Applied Mechanics and Materials Vols. 90-93

Abstract: The presence of incline-piles can provide some advantages when the group is subjected to vertical loadings. Based on model tests of the static pressed pile groups, this paper describes the bearing capacity of incline-pile groups in soft soil. In order to study the incline-pile groups capacity behavior , a series model test and computer analysis were performed. In the model tests, a series of static vertical load tests were conducted on a group of eleven piles arranged in interval pattern., that constructed with aluminum tube, each 1.20m long, were used as pile groups with inclination angle of 0°,5°,8°and12°.And there is an optimal angle, which close to 8°, corresponding to the maximum bearing capacity. A single isolated pile was also tested for comparison to the group response. By comparison with the experiment result, a finite difference method was employed to simulate the incline-pile groups capacity behavior. The agreement between the experimental results and the numerical predictions is shown to be reasonably good. Therefore, accurate prediction of the ultimate bearing capacity of incline-pile groups in a mixed soil is very challenging. But the work is helpful to the design and construction of the incline-pile groups in thick soft soil.

Abstract: Duncan-Chang nonlinear model has been modified and applied to the structural loess calculation. Based on structural studies and conventional triaxial tests, this paper has analyzed the mechanical properties of intact loess and the relationship between the stress ratio structural parameters and the strain, then the expression of generalized shear strain and stress ratio structural parameters are given to facilitate the engineering applications. On this basis, the stress-strain curve of intact loess was corrected by the use of the stress ratio structural parameters. The form of the intact loess stress-strain curves which have been revised has changed hardening from the softening or weak softening. The results show that the modified stress-strain curves of intact loess can apply Duncan- Chang nonlinear model to calculate and the model parameters are reasonable and effective. This method provides Duncan-Chang nonlinear model which is widely used in engineering with a new ways and means in intact structural loess application.

Abstract: Choosing an appropriate geosynthetics creep constitutive model is the key issue of determining its creep performance. In this paper, a creep overlay model with 7 parameters was put forward based on the analyses of current models. Moreover, the identification of this overlay model was realized by taking use of genetic algorithm MATLAB program. This method proved to be workable by practical example, so it provides a new idea for establishing geosynthetics constitutive model. Creep constitutive model has been the core issue in the research on geosynthetics performances. Although the model identification has gained rich achievements in theory, it is still a problem in practical application. In literature [1] the author adopted Laplace transform to prove that overlay model is strongly inclusive and various creep models could be obtained by selecting different parameter values. So the model identification could be transformed to parameters identification, and in fact both could be realized simultaneously. This avoids overdependence on specific model in the process of identification and the subjectivity of engineering calculation in choosing the constitutive model. This paper will combine overlay model and genetic algorithm to identify the geomembrane creep constitutive model.

Abstract: Referred the vehicle-track coupling dynamics theory [1] and the vertical dynamic analysis models of Bridge-Subgrade transition developed by Zhai [2] ，Wang [3] and others [4]. This article takes account of the interaction between different structural layers in the subgrade system further by using the dynamic ballastless track model and finally establishes a space dynamic numerical model of the vehicle-track-subgrade coupled system. The dynamic response of the coupled system is analyzed when the speed of the train is 350km/h and the transition is filled with graded broken stones mixed with cement of 3%. Results show that the setting forms of Bridge-Subgrade transition have little effect on the dynamic responses, so designers can choose it on account of the practical situation. Due to the location away from abutment about 5m has greater deformation; the stiffness within 5m should be designed alone. Based on the study from vehicle-track dynamics, we suggest that the maximum allowable track deflection angle is 0.9‰ and K₃₀ 190Mpa within 5m behind the abutment.

Abstract: It is quite important and complicated to simulate sequential excavation and support process effectively and reasonably in underground engineering. To solve this problem, firstly a numerical equation to calculate excavation release loads is proposed concerned with the numerical format of finite element method. And then, an approach to dynamically simulate the excavation and support construction sequentially is put forward, in adopt of the load distribution. On the basis of the distribution of plastic coefficient of the surrounding rock, the load distribution coefficient is identified. The sequential excavation problem is transformed to simple load operation through the FEM calculation. Finally, a case study is further illustrated and it is proved that the approaches could reasonably simulate the dynamic excavation and support process and the effect of support.

