| Highway system plays a more and more important role in the national economy. In the past ten odd years, a great progress has been made in highway construction. The total length of road, the length of good quality highway, number of the bridges and tunnels are all increased and increasing remarkably. Seismic damage of highway system caused in strong earthquake worldwide indicated that modern Highway system is still vulnerable, it may be damaged extensively and slow down so much as shut down the local traffic, which always makes big troubles for rescue in a past earthquake situation. The earthquake damage of Highway system shows that the failure of retaining structures is sometimes one of the main causes of road damage and bridge collapse. The pseudo-static method (static method in brief) is now currently adopted in seismic analysis of retaining structures for some well known limitation. The study on seismic inertia and seismic soil pressure is a significant task to be deeply treated with and improved in the static analysis of retaining structures. The currently used Chinese Earthquake Resistant Design Code for Highway Construction (JTJ 004-89) was issued a dozen years ago. During this period. Highway construction increased very fast in China and the scale was much larger than ever before, while the technology was developed quite great. Some contents of the code now have dropped behind the progress of science and technology and the development of the epoch and can not meet the requirement of the development of highway construction any longer. Therefore the code needs to be updated by some more advanced and mature theories and approaches. On basis of a review of the recent achievements, the distribution of the lateral seismic inertia force along the height of retaining wall and/or bridge abutment, and the calculation of the seismic soil pressure of cohesive backfill are treated with in this paper, for the revision of Chinese Earthquake Resistant Design Code for Highway Construction, and a suggestion to combine seismic design of retaining wall and of bridge abutment together into one chapter from the past in two chapters in the previous version is also worked out. The main contents are summarized as follows:1. The evolution, state of the art and the developing trend of the lateralseismic inertia force calculation for retaining wall and/or bridge abutment and the calculation of the seismic cohesive backfill soil pressure are reviewed. The approaches of seismic analysis of retaining walls and bridge abutments in the current Highway codes of China are studied in detail and the shortcomings in the analysis procedure and the necessity of further improvements to them are pointed out.2. Total 18 simulated acceleration time histories for Intensity 6, 7, 8 and 9 are adopted as inputs, 6 typical retaining walls heights and 2 bridge abutments with difference are selected as the structural models of soil-structure system, the seismic responses of the system and the horizontal variation of the maximum response accelerations at different height levels are analyzed by means of a wave propagation finite element program. The numerical results show that the horizontal variation of response acceleration of gravity retaining wall is quite small since its lateral rigidity is large enough, the response at a given height level can be considered as the same, the maximum accelerations at different heights on the central vertical line can describe the distribution of earthquake load along the wall height in static analysis very well. The acceleration changes along the height direction nonlinearly with a little bit complicated pattern, and the changing patterns, in general, are similar. The acceleration does not increase immediately after the wall height is getting taller from the bottom of the retaining wall, and it starts to increase rapidly with the height level at a height of half to two thirds of the total wall height. It gets a maximum amplification value of 1.1 to 2.0 at the top of the wall. The ratios between accel...
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