Geotechnical Uncertainty Research Articles

Combining association rules mining with complex networks to monitor coupled risks

Due to geotechnical uncertainties, existing underground infrastructure, the construction of deep-pit foundations in dense urban areas is particularly challenging as there is a propensity for building and structural settlement to occur. Recognizing the need to proactively manage safety risks during construction, a new risk analysis approach that combines complex networks and association rules mining (ARM) is proposed. An improved Apriori algorithm is developed to unearth abnormal monitoring types. Then, complex network theory is introduced to examine the characteristics of the coupled relationships existing between different types of abnormal monitoring types. This research identifies and examines complex network measures to understand the topology of settlement networks. It is revealed that settlement networks confirm to both scale-free and small-word properties indicating that risks are not random events. This new approach of combining ARM with complex network is applied to examine deep foundation pits that are constructed for a subway project in Wuhan, China. It is demonstrated that proposed approach can successfully reveal the association rules between safety risk monitoring types and the coupling of risks. Preventative actions can therefore be undertaken in advance to mitigate against potential risks that are identified from the abnormal monitoring combinations.

Optimizing site-specific geostatistics to improve geotechnical spatial information in Seoul, South Korea

Subsurface soil and rock profiles are commonly interpreted from borehole log datasets. These datasets include three-dimensional spatial coordinate information, layer information, and standard penetration test results. More reliable spatial distribution of target physical properties can be obtained from additional testing at locations characterized by outlier observations and geotechnical uncertainties. At a given site, irregular measurements typically differ significantly from bulk measurements or proximal observations. In this study, a process for optimizing site-specific geostatistics, which uses geotechnical spatial information and applies optimum outlier thresholds with a multi-clustering method, is proposed to incorporate site-specific geo-layer uncertainties and identify their geotechnical value. Optimized geostatistical characteristic information for geological strata boundaries was derived and verified based on a sequential procedure applied to representative test areas in Seoul, South Korea.

Slope hazards on the Ethiopian road network

Jointed rock masses, adverse lithological sequences, often deeply-weathered soil profiles, seasonal rainfall, stream erosion and seismicity have created conditions favourable to the development of landslides in many parts of Ethiopia. Large, deep-seated landslides occupy many hillsides and some may date from the late Pleistocene–mid Holocene. Others are more recent and their activity is controlled by rainfall and, in some cases, the effects of land use change and road construction and widening schemes. The road network of Ethiopia has been expanding significantly over recent decades and has been impacted in many areas by reactivated ground movements and new, first-time failures. The Ethiopian Roads Authority (ERA) has undertaken a number of initiatives to combat these problems, including a research programme aimed at developing mitigation designs for 118 locations on the federal road network of the country. Engineering geological mapping formed the cornerstone of the geotechnical investigations, together with targeted trial pitting, drilling and geophysical investigations, that allowed remedial options to be scheduled. Nevertheless, geotechnical uncertainty prevailed at several locations, especially where ground investigation was precluded by budget constraints. A pragmatic approach had to be applied to the construction contract documentation that made provision for confirmatory ground investigation prior to design finalization and geotechnical inspection and interpretation during construction.

Reliability sensitivity analysis of geotechnical monitoring variables using Bayesian updating

Determining the sensitivity of monitoring variables is essential to field monitoring design for effectively monitoring the safety and reliability levels of geotechnical structures in uncertain environment. Reliability sensitivity analysis of monitoring variables provides a rational approach for identifying sensitive monitoring variables and is capable of accounting for geotechnical uncertainties. It, however, can be computationally expensive, especially when sophisticated numerical models (e.g., finite difference model, FDM) are involved and repeated simulation runs are required. This paper proposes a reliability sensitivity analysis method that leverages on the robustness of direct Monte Carlo simulation (MCS) and the Bayesian Updating with Structural Reliability Methods. The proposed approach allows performing the reliability sensitivity analysis of a monitoring variable by a single run of direct MCS, avoiding repeated simulation runs for different possible observational values of a given monitoring variable. Illustrative examples demonstrate the capability of the proposed approach in identifying the most sensitive monitoring variables among candidates. It is possible to achieve a significant reduction in the number of evaluations of numerical models for reliability sensitivity analysis of monitoring variables using the proposed approach.

