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Performance period or life span of a flexible pavement is dependent upon the load carrying capacity of its base and subbase layers. Pavement strength characteristics influenced by material properties of these foundation layers are of utmost importance in the pavement design. In this experimental study, the goal was to adequately define the limits of different unbound aggregate properties influencing the strength of unbound aggregate. Material type, gradation, maximum particle size, fines content, dust ratio and plasticity index were among the different properties studied. Dust ratio is defined as the ratio of material passing the No. 200 sieve (i.e. fines content) to material passing the No. 40 sieve. As for the aggregate materials, crushed limestone and crushed gravel, commonly used in Illinois in base/subbase applications, were considered. Illinois dense graded base specifications allow aggregate materials with a maximum particle size of 25 mm for the CA 6 specification and 50 mm maximum particle size for the CA 2 aggregate. Plasticity index, fines content, and dust ratio ranged from 5% to 13%, 5% to 12%, and 0.4 to 1.0, respectively. California Bearing Ratio (CBR) and staged triaxial tests were performed to characterize the material strength. Higher strength values were obtained for the CA 6 aggregates with 25-mm maximum particle size compared to the aggregates tested for CA 2 specification. Considering typical property ranges, a dust ratio of 1.0 was found to be a viable option in some cases for base/subbase applications providing an acceptable soaked strength for both crushed limestone and crushed gravel. However, for both material types, the combination of a dust ratio of 0.4 and a fines content of 12% posed a severe negative effect on aggregate strength.

The seismic motion response of a cantilever retaining wall with cohesive and cohesionless backfill materials was evaluated using fully dynamic analysis based on finite difference method. The dynamic analysis was validated based on experimental test results and then compared to analytical and empirical correlations based on Newmark sliding block method. Seven different earthquake events and the backfills with low to high levels of cohesion were considered. Nonlinear regression analyses were carried out to provide correlations between free-field peak ground acceleration (PGA) and maximum relative displacement of the retaining wall. These results were compared to results from empirical and analytical methods. Furthermore, fragility analyses were conducted to determine the probability of damage to the retaining wall for different free-field PGAs and backfill cohesions. It is demonstrated to what extent a small amount of cohesion in backfill material can influence displacement of the retaining wall and probability of damage in seismic conditions.

Characterizing soil erosion and predicting levee erosion rates for various levee soils and storm conditions during floodwall overtopping events is necessary in designing levee-floodwall systems. In this study, a series of laboratory scaled levee-floodwall erosion tests were conducted to determine erosion characteristics of fine grained soils subject to overtopping from different floodwall heights with variable flow-rates. A decreasing rate of erosion was observed as a pool of water was generated in the created scour hole at the crest of the levee model. The erosion rates were also assessed using jet erosion test (JET) and erosion function apparatus (EFA) tests. The results of levee-floodwall overtopping along with soil geotechnical characteristics such as plasticity index, compaction level, and saturation level of the levee soils as well as hydraulic parameters such as water overtopping velocity were used to develop a levee-floodwall erosion rate prediction model. Then, the results of JET and EFA were integrated to develop another prediction model for levee-floodwall erosion rate estimation. Consequently, the prediction models were evaluated by conducting additional tests and comparing the prediction results with the actual measured erosion rates.

Resilient modulus (Mr) and permanent deformation (PD) characteristics of unbound aggregates under repetitive traffic loads dictate the structural response and performance of pavement base and subbase layers. Aggregate material behavior is dependent on the amount of fines in particulate matrix, also referred to as fines content (percent passing number 200 sieve), as well as plasticity index, dust ratio (percent passing number 200 sieve to percent passing number 40 sieve), material type, aggregate gradation/packing and the interactions of these properties with each other. In this study, repeated load triaxial tests were conducted on crushed limestone and crushed gravel aggregates. Fines content and plasticity index were varied from 5% to 12% and 5% to 9%, respectively. Two most typical gradations of aggregates used in roadway construction in Illinois were utilized with dust ratios ranging from 0.4 to 1.0. The results of these tests were analyzed using the shakedown theory for evaluating typical base/subbase permanent deformation or rutting trends linked to practical design considerations. Charts were also established for the modulus and deformation characteristics of unbound aggregates to designate the material quality with performance trends. Such guiding charts were compared with others developed in previous studies by authors for determining aggregate behavior under monotonic loading tests such as California Bearing Ratio (CBR). The comparisons provide valuable insights on how each aggregate property influences strength, modulus and permanent deformation behavior under different loading conditions.

