Finite-element analysis of deep excavation in layered sandy and clayey soil deposits

1994 ◽  
Vol 31 (2) ◽  
pp. 204-214 ◽  
Author(s):  
Chang-Yu Ou ◽  
Ching-Her Lai
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Clayey Soil ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Deep Excavation ◽  
Element Analysis ◽  
Modified Cam Clay ◽  
Soil Deposits ◽  
Cam Clay

This paper presents an application of finite-element analysis to deep excavation in layered sandy and clayey soil deposits using a combination of the hyperbolic and the Modified Cam-clay models. In the analysis, the drained behavior of cohesionless soil and the undrained behavior of cohesive soil were simulated using the hyperbolic and Modified Cam-clay models, respectively. A rational procedure for determining soil parameters for each of the models was established. A simulation of the dewatering process during excavation was proposed. The analytical procedure was confirmed through an analysis of three actual excavation cases. Finally, analyses considering pore-water pressure dissipation during the actual elapsed time for each construction phase were carried out. The results indicate that the calculated displacement of a retaining wall during excavation is smaller than that given by undrained analysis. It was thought that some degree of pore-water pressure dissipation actually occurs during the intermediate excavation stages. This results in a decrease in the final deformation of the wall and ground.-surface settlement than would be predicted by undrained analysis. Key words : finite-element analysis, deep excavation, hyperbolic model, Cam-clay model.

scholarly journals Numerical modelling of soft soil stabilized by vertical drains, combining surcharge and vacuum preloading for a storage yard

2007 ◽  
Vol 44 (3) ◽  
pp. 326-342 ◽  
Author(s):  
Cholachat Rujikiatkamjorn ◽  
Buddhima Indraratna ◽  
Jian Chu
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Plane Strain ◽  
Water Pressure ◽  
Vacuum Pressure ◽  
Element Analysis ◽  
Prefabricated Vertical Drains ◽  
Vertical Drains ◽  
Modified Cam Clay ◽  
Surcharge Load

This paper presents a finite element analysis of a case study of a combined vacuum and surcharge load through prefabricated vertical drains (PVD) at a storage yard at Port of Tianjin, China. The top 15 m of soil at this site was very soft to soft and needed to be improved using preloading surcharges of more than 140 kPa. To avoid any stability problems associated with a high surcharge embankment, 80 kPa vacuum pressure combined with fill surcharge was applied (40 and 58 kPa for sections I and II, respectively). A plane strain analysis was performed using equivalent permeability and transformed unit-cell geometry. The converted (equivalent) parameters were incorporated in the finite element code ABAQUS, using the modified Cam-Clay theory. The performance of a trial embankment at the site of the storage yard is predicted on the basis of a constant vacuum pressure applied on the soil surface and distributed along the length of the drain. The predictions of settlement, pore-water pressure, and lateral displacement were compared with the available field data, and an acceptable agreement was found based on this numerical approach. The combination of vacuum and surcharge load can effectively shorten the preloading period, reduce the height of the embankment, and counterbalance excessive lateral displacements.Key words: consolidation, finite element analysis, plane strain method, soil improvement, vertical drains.

scholarly journals Effect of Reduced Zone on Time-Dependent Analysis of Tunnels

2011 ◽  
Vol 2011 ◽  
pp. 1-12
Author(s):  
Mohammed Y. Fattah ◽  
Kais T. Shlash ◽  
Nahla M. Salim
Keyword(s):  
Finite Element ◽  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Outer Diameter ◽  
Transient Effects ◽  
Excess Pore Water Pressure ◽  
Modified Cam Clay ◽  
Tunnel Diameter ◽  
Excess Pore

The problem of the proposed “Baghdad metro line” which consists of two routes of 32 km long and 36 stations is analyzed. The tunnel is circular in cross-section with a 5.9 m outer diameter. The finite element analyses were carried out using elastic-plastic and modified Cam clay models for the soil. The excavation has been used together with transient effects through a fully coupled Biot formulation. All these models and the excavation technique together with Biot consolidation are implemented into finite-element computer program named “Modf-CRISP” developed for the purpose of these analyses. The results indicate that there is an inward movement at the crown and this movement is restricted to four and half tunnel diameters. A limited movement can be noticed at spring line which reaches 0.05% of tunnel diameter, while there is a heave at the region below the invert, which reaches its maximum value of about 0.14% of the diameter and is also restricted to a region extending to 1.5 diameters. The effect of using reduced zone on excess pore water pressure and surface settlement (vertical and horizontal) was also considered and it was found that the excess pore water pressure increases while the settlement trough becomes deeper and narrower using reduced .

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