree derived from a fuzzy treatment of the grades. Finally, a misclassification cost is defined for each block based on the expected economic effects of ore loss and waste dilution. As a result, an index for the selection of additional boreholes was introduced in order to maximize the kriging standard deviation, the ore misclassification cost, and the ore value and to minimize the confidence measure. Applied to the Kahang copper deposit, this index allowed the prioritization of areas for infill sampling, leading to the recommendation for eight vertical and two directional additional boreholes.

An Uncertainty-driven Peak-integration (UP) Strategy for 3D Borehole Layout Planning

Equal-spaced borehole drilling is commonly adopted in practice for site investigation, which ignores spatial uncertainty and might result in insufficient site characterization. Model-driven precise drilling is regarded as a potential solution. In this study, an uncertainty-driven peak-integration (UP) strategy is proposed to improve decision-making in 3D borehole planning. The UP strategy consists of stratigraphic uncertainty modelling and peak-integration method. The random field-based uncertainty modelling approach has been improved by employing stratum-informed Scales of Fluctuation and a novel site division method to capture the site-specific uncertainty distribution with sufficient interpretation. The peak-integration method is proposed to consider the uncertainty around peaks, as improvement of existing peak uncertainty-based borehole planning strategy. To provide an objective evaluation for borehole layout planning, a new index “Contribution of Borehole” (CoB) is proposed for the first time, using the Earth Mover’s Distance, to quantify the net changes of stratigraphic distribution revealed by additional boreholes and offer validation for every decision-making. The feasibility and practicability of the proposed strategy are demonstrated by applying to an artificial geological model created based on real borehole data. The superiority of the proposed strategy is elucidated by comparing with equal-spaced strategy, via both CoB and conventional entropy reduction with detailed discussion.

An efficient model to estimate the soil profile and stratigraphic uncertainty quantification

Comprehensive geological information is very important and needed in underground construction and underwater infrastructure. However, it is quite difficult to reveal the configuration of different soil features of underground with sparsely measured data. In this study, a new algorithm named General Regression-Markov Chain (GR-MC) was proposed by coupling the general regression neural network and the Markov chain method together to reproduce the characteristics of underground stratification based on rare borehole information. The general regression neural network method was introduced to evaluate the geological variation along the inclined orientation, while the Markov chain method was applied to examine the change in soil types along the depth. The spatial coordinates of the treated construction site were designed as the input variables, while a vector including the probability information of different soil types was set as the output. The proposed GR-MC method is very intuitive and can be efficiently implemented to predict the geological model using only the coordinates as inputs. Moreover, the proposed method can be smoothly extended into a three-dimensional case with low computational resources. Compared to the existing methods, the proposed GR-MC algorithm is computationally efficient and robust. Three cases from real practice were evaluated and the calculated results were consistent with the known borehole information. Besides, the stratigraphic uncertainty was quantified based on information entropy theory. The results can visually reveal the zones of the estimated soil profile with relatively large uncertainty. The practical application is that possible additional borehole locations were identified to reduce the stratigraphic uncertainty of a construction site.

Improvement of blasting efficiency with pre-softening of rock mass

The substantiation is given support preliminary softening of rock mass to enhance blasting efficiency. The proposed technology was subjected to pilot testing in Ayak-Kodzhan mine, Republic of Kazakhstan. A total of 5 explosions were carried out using the technology with preliminary softening and 5 explosions were executed using the standard technology, with variation in drilling and blasting parameters to determine the optimized drilling and blasting pattern design toward enhanced blasting efficiency. In processing the data of pilot explosions, the dependences of the oversize yield and powder factor on the least burden were obtained using the standard and proposed technologies. Based on the experimental blasting, it can be concluded that the best fragmentation quality is achieved during the first experimental explosion with a drilling pattern 4×4 m and with the use of additional boreholes for preliminary softening of rock mass. The oversize yield is 0.6%. However, during this explosion, the highest powder factor is recorded—1.36 kg/m3. The best economic parameters are obtained in the second experimental explosion with the borehole pattern 4.5×4.5 m. In this case, the oversize yield is 0.8% and the powder factor is 1.05 kg/m3. Moreover, the excavation velocity is increased by 10% as a result. The authors obtain the relationship of the oversize yield and the powder factor with the least burden in the technology with preliminary softening of rock mass. The practical significance of the study lies in the justification of the blasting technology with preliminary rock mass softening and in the optimization of drilling and blasting design to achieve the required fragmentation quality.The authors express their gratitude to NPP Interrin management represented by CEO P. G. Tambiev for the help and contributory influence during pilot testing.

