جستجوی مقالات مرتبط با کلیدواژه "surcharge" در نشریات گروه "عمران"

The rapid developments of infrastructures, especially in far less developed areas or in the coastal regions, necessitates new technologies to elevate the efficiency of the existing systems. One of the obstacles in such areas is the existence of weak soils that are not suitable at all for construction. Soil treatment process, especially in such areas, is very time consuming and expensive. The common method for land reclamation consists of application of prefabricated vertical drains (PVDs), surcharge with or without vacuum preloading. Even by applying vacuum preloading, the time needed for compilation of the project is still considered long. In this literature a new method is introduced as a new preloading agent to accelerate the soil treatment process and decrease the cost and time required for the compilation of the reclamation process. Blast preloading might be a substitution or a companion for existing methods. First, a case history was introduced and verified using finite element modeling (FEM) that includes surcharge and vacuum preloading. Then the blast was applied to verified models, and the efficiency of it was investigated for every possible situation. It was shown that blast preloading has the potential to be used in soil treatment systems, as the required time was halved in many cases and the settlement increased from 20 to 50 percent, in comparison to cases without blast preloading. Even in cases in the absence of surcharge or vacuum, the blast preloading acts the same as surcharge or vacuum. Although it should be noted that it is still a preliminary investigation, more extensive lab and field tests are required for adoption of blast preloading as a new technique in soil treatment systems.

Three trial embankments as TS1, TS2, and TS3 that were built for the investigation of a soil treatment project in Bangkok were modeled and verified based on the reported data. To clarify the importance of integration of the hydraulic modifier function vs stress, in the verified models, the modifier functions were omitted and the FEM models were run in the absence of the function. It was shown that after the omission of the hydraulic modifier, the results were overestimated especially for the TS1 and TS2, which had smaller PVDs (prefabricated vertical drains) distance. For the TS1 embankment, the settlement increased from 0.78 m to 0.87 m in 210 days. In 365 days, the settlement increased from 1.27 m to 1.44 m. For the TS2 embankment, the settlement increased from 0.93 m to 1.67 m in 230 days. In 410 days, the settlement increased from 1.36 m to 2.27 m. For the TS3 embankment, the settlement increased from 1.15 m to 1.79 m in 230 days. In 410 days, the settlement increased from 1.52 m to 2.24 m. The inclusion of the hydraulic function that calibrates the model for every step of loading is essential in the modelling such problems. For the design phase, this function should be calculated from lab tests, preferably undisturbed samples that were bored from the site, and the resultant function be used as an inseparable part of modeling and calculations.

In Finite element modelling (FEM) of the soil treatment systems that includes prefabricated vertical drains (PVDs), either for preliminary designation, or in the evaluation period, one the main challenges of geotechnical engineers are the correct estimation of the parameters used in the model. The main objective of these kind of soil treatment is the acceleration of the consolidation process to reinforce the weak soft clay stratum underneath. In the consolidation process the initial soil parameters changes, such as void ratio, hydraulic conductivity, swelling and compression index and so on and that is why the modelling of such reclamation process is so challenging. In previous published literature, there was no paper, especially concentrate on the sensitivity analysis. In this literature first, a case history is presented and verified, and then base on the verified model, the following parameters as: void ratio, vacuum pressure, phi and over consolidation ratio, rate of loading of the surcharge embankment, mesh size, Lambada (𝝀) and Kappa (𝜿), Hydraulic conductivity ratio and Mesh type were parametrically investigated. It was shown that, even a minute change in the quantity of some parameters can adversely affect the precision of the prediction of the model. The results of this study can be used by both field and design engineers, involved in the construction of embankments on soft ground for soil treatment systems in weak and rate-sensitive clays.

Rapid developments of industrial and urban structures and infrastructures necessitate the utilization of remote or unsuitable lands that were not considered for construction in the past. The application of surcharge and prefabricated vertical drains (PVDs) is one the popular methods that is used all around the world as a result of simplicity and high efficiency. One of the issues that may occur in such reclamation projects, is the existence of sensitive infrastructures or structures in the vicinity of the treatment area. There are many variables that affect the diameter of the influence zone such as: the compressibility of weak layers, the height of clay stratums, length of the PVDs and the height of surcharge embankment and so on. In this literature the impact of spacing between PVDs was investigated using finite element modelling. Three test embankments as TS1, TS2 and TS3 were modeled and verified for the study. For TS1 (PVDs with 1.5 m spacing), TS2 (PVDs with 1.2 m spacing) and TS3 (PVDs with 1.0 m spacing) the diameters of the influence zone were 54.8, 46 and 42.3 m respectively. As the distance between the PVDs decreases, the influence zone decreases as well and becomes smaller. For the FEM simulation of only surcharge embankment in the absence of PVDs the influence zone after 400 days was 64 m in the case that only 0.65 settlement was reached. It can be seen that the inclusion of PVDs and the utilization of smaller quantities of spacing can be an effective way for the reduction of influence zones where there are concerns regarding adjacent structures or infrastructures.

This paper describes the behavior of soft soil foundation under Surcharge and with and Without prefabricated vertical drains (PVDs) or Vacuum Preloading base on a trial embankment which was built in Bangkok International Airport, Thailand. An analytical solution considering the variation of soil permeability and compressibility was adopted. Three scenarios were modeled and analyzed for Bangkok airport as: Model A: Application of surcharge load alone (i.e., no vacuum and PVD installation), Model B: Application of surcharge load combined with PVD (i.e., no vacuum application), Model C: Application of surcharge load combined with PVD and 60 kpa constant vacuum preloading and Model D: Application of surcharge load combined with PVD and field vacuum that was applied on site. The associated settlements at the embankment centerline are predicted and compared with the available field measurement. The field data show that the efficiency of this soil treatment technique depends on the magnitude and distribution of vacuum pressure. The height of surcharge and consolidation time can be significantly reduced in comparison with the conventional method of surcharge alone or surcharge and pvd alone. The findings of this study are expected to be useful to design engineers involved in the construction of embankments on weak grounds.