Geotechnical Engineering Group
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  Research in Soil Mechanics and Foundation Engineering  

Design and Performance of Tied-Back Excavation Walls
J. H. Long,* E. J. Cording,* J. Ghaboussi, C. Mueller, G. Larson
Federal Highway Administration; Schnabel Foundation Co.

Ground movements and the distribution of stresses on an excavation wall are dependent on construction procedures and the relative stiffness of the support elements with respect to the soil. These characteristics are being studied using numerical analyses, full-scale field tests, and large-scale model tests. Model tied-back walls constructed in the soil model test facility will be tested to determine displacements and stresses resulting from normal construction sequences, as well as failure. Model performance will be compared with finite-element analyses, and techniques will be developed that will permit analysis of both limit equilibrium and soil-structure interaction effects.

Determination of the Axial Capacity of Drilled and Grouted Piles Using a Database of Load-Test Data on Drilled Foundations
J. H. Long,* M. Wysockey
Amoco, Exxon, Mobil, Shell, ADSC; The Association of Foundation Drilling; Shell Foundation Faculty Fellowship

Drilled and grouted piles offer advantages over driven piles when driving is uneconomical or impractical because of subsurface and environmental conditions, such as very deep water, very hard driving conditions, or calcareous soils. The goal of this project is to develop design/analysis procedures for predicting the axial load capacity of drilled and grouted piles (and drilled foundations) based upon a large database collection of results from load tests on drilled foundations. Currently, over 950 load tests on drilled foundations (drilled and grouted piles, drilled shafts, auger-cast piles, and tiebacks) have been collected. The database of load tests is being used to provide insight regarding the effect of length, diameter, construction procedure, grout pressure, soil type, etc.

Friction-bearing Design of Steel H-Piles
J. H. Long,* M. Wysockey, M. Maniaci
Illinois Transportation Research Center, ITRC Project IA-H3

This effort is to assess current Illinois Department Transportation (IDOT) recommendations for estimating the axial capacity of friction H-piles driven in layered soils. The effort investigates methods for predicting axial capacity including (1) current IDOT recommendations (IDOT Specification Art 512.14), (2) conventional methods that include soil strength parameters, (3) wave equation analysis (WEAP), and (4) pile driving analyzer (PDA) results. The scope of this effort will include monitoring pile response during driving and conducting axial load tests on H-piles driven at a minimum of three construction sites in Illinois. The results of the study will be used to provide recommendations to IDOT for improving estimates of axial capacity for friction H-piles.

Axial Capacity of Drilled Shafts in Sand
J. H. Long,* C. Berger
University of Illinois; Hanson Engineers, Inc.

Relationships for the behavior of sands are being used to develop a method to predict the axial capacity of drilled shafts in sand. These relationships are based on characteristics of the soil, such as grain size, soil density, dilational behavior, and the stress at failure along the perimeter of the drilled shaft. Results of soil tests will be used to develop relationships for the soil behavior and design charts for the resistance provided by the soil. Results of axial load tests on drilled shafts are being used to calibrate the model.

Accuracy of Methods Using Driving Resistance for Predicting Axial Pile Capacity
J. H. Long,* B. Leoro
University of Illinois

Improvements for estimating pile capacity have been made in recent years by instrumenting piles, monitoring their behavior during driving and during retapping, and modeling their dynamic response. A database of load tests on driven piling is being used to assess the accuracy at which these methods can predict axial capacity. The database consists of over 100 piles in which dynamic measurements, wave equation analyses, and static load tests were conducted. Each method is being compared in terms of accuracy and in terms of cost of the resulting foundation. Effects of setup and relaxation for driven piling are also being used to study and quantify time effects and their effect on pile capacity.

Foundation Improvement for Bridge Columns
J. H. Long,* B. Leoro, T. Hunt
NSF Mid-America Earthquake Center

The goal of this project is to investigate, experimentally and analytically, the use of micropiles and deep soil mixing as means of retrofitting existing foundations for bridge columns. Results of the project will provide the practicing engineer with information on the suitability of these two alternatives for the seismic retrofit of bridge foundations in the mid-America region. The study will assess the behavior of the original foundation and predict the retrofit behavior with micropiles and with deep soil mixing. The study will also identify the suitability of each method to seismic retrofit needs (e.g., lateral load, overturning, tension, etc.).

