Abdolreza Osouli

Results of soaked and unsoaked California bearing rate tests on unbound aggregates with varying amounts of fines and dust ratios

Unbound aggregate base and subbase courses consist of coarse-grained materials with limited percentages of fines (i.e., passing the No. 200 sieve) allowed. The fines are mineral fillers that occupy the void spaces between the sand and gravel-sized particles. An excessive quantity of fines can negatively affect the strength characteristics of unbound aggregate layers, and this effect can easily be aggravated when the matrix is saturated. A set of unsoaked and soaked California bearing ratio (CBR) tests were performed on engineered gradations of unbound aggregate samples so that the effect of soaking on CBR test results could be studied. A detailed comparison between soaked and unsoaked CBR results was carried out by considering various index properties, such as the fines content, plasticity index, and dust ratio (percentage passing the No. 200 sieve divided by the percentage passing the No. 40 sieve). It was found that higher plasticity indexes, such as 9% and 13%, have a negative effect on both soaked and unsoaked CBR values for samples with a dust ratio of 1.0. Samples with a dust ratio of 0.4 were, in general, not influenced by soaking in terms of the CBR index. Moreover, the effect of soaking on strength reduction was noticeable when the fines content was as high as 12% and the dust ratio was greater than 0.6. Furthermore, a correlation between soaked and unsoaked CBR is also proposed on the basis of experimental results obtained from this study.

Seismic Performance of Cantilever Retaining Walls with Clayey Backfills

Current engineering design methods for evaluating the seismic lateral earth pressures of retaining walls are based on limit equilibrium Mononobe-Okabe method. In limit equilibrium method, the effect of dynamic loading is introduced to the soil wedge behind the retaining wall as lateral and vertical inertia forces. The two most important simplifications of these methods are application of pseudo-static solution procedure for a fully dynamic problem and assumption of cohesionless backfill material. In this investigation, a full dynamic numerical modeling on a retaining wall with low frictional angle backfill material is conducted to evaluate the seismic performance of retaining wall and lateral earth pressure variation during the earthquake. A 6-meter high cantilever wall with a base width of 4 m and thickness of 0.5 m is represented by structural element. The concrete wall was assumed to perform elastically and the Mohr-Coulomb constitutive model was selected for soil material. The interaction between concrete wall and soil was modeled by using elasto-plastic bilinear model to account for shear sliding and normal separation of wall and soil. The performance of the retaining wall was analyzed under three distinct earthquakes. The lateral earth pressure distribution along the wall height was evaluated during the earthquakes and was compared to static earth pressure. Furthermore, a set of dynamic analysis were conducted with normalized peak ground acceleration, PGA, of the earthquakes. The dynamic lateral earth pressure coefficients along the stem, middle and heel of the wall during the earthquake were analyzed for various horizontal PGAs induced by earthquakes. Consequently, the lateral earth pressure coefficients along the wall were compared to those concluded by Mononobe-Okabe method. According to the results, in low frictional angle soil backfills that have some cohesion, the lateral earth pressures are overestimated by Mononobe-Okabe method.

Influence of Maximum Particle Size, Fines Content, and Dust Ratio on the Behavior of Base and Subbase Coarse Aggregates

Unbound aggregate base and subbase layers are the main load-bearing layers in a pavement structure. Size and shape properties of these aggregate materials should be controlled to ensure proper workability during construction and improved performance for pavement longevity. The effects of gradation, maximum particle size, fines content (percentage passing the No. 200 sieve), and dust ratio on the quality of aggregates were investigated by performing many soaked California bearing ratio tests on a crushed limestone material. The dust ratio represents the amount of fines content divided by the amount of minus No. 40 sieve material. The dust ratios studied were 0.4, 0.6, and 1.0. Two gradations commonly used in Illinois, with maximum particle sizes of 1 in. and 2 in., were studied to analyze the effect of fines content with respect to maximum particle size in the gradation. A typical range of fines contents (i.e., 5%, 8%, and 12%) was also considered. The results show that the gradation, dust ratio, and fines content should be taken into account in the selection of aggregate properties for stability requirements. Aggregates with larger maximum size particles provide high strength, and they are not affected as much as aggregates with smaller maximum size particles by an increase in fines content. The aggregates with smaller maximum size particles provide lower strength. It was also concluded that samples with a dust ratio of 1.0 do not necessarily result in an aggregate material with low strength.

