Papers by Keyword: Soft Soil

Abstract: Structures with circular foundation (chimney, silo, oil tank) constructed on compressible soft soil, often have to opt for ground improvement like stone columns before construction. In this paper, the stress distribution on stone column-reinforced ground under cylindrical storage tank has been presented. Actual foundation soil reinforced with stone column is assumed as composite ground of soil and hollow cylindrical stone rings keeping the area ratio constant to carry the analysis in axi-symmetric condition. The soft soil, stone columns and granular fill are idealized using mechanical elements. The floor slab of the storage tank is assumed to be flexible enough to satisfy the theory of thin plate. Governing differential equations are derived to determine the vertical settlement and solved with finite difference technique. Contact stress at ground level is calculated from vertical settlement. It is observed that soft soil experiences heavy settlement and contact stress when the tank is full despite of low spacing to diameter ratio (S/d_c = 3) and reasonable modular ratio (E_c/E_s = 20). It is also observed that stress acting on edge stone column is lower as compared to the stress acting on center stone column even under uniformly loaded condition.

Abstract: Based on Newmark-β gradual integration method and elastic-plastic mechanical theory, numeriacl analyses of effects of soft soil depth and thickness and pile length on the characteristics of horizontal seismic response of bridge-foundation interaction system with soft layers conducted by using finite element program Midas/GTS. The numerical results show that: (1) The high frequency components of seismic excitations can be filtered and the low frequency components are amplified correspondingly when seismic waves are transmitted through soft soil layer, and thicker and lower soft soil layer can amplified this effects; (2)The extremum force of abutment shows decreases first then increases with depth decreasing, and displacement of abutment top and bottom has the same law with seismic waves, and the thicker and lower soft soil layer or shorter piles can aggravate abutment force and deformation; (3)Shear extremal stress shows decrease from top to bottom and the thicker and lower soft soil layer or shorter piles are adverse on piles; (4)Moment extremal expresses first increase then decrease with pile length and the lower and thicker soft soil layer or shorter piles can enlarged piles moment.

Abstract: It has been a technical problem of upward movement for shield tunnel segment during construction. a segment floating calculation formula was deduced through using basic theory of mechanics and mathematics, detailed tension analysis of segment. The computation example of engineering showed that the result obtained by the proposed calculation formula was well consistent with the monitoring result and could be used to analyze the upward movement of shield tunnel. Moreover, the conclusion provided some reference to similar projects.

Abstract: In this paper, with the in-situ engineering project Shiziyang tunnel of Guangzhou-Shenzhen Railway, under the disturbance of high-speed train vibration load, the shield tunnels dynamic response and foundations sand liquefying phenomenon are studied ,where they are mainly located in saturated and soft soil. Due to the tunnel going through the paralic deposited silt layer, silty soil, alluvial clay layer and the layer of fine sand or coarse sand layer, under the condition that enduring a long time of high-speed train running, which may easily lead to the foundation liquefaction and asymmetric settlement. At the entrance of the tunnel, with the poor geological conditions and weak cladding, which can easily induce sliding and collapse, where the geological conditions of this part is the most unfavorable place. Through numerical simulations, the main factor the constitutive model is explored, which may affect the single high-speed train loads on the vibration response of the train in shield tunnel and the law of accumulation and dissipation for pore water pressure.

Abstract: The marine sedimentary strata are spread in coastal area of Tianjin. Due to low soil strength, high underground water level and strong soil plasticity flow, instability accidents happened frequently in soft soil area. In the foundation excavation of underground station, because of stress release and change in ground water level, the differential settlement of surrounding buildings, ground crack and deformation of underground pipeline will happen. The stability of surrounding rocks in the foundation excavation of underground station has been calculated and analyzed by using numerical simulation method. The Surrounding soil deformation of foundation pit has been gotten to analyze.

Abstract: By using the finite element method, the settlement of soft soil subgrade with a crust layer has been investigated. To find the influence of thickness of the crust layer on the settlement, four different thicknesses, which are 0.0m, 1.5m, 3.5m and 5.5m, are selected. Besides, the settlement during the construction and post construction are also analyzed. It is found that the crust layer can reduce the settlement and uneven settlement of subgrade effectively. Besides, the settlement of the subgrade decreases with the increase of the thickness of crust layer. Moreover, with the increase of time, the uneven settlement of the pavement increases gradually. And when the time is up to a certain degree, the uneven settlement tends to be stable.

Abstract: The advantages and disadvantages of the existing mathematical models to determine soft soil pre-consolidation pressure were compared. Based on the practical shape of e-logP curve, it is discovered that the Harris model is more fit to the e-lgP curve of soft soil in Dongting Lake area than the traditional cubic or quartic polynomial models. Besides, it avoids the impact of human subjectivity of Casagrande method effectively. Consequently, the Harris model was finally selected to calculate the pre-consolidation pressure of soft soil in Dongting Lake area by numerical method.

Abstract: The behavior of reinforced and unreinforced embankment on soft and stiff grounds has been investigated using the centrifuge tests and verified using numerical simulations. Four different cases have been investigated in this study based on various types of foundation materials and reinforcement condition. Two-dimensional (2D) and three-dimensional (3D) finite element programs, Plaxis 2D and Plaxis 3D Foundation respectively used to simulate and analyze the prototypes behavior provided by centrifuge tests. Deformation behavior, settlements and effect of reinforcement have been studied in this study. Comparison of the results of the numerical analysis with the measurements obtained from the centrifuge tests shows good agreement in terms of settlement and the reduction of settlement due to geosynthetics reinforcement.

Abstract: In this paper use the shield construction of Dalian subway 202 bid section as an example, carried out the monitoring measurement of surface subsidence and crown surface subsidence during the shield construction, detailed analysis the monitoring data, explored the characteristics and distribution of surrounding rock and surface deformation of large cross section shield construction. Construction transverse deformation has a relationship with lateral position and the tunnel excavation length. The closer from shield machine working face, the closer to the center line of the tunnel, the greater impact is. The research results have reference value for the future similar engineering design and construction.

Abstract: In order to overcome the defects of the classical model in the description of the rheological properties of soft soil, an Abel glue pot was defined based on the fractional derivative theory by the fractional calculus of Riemann-Liouville. Three components fractional order derivative solid model was built with Abel glue pot. Then the experimental data was fit using the new model. The simulation results show that the three components fractional order derivative solid model is more accurately than the generalized Kelvin model or Burgers model and that it has few parameters.