Foundation Remediation for Buildings
J. H. Long,* B. Leoro, T. Hunt
NSF Mid-America Earthquake Center

The goal of this project is to provide practicing engineers with detailed information for guidance in rehabilitating foundations of essential facilities in the mid-America region. The project will investigate methods for rehabilitating foundations under typical low-rise essential facilities. These methods will include both soil improvement and retrofit of existing foundations. Assessment of various methods for foundation remediation will include information on cost of implementation as well as the associated risks. Foundation remediation methods will be presented in a set of guidelines for practicing engineers, allowing them to develop and compare different strategies for rehabilitating foundations.

Soil Improvement by Vertical Drains
G. Mesri,* M. M. Shahien, M. A. Ajlouni
University of Illinois

The computer program ILLICON-I for settlement and pore water pressure analyses, which is based on a theory of consolidation developed at the U of I, has been successfully used for designing dykes on highly compressible clays and for analyzing case histories of test fills on soft ground. Embankment construction on deep deposits of highly compressible soils generally requires the use of vertical drains to speed up the hydrodynamic consolidation stage. The new generation of the program, ILLICON-II, includes all the features of ILLICON-I and incorporates partially or fully penetrating vertical drains with well-resistance and smear zone. The program is being used to analyze case histories of embankments on soft ground with sand or prefabricated drains.

Undrained Shear Strength of a Glacial Clay
G. Mesri,* S. Ali
University of Illinois

Stability analysis of embankments, foundations, and excavations on clays requires evaluation of the undrained shear strength mobilized along a potential surface of slip. Mode and rate of shear, as well as progressive yielding and soil disturbance, are major factors that influence evaluation of mobilized strength from laboratory measurements. Excellent quality undisturbed block specimens of Boston blue clay have been used to investigate mobilized undrained shear strength of a glacial clay. The natural clay used in the study was characterized by means of a complete spectrum of structural, mechanical, and hydraulic properties.

Compressibility and Consolidation of Soils
G. Mesri,* T. W. Feng, M. M. Shahien
University of Illinois

This research program is concerned with compressibility and consolidation of soft clay and silt deposits. The uniqueness principle of soil compressibility is being investigated by means of laboratory measurements of consolidation of half a meter thick natural soft clay specimens. This principle allows direct application of compressibility information from small-scale laboratory tests to full-scale field settlement problems. Surcharging of soft clays, peats, and silts for ground improvement is another subject of this investigation. Surcharging is used to speed up ground modification and minimize postconstruction deformation damage to structures. The objective is to develop a methodology for engineering surcharging operations.

Settlement of Granular Soils Subjected to Static or Dynamic Loading
G. Mesri,* M. M. Shahien
National Science Foundation, CMS 95-30464

This research program is developing methodologies for settlement analysis of structures on granular soils subjected to repeated loading. Two independent methods based on in situ penetration tests are being evaluated using field performance records. One empirical method is based on the drive sampler penetration text (DSPT), and the second method uses push cone penetration test (PCPT) measurements. Settlements taking place during static or dynamic external loading and those that follow with time are being evaluated. Variables other than the condition of granular soil and nature of loading include depth of foundation and adjacent structures.

Settlement Resulting from Flow of Soil
G. Mesri,* M. Smadi
National Science Foundation, CMS 95-30464

Settlement of structures on soft clay deposits results from flow and consolidation of soil. In the latter case, water squeezes out from under the structure, whereas in the former case, soil squeezes out. Settlement resulting from flow of soil depends on the factor of safety against undrained instability. In construction situations where the factor of safety is small, an accurate prediction of settlement resulting from flow of soil is required. Field measurements of horizontal deformation of soft clays during construction of embankments and storage facilities are being used to develop a practical procedure for computing settlements resulting from flow of soil.