Quantifying cost-effectiveness of subsurface strata exploration in excavation projects through geostatistics and spatial tessellation

Abstract A major source of uncertainty in civil engineering projects arises from the geological and geotechnical variability at the project site. This paper presents an approach to quantify such uncertainty, and to rationally incorporate them into estimates of cost contingency. Contrary to the conventional approaches that rely on individual expert's opinion or data from past projects, the proposed approach allows site-specific assessments of the intrinsic geotechnical variability through geostatistical techniques. Such uncertainty can be reduced through geotechnical investigation, and spatial tessellation techniques are proposed to facilitate determination of the optimal locations of new boreholes. Cost-effectiveness of the boreholes can be evaluated based on the corresponding reductions in geotechnical uncertainty and their influence on the budget. The approach is illustrated using a hypothetical excavation scenario, where the project costs are affected by uncertainty in the subsurface strata, particularly the rockhead level across the site. Under the specific site conditions, a Pareto frontier is developed to reveal the relationship between the number of boreholes to be drilled and potential savings in contingency budget. Through this approach, the study promotes better utilization of geotechnical information and rational assessments of project risks associated with their variability, which may lead to improved project planning and resource allocation.

The Anatomy of Geotechnical Risk Factors in Transportation Infrastructure Projects

Ground conditions constitute a key risk factor that can ultimately determine the successful performance of construction contracts, with the literature reporting statistics of projects which have significantly exceeded their initial budget due to geotechnical uncertainties. The study explores the nature of geotechnical risk factors in transportation infrastructure projects, which potentially lead to cost overruns. The study provides a kaleidoscopic view of the various routes to managing risks due to the ground, at the preconstruction phases of highway projects, and how a lack thereof, can culminate to determine the trend of high-cost overruns in highway projects. The study findings reveal arguments and widely contested issues in geotechnical practice, which to various degrees, can have a significant financial impact on project completion cost in highway projects. The findings uncover various error traps and gaps in practice such as the lack of deterministic costing methods that better reflect heterogeneous ground conditions; insufficiency of preliminary geotechnical exploration; poor geotechnical risk containment in contracts as well as non-deployment of multi-dimensional geotechnically bespoke contractor selection algorithm. The study submits that these gaps in practice constitute the various trajectories through which geotechnical risk can trigger inefficiency and wastage of financial resources, leading to cost overruns in transportation infrastructure projects.

MRPN Technique for Assessment of Working Risks in Underground Coal Mines

ABSTRACT Accidents in underground collieries, under geological and geotechnical uncertainties, cause some irrecoverable consequences for workers. Recognizing and studying the effective factors in the occurrence of such accidents have a very crucial impact on improving worker safety and reducing mining costs. This paper introduces a new and beneficial technique named “modified risk priority number (MRPN)” for recognizing and assessing those risks which may cause working accidents in Iranian underground collieries. The available qualitative data from the mines was quantified using standard tables established for risk assessment. The technique was exemplified using data from mine accidents in Kerman and East-Alborz regions. Roof-fall was found to be the most significant risk factor in the mines that were investigated.

Assessment of State Agencies’ Practices in Managing Geotechnical Risk in Design–Build Projects

Policies and procedures of state highway agencies for articulating geotechnical information and requirements on design–build (DB) projects are the means to manage the geotechnical risk. Successful approaches and practices to managing geotechnical risk not only reduce the level of geotechnical uncertainty for both the owner and the competing design–builder but also distribute the remaining geotechnical risk between the parties. Discussed here are the differences with regard to geotechnical risk management, aspects of the DB procurement process, and contract aspects between state departments of transportation (DOTs) with experience delivering projects using the DB process versus those that are not as experienced. Results are presented from two independent sources of information: one was obtained through a literature review of aspects related to geotechnical requirements and management of DB projects and the other was obtained through an online survey of 38 state DOTs. Results of the study statistically demonstrate the value of DB experience in managing geotechnical risk and, accordingly, a set of recommended practices for agencies that are relatively new to DB project delivery, during both procurement and contract formation, is presented.

