Reliability of high dams with consideration of dynamic processes

153A

SURFACE STRUCTURES:GEOLOGICAL FACTORS study the ground motion in 2-D structures that exhibit irregular topography and interface, and whose shear wave velocity varies linearly with depth, for incident plane SH waves. The results for a mountain model show that the amplification on its top, predicted by the 2-D modelling when the velocity is constant, is enhanced when the velocity gradient is present, for all frequencies and by a factor up to 3. In the basin model, results show that the velocity gradient; 1) enhances the amplification at the edges of the valley, 2) makes the reverberations due to 2-D resonance have larger amplitudes and shorter intervals between arrivals, 3) shortens the total duration of the seismograms at all stations within the basin. -from Authors 943253

A

semi-analytical

solution

procedure

for

The paper reports on the initial phase of assessing numerically the seismic vulnerability of sections of the Temple of Apollo in Bassae, in the W. Peloponnesus, Greece. The site is exposed to large subduction earthquakes and to smaller local extensional events. The analysis confirms the highly non-linear nature of the response of megalithic structures relying for their stability on the friction and cohesion between the constituent blocks. Intact sections of the Temple showed substantial resistance to strong ground motions due to their capacity to absorb energy with large relative movements of the building blocks that do not impair the stability of the structure. This analysis quantifies the effects of weaknesses of the structure and allows testing the effectiveness of strengthening procedures. -from Authors

predicting damage evolution at interfaces

Zhen Chen, International Journal for Numerical & Analytical Methods in Geomechanics, 17(11), 1993, pp 807-819. A semi-analytical solution procedure is developed to predict damage evolution at the interface between two dissimilar geologic materials. The procedure consists of an analytical field solution within each finite element, and a numerical scheme for simulating structural responses. For static problems, an incremental-iterative solution strategy is constructed through the use of an initial elasticity stiffness matrix, and an evolving-localization constraint in terms of a suitable measure of damage at the most severely damaged element. -from Author 943254 Reliability of high dams with consideration of dynamic processes A. N. Marchuk & A. I. Savich, Hydrotechnical Construction, 26(11), 1993, pp 693-697; translated from: Gidroteknicheskoe Stroitel'srvo, 11, 1992, pp 1-5. A novel approach to the assessment of the reliability of high dams xs presented. Consideration is also given to the experimental investigation of geodynamic processes affecting the safety of such structures. The increasing need to build high dams in complex mountainous sites, particularly in seismically active regions, makes it necessary to consider the effect of dam projects on natural and technogenie geodynamic processes. Experience from full-scale studies at existing hydroelectric schemes is cited. -D.W.Taylor 943255 The susceptibility of rock slopes to earthquake-induced failure D. K. Keefer, Bulletin - Association of Engineering Geologists, 30(3), 1993, pp 353-361. Failure of rock slopes is a major cause of damage and casualties during moderate and strong earthquakes. This article presents a method for assessing the seismic stability of rock slopes, which can be applied on a regional scale, using data trom existing maps, reports, aerial photographs, and reconnaissance-level field observations. The method is based on observed associations between landslide concentrations and slope characteristics in 24 earthquakes that occurred in various parts of the world. -from Author 943256 Modelado sismico de la cuenca de la ciudad de Mexico (Seismic modelling of the Mexico City Basin) S. Chavez Perez, Geofisica Internacional, 32(1), 1993, pp 111-130. Numerical results are presented of seismic modeling with finite differences on a staggered grid. Stable, precise and reliable solutions for the Mexico City basin are obtained. The response of simplified geologic models suggests that the influence of the deep subsoil (down to 1.5 km) can be important in ground motion evaluation for low frequencies (0.5-1.5 Hz). Spatial variations and long duration of ground motion in Mexico City may be due, among other possible causes, to the induction, due to the closed basin effect, of surface waves propagating laterally and in opposite directions. -from English summary 943257 Seismic response of classical monuments - a numerical perspective developed at the Temple of Apollo in Bassae, Greece D. Papastamatiou & I. Psycharis, Terra Nova, 5(6), 1993, pp 591-601.

943258 Neotectonics and mass movements in the loess of north-central China

T.

Dijkstra, E.

Derbyshire

&

Meng

Xing

Min,

Quaternary Proceedings, 3, 1993, pp 93-110. The distribution of seismically triggered landslides in northwestern China during historical times follows closely the known distribution of large fanlt systems. A major factor involved is the continuing uplift of the Tibetan Platean and the consequent neotectonic movements. Historical records for Gansu Province going back over 2000 years include evidence of four earthquakes with a magnitude in excess of 8, fourteen over 7 magnitude, and at least 162 with a magnitude over 4. These have triggered several thousand landslides, many of which are well documented. The effects of ancient earthquakes are ubiquitous in eastern Gansu Province. Alon~ the vaUey of the Wei He and one of its tributaries the Qx He near Tianshui the 1654 earthquake produced a landscape in which virtually every slope shows the effects of landsliding. At present, the slip surfaces of the slides on these slopes need only minor triggers to instigate further movement. -from Authors 943259

Research on incompetent rocks in Qingshan

Dam foundations

Lin Tehong & Yah Xiankun, in: The engineering geology of weak rock. Proc. conference, Leeds, 1990, ed J.C. Cripps & others, (Balkema; Engineering Geology Special Publication, 8), 1993, pp 473-477. Qingshan dam is founded on a marble intercalated weaken low strength beds. High seepage pressures are liable to cause probiems including differential settlement to the foundation, and consequently in terms of dam stability the site is extremely disadvantageous. Therefore, considerable experimental and research efforts have been devoted to the investigation of the geology and engineering geology of the dam site, the genesis, distribution, composition and basic properties of materials, failure mechanism and effects of seep.age pressures. The strength characteristic are also described with particular respect to time dependent effects and the effects of cyclic loads. In addition, variations in the long-term rheologic strength are discussed and geological agents which influence the strength are also analysed. -Authors 943260 Underlying rock type controls of hydrological processes and shallow landslide occurrence Y. Onda, in: Sediment problems. Proc. international symposium, Yokohama, 1993, ed R.F. Hadley & T. Mizuyama, (IAHS; Publication, 217), 1993, pp 47-55. Hydrological observations were conducted in the areas where the shallow landslide density varied with rock types, and determined that the difference in landslide occurrence density can be explained by the different hydrological environment. In Obara region, central Japan, where few landslides were observed in the Granodiorite area and many in granite area, occurrence of landslides was found not to be controlled by regolith shear strength, instead by regolith zone thickness, which determines storm water storage capacity. In Niigata region, central Japan, few landslides were observed in Paleozoic sedimentary rock area and many in granite area. Hydrological observation showed that in Paleozoic basin, storm water can be discharged by Hortonian overland flow, whereas in Granite