Embankment Stability Following Reservoir Drawdown
G. Mesri,* M. Alzoubi
National Science Foundation, CMS 95-30464

Embankment dams or dykes may experience undrained instability during rapid drawdown of the reservoir. Drainage may not occur in compacted clay of a homogeneous embankment or a core upon rapid drawdown. Undrained shear strength at yield of the compacted clay, consolidated under predrawdown shear stress and effective stress conditions, is required for stability analysis. Undrained strength may be expressed in terms of post-drawdown effective stress condition and strength parameters (ESSA), or in terms of predrawdown effective stress conditions and undrained shear strength ratios (USSA). Both approaches are being evaluated in laboratory undrained shear tests on saturated compacted clays and by full-scale stability analyses.

Geotechnical Characteristics of Pisa Clay
G. Mesri,* J. E. Hedien, M. Shahien
University of Illinois

The subsoil of the Leaning Tower of Pisa is of interest because the historic tower has been tilting since its construction in 1173 to 1370. There is concern about the stability of the tower, and remedial measures are currently underway to arrest further tilting and possibly to decrease the angle of inclination. A main source of the settlement of the tower is the upper Pisa (Pancone) clay. A comprehensive investigation of the geotechnical characteristics of a sample of Pancone clay has been carried out. Based on these measurements, it is possible to speculate on the long-term response of the tower to the recent surcharging of the northside to arrest tilting and possibly to decrease the angle of inclination.

Secondary Compression of Peat
G. Mesri,* T. D. Stark,* M. A. Ajlouni
University of Illinois

Secondary compression is most important in peat deposits because they exist at high void ratios and exhibit high values of compression index Cc, display the highest values of Ca/Cc among geotechnical materials, and primary consolidation is completed in weeks or months in typical field situations. Secondary compression of Middleton peat was investigated by oedometer tests on undisturbed specimens. The observed secondary compression behavior of this fibrous peat, without or with surcharging, is completely in accordance with the Ca/Cc law of compressibility. It is possible to predict settlement of embankments on peat without and with surcharging. The next phase of the research concerns primary consolidation of peat.

Electrical Treatment of Soils
G. Mesri,* V. Schifano
University of Illinois

Electrical flow of pore fluid and associated electrochemical reactions have been used for permanent or temporary stabilization of soft clay and silt deposits. Important manifestations are consolidation and associated deformations, improvement of mechanical properties resulting from consolidation and electrochemical hardening, and favorable porewater flow resulting in an increase in effective stress. Although considerable attention has been directed recently to electrokinetics as a means of cleaning contaminated ground, important uncertainties remain in relation to electrokinetic processes in soils as well as practical details of treatment. The physical and chemical processes are under detailed review and analyses for developing a formulation for predicting time-rate of electrochemical ground modification.

Maintenance Monitoring of Facilities on Expansive Soils
G. Mesri,* G. K. Al-Chaar*
University of Illinois

Facilities that are located on expansive soils are not permanently stable because the moisture environment that determines the expansive soil response may not remain constant. Moisture environment is controlled by climatic cycles and events, landscaping, vegetation, drainage systems, and facility functions, and development of a build-up area. Distress may develop at any time during the useful life of the facility.A program of maintenance monitoring of the facilities is being developed to: (1) identify previous distress and recommend remedial corrections, (2) identify current distress and recommend measures to alter conditions to stop damage, and (3) detect signs of imminent distress and propose measures to avoid damage.

Granular Soils Improved by Dynamic Methods
G. Mesri,* M. Smadi, B. Vardhanabhuti
National Science Foundation, CMS 95-30464

Geostatic horizontal stress plays a dominant role in ground response to in situ penetration tests that are frequently specified for the control of granular soil improvement by dynamic methods. These include densification by impluse loading, such as explosives or heavy tamping, and by steady vibration such as vibrocompaction. Each compaction method produces a different history of preshearing resulting in different magnitudes of horizontal stress in densified ground. Laboratory measurements of horizontal pressure in sand specimens that are densified by different impulse or steady vibration methods are intended for a better interpretation of post-densification penetration resistance.

