IDENTIFICATION AND STABILIZATION METHODS FOR PROBLEMATIC SILT SOILS
Author: McManis, K Nataraj, M Barbu, B G | Size: 8.09 MB | Format:PDF | Quality:Original preprint | Publisher: University of New Orleans | Year: 2001 | pages: 184
Many areas of Louisiana consist of soils with high silt contents, low strengths, and minimal bearing capacity. Construction traffic in these soils can cause detrimental pumping action in areas with a high water table. These wet subgrades under Louisiana pavements cause both construction and performance problems. Common solutions to the problem include excavation and replacement, lime treatment, or cement stabilization. Special provisions are often included in the contract for chemical additives in lieu of undercutting. The research emphasis of this study was placed on efforts to refine the pumping problem and on the development of guidelines for identifying the problem silt-soils. Secondary importance was given to the identification of alternate methods for stabilization. The study consisted of two phases. Phase 1 documented the field experiences of the Louisiana Department of Transportation and Development (DOTD) districts. Phase 2 consisted of a testing program to investigate the nature of the problem, the character of the silt materials, and their performance with modifying and stabilizing agents. Eight soil samples from four of the DOTD districts were used in the laboratory program. The soils were typical examples of those commonly encountered with a high-silt content. Several were acquired from current projects in which pumping problems were occurring. The basic characteristic-parameters of the natural samples were determined with standard laboratory tests. The response and stability of the silts under compaction and loading with various moisture levels and compaction efforts were also tested. The susceptibility to pumping of the different samples was reviewed in terms of their physical characteristics. In addition to the silt content percentage, the plasticity character was noted as significant during testing. Anomalies were also found to exist between the DOTD's earthwork specifications and the physical properties of the high silt-content soils. The potential for the modification and stabilization of the problem silt soils was also studied. The laboratory tests were selected with respect to construction needs and possible post construction conditions. A limited number of specific additives were proposed with consideration for their ability to dry the subgrade silts sufficiently in order that they be compacted and with the strength to provide a working table for the construction of the base and pavement. The additives selected included hydrated lime, portland cement, and Class C fly ash. Limited tests for evaluating long-period stability of the stabilized silt-subgrade subjected to accelerated curing followed by vacuum-saturation conditions were also conducted.
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Load and Resistance Factor Design (LRFD) for Reliability Analysis/Design of Piles Axial Capacity
Author: Rahman, M Shamimur | Size: 3.28 MB | Format:PDF | Quality:Original preprint | Publisher: North Carolina State University, Raleigh | Year: 2002 | pages: 347
Resistance factors were developed for use as a part of the implementation of the Load and Resistance Factor Design (LRFD) method of driven piles’ axial capacity. Resistance factors were calibrated in the framework of reliability theory utilizing pile load test data available from North Carolina Department of Transportation (NCDOT). Resistance statistics were evaluated for each data case in terms of bias factors. Reliability analyses on the current practice of pile foundation design by the Vesic, Meyerhof, and Nordlund methods were performed to evaluate the level of safety and to select target reliability indexes. Two types of First Order Reliability Method, Mean Value First Order Second Moment method and Advanced First Order Second Moment method, were employed for the reliability analysis and the calibration of the resistance factors. Recommended resistance factors for the three design methods (Vesic, Meyerhof, and Nordlund) are presented for the target reliability indexes of 2.0 and 2.5. Seven design categories for which the resistance factors are recommended are coastal concrete square pile with N@Toe<=40, coastal concrete square pile with N@Toe>40, coastal steel HP pile, coastal steel pipe pile, coastal concrete cylinder pile, piedmont concrete square pile, and piedmont steel HP pile. The resistance factors were calibrated separately for total, skin and toe capacities in an attempt to develop a correlation between the three resistance factors for each design category. In many cases, however, the resistance factor for total capacity is larger than both the skin and toe resistance factors and only total capacity factors are recommended. The resistance factors developed and recommended from this research are specific for the distinct soil types of North Carolina and for the unique practice of pile foundation design in the NCDOT.
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"Continuum Damage Mechanics and Numerical Applications" presents a systematic development of the theory of Continuum Damage Mechanics and its numerical engineering applications using a unified form of the mathematical formulations in anisotropic and isotropic damage models. The theoretical framework is based on the thermodynamic theory of energy and material dissipation and is described by a set of fundamental formulations of constitutive equations of damaged materials, development equations of the damaged state, and evolution equations of micro-structures.