Modelling spatial variability in as-laid embedment for high pressure and high temperature (HPHT) pipeline design

Subsea pipelines are being designed to accommodate higher temperatures and pressures. Current modelling approaches that adopt constant lateral seabed resistance along the pipeline do not capture the high spatial variability in as-laid pipeline embedment from field observations, which strongly affects the lateral resistance. Ignoring spatial variability when designing pipelines with engineered buckles leads to higher predictions of axial force along the pipeline, with reduced likelihood of buckle formation. This can result in excessive mitigation measures being adopted, such as sleepers or counteract structures, which significantly increase project costs. Spatial variability of pipeline embedment is not currently handled rationally in design because an understanding of the physical mechanisms that cause as-laid embedment and methods for accurately predicting it have only recently emerged. This paper illustrates how the influence of these physical mechanisms that drive embedment can be extracted from field survey data and then modelled synthetically in design analyses. The impact of embedment variability and the resulting variation in lateral seabed resistance on the lateral buckling response is illustrated. The framework represents an improvement in the way geotechnical uncertainty and variability is handled in pipeline–seabed interaction analyses for use in pipeline design, and has already begun to be implemented in practice.

Verification of a rheological constitutive model for shotcrete through back‐analysis

AbstractTunnel excavation represents a particularly challenging problem from the design point of view, mainly due to the uncertainties characterising the soil or rock mass behaviour and to the difficulties in the prediction of the stress state on the structural supports. This explains why tunnel designers mostly rely on observational data, adapting excavation sequences and support measures during the construction phase (at least in the case of traditionally excavated tunnels), especially for deep tunnels, where the geological and geotechnical uncertainties can be significant. However, the observational method requires a reliable monitoring system as well as considerable work to interpret and back‐analyse data measured during construction. On the other hand, this interpretation and back‐analysis represent an important step in gaining better understanding of the system response and allowing improvement of the design, thus avoiding excessively conservative and uneconomical solutions. In this paper, a back‐analysis of stress and displacement measurements is presented for a NATM tunnel excavation in rock, carried out using a rheological model for shotcrete. It is shown, consistently with the previous literature on the topic, that the use of an advanced model improves the prediction of tunnel behaviour compared to the common practice of using quasi‐elastic E‐moduli.

Contractual Approaches to Address Geotechnical Uncertainty in Design-Build Public Transportation Projects

AbstractGeotechnical uncertainty may be the most difficult risk to manage in construction. In design-build (DB), where the project’s price is fixed before design and in many cases the subsurface in...

Visible Assessment of Earthquake-induced Geotechnical Hazards by Adopting Integrated Geospatial Database in Coastal Facility Areas

Earthquake event keeps increasing every year, and the recent cases of earthquake hazards invoke the necessity of seismic study in Korea, as geotechnical earthquake hazards, such as strong ground motion, liquefaction and landslides, are a significant threat to structures in industrial hub areas including coastal facilities. In this study, systemized framework of integrated assessment of earthquake-induced geotechnical hazard was established using advanced geospatial database. And a visible simulation of the framework was specifically conducted at two coastal facility areas in Incheon. First, the geospatial-grid information in the 3D domain were constructed with geostatistical interpolation method composed of multiple geospatial coverage mapping and 3D integration of geo-layer construction considering spatial outliers and geotechnical uncertainty. Second, the behavior of site-specific seismic responses were assessed by incorporating the depth to bedrock, mean shear wave velocity of the upper 30 m, and characteristic site period based on the geospatial-grid. Third, the normalized correlations between rock-outcrop accelerations and the maximum accelerations of each grid were determined considering the site-specific seismic response characteristics. Fourth, the potential damage due to liquefaction was estimated by combining the geospatial-grid and accelerations correlation grid based on the simplified liquefaction potential index evaluation method.

Comparison of geotechnical uncertainties linked to different soil characterization methods

ABSTRACTOne of the essential inputs in settlement prediction models is the soil modulus, which may be obtained from laboratory tests or estimated from in situ measurements. The total uncertainty in predicting the confined modulus of a sandy soil is quantified with data from side-by-side in situ testing using the standard penetration test, the static cone penetration test, the light dynamic probing and the laboratory oedometer test. To estimate transformation errors, correlations are proposed between in situ and laboratory data. The results indicate that similar magnitudes of total uncertainties are associated with the in situ methods, which are approximately twice as high as those from the direct oedometer method. The quantified uncertainties are an important input for reliability-based designs of foundations under similar soil conditions.

