Damage to Railway Structures

A vast amount of railway structures were seriously damaged, which includes RC frame structures supporting elevated railway tracks, RC station structures, embankments, and retaining walls. A length of underground RC box structures of subways, constructed by the cut-and-cover method, was also seriously damaged

Importance of controlling the degree of saturation in soil compaction

n the typical conventional fill compaction, the dry density ρd and the water content w are controlled in relation to (ρd)max and wopt determined by laboratory compaction tests using a representative sample at a certain compaction energy level CEL. Although CEL and actual soil type affect significantly the values of (ρd)max and wopt, they change inevitably in a given earthwork project while CEL in the field may not match the value used in the laboratory compaction tests. Compaction control based on the stiffness of compacted soil in the field has such a drawback that the stiffness drops upon wetting more largely as the degree of saturation, Sr, of compacted soil becomes lower than the optimum degree of saturation (Sr)opt defined as Sr when (ρd)max is obtained for a given CEL. In comparison, the value of (Sr)opt and the ρd/(ρd)max vs. Sr - (Sr)opt relation of compacted soil are rather insensitive to variations in CEL and soil type, while the strength and stiffness of unsoaked and soaked compacted soil is controlled by ρd and “Sr at the end of compaction”. It is proposed to control not only w and ρd but also Sr so that Sr becomes (Sr)opt and ρd becomes large enough to ensue soil properties required in design.Fundação para a Ciência e Tecnologia (FCT)info:eu-repo/semantics/publishedVersio

Stability Analysis of the Geosynthetic-Reinforced Modular Block Walls Damaged During the Chi-Chi Earthquake

Psuedo-static stability analysis based on “Coulomb’s one-wedge” and “two-wedge” methods was performed for two geosynthetic-reinforced modular block walls which were either collapsed or lightly damaged during the 1999 Taiwan Chi-Chi earthquake It was shown that two-wedge failure mechanism is a dominant one for the walls investigated. Difference in the seismic behavior of these walls was partially explained based on the psuedo-static analysis. It was also shown that seismic stability of the reinforced wall depends largely on the connection strength between the facing and the geogrid

Deformation Characteristics of Soils and Soft Rocks under Monotonic and Cyclic Loads and Their Relationships

For a wide variety of geomaterials, cohesionless and cohesive soils and sedimentary soft rocks and cement-mixed soils, the importance and advantages of measuring the deformation characteristics accurately and continuously for a strain range from less than 0.001 % to several % by a single static test using a single specimen are demonstrated. It is also shown that the deformation characteristics at strains of less than about 0.001 % is essentially elastic and the elastic stiffness values evaluated under static (monotonic and cyclic) and dynamic (fast cyclic) loading conditions are the same from the engineering point of view. It is discussed that the plastic deformation characteristics including the damping ratio, the decay characteristics of stiffness and the liquefaction potential are not uniquely linked to the elastic properties

Stiffness and Damping of Sands in Torsion Shear

A laboratory investigation was carried out into stiffness and damping of sands as sheared in a torsional shear apparatus. In the drained monotonic and cyclic loading tests, a particular care was taken of the small strain measurements in which the secant stiffness was measured over a wide range of shear strain from about 10-6 to 10-2. Despite the marked differences in the grain size and the sample preparation method among the sands, a fairly good coincidence of the secant stiffness was seen, in common, in the range of shear strain less than about 1 x 10-5 between two types of tests using the monotonic and cyclic loadings. However, the response was softer in the monotonic loading tests for the larger strains. It has also been pointed out that the damping when examined in relation to the normalized secant shear modulus was scarcely affected by the confining pressure, and that the values of damping were smaller than those so far available in the literature

Cyclic Undrained Behavior of an Undisturbed Gravel for Aseismic Design of a Bridge Foundation

For the aseismic design of a pier foundation constructed on a lightly cemented dense gravel deposit of a 3,910m-long suspension bridge, cyclic and monotonic undrained triaxial tests were performed on undisturbed specimens with a diameter of 30cm taken from the deposit under a sea depth of about 55m. Using the results of the cyclic undrained triaxial tests together with irregular cyclic stresses evaluated for the design earthquake motion by a dynamic FEM analysis, maximum strains in the gravel deposit were obtained by the cumulative damage concept. The strain values thus estimated indicated a sufficiently high degree of seismic stability of the foundation. Further, for the same initial mean Principal stress, the strength for monotonic undrained triaxial compression of isotropically consolidated specimens was found not greater than the strength against irregular cyclic undrained loading of the specimens anisotropically consolidated as in the field. This means that the former strength can be used as an approximated value of the latter

Stability of existing bridges improved by structural integration and nailing

AbstractTo examine whether and how the seismic stability of existing bridges can be substantially improved by integrating the girder, the abutments and the backfill, a series of shaking table tests were performed in 1 g. The tested small bridge models are (1) a conventional-type comprising a girder, supported by a pair of gravity-type abutments (without pile foundation) via bearings (fixed and movable), and unreinforced backfill, (2) the girder and the abutments of the above are integrated (without using bearings), (3) the backfill of the above is reinforced with two layers of large-diameter nails connected to the abutment top and the toe or the heel of the abutment footing and (4) the bottom nails of the above are replaced with longer ones connected to the toe of the abutment footing. Their dynamic behavior was analyzed as a damped single-degree-of-freedom system. The dynamic stability of the bridge was found to increase with an increase in (i) the dynamic strength against the response acceleration, (ii) the initial stiffness, (iii) the dynamic ductility (i.e., a smaller decreasing rate of stiffness during dynamic loading) and (iv) the damping ratio. When factors (ii) and (iii) are high enough, the natural frequency of a bridge can be kept much higher than the input frequency, and thus, the response acceleration can be kept low. All these factors can be improved by integrating the girder, the abutments and the backfill together with part of the supporting ground. In a series of static model tests, lateral cyclic displacements, caused by the seasonal thermal deformation of the girders with prototypes, were applied to the top of a small abutment model. The active failure in the backfill and the detrimental effects of large passive pressure, both developing due to the dual ratchet mechanism, can be effectively restrained by reinforcing the backfill and supporting the ground with nails connected to the top and the bottom of the abutments