According to concepts of damage-dissipation of the material state and effective evolution of material properties, all these advanced equations, which take nonsymmetrized effects of damage aspects into account, are developed and modified from the traditional general failure models so they are more easily applied and verified in a wide range of engineering practices by experimental testing.
Dr. Wohua Zhang is a Professor at Engineering Mechanics Research Center in Zhejiang University of China. Dr. Yuanqiang Cai is a Professor at Department of Civil Engineering in Zhejiang University of China.
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Exercises in Building Construction, Fourth Edition provides a fully revised, user-friendly exercise book to supplement the fourth edition of Fundamentals of Building Construction.
* Includes more than 40 exercises in "real world" construction problem solving; encourages students to apply information learned in classroom.
* Exercises are clearly presented with detailed line drawings; easy for student and instructor to follow.
* Revised to correspond with the fourth edition of Fundamentals of Building Construction.
* Includes companion web pages for instructor use, containing Answer Key and sample drawings.
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Based on standard platforms, ProStructures easily allows structural engineers, detailers and fabricators to create 3D models for both concrete and steel. ProStructures provides automatic creation of documentation, details and schedules. The open working environment and programming interface supports standardization of the program.
Bentley’s ProStructures includes ProSteel and ProConcrete. Both are advanced 3D modeling programs supporting your construction and planning tasks.
ProSteel provides detailing for structural steel and metal work and ProConcrete detailing and scheduling of reinforced insitu/precast and post-tensioned concrete structures.
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IMPORTANT NOTICE: You may use this software for evaluation purposes only.
If you like it, it is strongly suggested you buy it to support the developers.
By any means you may not use this software to make money or use it for commercial purpose.
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Author: Hoppe, Edward J | Size: 1.15 MB | Format:PDF | Quality:Original preprint | Publisher: Virginia Transportation Research Council | Year: 2006 | pages: 30
The purpose of this study was to evaluate the field performance of the first pile-supported highway embankment constructed in Virginia. The project involved construction of an approach to the new bridge over the Mattaponi River, replacing the existing Lord Delaware Bridge at West Point. The scope of work included field instrumentation and data gathering as related to stress transfer and settlement. The objective was to measure actual soil pressures that are exerted at the geotextile fabric bridging pile caps and to measure stresses acting over pile caps. In addition, data analysis was to be carried out to provide information that Virginia Department of Transportation (VDOT) engineers could use to optimize future designs of pile-supported embankments. This report contains field monitoring data and analysis. Prestressed concrete piles were driven at 7-ft (2.1 m) spacing and topped with 3 ft by 3 ft (0.9 m by 0.9 m) precast concrete pile caps. Several layers of high-strength geosynthetic fabric were used for base reinforcement. The maximum embankment height was approximately 6 ft (1.8 m). Earth pressure sensors installed onsite confirmed the formation of soil arching in the embankment fill between columns. Numerical analysis pointed to the large impact of the upper foundation soil layer properties on the magnitude of the final embankment settlement and fabric strain. This shows that accurate material characterization is essential for a cost-effective design. Construction of the pile-supported embankment was carried out by a general contractor. No specialized equipment or methods were required. A rapid increase in the subgrade bearing capacity was observed as the construction proceeded. This method appears particularly well suited to time-critical projects.
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Author: Gupta, Satish C | Size: 3.82 MB | Format:PDF | Quality:Original preprint | Publisher: University of Minnesota, St Paul | Year: 2007 | pages: 245
Pavements are constructed on compacted soils that are typically unsaturated. The negative pore-water pressure (soil suction) due to the ingress of water in between soil particles has a significant effect on pavement foundation stiffness and strength. The study characterized the effects of soil suction on shear strength and resilient modulus of four soils representing different regions of Minnesota. The deviator stress in shear strength measurements followed a power function relationship with soil suction. Resilient modulus also followed the power function relationship with suction but these relationships fell within a narrow range. The authors present models for incorporating suction effects in shear strength and resilient modulus measurements of highly compacted subgrade soils. They also briefly outline a framework for incorporating these models in the resistance factors of MnPAVE. Since soil water content and the resulting soil suction under the pavement varies with season, adjustments are needed to account for increased strength and stiffness of the material as a result of unsaturated soil conditions. These adjustments will not only reflect the more realistic field conditions but will result in more reliable performance predictions than the current pavement design method.