Late Pleistocene-Holocene Evolution of Malé Island (North Malé Atoll Rim, Republic of Maldives)

Malé, the capital of the Republic of Maldives, is established on an island of about 6.8 square kilometres, with a maximum relief of 2.7 m and a population of 236,000 inhabitants. It is amongst the most densely populated areas on Earth and located virtually at sea-level. This study focuses on the late Pleistocene-Holocene evolution of Malé island that recently formed as part of the discontinuous North Malé Atoll rim. Understanding the formation of Malé Island is relevant in predicting its future in the context of accelerating rates of sea-level rise in the next centuries due to anthropogenic global warming. Analyses of two boreholes up to 35 m-long, published information from additional boreholes drilled on Malé Island and a high-resolution multi-beam bathymetric survey acquired along its upper slopes and deep surroundings were available for this study. Two distinct sedimentary units were recovered from the boreholes. Facies analyses of the lower unit reveal an overall deepening coralgal reef that accumulated probably during the previous interglacial (Marine Isotope Stage = MIS 5e) and which was subsequently altered by meteoric diagenesis during a 100 kyr-long time of exposure. The upper unit consists of Holocene unconsolidated coralgal accumulation, unconformably overlying the lower karstified coralgal MIS 5e unit. The upper unit, protected behind a karstified late Pleistocene reef, was initiated at ~8200 yr BP and vertically grew 25 m-high until 6510 yr BP in the northern part of the Malé Island area, which at the time was a karstified limestone island with a central geomorphological depression. The narrow, 30 to 35 m-deep, newly formed central faro lagoon started to fill ~ 5500 yr BP, when a reef initiated on top of the southern highest Pleistocene karstified reef and sea-level rise stalled. The infilling of the faro lagoon was completed ~ 4500 yr BP. An island formed that was flanked on its south side by a shallow lagoon and surrounded by a reef flat. Through several phases of land reclamation since the 1950s, the shallow lagoon was infilled and the reef flat buried with sand and rubble to form Malé Island as it is known today.

Evaluating the Hydraulic Performance of Existing Water Supply Distribution System: The Case of Tebela Town of Wolaita Zone, Southern Ethiopia

The adequate and reliable water supply in the developing towns of Ethiopia is becoming a challenge for most water utilities especially public service providers like Tebela town. The main objective of this research was to check the hydraulic performance of Tebela town's water distribution system by evaluating water demand and production, losses of water, and hydraulic parameters. Both secondary and primary data sources were used for this study. Primary data was collected through field surveys and photographs of relevant sites and infrastructures. The secondary data was collected from design documents, literature, journals, and office. Moreover, to analyse the existing water distribution system, a model was developed by using WaterGEMSv8i software. The model simulation run was performed for peak and low demand scenarios to analyze the distribution system. The analysis shows that the water supply coverage was 25.9%. The water loss of the town was 17.2% from the total water production. Modeling results showed violation of maximum and minimum pressure and velocity criteria at different junctions and pipes. After modifying the existing water distribution system, 96.23% of the junctions are in the recommended pressure range and 73.50% of the pipes are in the recommended velocity range at minimum hourly consumption. Generally the result of the analysis shows that the overall hydraulic performance of water distribution of the town was moderate, which is reflected by medium water production rate, water consumption, and nonrevenue water, also low water coverage, some velocity and pressure is not in permissible range. Therefore, it is important to rehabilitate and improve the water distribution system capacities, establish pressure zones, increase pumping rates, and drill additional boreholes to meet the current water demand and future demand.