Long-Term Stability of Stiff Clay Slopes
G. Mesri,* M. M. Shahien
University of Illinois

The stability of stiff clay slopes is time-dependent because shear strength may deteriorate from the intact value to the residual condition. Because it is not readily possible to specify the dynamics of deterioration in terms of the environmental, hydrologic, and detailed geologic conditions, a precedent-based approach is used to forecast instability. The empirical method is constructed using back-analyses of failures of cut slopes of known age, together with interrelationships for intact and residual strength. For a stiff clay slope, it is possible to predict a stable age which may range from less than a year to over 200 years.

Geotechnical Properties of Peat
G. Mesri,* M. A. Ajlouni
University of Illinois

Peatlands constitute 5% to 8% of the world's land. Peat deposits, the remains of plants, have a chemical composition and structure significantly different from those of inorganic soils. Peat exists at very high water contents and displays very large compressibility. It is no longer economical to avoid peat deposits in siting of infrastructure, including transportation facilities. Innovative engineering requires a fundamental understanding of peat behavior. Undisturbed samples of Middleton peat from Wisconsin and James Bay peat from Quebec are being used in a detailed laboratory study of geotechnical characteristics of peat.

Lime Stabilization of Clay Slopes
G. Mesri,* D. Rydeen,* N. Schwanz,* M. Al-Zoubi, V. C. Schifano, M. M. Shahien
U.S. Army Construction Engineering Research Laboratories, DACW37-98-M-0458

Stability of levees and banks of the Red River has a profound influence on land use in adjacent communities. Slope movements damage adjacent structures, and during the spring 1997 flood, overtopping of levees caused catastrophic flooding in North Dakota and Minnesota. Programs are underway to stabilize river banks and improve the levee system. One scheme is lime treatment of river bank clays. Adsorption of calcium hydroxide, together with formation of calcium silicates and aluminates, may lead to aggregation of clay particles. Direct shear testing is being used to investigate a possible permanent increase in frictional resistance of lime-treated Brenna and Sherak formations.

Undrained Residual Strength of Cohesive Soils and Landslides during Earthquakes
T. D. Stark,* I. Contreras
U.S. Geological Survey, 1408-0001-G1953

A constant volume ring shear apparatus has been developed to measure the undrained peak and residual shear strengths in cohesive soils. It allows the undrained post-peak strength loss to be quantified for seismic slope stability evaluations. Undrained ring shear tests are being conducted on Bootlegger Cove Clay from the Fourth Avenue landslide that occurred during the 1964 Alaskan earthquake to measure the undrained peak and residual shear strengths. These shear strengths are compared to the back-calculated shear strength. This comparison is providing an estimate of the undrained strength mobilized at the time of sliding and a relationship between strength loss and displacement for seismic stability evaluations.

Performance of Three-dimensional Slope Stability Methods
T. D. Stark,* P. T. Eickenberg
National Science Foundation, BCS 93-00043

The 1988 slope failure at the Kettleman Hills Waste Repository forced engineers to consider 3-D slope stability analyses. However, 3-D slope stability analyses are new and not readily available to practicing engineers or government agencies. The main objectives of the research are: (1) improved understanding of the accuracy and applicability of existing 3-D slope stability methods to field conditions, (2) clarifying the parameters or assumptions that significantly affect the 3-D factor of safety, (3) field situations, if any, where 3-D factors of safety are less than 2-D factors of safety, and (4) improved understanding of 3-D effects on 2-D back-calculated shear strength parameters.

Static and Dynamic Geosynthetic Interface Strengths
T. D. Stark,* R. Hillman
Illinois Office of Solid Waste Research, OSWR-07-001; PVC Geomembrane Institute

The stability of a composite liner or cover system for landfills and reservoirs is dependent upon the interface strength between the various components within the system. This study is developing a test methodology and a database of interface strengths for the various interfaces in a composite system. Torsional ring shear tests, instead of reversal direct shear, are being performed to investigate the interface strength and its degradation with shear displacement. The effect of displacement rate and flexible geomembranes are also being investigated to evaluate the dynamic interface strength. Case histories are being used to estimate the magnitude of the laboratory strength that is actually mobilized in the field.