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Granular shoulders are an important element of the transportation system and are constantly subjected to performance problems due to wind- and water-induced erosion, rutting, edge drop-off, and slope irregularities. Such problems can directly affect drivers’ safety and often require regular maintenance. The present research study was undertaken to investigate the factors contributing to these performance problems and to propose new ideas to design and maintain granular shoulders while keeping ownership costs low. This report includes observations made during a field reconnaissance study, findings from an effort to stabilize the granular and subgrade layer at six shoulder test sections, and the results of a laboratory box study where a shoulder section overlying a soft foundation layer was simulated. Based on the research described in this report, the following changes are proposed to the construction and maintenance methods for granular shoulders: (1) A minimum California bearing ratio (CBR) value for the granular and subgrade layer should be selected to alleviate edge drop-off and rutting formation; (2) For those constructing new shoulder sections, the design charts provided in this report can be used as a rapid guide based on an allowable rut depth. The charts can also be used to predict the behavior of existing shoulders; and (3) In the case of existing shoulder sections overlying soft foundations, the use of geogrid or fly ash stabilization proved to be an effective technique for mitigating shoulder rutting.
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Uncertainty, imprecision, complexity, and non-linearity are inherently associated with many problems in geotechnical engineering. The conventional modeling of the underlying systems, tend to become quite intractable and predictions from them are very difficult and unreliable. The general nature of geotechnical problems makes them ideally amenable to modeling through emerging methods of fuzzy and neural network modeling. Piles have been used as a foundation for both inland and offshore structures. The evaluation of the load carrying capacity of a pile, setup, and its drivability are important problems of pile design. In this study, Back Propagation Neural Network (BPNN) models and Adaptive Neuro Fuzzy Inference System (ANFIS) models are developed for: i) Ultimate pile capacity, ii) Pile setup, and iii) Pile drivability. A database for ultimate pile capacity and pile setup has been developed from a comprehensive literature review. Predictions for the above are made using BPNNs as well as commonly used empirical methods, and they are also compared with actual measurements. For the pile drivability analysis, a database of a number (3,283) of HP piles is developed from the data on HP piles from 57 projects in North Carolina (with both GRLWEAP data and soil profile information and without PDA and CAPWAP analyses). All of the programs are developed within MATLAB (and its toolboxes) with its Graphical User Interface (GUI). It is found that ANFIS and BPNN models for the analyses of pile response characteristics provide similar predictions, and that both are better than those from empirical methods, and can serve as a reliable and simple tool for the prediction of ultimate pile capacity and pile setup. Also, the BPNN model developed for pile drivability analysis provides good predictions. BPNN may be considered to be more efficient than ANFIS, as the BPNN model trains much faster, while both provide equally good predictions. However ANFIS models with some additional work will be more desirable for those cases in which one or more input variables may be available only in ‘fuzzy’ terms, and when the model is developed with a limited data range, because in ANFIS extrapolation beyond the data range is made through the membership functions.
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Axial Capacity of Piles Supported on Intermediate Geomaterials
Author: Mokwa, Robert | Size: 669 KB | Format:PDF | Quality:Original preprint | Publisher: Western Transportation Institute | Year: 2008 | pages: 91
The natural variability of intermediate geomaterials (IGMs) exacerbates uncertainties in deep foundation design and may ultimately increase construction costs. This study was undertaken to investigate the suitability of conventional pile capacity formulations to predict the axial capacity of piles driven into IGM formations. Data from nine Montana Department of Transportation bridge projects were collected, compiled, and analyzed. Axial pile analyses were conducted using a variety of existing methods and computer programs, including: DRIVEN, GRLWEAP, FHWA Gates driving formula, WSDOT Gates driving formula, and an empirical method used by the Colorado Department of Transportation. The results of the analyses were compared to pile capacities determined using PDA measurements obtained during pile driving and wave equation analyses conducted using the CAPWAP program. The capacity comparisons clearly demonstrated the inherent variability of pile resistance in IGMs. Most of the projects exhibited considerable variation between predicted capacities calculated using DRIVEN and measured CAPWAP capacities. For example, five of the six restrike analyses were over predicted using DRIVEN, one by as much as 580%. The majority of shaft capacity predictions for cohesionless IGMs were less than the measured CAPWAP capacities; the worse case was a 400% under prediction (a factor of 5). Toe capacity predictions were also quite variable and random, with no discernible trends. This study indicates that traditional semiempirical methods developed for soil may yield unreliable predictions for piles driven into IGM deposits. The computed results may have little to no correlation with CAPWAP capacities measured during pile installation. Currently CAPWAP capacity determinations during pile driving or static load tests represent the only reliable methods for determining the capacity of piles driven into IGM formations.
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