Testing the Utilization of a Seismic Network Outside the Main Mining Facility Area for Expanding the Microseismic Monitoring Coverage in a Deep Block Caving

In the case of mining in an inclined intrusion using the block caving method, the highest stress is usually concentrated in the seismogenic and abutment zones, especially in the front of the sloping area. In an inclined intrusion of more than 40°, the seismometer network is usually distributed in the facility area where the footwall area is also located. This causes a limitation in microseismic monitoring due to ray coverage. In this study, we conduct a seismometer deployment outside a mining facilities area with borehole seismometers. The study aims to maximize the resolution and minimize the monitoring uncertainty of underground mines. We created two scenarios of seismometer deployment: (i) seismometers are deployed following the intrusion mining level in the mining facility area; and (ii) additional seismometers are deployed in off-facilities areas. Both areas were tested for their raypath responses and sensitivity using the Checkerboard Resolution Test (CRT). The monitoring resolution influenced by the additional borehole seismometers in the off-facilities area can be quantified. The results suggest that the additional seismometers in the off-facilities areas can increase resolution by 30% in the seismogenic and abutment zones.

Risk-based methodology to optimize geotechnical site investigations in tunnel projects

The scope of geotechnical investigations in tunnel projects is generally driven by the allocated resources rather than the expected variability in the ground conditions. Uncertainties in ground conditions may lead to poor decisions in project planning and active risk management. This paper presents a systematic and rational methodology to identify priority locations of additional geotechnical investigations for soft ground tunneling applications based on tunnel risks, site conditions, and project-related constraints. The methodology is applied to the cutter tool wear risk and quantifies the uncertainty in soil abrasivity index (SAI), the relevant geotechnical parameter. Preliminary geotechnical investigation data and site conditions from an actual tunnel project in an urban environment are used to illustrate the proposed methodology and demonstrate its effectiveness. Pluri-Gaussian simulation and sequential Gaussian simulation are used to characterize the 3D spatial variability in soil units and soil abrasivity, respectively, along the tunnel alignment. The study integrates geospatial assessments of SAI uncertainty and consequences of tool wear to develop an R index map that delineates the impact of uncertainty in tool wear rate. Project constraints of drilling accessibility and budget are incorporated in the R index map to find locations of additional geotechnical investigations. The study simulates a virtual sampling of additional boreholes and quantifies the reduction in uncertainty in tool wear rate and tunnel boring machine (TBM) intervention locations. Additional investigation at priority locations is found to reduce cutterhead intervention location uncertainty by approximately 90 rings (160 m). Further, integrating the uncertainty in tool travel distance is found to influence the cutterhead intervention location uncertainty by approximately 40 rings.

A Monte Carlo Simulation-based algorithm for updating Combined Variance cost function in optimally locating additional drillholes

ABSTRACT Optimally locating additional boreholes in the boundaries of ore deposits is an important problem in mining projects. To solve this problem, combined variance has been proposed as a cost function to be minimized. An issue about combined variance is its dependence on the value of variable at unknown location. This value is achieved through a round-based algorithm that estimates the probability of occurrence of ore and rounds it to the nearest integer without considering all scenarios. This study aims to consider all scenarios using a Monte Carlo simulation-based algorithm. This approach uses ordinary cokriging to estimate the probability of occurrence of ore at unknown locations. Then, the estimated probabilities are entered into a Monte Carlo simulation procedure to generate various realizations. The method was applied in the Chadormalu ore deposit to propose ten additional boreholes. The round-based algorithm proposed additional drill holes in the middle of ore-intersected and non-intersected initial drill holes. However, the Monte Carlo-based algorithm is sensitive to the thickness such that in boundaries with thicker ore, the additional boreholes are suggested farther away from the ore-intersected drill holes and closer to the non-intersected ones and vice versa.