Long-Term Performance of Compacted Soil Liners
T. D. Stark,* D. E. Daniel,*I. G. Krapac*
Illinois Office of Solid Waste Research, OSWR-11-002

Although compacted soil liners are widely used for waste-containment facilities, there is little information on their long-term performance. A heavily instrumented soil liner (plan dimensions 8 m 15 m and 0.9 m thick) has been monitored for approximately eight years. Evaluation of the resulting data provides a unique opportunity to quantify the long-term advection and diffusion of compacted soil liners. In addition, excavation/dissection of the soil liner will provide insight to the effect of compaction on soil micro- and macrofabric.

Soil Strength of Liquified Soils
T. D. Stark,* S. M. Olson
National Science Foundation, CMS 95-31678

A method for estimating the shear strength ratio of liquefied soil using cone penetration test (CPT) results is being developed. The strength ratio from 30 field case histories of liquefaction flow failure and lateral spreading is being used to develop a relationship between equivalent clean sand corrected CPT tip resistance and mobilized strength ratio. This project also involves convening an international workshop to evaluate the state-of-the-art and state-of-the-practice of determining the shear strength of liquefied soil for use in stability and deformation analyses and to identify and prioritize research needs.

Paleoliquefaction and Paleoseismology in Mid-America
T. D. Stark,* S. M. Olson
NSF Mid-America Earthquake Center

Sites that experienced liquefaction and/or lateral spreading during the 1811-1812 New Madrid earthquakes and possibly during prehistoric earthquakes in the New Madrid seismic zone are being studied to improve the paleoearthquake chronology of the region. Geotechnical investigations are being performed at these sites to enhance understanding of the formation of the liquefaction features and to back-calculate the levels of ground shaking required to form these features. In addition, levels of ground motion inferred from this study will be used to improve ground motion estimates, earthquake magnitude estimates, and liquefaction hazard maps throughout mid-America.

Seismic Performance of Waterfront Structures
G. Mesri,* W. J. Hall,* T. D. Stark,* R. M. Ebeling,* M. Shahein
NSF Mid-America Earthquake Center

This project investigates the seismic design of river and port facilities in the mid-American transportation network. The objectives of the research for mid-American waterfront structures are to: (1) examine performance during previous earthquakes, (2) identify the typical design conditions, (3) develop a simplified design procedure, (4) develop a fragility relationship for typical mid-American waterfront structures, and (5) prepare a brief nontechnical document for port owners and operators to alert them to the potential consequences of an earthquake in the region.

PVC Geomembrane Institute Technology Program
T. D. Stark,* D. E. Daniel,* K. R. Reddy*
PVC Geomembrane Institute

A technology program was established for the PVC Geomembrane Institute to develop and disseminate information on PVC geomembranes. The PGI is a nonproduct, industry-based consortium founded in 1988 to convey the advantages and disadvantages of PVC geomembranes. The research that is conducted involves thermal seaming, interface strengths, durability, and chemical compatibility. The information dissemination involves publishing technical bulletins, reports, and papers, establishing and maintaining a website, conducting workshops and short courses, and incorporating the information in existing courses.

Guidelines for Geofoam Applications in Embankments
T. D. Stark,* J. M. Horvath,* D. Leshchinsky*
National Cooperative Highway Research Program, 24-11

The main objective of the proposed research is to develop guidelines for the use of geofoam, i.e., expanded polystyrene, as a super-lightweight fill in roadway embankments and bridge approaches over soft ground. These guidelines will facilitate the use of geofoam in civil engineering projects by providing engineers with design procedures, historical data, and durability information.


 

Geotechnical Engineering Group
  Soil Mechanics-Behavior and
Foundation Engineering
Rock Mechanics and Tunneling Computational Geomechanics  
 
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