Performance indicator of tunnel linings under geotechnical uncertainty

AbstractIn the process of dimensioning a tunnel lining support an optimized structural system is pursued that can accommodate the inherent uncertainties associated with the geotechnical, hydro‐geological, and environmental conditions. Particularly for geotechnics, uncertainty has become a major issue of scientific discussion according to a number of recent publications. At the same time, advanced performance criteria often require probabilistic assessments in order to quantify a structure's safety and reliability or to inform life‐cycle engineering decisions. This contribution demonstrates a novel design approach for the design assessment of concrete tunnel linings. The Index for the Capacity Utilization of Linings in Tunnels (CULT‐I) introduced herein, facilitates the quantification of reliability of a tunnel lining support, while it aids toward a rationalized, performance‐based design optimization with considerations on geotechnical uncertainty. A typical case of a shallow urban tunnel excavated in soft ground using the TBM method is presented, demonstrating the practical application and feasibility of the proposed approach.

Using HEC-FIA to identify Indirect Economic Losses

The United States Army Corps of Engineers’ Hydrologic Engineering Center developed the HEC-FIA (Flood Impact Analysis) software to assist in the estimation of consequences with uncertainty. By estimating the consequences, the benefits of existing and future flood risk management measures can be evaluated and compared.HEC-FIA utilizes geospatial datasets to help users build structure inventories and assign values and population per structure. Using this information and geospatially derived flood depth grids (provided by most hydraulic models), HEC-FIA estimates direct economic, indirect economic, agricultural, and life loss consequences for flood hazards. HEC-FIA can compute results for a single event in either deterministic mode or in uncertainty mode which utilizes a Monte Carlo approach. The user can define the uncertainties about any structure in the floodplain in many ways, and each has various impacts on the different consequence calculations. For example, foundation heights, structure values, and depth-damage relationships impact economic consequences, while foundation heights, warning issuance times, and fatality rates impact the life loss calculations. All of these parameters can be defined with uncertainty. HEC-FIA can also be linked into HEC-WAT (Watershed Analysis Tool) with the FRA (Flood Risk Analysis) compute option to randomize the hydraulic events being evaluated in HEC-FIA so that hydrologic, hydraulic, geotechnical, and economic uncertainties can all be represented and evaluated by alternative within the floodplain.This paper will describe how HEC-FIA can be utilized to help evaluate the indirect economic consequences for various alternatives within a floodplain. The computational methods for indirect economic losses utilize a Computable General Equilibrium model to describe the secondary and tertiary impacts of loss of service, loss of laborers, and reductions in demand for intermediary goods.

Rainfall infiltration in a landslide soil deposit: Importance of inverse particle segregation

Coarse particles move towards the front and surface of the deposit, while fine particles stay in the rear and bottom. Accordingly the coefficient of permeability of the soil statistically tends to decrease from the surface to the bottom and from the toe to the apex of the deposit. This feature can be described by trend functions that describe the changes in particle size and permeability inside the soil deposit. In this paper, attempts are made to include the physical background in the characterization of geotechnical uncertainties. The objectives of this paper are to simulate non-stationary fields of particle size and coefficient of permeability in a landslide soil deposit, and to analyse rainfall infiltration in the non-stationary random fields. The soil deposit is assumed to consist of inter-layers parallel to the slope surface. The soil deposit is also assumed to be axisymmetric; therefore, any vertical section of the deposit can be selected to generate two dimensional non-stationary random fields. Each of the non-stationary random fields is formulated by adding a trend surface to a residual stationary random field with orthogonal major and minor scales of fluctuation. The produced random fields follow an exponential correlation structure. Subsequently, steady-state rainfall infiltration in the anisotropic non-stationary heterogeneous random fields is analysed. The effects of variations of saturated permeability and scale of fluctuation on the pore-water pressure regime are also investigated.

Challenging the standard dike freeboard: Methods to quantify statistical uncertainties in river flood protection

In most developed and developing nations, a freeboard is being applied to flood defense structures as a margin of uncertainty in the estimated flood stage. In some jurisdictions, practice is shifting towards the use of confidence intervals based on the fitted flood probability distribution, albeit often relying on only one statistical distribution and on only annual maximum flows. In this paper, we argue that, independent of geotechnical, geomorphological or hydrological uncertainties pertaining to the estimation of flood stage, the application of standard freeboards ignores stochastic uncertainty, the inclusion of which would provide a more scientifically defensible measure for allowable freeboard. The river stage estimate is subject to multiple sources of uncertainty, including but not limited to model and parameter uncertainty. Consequently, freeboards should be determined via a frequency analysis that explicitly takes into consideration, as well as minimizes, the uncertainty of the estimate due to known factors. Confidence intervals are a common way to represent uncertainty of a statistical estimate such as for the river stage. The choice of the confidence level will be critical, and in many cases will be associated with significant cost implications for the construction or upgrade of flood defense structures. Quantitative flood risk assessments, which are emerging as a standard in developed nations, are well suited to address this issue by allowing loss and mitigation cost comparisons for different flood scenarios. Our paper provides guidance for confidence interval calculations of river stage using an extension of the classical peaks-over-threshold method for daily river levels.