Floodwall overtopping erodes the levee surface. A better understanding of the erosion rate of levee-floodwall systems is crucial for designing such structures. Scouring induced by overtopping during storm events can cause failure of these geo-structures. In this study, the contributing factors such as floodwall height, soil characteristics, and hydraulic characteristics of overtopped flow are considered to predict erosion rates for such levees built with fine-grained soils. Using over 60 simulated scaled levee-floodwall test results, the effect of the contributing parameters on soil erosion are described and quantified. The tested soils had relatively wide ranges of plasticity index (non-plastic (NP) to 40 %), degree of compaction (70 to 90 %), and degree of saturation (15 to 85 %). Various scales of the floodwalls (1:20 to 1:2) and overtopped flow velocities (FV) (0.2 to 0.6 m/s) were used. The response of soils with high plasticity and low plasticity was different to erosion. Highly plastic soils experienced sloughing and more resistance toward erosion, whereas in low plastic soils scour developed. Also, the erosion rates are more sensitive to plasticity index and floodwall height than degree of compaction or degree of saturation. Using the lab-scaled simulation results, a prediction model was developed to estimate erosion rates. The developed model was used to estimate the erosion rates in three case histories and compared with measured values. The limitations and advantages of the model were analyzed and discussed.

The United States witnessed its deadliest landslide on March 22, 2014 in Oso, Washington. Forty-three people were killed and the direct financial damage exceeded 170 million dollars. The topography of the slope prior to this landslide was complex due to the occurrence of several historical landslides on the same slope and three-dimensional (3D) features of the slope. This paper utilizes an inverse 3D limit equilibrium analysis to propose a 3D failure mechanism and sequence for the 2014 Oso Landslide. The 3D mechanism consists of two main phases (Phase I and II) with three retrogressive slides that were identified during field reconnaissance and confirmed via the 3D limit equilibrium slope stability analyses. The 3D analysis suggests that Phase II of the Stark et al. (2017) mechanism consists of two separate retrogressive slides instead of a single slide. The two slides of Phase II are referred to as Phase IIa and Phase IIb herein for comparison with Stark et al. (2017) . Photographs herein show the geometry and runout of Phases IIa and IIb. After Phase IIa, sloughing of the steep scarp in the upper plateau onto the Phase IIb slide mass continued for months. The 3D analysis includes the complexities of the ancient landslide bench along with surrounding slope geometry and features, which help explain the initiation and direction of slide movement.

The analyses of retaining walls in California showed many backfills are coarse material with some cohesion. In this investigation, seismic response of cantilever retaining walls, backfilled with dirty sandy materials with up to 30 kPa cohesion, is evaluated using fully dynamic analysis. The numerical simulation procedure is first validated using reported centrifuge test results. The validated methodology is then used to investigate the effects of three earthquake ground motions including Kobe, Loma Prieta, and Chi-Chi on seismic response of retaining walls. In addition, the input peak ground acceleration values are varied to consider a wide range of earthquake acceleration intensity.

Proper characterization of a dense-graded aggregate base/subbase material should include both quality and strength aspects. Gradation, passing the No. 200 sieve (smaller than 0.075 mm) fines content, and Atterberg limits for plasticity index (PI) are the most important properties that affect the quality and longevity of aggregates used as unbound layers in flexible pavement applications. The criterion used for allowing fines in high quality aggregates for highway applications vary among the state agencies. Most specifications call for controlling fines content, PI and the dust ratio, which is defined as percent passing the No. 200 sieve divided by percent passing the No. 40 sieve. In this study the effect of these fines on moisture-density relationship and strength of a crushed limestone aggregate with 25.4-mm (1-in.) maximum particle size was investigated. A typical range of 5–12% fines content inclusion with plasticity indices of 5–13% and dust ratios of 0.4–1.0 were studied. In order to evaluate the influence of each of these properties of the fines, a comprehensive number of samples were tested for the soaked California Bearing Ratio (CBR). The moisture sensitivity of aggregate strength was evaluated within ±1.5% of the optimum moisture content. The findings were summarized to propose a new approach for proper material selection based on the fines content and dust ratio.

This study focuses on the performance analysis of mine roof rock due to moisture variation using a case study, which experienced roof falls. The roof layer types, thicknesses, and properties were determined using extensive lab and field data. A novel numerical model is developed using site information and observed field performance to incorporate: (1) the interaction between roof rock unit beddings, (2) the interaction of roof bolts and rock units, and (3) the effect of moisture increase on roof deformation and failure. Using the proposed methodology, the mine roof layers’ allowable maximum moisture contents prior to failure can be estimated.

