The large displacement shear box (LDSB) allows testing of interfaces as large as 711 by 406 mm (28 by 16 in.) with maximum interface displacements of 305 mm (12 in.). This device has been used to investigate the response of a variety of interfaces, including clay-geomembrane interfaces for which large displacements are important. The most recent application of the LDSB was to study the response of several sand-to-concrete interfaces under complex loading paths. In this application, the relevant characteristics of the LDSB are its geometry, which reduces the significance of end effects, its ability to apply monotonic and cyclic loading, and its ability to apply simultaneous changes in shear and normal stresses so that complex loading paths can be followed. This paper describes the main features of the LDSB, as well as the testing procedures and results of the sand-to-concrete interface tests that were performed. A procedure for normalizing the interface shear test data is also presented. This procedure facilitates comparative evaluations of interface response to different types of loading. The test results formed the basis for development of an extended hyperbolic model for interfaces that has been implemented in finite element analyses of soil-structure interaction problems.

Sand-to-Concrete Interface Response to Complex Load Paths in a Large Displacement Shear Box

: Soil-Structure Interaction (SSI) analyses have proven to be powerful tools for use in analyzing, designing, and monitoring geotechnical structures. SSI analyses are particularly useful in problems of complex geometry and loading conditions such as lock walls. Several SSI analyses of Corps of Engineers lock walls have shown that the behavior of the soil-structure interface has a significant influence on the magnitudes of the loads acting against a lock wall. They have also illustrated that the pre- and post-construction field stress paths followed by interface elements often involve simultaneous changes in normal and shear stresses, as well as shear stress reversals. The hyperbolic formulation for interfaces, used commonly in SSI analyses, models interface behavior in the primary loading stage very closely. However, it has not been extended to accurately model simultaneous changes in shear and normal stresses, reduction of shear stress, reversals in the direction of shear, or unload-reload cycles at the interface. The purpose of this research is to develop an interface model capable of giving accurate predictions of the interface response under field loading conditions. In order to develop the necessary test data, the Large Displacement Shear Box (LDSB) at Virginia Polytechnic Institute and State University, Blacksburg, VA, was modified to permit soil-to-concrete interface testing. A. concrete specimen for interface testing was prepared with a surface texture similar to that of concrete retaining walls in service. A number of tests were performed on the interface between this concrete specimen and a uniform dense sand: initial loading, shear reversals, staged shear, and unloading-reloading of the interface. This research is being conducted in two phases. This report presents the results of the testing performed for the Phase I research.

/pdf/development-of-an-improved-numerical-model-for-concrete-to-2ofxfz3729.pdf

Development of an improved numerical model for concrete-to-soil interfaces in soil-structure interaction analyses. Report 1, Preliminary study

: This report focuses on an investigation into the engineering characterization of the axial stiffness of individual compression piles embedded within soil. This characterization of axial stiffness is used in the analysis of a clustered pile groups deformation and load distribution response. Its impact on the computed pile group response is most pronounced among a clustered pile group containing batter piles.This characterization is important because the Corps is moving toward low-cost, pile-founded flexible lock approach walls. These walls absorb kinetic energy of barge-train impacts, which occur as the barge train aligns itself to enter the lock. One type of wall is comprised of an elevated impact deck supported by groups of clustered piles, some with batter. These impact decks are supported tens of feet above the mudline.A pushover analysis technique is used to establish the potential energy (PE) capacity and displacement capacity of individual batter pile groups accounting for the various pile failure mechanisms. An appropriate axial stiffness characterization will increase the accuracy of this computation. The total stored energy (PE) of the approach wall system will be the sum of the stored energy of all the pile groups reacting to the barge impact. The study concludes with a pushover analysis of a batter pile configuration used at Lock and Dam 3 flexible approach wall extension.Batter pile groups are constructed of steel pipe or H-piling, which are conducive to in-the-wet construction. This type of construction leads to a cost savings for Corps projects.

/pdf/characterizing-axial-stiffness-of-individual-batter-piles-5az2jdg37d.pdf

Characterizing Axial Stiffness of Individual Batter Piles with Emphasis on Elevated, Laterally Loaded, Clustered Pile Groups

: Uplift is one of the major forces affecting stability of rock-founded concrete dams. Problems occur in determining the magnitude and distribution of uplift pressures within rock foundations and in extrapolating uplift pressures to reservoir levels above the pool of record. Uplift is controlled by the flow regime within the rock foundation. The flow regime is a function of the geology. The goal of research in uplift uncertainty and probabilistic modeling is to develop a methodology, analytical procedures, and software to assess uplift pressures and forces within rock foundations for use in the assessment of the reliability of rock-founded concrete gravity dams. The objectives of this study were to identify geological factors affecting the prediction and modeling of flow and the development of uplift pressures in rock foundations; to identify the kinds of uncertainty in uplift prediction resulting from geological investigations, particularly in testing and description of rock discontinuities; and to select a case history for assessing the uncertainties associated with geological and uplift analysis of a large dam. Much uplift prediction uncertainty is caused by insufficient investigation or treatment of rock discontinuities, or by deformation of discontinuities with resulting changes in discontinuity aperture and in the flow regime caused by stresses imposed by the dam and reservoir. Tight discontinuities, those with mechanical apertures less than about 250 microns, may cause a nonlinear response in uplift pressure with rising headwater. Apertures can be estimated from foundation borehole pressure tests using the cubic law, which relates flow rate to joint aperture. There is uncertainty in determining the persistence of aperture and condition of discontinuities through the foundation rock mass.