Shallow foundation response variability due to soil and model parameter uncertainty

Geotechnical uncertainties may play crucial role in response prediction of a structure with substantial soil-foundation-structure-interaction (SFSI) effects. Since the behavior of a soil-foundation system may significantly alter the response of the structure supported by it, and consequently several design decisions, it is extremely important to identify and characterize the relevant parameters. Moreover, the modeling approach and the parameters required for the modeling are also critically important for the response prediction. The present work intends to investigate the effect of soil and model parameter uncertainty on the response of shallow foundation-structure systems resting on dry dense sand. The SFSI is modeled using a beam-on-nonlinear-winkler-foundation (BNWF) concept, where soil beneath the foundation is assumed to be an assembly of discrete, nonlinear elements composed of springs, dashpots and gap elements. The sensitivity of both soil and model input parameters on shallow foundation responses are investigated using first-order second-moment (FOSM) analysis and Monte Carlo simulation through Latin hypercube sampling technique. It has been observed that the degree of accuracy in predicting the responses of the shallow foundation is highly sensitive soil parameters, such as friction angle, Poisson’s ratio and shear modulus, rather than model parameters, such as stiffness intensity ratio and spring spacing; indicating the importance of proper characterization of soil parameters for reliable soilfoundation response analysis.

Guidelines to design the scope of a geotechnical risk assessment for underground mines

Risk assessment has been seen as an important tool in reducing accidents. Use of risk assessment tools also has its significant presence in the underground mining industry in preventing work related hazards. Geotechnical uncertainty however is among the leading cause behind major accidents such as roof collapse, airblast etc., which leads to multiple fatalities and financial loss. Geotechnical risk assessment done at stages as early as mine design can help justify a different mine design aspect such as support methods for a risky area different from the rest of the mine. The aim of this paper is to organize the geotechnical risk assessment process to suit the underground mining needs. A numerical ranking system has been developed to plan the risk assessment process and choose amongst the risk assessment tools. The risk assessment process has been redefined into four sections namely — hazard identification tool, risk assessment approaches, risk assessment parameters and risk representation tool. Risk identification tools have been shortlisted to suit underground mining needs through literature review. Risk assessment approaches have been defined into deterministic, probabilistic and possibilistic approaches with relevance to geotechnical assessment. Elements to be considered in an underground mine for a geotechnical risk assessment have been structured into classes. Establishment of scope of a geotechnical risk assessment based on these classes has been explained. Selection guideline for the appropriate risk identification tool has been defined based on the scope of risk assessment. The significance of the risk assessment approach has been explained and a numerical ranking system has been formulated which can be used by an underground mine to choose among the probabilistic, possibilistic and deterministic approaches.

Managing geotechnical risk on US design-build transport projects

Awarding design-build (DB) contracts before a complete subsurface investigation is completed, makes mitigating the risk of differing site conditions difficult, if not impossible. The purpose of the study was to identify effective practices for managing geotechnical risk in DB projects, and it reports the results of a survey that included responses from 42 of 50 US state departments of transportation and a content analysis of DB requests for proposals from 26 states to gauge the client’s perspective, as well as 11 structured interviews with DB contractors to obtain the perspective from the other side of the DB contract. A suite of DB geotechnical risk manage tools is presented based on the results of the analysis. Effective practices were found in three areas: enhancing communications on geotechnical issues before final proposals are submitted; the use of project-specific differing site conditions clauses; and expediting geotechnical design reviews after award. The major finding is that contract verbiage alone is not sufficient to transfer the risk of changed site conditions. The agency must actively communicate all the geotechnical information on hand at the time of the DB procurement and develop a contract strategy that reduces/retires the risk of geotechnical uncertainty as expeditiously as possible after award.