Unbound aggregate base and subbase layers distribute wheel load induced stresses to protect subgrade. Standards such as AASHTO and individual states specifications have set several quality control limits for a variety of properties of aggregates used in the pavement base and subbase courses. Most standards and DOT specifications suggest that the ratio of percent passing No. 200 sieve to percent passing No. 40 sieve should not be greater than two thirds, and plasticity index of the material passing No. 40 sieve should be less than 6%. The ratio of percent passing No. 200 to percent passing No. 40 sieves is called the dust ratio (DR). There are many states that have either waived the standard limits or adopted their own quality control method. In this study the effect of dust ratio, percent passing No. 200 sieve and plasticity index (PI) affecting moisture-density and strength characteristics of crushed limestone aggregates are investigated. The prepared samples represented one of the most commonly utilized dense-graded standard aggregate gradation in Illinois, i.e. CA6. Standard Proctor compaction and soaked California Bearing Ratio (CBR) tests were conducted on specimens to determine the moisture-density and strength characteristics of the material with moisture content, respectively. In addition, two staged triaxial tests using three confining pressures were performed to study the effect of confining pressure and fine quantity on strength of aggregates. According to the results, the effect of percent passing No. 200 sieve on strength variation is significant in unbound aggregates. The sensitivity of aggregate strength to moisture content variation is also discussed.

Foundations on claystone with swell potential may experience upward movement and failure. In this case study, the cause of 58 mm upward movement of drilled-in piers is analyzed using survey data, extensometer readings, and moisture content monitoring of claystone at the site. Laboratory swell tests were conducted to characterize the swelling characteristics of the weathered rock. A swell potential analysis for the pier group foundations is presented. The interaction of the pier group with the swelling rock is considered in analyzing the initiation of the upward movement. Furthermore, a novel inverse analysis method is presented to integrate the laboratory swell test results and numerical modeling to identify the representative swell pressures acting on the pier group as well as upward movement of the pier system. The numerical analysis indicates that the studied pier system is expected to have 135 mm heave and its rate of upward movement is compared with field observations. The behavior of the pier group foundation in swelling rock under various pier spacings and superstructure pressures shows that the uplift is considerably less for piers with smaller center-to-center spacing. The results of pier group numerical modeling provide the correlation of upward deformation changes due to center-to-center spacing of the piers, pier diameters and superstructure pressures.

Among all United States underground coal fields, those in Illinois have the highest rate of roof fall events due to their weak and severely moisture sensitive roof rock units. Rockmass characterization is the key initial step in designing safe and economical roof control measures in underground coal mines. In this study, a performance-based roof rockmass characterization is investigated. The geologic conditions as well as underground mine geographic specifications, roof fall analysis, mining method, utilized supplemental roof control measures, and geotechnical properties of roof rock units were considered to link the roof performance to rockmass characterization. The coal mine roof rating (CMRR) rockmass characterization method was used to evaluate the roof conditions and roof support design for an underground coal mine located in the Illinois Coal Basin. The results of several mine visit mappings, laboratory test results, and geotechnical issues and concerns are presented and discussed. The roof support designs are analyzed based on the rockmass characterization and are compared with the observed performance. This study shows that (1) CMRR index is a reasonable method for characterizing roof rockmass; (2) moisture sensitivity and bedding strengths in the horizontal direction are essential parameters for roof support design in mines with weak roof conditions; and (3) the applicability of the analysis of roof bolt system for roof support design of the studied mine is questionable.

This paper introduces a new approach that considers the effect of softening to more accurately calculate floor-bearing capacities where difficult mine conditions are present. Because of softening and changes in confining pressures, the geotechnical properties of immediate fine-grained rock vary in the mine floor. Therefore, when floor softening is present, the conventional equations used to determine the floor-bearing capacity are not very accurate. In this study, a methodology is presented that considers the floor softening and existence of a durable layer in the mine floor. The proposed method is based on analysis of a case study located in central Illinois utilizing finite-element method (FEM) and rock mechanics laboratory data. For this case study, extensive geological mapping and laboratory tests, including rock classification, rock swell properties, and triaxial compression tests, were conducted on samples of fine-grained rocks that predominantly consisted of mudstone. The results of laborat...