Dynamic drill-string modeling for acoustic telemetry

Directional drilling techniques require real-time sensing of the drill bit direction and the downhole environment from the measurement-while-drilling (MWD) sensor module. Traditional telemetry methods such as the mud-pulse telemetry are limited to low transmission rates. Acoustic telemetry is a method used for transmitting downhole sensor data and it is orders of magnitude faster than conventional telemetry techniques. However, the selection of appropriate carrier frequencies is critically important to transmit measured data. This study proposes a finite element (FE) model based on the Timoshenko beam theory that predicts dynamics of a drill-string over a wide frequency range and boundary condition. Additionally, a modulated acoustic transmission is developed and performed using the determined carrier frequencies. The signal is modulated using differential binary phase shift keying (DBPSK) and is up-converted to the carrier frequency used for the excitation of the drill-string. Packets of bits are first generated as the telemetry data and then convolutionally encoded to reduce errors at the receiver. The receiver at the surface demodulates and decodes the received acceleration signals to recover the transmitted bits through a digitally implemented lock-in amplifier (LIA). Finally, the transmitted and received bits are compared to calculate the bit-error rate (BER) for each signal-to-noise ratio (SNR) condition. By using the LIA, the receiver can extract severely attenuated acoustic signals, but the dynamics of the drill-string and the additional borehole interactions can degrade the performance of the acoustic telemetry system.

Seismic site classification from HVSR data using the Rayleigh wave ellipticity inversion: A case study in Singapore

Shear wave velocity (Vs) profile is one of the critical geotechnical measurements of soil layers for seismic hazard assessment and liquefaction potential evaluation. Enhancing the effectiveness of in-situ Vs profiling by reducing time and cost is of great interest. For that reason, this study aims at assessing Vs profile generation from a single-station three-component geophone with additional borehole log data for constraining parameter space. Based on multichannel analysis of surface waves (MASW), and microtremor array Measurements (MAM) conducted previously at seven sites located in Bukit Timah Granite, Singapore, this study utilized HVSR signals for Rayleigh wave ellipticity (ellipticity curve) inversion with additional inversion constraint using borehole log data. The resulting Vs profiles and reference Vs profiles from MASW and MAM were quantitatively compared using average Vs of 30 m (Vs30). The profiles generated from ellipticity curve inversion revealed a good agreement with Vs reference profiles. Vs30 based site classification results also indicated a good fit of two test results. Therefore, HVSR measurements for further ellipticity curve inversion, with already available borehole log data for constraint, is considered as a promising cost and time-effective site classification approach.

Rock characterisation for a road tunnel in Mumbai (India)

The Mumbai Coastal Road is a freeway currently being constructed along the western coast of Mumbai. A key element of this route is a twin-bore tunnel with total length of about 3km (a 2km TBM-excavated central section, plus cut-and-cover ramps at both ends). The tunnel alignment underpasses Malabar Hill and then runs under Chowpatty Beach for most of its length. The central section is located below the sea level with ground covers ranging from a maximum of 70m at Malabar Hill to less than 15m under Chowpatty Beach. Each bore, excavated by Tunnel Boring Machine (TBM), has an internal dimeter of 11m and includes a section with a horizontal radius of curvature tighter than 400m. This paper describes (i) the desk studies and the geological survey which provided the basis for an additional ground investigation plan, (ii) the results of the additional boreholes, in situ test and laboratory test, (iii) the overall characterisation of the rock mass (and of the overlying soils) based on the entire set of old and new data. The rock characterisation provided the fundamental information for the TBM type selection, and for the design of all the underground works. The launching chamber and the first part of the TBM drive are located within a Basaltic lava flow, while the second part of the alignment is set in Volcanic Breccia underlying the fine-grained soils and made ground of Chowpatty Beach.

Inclination monitoring at tunnel crown to predict change in ground stiffness ahead of excavation face

The safe and cost-effective excavation of mountain tunnels requires appropriate prediction and evaluation methods for ground conditions ahead of the tunnel face, since appropriate choice of support members and auxiliary tunneling methods depends on such data. The authors have developed a new prediction method based on monitoring tunnel crown inclination in the direction of the tunnel axis and have implemented it in field tests. The new method has the significant advantage of not hindering tunneling work, as neither additional borehole explorations nor blasting work around the face are required. This paper provides a systematic description of the basic concept of this inclination monitoring method and includes an outline of the tilt sensor, which has been designed for quick and easy installation. A field verification test is also reported. Numerical analysis is used to demonstrate that the proposed method is more sensitive to change in ground stiffness ahead of the face than conventional prediction methods using displacement monitoring, taking actual measurement accuracy and measurement intervals into consideration.

