Geotechnical Engineering Group
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  Research in Rock Mechanics and Tunneling  

Jacking Loads and Ground Deformations Associated with Microtunneling
R. D. Bennett,* E. J. Cording
U.S. Army Waterways Experiment Station

Tunneling with remotely operated, small-diameter machines is increasingly used in lieu of open trenching for installation of utilities. The performance of three tunneling machines was investigated by advancing them through test beds constructed at the Waterways Experiment Station containing a sequence of soil and groundwater conditions. These results, combined with results of field measurements on microtunneling projects in several natural soil deposits, are being used to investigate the effect of soil conditions, construction procedures, and tunnel machine design on the forces required to advance the pipe and the ground movements associated with the tunnel advance.

Coupled Hydraulic-Mechanical Behavior of Jointed Rock Masses with Applications to Pressure Tunnels
E. J. Cording,* G. Fernandez,* S. Choi, S. Lee
National Science Foundation, CMS 96-10545

Failure and leakage of high-pressure water tunnels have occurred when the effect of geologic features, such as rock joints and in situ stresses, on hydraulic behavior were not adequately considered. In this study, the coupled hydromechanical behavior of rock joints surrounding lined pressure tunnels is investigated using the discrete finite-element method. Procedures have been developed in this study to excavate the tunnel and install a lining and to accommodate joint dilatancy with shear. Stresses and flow in the jointed rock mass are observed as the tunnel is excavated and pressurized. A series of rock slope and rock joint geometries are being modeled and results compared with pressure tunnel cases and existing design criteria.

Performance of a Tunnel in Soft Clay
E. J. Cording,* N. Kawamura
University of Illinois; McNally Tunnelling Co.

A tunnel excavated in soft clays in the Chicago, Ill., area has been instrumented to evaluate the interaction of the tunnel shield machine and the installed lining with the ground. The tunnel was advanced through clusters of instruments that monitor vertical and lateral displacements and porewater pressures in the clay. Deformation and loads on the tunnel lining were measured as the lining was installed and as it took load with time. Effect of stress and pore pressure changes on immediate and long-term ground movements in the clay have been investigated. Ground behavior with current tunneling equipment and methods has been contrasted with earlier tunneling experience in Chicago and other tunnels in clay.

Subsurface Construction, Resulting Ground Movements, and Protection of the Built Environment
E. J. Cording,* J. Long, D. Laefer, B. Ghahreman, T. Geilen, M. Son, J. Klecker
National Science Foundation, INT 97-22877, 97-13854; University of Illinois

Of prime concern in excavating or tunneling in urban areas is the protection of nearby structures and utilities from damage induced by ground movements. Case histories are being collected and observations are being made on projects in which ground movements and building response have been measured in the U.S. as well as in Seoul, South Korea, and London, England. Numerical analyses of wall-soil and building-soil interaction are underway. Planned are a series of model building experiments in the Illinois large soil model test facility. Workshops will be conducted with engineers, contractors, and preservationists to develop guidelines for evaluating, monitoring, and controlling ground movements affecting buildings.

Performance of Segmented Tunnel Linings
S. Paul,* E. J. Cording, F. Shalabi, S. W. Lee
Los Angeles (California) Metro

Performance of gasketed concrete segments used for tunnel linings is being investigated under varying loading conditions, including cyclic loads and displacements equivalent to earthquake effects. The gaskets are pressurized with gas or water to determine their ability to prevent leakage under a range of loading conditions.

Hydromechanical Evaluation of Flow in Rock Foundations of Concrete Dams
G. Fernandez,* E. J. Cording,* E. Gimenes, S. H. Choi
National Science Foundation, CMS 96-10545

Case studies and numerical analyses are being used to investigate flow in jointed rock foundations of concrete dams and the resulting uplift pressures in concrete dams. Coupled hydromechanical numerical models are employed using the direct finite element method and UDEC, another discrete element method. The effect of reservoir loading and unloading and drainage beneath the dam foundation and their effect on joint aperture changes and uplift pressures are being studied.

Performance of Gasketed Precast Concrete Segments for Tunnel Linings
E. J. Cording,* S. L. Paul,* M. J. Rood, F. Shalabi, S-W. Lee
Los Angeles Metropolitan Transportation Authority

Precast concrete segments assembled in rings are used as both immediate and long-term tunnel support. Their ability to control leakage of gas and water when joints between segments are misaligned or subject to rotation and displacement during installation and subsequent seismic ground motions was investigated in a series of load, relaxation, and leakage tests on assemblies of gasketed concrete segments. Rates of methane and water leakage were determined as a function of gasket pressure and joint gap. Destructive testing was performed to evaluate and improve segment load capacity. Procedures were developed to control leakage with secondary joint grouting.

Strength of Jointed Rock Masses
E. J. Cording,* O. Mughieda
University of Illinois

The strength and deformability of rock slopes and tunnels are largely controlled by natural fractures (joints) in the mass. To investigate these effects, a procedure was developed for forming parallel joints in a model rock material. A series of biaxial load-deformation tests were performed on 30 30 60-cm models containing nonpersistent joints of varying length, spacing, frictional strength, and orientation. The results have provided information on the strengthening effect of the rock bridges between joint segments. Reductions in strength result from conditions causing tensile stress concentrations, rotation or reduced confinement near the bridge, or progressive failure of multiple bridges.

 

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