جستجوی مقالات مرتبط با کلیدواژه "pvd" در نشریات گروه "فنی و مهندسی"

In projects that involve surcharge and prefabricated vertical drains (PVDs) systems for the treatment of weak underlying layers, embankment failures, tension cracks, and differential settlements, surficial heaves, and foundation failures were addressed in various literature. Overestimation and unrealistic design assumptions made by geotechnical and structural engineers are the main reasons for most of the cases. In all these cases a simple collaboration between different parties in the project ranging from designers to field engineers could have decreased or prevented these undesirable outcomes. The problem of neglecting the infiltration of the embankment in the ground as a new distinct layer with all the necessary requirements, and also disturbance caused as a result of PVDs installation in four cases: preloading case, fill removal, main structure construction, and post- construction phase are discussed. A few design recommendations are given regarding the stated issues. Since after the completion of soil treatment operations, the soil engineering parameters and in some cases even soil stratification had changed, care should be taken to use the new treated parameters in the final design process, not the preliminary site report parameters. Neglecting this issue may lead to severe malfunctions and even unpredictable failures. BIM technology has the possibility of integrating all aspects, and complexities of geotechnical engineering in the structural-architectural platform as a whole, which would revolutionize the construction industry. Till now only the structural-architectural part is done and further research and investment are necessary for the geotechnical aspect.

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.

One of the important parameters that should be considered in designation of weak clay and peats treatment systems is the influence zone wherever there are infrastructures or sensitive buildings in the vicinity of the treatment area. Since large vertical and horizontal displacements occur in these treatment systems, the soil around the project undergoes large strains that should be accounted for in project planning prior to finalization of the treatment system. The treatment systems for weak clays and peats are often a combination of prefabricated vertical drains plus vacuum and/or surcharge preloading. For investigation of the impact of preloading agents, and FEM simulation of two case histories were performed. One the project incorporates the combination of surcharge and vacuum preloading while the other one consisted of only vacuum preloading without surcharge embankment. Based on the verified models, different scenarios were introduced for comparison of impact of the vacuum and preloading agents on the magnitude of the influence zone. Regarding the impact of surcharge embankment, it was shown that reducing the height of surcharge can drastically reduce the influence zone in both numerical simulations. The application of vacuum preloading as the only preloading agent has decreased the influence zone drastically and for urban areas or places that sensitive infrastructures exist might be an ideal option for similar cases. Regarding the impact of magnitude of vacuum pressure on the influence zone it was shown that application of a stable high vacuum pressure can significantly reduce the diameter of the influence zone.

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.

One of the new technology that is widely used in all the world is the vacuum preloading that accelerate the process of dewatering and consolidation process along with prefabricated vertical drains (PVD)s with or without surcharge preloading. In the finite element modelling (FEM) modelling process, the reduction in conductivity due to the consolidation and increase in stress of underneath layers, plays a dramatic role in prediction of the settlement. Appling a modifier function is a good means to account for reduction in the hydraulic conductivity in FEM modelling. To illustrate the importance, the importance of applying this function in the modelling, TV2 trial embankment in Bangkok airport was appointed as a case history. After the verification of the model, the model was run in the absence of hydraulic modifier. It was observed that the predicted final settlement after 160 days is increased from 0.94 m to 1.19. Also the curve pass is unreal base on the verified model, and the quantity of the calculated settlements are 10 to 25 percent overestimated. Since the clogging of PVDs pore, is one the obstacles in modeling procedure of the vacuum preloading, the clogging effect can be applied as a modification in the resultant hydraulic modifier function derived from lab tests. By applying the proper modifier function, more realistic results can be obtained in FEM modelling in such models including PVDs and vacuum and/or surcharge preloading.

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.