Acquiring soil’s critical load is very important when designing soil foundation and soil subgrade with overloading method. Mohr-Coulomb strength theory is combined with slip-line field theory, then a theoretic method which is practicable to analyze critical load of soil come out. Analyzed theoretically and compared with others, the theoretic method is applied to describe the relationship between internal friction angel, internal cohesion, δ, lateral pressure and critical load, which express that this theoretic method is rational. Numerical analysis is adopted which make it clear that soil subgrade’s yield zone is small when it is under the critical pressure, which approve that this theory is very close to lower limit of soil’s critical load. The theoretical method can provide useful information to engineering designers and researchers.

Because development degree and order as well as decay rate and degree of shear strength indexes, cohesion C and angle of internal friction , are not equal as slope failure, both should have their own security reserve. For this reason, it was proposed that C and  should have different reduction-factors, rather than same about strength reduction method (SRM). And to take a slope as an example, by FLAC SRM and strength reduction slice method (SRSM), reduction-factors of the two indexes and dangerous slide surfaces of the slope were computed and comparatively analyzed under 9 different reduction conditions. The results obtained by FLAC SRM and SRSM accorded with each other well. Therefore conclusions can be drawn that different reduction conditions correspond to different two reduction-factors and dangerous slide surfaces, so that all these dangerous slide surfaces form a dangerous slide region; single reduction-factor method that reduction-factors of C and  are same is only a special case of two reduction-factors method; two reduction-factors method can just reasonably reflect respective roles of C and  as slope instability. The conclusions in turn confirm the above-mentioned viewpoint again.

The natural frequency vector method for damage identification was inferred theoretically, on the basis of the natural frequency vector and its assurance criterion. Take the simple supported beam as an example to carry out numerical research: used the modified dynamic model and the method of rigidity reduce to simulate the damage at different degrees and different positions, calculated the damage structure sequence natural frequency, and formed the natural frequency vector damage features database; and then simulated 3 conditions, calculated and compared the natural frequency vector between different conditions and the damage features database, so that the damage position and degree could be detected. The result showed that this method can distinguish the damage position and degree accurately.

The height from the bridge deck of 5th main pier to ground surface is about115m, and the depth from the top surface of pier cap to water surface is 65m. Reinforcement measures such as flaw detection by frogman, hole plugged, steel caisson placing, steel caisson modeling, high performance concrete seal cracks perimeter. Reinforcement show that, the effect of high-pressure water jet roughening and hole plugged is well; the steel caisson which weighs about 400t sinking stablely and reaching the intended design location; great liquidity, high performance concrete has good workability , 28d strength is above the design and specification demands, bridge static and dynamic tests meeting the design requirements. The research is important for bridge strengthening, and provides reference for the reinforcement design and construction of the same type bridge.

To investigate the rainfall-induce the seepage field of a high slope and effect factors, the theory of saturated-unsaturated infiltration was employed, and the numerical model of slope infiltration subjected to the rainfall are developed and programmed. The numerical results shown that, (1) With the increasing of the rainfall duration, rainfall water infiltration formed a transient saturated zone at slope surface, when the moist frontal surface reached to the groundwater level, the rainfall water would supply the groundwater. (2) Each effect factors on the seepage field play a strongest roles on the slope toe, weaker role on the middle part slope and weakest role on the top slope. (3) The longer rainfall duration, the deeper of infiltration depth. It also be deeper with the larger rainfall intensity, coefficient of permeability, the initial moisture content of the surface and the surface waterlogging depth. (4) The effect on seepage field would be faintly and could be ignored when the rainfall intensity was greater than 65.9mm/h and the surface waterlogging depth is greater than 0.3m. All above could provide technical ideas for analyzing slope seepage field under rainfall and accumulate fundamental data for early warning and preventing mud-rock flow and landslide.