Numerical models are commonly used to estimate excavation-induced ground movements. Two-dimensional (2D) plain strain assumption is typically used for the simulation of deep excavations which might not be suitable for excavations where three-dimensional (3D) effects dominate the ground response. This paper adapts an inverse analysis algorithm to learn soil behavior from field measurements using a 3D model representation of an excavation. The paper describes numerical issues related to this development including the generation of the 3D model mesh from laser scan images of the excavation. The inverse analysis to extract the soil behavior in 3D is presented. The model captures the measured wall deflections. Although settlements were not sufficiently measured, the predicted settlements around the excavation site reflected strong 3D effects and were consistent with empirical correlations. Copyright © 2010 John Wiley & Sons, Ltd.

cited By 41; International audience; Performance observation is a necessary part of the design and construction process in geotechnical engineering. For deep urban excavations, empirical and numerical methods are used to predict potential deformations and their impacts on surrounding structures. Two inverse analysis approaches are described and compared for an excavation project in downtown Chicago. The first approach is a parameter optimization approach based on genetic algorithm (GA). GA is a stochastic global search technique for optimizing an objective function with linear or non-linear constraints. The second approach, self-learning simulations (SelfSim), is an inverse analysis technique that combines finite element method, continuously evolving material models, and field measurements. The optimization based on genetic algorithm approach identifies material properties of an existing soil model, and SelfSim approach extracts the underlying soil behavior unconstrained by a specific assumption on soil constitutive behavior. The two inverse analysis approaches capture well lateral wall deflections and maximum surface settlements. The GA optimization approach tends to overpredict surface settlements at some distance from the excavation as it is constrained by a specific form of the material constitutive model (i.e. hardening soil model); while the surface settlements computed using SelfSim approach match the observed ones due to its ability to learn small strain non-linearity of soil implied in the measured settlements. © 2009 Elsevier Ltd. All rights reserved.

Instruments are installed during the construction of urban excavations to monitor ground response at discrete locations to various construction activities, to verify design assumptions and to effectively apply the observational approach. Inverse analysis approaches are often used to develop improved soil models suitable for representing soil response during excavation from these measurements. We propose that through the integration of inverse analysis and instrument measurements, it is possible to provide information on excavation performance at locations where no instrumentation is available. Therefore, this study examines the relationship between various instruments typically used on an excavation project and the quality of information that can be extracted for excavation modeling. A synthetically generated set of instrument measurements that include inclinometers, surface settlement points, extensometers, heave gauges, piezometers, and strain gauges, using an idealized soil profile are initially used. The analyses show that in addition to the measurements of lateral wall deflections and surface settlement, inclinometers placed some distance behind the wall and measured forces in the struts significantly improve the quality of the extracted soil behavior. These findings are further demonstrated with a well instrumented deep excavation case study in Taipei. The inclinometers at the wall and at farther distance from the wall are used to extract the soil behavior. The extracted soil model used in a numerical analysis provides a good prediction of excavation behavior elsewhere around the excavation including surface settlements.

Estimate of deformations around urban excavations is a primary concern for designers, contractors, owners, and potentially affected third parties. Significant efforts have gone into the development of empirically based methods to estimate deformations relying on a large number of case histories. The construction of the deep excavations for the central artery/tunnel project provides valuable information on observed deformations due to the construction of these excavations. Lateral deformations and surface settlements for three construction contracts are collected and summarized in a form similar to published empirical charts. The stiff support system used in these braced excavation and the embedment of the wall into stiff strata control deformations to minimal levels. The data show that surface settlements, although small, extend farther away from the excavation than previously reported.

The erodibility of levee material has an influence on scour generation in levee-floodwall systems. In this investigation, the effect of various soil parameters including compaction level, plasticity index, and saturation ratio on erosion rates was studied using two methods: lab-scaled physical models of levee-floodwall systems and the Erosion Function Apparatus (EFA). For physical models, a 1:20 scale of a typical levee on the banks of the Mississippi river was constructed. The effect of the floodwall and its inclination on levee erosion were investigated. For EFA tests, the soil samples were prepared in the same way as the materials prepared for physical model tests in order to compare the erosion rate characteristics of these methods. EFA test results show that the erosion rate for soils with more than 60 % saturation levels is more sensitive to change in saturation levels than changes in plasticity index or compaction levels. An erosion rate prediction model was developed for various soils using EFA tests. The levee-floodwall tests show that the erosion rates at the crest are significantly more sensitive to soil parameters than at the slope. The erosion rates for levee-floodwall tests are much greater than the ones for EFA tests. Furthermore, the effect of floodwall inclination and presence in levees are discussed.