The Bump at the End of the Bridge

The nature and causes of the differential settlements between a bridge deck and the adjoining highway approach pavement have been the subject of an increasing number of investigations in recent years. This settlement of the highway approach pavement not only presents a hazardous condition to rapidly moving traffic, but creates a rough and uncomfortable ride. These defects of the pavement surface require costly maintenance and, where a heavy traffic flow exists, the maintenance operation may tend to impede the normal flow. Bridge abutments in Kentucky are usually founded on relatively a stable foundation such as rock or point-bearing piles to rock, and practically speaking, cannot settle. Highway approach pavements, on the other hand, are located on an embankment and foundation which are potentially free to settle. The extent to which either settlement of the embankment or foundation contributes to the approach settlement will obviously depend on the particular conditions at any given bridge site. Data obtained from a survey of existing bridge approaches conducted in the summers of 1964 and 1968 have provided general information as to the prevalence of the problem in Kentucky. In addition, these data imply there is a general relationship between development of the approach fault and such possible causative factors as the type of abutment, geological conditions, and soils conditions. This report surrnnarizes the general relationship between the occurrence of bridge approach settlement and various conditions at the bridge sites

Kentucky CBR’s and the Soil Support Value

Several ASTM and Kentucky CBR tests were performed at different molding moisture contents and compactive energies on the AASHO embankment soil, four representative Kentucky soils, and one soil from Ohio. These data were compared to CBR data previously reported by Shook and Fang. For CBR\u27s ranging from about 4 to 12, a relationship was developed between Kentucky and ASTM CBR\u27s. Within this range, Kentucky and ASTM CBR\u27s are approximately equal. Molding specimens under the static pressure of 2000 pounds per square inch as used in the Kentucky CBR procedure produced specimens with initial dry densities that averaged about 6 percent higher than those obtained by AASHO Designation: T99-57. CBR\u27s and axial swell values were also higher. For soil specimens molded at the same initial dry density, CBR\u27s of statically compacted specimens are distinctively lower than those observed for dynamically compacted specimens. For relatively small decreases in initial dry densities, there were very large decreases in CBR\u27s. This probably accounts for discrepancies that have been observed between field and laboratory CBR\u27s. Three different correlations between Kentucky CBR\u27s and the AASHO Road Test soil support values were developed. The first relationship was made by assuming a logarithmic scale between Kentucky CBR\u27s of 5.2 and 100, which corresponded to values on the soil support scale of 3 and 10, respectively. The Kentucky CBR of 5.2 was determined by performing tests on the AASHO road subgrade soils. For practical purposes, the AASHO Road Test crushed stone base material was assumed to be a 100 percent CBR material (this assumption was based on CBR data previously reported by Shook and Fang). The second correlation was obtained by assuming a logarithmic scale between Kentucky CBR\u27s of 5.2 and 90, corresponding to values on the soil support scale of 3 and 10, respectively. The third relationship was constructed through computations using the Kentucky flexible pavement design curves and the AASHO Design Chart (Pt= 2.5). A correlation was found between a Kentucky CBR of 5.2 determined by tests and 5.7 determined through computations based on 1958 design curves and 6.2 based on 1971 curves

Identification of Shales

Engineering tests were performed on 40 different types of shales. Both hard and soft shales, as well as shales having histories of embankment failures and shales having little known involvements, were tested. The suitability of ten different slake-durability test procedures were evaluated as a means of broadly characterizing the engineering performance of Kentucky shales. Two procedures devised during the study appeared to better characterize slake-durability properties than procedures previously proposed. Natural water contents and jar slake tests were performed to determine if such tests might provide a fairly rapid means of identifying troublesome shales. The natural water content of a shale was a strong indicator of the slake-durability properties. Swelling properties of ten shale types were examined. A good correlation was obtained between a newly devised slake-durability index and the water content of a shale after swelling was completed. When exposed to water, most of the shales exhibited high swell pressures

Mercury-Filled Settlement Gage

A description is given of a remote sensing, multiple-point, mercury-filled settlement gage designed for measuring in-place settlements. The gage consists of settlement units positioned at locations where settlement measurements are desired and a monitoring unit located outside of construction limits. Settlement readings are observed on a mercury manometer located at the monitoring site and are· equal to the differences in initial and subsequent pressure head readings. Comparisons of measurements obtained at a highway construction site from mercury gage settlement units and conventional settlement platforms are presented and show very good agreement. With the mercury gage, a large amount of settlement information can. be obtained per installation, and the gage does not have many of the disadvantages associated with the settlement platform

