Enhancement of efficiency of prefabricated vertical drains using surcharge, vacuum and heat preloading

Abstract

This paper focuses on increasing the efficiency in accelerating the rate of consolidation of prefabricated vertical drains (PVDs) in improved soft Bangkok clay using vacuum and heat preloading. Laboratory model tests were performed in new, large-scale consolidometers with PVD-improved reconstituted specimens using the following four schemes: surcharge preloading (PVD only), surcharge combined with vacuum pressure preloading (vacuum-PVD), surcharge combined with heat (thermo-PVD), and surcharge combined with heat and vacuum pressure (thermo-vacuum-PVD). Subsequently, the flow parameters in terms of the horizontal coefficient of consolidation (Ch) and the ratio between the horizontal hydraulic conductivity in the undisturbed zone (kh) to the horizontal hydraulic conductivity in the smear zone (ks), based on Hansbo's method. were investigated by back-calculation. The results show that the values of Ch were 1.93 m2/yr, 2.23 m2/yr, 4.17 m2/yr and 4.37 m2/yr for the PVD, vacuum-PVD, thermo-PVD and thermo-vacuum-PVD, respectively, with corresponding kh/ks values of 3.0, 2.7, 1.4 and 1.1, respectively. On the other hand, the increase in Ch of reconstituted specimens using the vacuum-PVD, thermo-PVD and thermo-vacuum-PVD were 15.54%, 116.06% and 126.42%, and the increases in kh/ks were 10.00%, 53.33% and 63.33%, respectively. Thus the vacuum-PVD can increase the horizontal coefficient of consolidation, Ch, resulting in a faster rate of settlement at the same magnitudes of settlement, compared with the PVD. The thermo-PVD and thermo-vacuum-PVD can further increase the coefficient of horizontal consolidation, Ch, with associated reduction of kh/ks values, by reducing the drainage retardation effects in the smear zone around the PVD, and consequently faster rates of consolidation were obtained. However, higher magnitudes of settlement were obtained upon application of heat owing to the associated collapse of the clay structure, similar to the results of previous investigations.

Analyzing consolidation data to predict smear zone characteristics induced by vertical drain installation for soft soil improvement

“…In all classical equations, smear zone characteristics including smear zone extent and permeability ratio are the initial assumptive parameters required to calculate the degree of consolidation changing with time. The Hansbo's (1981) equation, which is being used by many researchers (e.g., Indraratna and Redana 1998, Saowapakpiboon et al 2010, Artidteang et al 2011, Dhar et al 2011, has been applied in this study to investigate the effect of the current variability of smear zone properties on PVD assisted consolidation. It is assumed that the discharge capacity of the drain is large enough to ensure efficiency of the drain.…”

Consolidation by Prefabricated Vertical Drains with a Threshold Gradient

“…Equations 7, (8), (9), and (13) constitute the governing equations of consolidation by vertical drains incorporating the threshold gradient under the equal strain condition. The boundary conditions and initial conditions are as follows:…”

“…Preloading with sand or prefabricated vertical drains has been successfully applied to accelerate the consolidation of compressible fine-grained soil deposits for decades. Many authors have developed the consolidation theory for the design of a vertical drain [1][2][3][4][5][6][7][8][9][10]. Among these theories, the analytic solutions developed by Barron [1] and Hansbo [3] remain popular and widely used because of their simplicity and ease of use.…”

The Settlement Models of Deep Vacuum Dewatering Method

“…Vacuum consolidation has been extensively applied [1][2][3][4][5][6] and proved very effective in improving soft ground [7,8]. Vacuum consolidation usually applies a vacuum pressure into soil and a sealing membrane at the surface of the ground.…”