Applied Mechanics and Materials Vols. 94-96

Abstract: This paper presented the construction technique of a double-layer spherical lattice shell with a diameter of 66m, while the small-unit cantilever erection method is adopted. The variations of internal forces during the different erection simulation procedures are also indicated. Meanwhile some suggestions are proposed to actual construction.

Abstract: Fengtail North Road Station uses a open and cover combination of laying fabricated strap method for the first time, so we monitor the Cover system very closely. We draw schedule curves and analysis the monitoring data for the main component’s monitoring projects of the Cover system. Results show that the deformation values of the components of the Cover system are small, but the values of piles top displacement and settlement are large, at the same time, the lattices of Cover boards have good wear-resistance ability. The conclusion has very great help for optimizing the system design and the promotion of laying fabricated strap method.

Abstract: There were four collapse accidents of fastener-style steel tubular formwork support being investigated in the article. The collapse mechanism was researched. According to the collapse accidents, the finite element model was established. The whole stability analysis was done. The analytical results were the same with the conditions of accidents. The collapse mechanism was verified. According to the collapse mechanism, the security technical measures of high formwork support were put forward.

Abstract: Basing on FLAC3D (Fast Lagrangian Analysis of Continua), the shield tunnel construction process is simulated, and the influence factors and their interaction for modeling are analyzed. Firstly, combing the influence factors on the reciprocity of the shield precursor with the rock-soil mass, the excavation process is simulated; at the same times, the tunnel ground subsidence and the tunnel upper vertical stress are calculated. Secondly, by mean of removing one of the factors from the stimulating model respectively, the parameters corresponding with them are also calculated. Finally, basing on Fast Fourier Transform, the ground subsidence and the vertical stress are analyzed by comparison, and the influence effects for modeling of all kinds of the factors are found out. Experimental results show that, on one hand, the influence effects to the ground settlement are more than to the vertical pressure of the tunnel; on the other hand, the factors to the simulation results include the soil-rock stress of the excavation workface causing by the shield boost, the temporary low support strength causing by the grouting at the end of the shield delaying the shield tunnel segment assembled and the soil-rock torsion force of the excavation workface causing by the shield cutterhead running.

Abstract: The Wenchuan earthquake of May 12, 2008(Mw=8.0) was the most significant earthquake that had affected Chinese Mainland since the Tangshan earthquake of 1976. The dense network of seismographs deployed in this region recorded ground motion acceleration data with good quality. In this paper, vertical ground motion characteristics of Wenchuan Earthquake are investigated from the database including 282 records at 94 stations. Special attention is focused on the behavior of the recorded vertical ground motion and its relation to the horizontal ground motion counterparts. The results indicate that the average value of the ratios of vertical to horizontal peak ground acceleration (av/ah) is 0.58, but the ratios of over 30% stations exceed the rule-of-thumb value of 2/3. This av/ah is much discrete in the near-fault region and tends to decrease with the increase of epicentral distance. Furthermore, site condition also influences this ratio. The curve of vertical to horizontal acceleration response spectral ratio (Sav/Sah) with period ranging from 0 to 6s appears to be saddle-shaped overall and Sav/Sah value varies within different period range. It is also can be seen that the vertical acceleration response spectrum (Sav) looks thin compared with the horizontal acceleration response spectrum (Sah). Except several stations, the ratio of vertical to horizontal ground motion predominant period (Tpv/ Tph) is less than 1.0, and it increases with the increase of epicentral distance and becomes smooth gradually.

Abstract: The Equivalent Linear Method is a common way used in earthquake engineering to analyze nonlinear site seismic response, but the response under strong motion is underestimated by the way. For analyzing nonlinear response more veritably, in the study, a time-domain nonlinear analysis method was proposed and used in a case for 1D seismic response analysis of soil layers under strong motion. The results obviously showed that, comparing with true nonlinear method, the Equivalent Linear Method underestimated in the case in natural period range of common civil engineering structures. The true nonlinear method adopted in the study is more fitful for nonlinear response of soil layers under strong motion.