Reliability of Coal Mine Roof Rating in Mining Applications

Reliable rock mass characterization is needed to design safer and more economical roof support systems of coal mines. Coal Mine Roof Rating (CMRR) index is a commonly used method by roof control engineers to characterize immediate rock units above the underground coal mines. This index ranges from 0 to 100 and was developed by studying the performance of the roofs in the Appalachian coal fields, which have typically strong roof units. Application of CMRR for weak and moisture sensitive rocks such as shale roof units in the Illinois Basin may misrepresent the rock mass. In this study, the rock laboratory test results are conducted to characterize the moisture sensitivity, axial and diametral strengths of roof units. The CMRR indexes and designed roof systems in a coal mine located in Illinois Basin will be presented. A sensitivity analysis is also performed to identify the most influential CMRR rock mass characterization parameters in weak rocks. This study shows while CMRR rock mass characterization has many advantages, it should be cautiously used for roof support design in weak and moisture sensitive roof conditions.

Influence of Specimen Size in Engineering Practice

A combined laboratory experimental and numerical analysis is presented to investigate the influence of specimen size and scale effect on engineering analysis and design. Laboratory triaxial compression and direct shear tests show that the size of the specimen has a significant influence on the stress-strain behavior of sands with larger specimens mobilizing smaller shear strengths. Shear strengths measured in laboratory direct shear tests are incorporated in a FEM and slope stability analyses to evaluate and compare the shear stress distribution and deformational behavior of a slope case study. The numerical analyses are conducted using ABAQUS and mohr-coulomb failure criteria. The performance of the slope under load application due to staged highway embankment construction is also evaluated. The analyses results show that the shear stresses and performance of slope and highway embankment are influenced considerably by the size of the triaxial specimens. This would have significant implications on engineering design and the choice of a representative sample size. In order to apply the shear strengths in design, it is suggested to employ larger specimen sizes to achieve the critical state strengths of the soil and better representation of field deformations.

Soaking Effects on Strength Characteristics of Crushed Gravel and Limestone Unbound Aggregates

Strength characteristics of unbound aggregate materials critically affect base and sub-base thickness designs of construction working platforms and flexible pavements. Unsoaked California Bearing Ratio (CBR) is commonly used by state transportation agencies for quality control and design. However, depending on the amount of fines content (i.e., passing No. 200 sieve), the strength characteristics of unbound aggregate layers may severely be affected after soaking. This study investigates any correlations that may exist between soaked and unsoaked strengths of crushed gravel and limestone aggregates commonly used in the State of Illinois. A test matrix was established to consider the effects of varying fines content at 5% and 12%, plasticity index (PI) at 5% and 9%, and dust ratio (DR) at 0.4, 0.6, and 1.0 on aggregate strength. DR is the ratio of percent passing No. 200 sieve to percent passing No. 40 sieve. Most of the aggregate strength characterizations with 5% fines content were not sensitive to soaking in terms of CBR index. However, significant reductions in soaked and unsoaked CBR values were observed when fines content increased from 5% to 12%. The crushed limestone aggregate strengths were more affected by soaking than the crushed gravel aggregates. A prediction model was developed to predict soaked CBR values from unsoaked CBR tests considering material type, fines content, PI and DR.

Crushed Limestone Aggregate Strength Influenced by Gradation, Fines Content, and Dust Ratio

AbstractQuality classes of aggregate materials used in unbound base and subbase construction are quite important for the longevity of highway pavements. Aggregate gradation, fines content, Atterber...

Erosion Rate Prediction Model for Levee-Floodwall Overtopping Applications in Fine-Grained Soils

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.

Performance Evaluation of Combined Linear BMPs for Reducing Runoff from Highways in an Urban Area

Roads, highways, and developed land can alter hydrologic pathways, cause erosion and pollution to nearby waters. Best management practices (BMPs) are commonly used to reduce adverse effects of post-construction runoff (e.g., peak flows and runoff volumes). By applying the personal computer stormwater management model (PCSWMM), this study took an idealized catchment area approach to evaluate the performance of linear BMP alternatives for retaining the first inch of stormwater runoff from highways and roads in Illinois. Various combinations of BMPs consisting of vegetated filter strip, bioswale, and/or infiltration trench were analyzed. Two types of grass covers were considered: prairie grass and turf grass. One-inch of 24-h accumulated rainfall was used for all of evaluated scenarios. The sizes and dimensions of the evaluated BMPs were extracted from Illinois Department of Transportation (IDOT) projects. Stormwater runoff from combined post-BMP construction under the two different grass covers were compared to pre-BMP construction under the condition of bare soil cover. Results indicated that runoff reduction ranges from 96 to 99% for combination of vegetated filter strip-bioswale, 89 to 100% for vegetated filter strip-infiltration trench, and 100% for bioswale-infiltration trench. Results also showed that prairie grass cover is more effective than turf grass in reducing runoff from various soil types. Findings from this study can benefit DOT to develop cost-effective solutions to manage storm runoff from roads and highways.

Roof Rockmass Characterization in an Illinois Underground Coal Mine

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.