UPDATING OF SURAKARTA SEISMIC SITE CLASS MAP BASED ON STANDARD PENETRTION TEST

<p>Surakarta is one of the cities in Java island with a high population growth rate, triggering the increase<br />in the construction, especially for high-rise buildings. The city is close to several earthquake sources,<br />causing a high level of seismic hazard. One of the main parameters of earthquake resistant building<br />design is the value of peak ground acceleration at surface level. It is obtained by multiplying the peak<br />ground acceleration in the bedrock by a multiplier factor that depends on the site class conditions of the<br />location. A previous study has been conducted in 2015 using 32 boreholes indicating that around 19.5%<br />of Surakarta area is classified as SC (hard soil), and 80.5% of the rest is SD (medium soil). To increase<br />the accuracy, another 31 additional boreholes data are adopted. The new result shows that Surakarta is<br />divided into three different seismic site class. Around 4.80% the area is classified as SC (hard soil),<br />94.50% is SD (medium soil), and 0,70% is SE (soft soil). The southern part of Surakarta has a higher<br />level of vulnerability to earthquakes, especially in the border area between Banjarsari, Laweyan, and<br />Serengan subdistricts which have a SE (soft soil) seismic site class.</p>

Improving Coal Quality Estimations with Geostatistics and Geophysical Logs

In most modern coal mines, there are many coal quality parameters that are measured on samples taken from boreholes. These data are used to generate spatial models of the coal quality parameters, typically using inverse distance as an interpolation method. At the same time, downhole geophysical logging of numerous additional boreholes is used to measure various physical properties but no coal quality samples are taken. The work presented in this paper uses two of the most important coal quality variables-ash and volatile matter-and assesses the efficacy of using a number of geostatistical interpolation methods to improve the accuracy of the interpolated models, including the use of auxiliary variables from geophysical logs. A multivariate spatial statistical analysis of ash, volatile matter and several auxiliary variables is used to establish a co-regionalization model that relates all of the variables as manifestations of an underlying geological characteristic. A case study of a coal mine in Queensland, Australia, is used to compare the interpolation methods of inverse distance to ordinary kriging, universal kriging, co-kriging, regression kriging and kriging with an external drift. The relative merits of these six methods are compared using the mean error and the root mean square error as measures of bias and accuracy. The study demonstrates that there is significant opportunity to improve the estimations of coal quality when using kriging with an external drift. The results show that when using the depth of a sample as an external drift variable there is a significant improvement in the accuracy of estimation for volatile matter, and when using wireline density logs as the drift variable there is improvement in the estimation of the in situ ash. The economic benefit of these findings is that cheaper proxies for coal quality parameters can significantly increase data density and the quality of estimations.

Quantifying spatial uncertainty in rock through geostatistical integration of borehole data and a geologist's cross-section

In order to increase understanding of spatial uncertainty in subsurface conditions for problems in geological and geotechnical engineering, this study develops a geostatistical approach for incorporating a geologist's interpreted cross-section to quantify spatial uncertainty of lithology. In this work, the Sequential Indicator Cosimulation (COSISM) algorithm and the information theory concept of entropy are utilized to generate uncertainty models. A sensitivity analysis is used to study how both borehole data and the cross-section are incorporated into the algorithm, which is quantified using entropy as a metric for uncertainty in geologic unit boundary locations. A verification methodology is then developed to identify the most appropriate combination of input parameters for combining these two data types; recommendations from the verification methodology are made by comparing the calculated entropy to accuracy at the global scale on a point-by-point basis. This methodology is then used to investigate how calibrated input parameters vary due to differences in the input cross-section based on different levels of understanding of the subsurface geology by iteratively providing a geologist with additional borehole data after a cross-section is developed. Results show that two of the parameters, variogram range and the number of conditioning data, can be used to most directly reflect geologist understanding in the simulations. Finally, this study provides guidelines for incorporating a geologist's understanding of a geological environment into this modeling framework, as results show cross-sections that are locally accurate are better represented by different parameters than cross-sections that are not locally accurate but are globally accurate. These guidelines are intended to aid geologists and engineers in understanding how to incorporate a geologist's interpretation of the subsurface lithology or categorical geotechnical parameters at a particular worksite into a structured geostatistical framework.