Abstract: Based on the analysis of the pretension force influence factors for geotechnical prestressed anchorage cables that are used in a practical engineering, the cyclic loading characteristics of prestressed force long-term variation is revealed, and the conception of large and small cycles of prestressed force variety are also put forward. Based on these analysis, a device for the fatigue failure test and the corresponding test methods are manufactured and developed to analyze the durability problem of the inner bond section of prestressed anchorage structure under repetitive loading and cyclic loading. In the experiment, the means of indoor similar model test is adopted, in which the different loading scheme and loading amplitude were taken into account. According to the test results, the fatigue failure regularities of inner bond section for geotechnical prestressed anchorage structure are revealed.

Abstract: In order to simulate the diffusion form of anti-dispersion grout, the first visual large-proportion plane fissure test system for the physical model of fracture-grouting in flowing water is developed in China. The plane fissure test system is made up of plane fissure test-bed, monitoring system, water supply and drainage system, grouting system, control system and data acquisition system. The fiber Bragg grating (FBG) sensors for pressure, velocity and temperature monitoring are employed because of its small size and high sensitivity. The U-shaped diffusion form of anti-dispersion grout is found by the plane fissure grouting test in the flowing water.

Abstract: According to the operating characteristics of pile which under the horizontal axial load effect,a mechanical model of pile and its surrounding soil interaction with pile shaft under horizontal axial load within elastic semi-infinite foundation was established.Based on the theory of elastic mechanics,mechanics of materials,soil mechanics,etc,solutions to undetermined parameters of mechanical models are deduced.The model in this paper has solid theoretical basis,few parameters,simple determine,and can reflect distributed rule of lateral soil resistance.Through the comparison of static loab test data of the pile foundation and the theoretical calculate value in some project,we know that the actual value and the theoretical calculate value were quite close,this have verified the correctness of the model.The calculation model has certain reference value to determine the horizontal axis bearing capacity of single pile.

Abstract: Through the investigation into composition of major shallow foundation soil mass and the correlation of mechanical indicators in this study, the regression equation of mechanical indicators of the features of local foundation soil mass and the data of in situ testing was obtained. Based on massive quantities of exploration materials, this study analyzed engineering features, distribution status, and the feasibility of silty clay to be used as the bearing layer of the pile in Layer ④₂ . The analytical results showed that the silty clay with the uniform depth of over 3.5m and the cone tip resistance in static sounding of over 400MPa could be used as bearing layer of the pile. This study could provide the reference for the accurate understanding of the engineering features of soil mass, and the design and evaluation of foundation in Jiaxing City.

Abstract: In view of the settlement problem of high loess-filled embankments themselves, with the reference of the 30m high embankment at K5 +536 of Lan Lin provincial expressway and by means of the centrifugal model test, the developing process of the settlement for embankment itself with time in different sections of embankment and the distribution laws of the settlement subjected from spatial effect in case of the different terrain conditions are studied. Compared with the actual measurement, the results show that: as far as the settlement of high-filled embankment itself is concerned, the settlement at the central part along the cross-section of embankment is larger than that at shoulder; When the stability of embankment is relatively poor because of the bigger slope ratio or faster speed of construction, the settlement at the shoulder caused by the lateral extrusion from the edge of embankment is larger; The settlement of embankment itself is approximately 0.5% -1% of the height of embankment, about 75% -85% of which occurred during the construction period and the remaining 15% -25% belongs to after construction. Furthermore, the 85% of the settlement belong to after construction will be completed within a year and about two years later the settlement tend to be stable; Owing to the affection of the spatial effect due to the valley terrain conditions, the settlement near the joint sites between the embankment and the gully is larger than that occurred in gentle slope and the central part of embankment. During the time of designing and construction for high-filled embankment, the location where the settlement influenced by the lateral extrusion and spatial effect should be paid attention to, so that, the security and stability of the embankment could be ensured.