Construction and Performance of Trial Section of Treated Shoulders on the Mountain Parkway Extension

In October 1966, J.W. Spurrier, Assistant Operations Management Engineer, requested that the Research Division make a study of a two-mile section of the shoulders on the Mountain Parkway Extension in Wolfe County (from Mile Post 43.8 to Mile Post 45.8) and make recommendations for design and construction procedures for cement stabilization of the shoulders. In compliance with this request, in January 1967, Research Division personnel made a survey of the full length of shoulder on the Mountain Parkway Extension. Included in this survey were measurements of depth of the dense graded aggregate, penetrations of the shoulder subgrade soil and samples taken of the DGA and soil. Compressive strengths were measured on sampled material treated with cement. A memorandum reporting the results of the shoulder survey, compressive tests, and recommended cement treatment design and construction procedures was prepared in March 1967 (see Appendix A). A typical section of the shoulder, as originally constructed, is shown in Figure 1

Some Uncertainties of Slope Stability Analyses

Some practical limitations of total stress and effective stress analyses are discussed. For clays having a liquidity index of 0.36 or greater, φ-equal-zero analyses based on laboratory undrained shear strengths give factors of safety close to the actual factor of safety. However, based on field vane strengths, φ-equal-zero analyses may yield factors of safety which may be too high. The difference between field vane and calculated shear strengths increased as the plasticity index increased. For clays having a liquidity index less than 0.36, φ-equal-zero analyses using laboratory undrained shear strengths give factors of safety that are much too high; but the strength parameters can be corrected by the empirical relationship presented herein. An empirical relationship for correcting vane shear strength is also presented. A method is proposed for predicting the probable success of a φ-equal-zero analysis. Data suggest that overconsolidated clays and clay shales or clays having a liquidity index less than 0.36 pose the greatest slope design dilemma. An effective stress analysis based on peak triaxial shear strength parameters generally yields factors of safety which are too high; residual shear strength parameters frequently yield factors of safety which are too low. To approximate the theoretical strength of an overconsolidated clay which has undergone a process of softening, the effective stress parameters might be obtained from triaxial tests performed on remolded, normally consolidated clay. It is suggested the soil be remolded to a moisture content equal to the plastic limit plus the product of 0.36 and the plasticity index

Effects of Water on Slope Stability

A brief state-of-the-art review of the effects of water on slope stability and the techniques for analysis is presented. The effective stress principle and basic considerations of slope stability, including design factors of safety, are discussed briefly. The derivations and effects of seepage forces and rapid drawdown on effective stress are also presented. Various conditions of external loading produce changes in effective stress. These changes are discussed and limiting conditions which should be analyzed are mentioned. Limitations of total stress analyses are discussed in detail. It appears that, for soils having a liquidity index of 0.36 or greater (normally consolidated), the undrained shear strength gives factors of safety close to the actual factor of safety. For soils with a liquidity index less than 0.36 (overconsolidated), the undrained shear strength gives factors of safety that are too high; but the strength parameters can be corrected by the empirical relationship presented herein. Data also show that the difference between vane and calculated shear strength increased as the plasticity index and (or) the liquid limit increased. An empirical relationship for correcting vane shear strength is presented. A discussion of effective stress analysis, including differences between peak and residual φ angles for normally consolidated and overconsolidated soils, is presented. The residual φ angle decreases logarithmically with increasing clay fraction. The critical state of a clay is also defined. Sheer strength parameters of a clay tested in that state correspond to the theoretical strength of an overconsolidated clay which has undergone a process of softening. To test a clay in the critical state, it is suggested herein the soil should be remolded to a moisture content equal to 0.36 times the plastic index plus the plastic limit. Water may cause unstable conditions in earth slopes due to changes in geometry. Erosion of the toe or the slope can induce damaging stress. Piping through heaving or erosion of subsurface layers can cause damage. Construction of side-hill embankments can cause danuning, resulting in a rise in the water table. Methods of water detection are also summarized. These include tracers, electrical resistivity, and water table observations. The tatter method apparently is the most successful. A discussion of ways to monitor water pressures, including the types and operations of piezometers, is given. Finally, suggested guidelines for the design of earth slopes are included

Mechanical and Engineering Properties of a Cherty Paleozoic Material

In September 1982, Research Report UKTRP-82-16 was issued to document the sampling of a cherty Paleozoic material from a test pit on Divide Cut Section 3A of the Tennessee-Tombigbee Waterway. Results of laboratory testing of the samples were also reported. Subsequent to the issuance of Report UKTRP-82-16, additional testing and analyses have been completed. The purpose of this report is to document the results of those tests and analyses