/pdf/assessment-of-geology-as-it-pertains-to-modeling-uplift-in-4v2f3l874w.pdf

Assessment of geology as it pertains to modeling uplift in jointed rock : a basis for inclusion of uncertainty in flow models

: The extended hyperbolic model for interfaces developed by Gomez, Filz, and Ebeling (Technical Report ITL-99-1; Report 2) can model the response of interfaces subjected to complex stress paths that may include simultaneous changes in shear and normal stresses and unloading-reloading. These types of loading can occur at soil-structure interfaces of multi-anchored systems used in navigation projects. Therefore, it is possible that finite element analyses of multi-anchored systems can be performed that incorporate the extended hyperbolic model for interfaces. Performance of the model is excellent for interfaces between fine sands and concrete. However, the model has not been evaluated against the results of shear tests between coarse sand and concrete. In this investigation, a number of interface tests between coarse sand and concrete were performed. Comparisons were made between the calculated and measured interface response. These comparisons show that the extended hyperbolic model is also accurate for this type of interface and, therefore, that it can be used for a large variety of interfaces between granular soils and concrete.

/pdf/extended-load-unload-reload-hyperbolic-model-for-interfaces-1wact8a701.pdf

Extended Load/Unload/Reload Hyperbolic Model for Interfaces: Parameter Values and Model Performance for the Contact Between Concrete and Coarse Sand

: The U.S. Army Corps of Engineers is responsible for designing and maintaining a large number of navigation and flood control structures. Many of the older massive concrete gravity hydraulic structures are being examined to determine if rehabilitation is required to meet stability criteria. The procedures currently used for evaluating the safety of existing massive hydraulic structures are the conventional equilibrium methods, which are the same general methods used in the design of these structures. Because the conditions of equilibrium are insufficient for a complete analysis of all aspects of structure foundation interaction involved in the stability and performance of these structures (soil structure foundation interaction in the case of earth retaining structures), these conventional equilibrium methods necessarily involve assumptions regarding aspects of the loading forces and the resisting forces that act on the hydraulic structures. Differences between actual field performance and calculations from conventional analysis have been noted for some existing hydraulic structures. Conventional design methods were developed based largely on classical limit equilibrium analysis without regard to deformation related concepts. Today, analytical tools such as the finite element method (FEM) are available which consider the manner in which the loads and resistance are developed as a function of the stiffnesses of the foundation rock, the structure foundation interface, and rock joints within the foundation. These analytical tools provide a means to evaluate the conventional equilibrium-based design methods used to evaluate the safety of existing hydraulic structures, and specifically, to identify and investigate key assumptions used in safety calculations from the conventional analysis.

http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA329714&Location=U2&doc=GetTRDoc.pdf

Repair, Evaluation, Maintenance and Rehabilitation Research Program: Evaluating the Stability of Existing Massive Concrete Gravity Structures Founded on Rock

: This report extends the 2007 investigation of I-wall performance during flood loading to I-walls located in regions of the United States outside New Orleans, Louisiana. Specifically, this study investigates I-walls embedded in level ground consisting of four different soils that are stronger and stiffer than the fine-grained New Orleans soils that were inspected during the 2007 Interagency Performance Evaluation Task Force (IPET) study. A focus of the study summarized in this report is the investigation of the development of a zone of separation along the flood side of the soil-to-I-wall interface. The effects of this zone of separation on the resulting deformation and stress conditions in the soil regime on both the flood side and landside of the I-wall system were then examined. This study is restricted to level soil flood wall sites. The landside is referred to as the protected side in some figures in this report. This investigation relies on a complete soil-structure interaction (SSI) method of analysis. In this procedure, the soil foundation, I-wall, and interface between the I-wall and the soil (on both sides of the I-wall) all are modeled using finite elements; both the soil and interface properties are modeled as nonlinear materials; and flood loadings are incrementally raised to the design flood pool elevation. A hydraulic fracturing criterion is applied to determine if a gap develops on the flood side of the I-wall and if it propagates down the soil-to-I-wall interface during the incremental flood loadings. Soil stresses, the level of mobilized shear strength, gap depth, I-wall deflections, shear forces, and bending moments internal to the sheet piling are computed in the complete SSI analyses at the incremental flood elevations. Results presented in this report will be used to prepare a U.S. Army Corps of Engineers (USACE) guidance document for flood I-walls.

Complete Soil-Structure Interaction (SSI) Analyses of I-walls Embedded in Level Ground During Flood Loading

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Repair, Evaluation, Maintenance and Rehabilitation Research Program: Evaluating the Stability of Existing Massive Concrete Gravity Structures Founded on Rock

Complete Soil-Structure Interaction (SSI) Analyses of I-walls Embedded in Level Ground During Flood Loading