Abstract: Taking the advantages of groove pedestal and pier pedestal, a new type of pre-tensioned pedestal is constructed. The new pedestal makes full use of the deck (also the bottom formwork of the beam) to bear the tensile force so as to reduce the quantity of the pedestal construction. The new pedestal can adapt to variable geotechnical conditions by properly enlarge the arm of the turnover moment and the self-weight. The new pedestal is optimized through the bearing capacity analysis of the anti-overturning, the anti-slipping, the table anti-compressing, the force transfer plate, and the cross tie beams. The stress distribution of local bearing bracket is calculated by the finite element method so as to be reinforced accordingly. Based on practical application in some project, the new pedestal has the features of technical feasibility, security & reliability, affordability, and convenience in operation.

Abstract: Through the large number uniaxial strength tests and the creep test tests of the artificially frozen soil of Cretaceous strata, we obtained that the frozen wall in Cretaceous strata met the Moore - Coulomb strength criterion, and the artificially frozen soil strength increased from 6.5MPa in -5 °C to 12.0MPa in -15 °Cwith the freezing temperature decreased, Poisson's ratio from 0.35 down to -5 °C -15 °C at 0.18. Using viscoelastic-plastic theory we got the deep frozen wall strength and thickness of the Bojiang - Haizi mine in Cretaceous strata, practice showed that: the design approach in this paper was reasonable.

Abstract: This paper takes the Daliushu Dam Site in Yellow River as an example, which is located near the active fault zone with high seismic intensity. It studies the seepage of dam abutment rock mass in meizoseismal area and the stability under earthquake condition. The assessments on the key engineering problems of this project are based upon a large number of investigations, in-situ and laboratory tests, etc., which are carried out in the field by the author. We know that the "5∙12" Wenchuan Earthquake in 2008 triggered strong ruptures and damages of massif, and destructed the concrete facing of the Zipinpu rock-fill dam in Minjiang River, which is very close to the earthquake source and sufferd a 0.56g' seismic acceleration. For this reason, this paper analyzes the possible damage on the Daliushu Dam site rock mass under the grouting in the future earthquake, returning to the present poor quality condition of rock mass, while this dam shares the seismic intensity, seismic acceleration, dam type and dam height similar to the Zipinpu Project. This paper puts forward a new research thought, which is the longtime -lasting strong earthquake,first causes the rupture of rock mass and the decrease of rock mass mechani cal parameters, and the lasting earthquake will then worsen the rock mass structure mechanics parameters, and even cause the large-scale massif damage. From this viewpoint, this paper, analyzes the stability of the dam foundation and abutment rock mass especially the stability of the thin massif of the right dam abutment by the numerical analysis. The analysis show that under the normal and the earthquake conditions (excluding the rock mass damage and mechanical parameters decrese resulted from the lasting earthquake), The Daliushu Dam Site and the right dam abutment are still stable when the safety factor is assumed to be 0.802 under the lasting earthquake. In addition, the calculation results show that the stability is not enough.

Abstract: On the basis of analyzing the occurring mechanism of pile skin friction, pile-soil relative displacement difference function is introduced, and the differential equation which depicts the relationship between pile skin friction and depth is derived, then the calculating model of pile skin friction with depth is established under considering the displacement-interaction process. Field monitoring data are employed to verify the rationality and validity of the model proposed. Through the established model, influences, exerted by pile-soil relative displacement difference, on the pile skin friction distribution are discussed and divided into three stages: I. stage of linear increase; II. stage of nonlinear increase; III. stage of convergence. Filed testing data comparing and theoretical analysis results indicate that the method proposed can describe the transferring process as well as the distribution law of pile skin friction under taking the pile-soil interaction into account, the parameters related and needed can be easily obtained, and the model suggested in this paper is of value in pile theory and engineering.