Vertical drains

The maximum theoretical surcharge that can be achieved by any vacuum system equals 100 kPa, but in practice this value will be significantly less as a result of losses in the system. Most methods operate in combination with vertical drains and may differ from each other in the way the soil mass is isolated from atmospheric conditions. Reference is made to Chu et al. (2009). 

Pre-loading alone has the disadvantage that the surcharge must remain in place for months or even years, often delaying further construction operations. A long consolidation period is generally the result of the thickness and the low permeability of compressible strata hampering the dissipation of excess pore pressures (see Section 8.5.3.4). 

Appendix D, section D.3.2 presents the calculation of the consolidation period as a function of the coefficient of consohdation of the compressible strata, the drain spacing and the drain diameter. To a certain extent the consolidation rate can be controlled by adjusting the drain spacing. 

Vertical drains may comprise prefabricated band drains or wick drains (maximum installation depth of approximately 60 m) or bored columns filled with sand (maximum installation depth approximately 30 m). The drains are normally installed in a triangular grid with a grid spacing between 1 to 3 m. 

The drains must be able to discharge the extracted pore water into a free-draining medium (sand or gravel layer, horizontal drains, etc.), usually—but not necessarily—located at the top of the vertical drain. It is essential to ensure that such a drainage blanket has sufficient permeability to handle the extracted water during all stages of the construction works. The hydraulic head within this horizontal layer or drain must be less than the hydrauhc head in the vertical drain in order to allow the pore water to be removed from the compressible soil mass. 

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Some vertical drain lines in a building were no longer needed, so they were disconnected and capped but left connected to the horizontal main drain below. The caps were fixed with tape but were not made watertight as there was no way. it seemed, that water could get into them. Fifteen years later a choke developed in the main drain, water backed up into the disused legs and dripped into an electrical switch box. All power was lost, and some of the switch gear was damaged beyond repair [23]. 

Naire, S., Braun, R.J. andSnow, S.A. (2001) An insoluble surfactant model for a vertical draining free film with variable surface viscosity. Phys. Fluids, 13(9), 2492-502. 

The data described above can be used to predict the location of better source rocks in vertically drained basins, especially in deltaic-type environments with relatively young source rocks. With long-distance vertical migration, some of the biomarker parameters may become skewed. A number of factors must first be considered before applying this approach first, some of the parameters vary with maturity second, C30 steranes are not present in lacustrine samples and so the approach will not work in that situation and finally, it will not work where the oils were deposited prior to land plant evolution, since no vitrinite was present at that time. Oils from mixed source rocks also complicate the issue. The ability to predict source rock properties on the basis of biomarker distributions in cmde oils is a very interesting concept, since most exploration efforts try to discover oil and not source rocks. 

Chai, Jun-Chun and Norihiko Miura, Investigation of Factors Affecting Vertical Drain Behavior, Journal of Geotechnical and Environmental Engineering, March, 1999, pp 216-226, ASCE, Reston, VA. 

Increase rete of consdidatton setllement Vertical drains, with or without surctiarga fills Ser>d end gravel compaction piles... 

In the framework of a land reclamation project, electrokinetics was applied in combination with preloading and prefabricated vertical drains to improve the mechanical strength of marine sediments intermittent current and noninsulated electrodes were adopted (Lo et al, 2000). The results showed that the mechanical properties of sediment were signiflcantly improved in the vicinity of the electrodes after 22-34 days, by applying voltage gradients ranging between 9.5 and 28.2V/m. 

The Development of Theoretical Models of Vertical, Draining Thin Liquid Model PU Films... 

When there is finite surface viscosity, the surface of the film is mobile. Lubrication theory for our vertical draining film gives a system of two partial differential equations describing the evolution of the film surface k z,t) and the velocity of the fluid at the surface w (z,t). These equations are... 

Surfactant transport is also important in the vertical draining film surfactant concentration gradients may develop, which may in turn strongly affect the fluid flow via the Marangoni effect. When surfactant transport is considered, lubrication theory then gives three nonlinear partial differential equations for the free surface shape k(z,t), the surface velocity w z,t) and the surface concentration of surfactant (, ). The mathematical problem to be solved for these dependent variables is ... 

S. Naire, R. J. Braun and S. A. Snow, An Insoluble Surfactant Model for a Vertical Draining Free Film II. Film Plus Meniscus in preparation, 2000. 

Consolidation of a very soft clay with vertical drains. Geotechnigue, 50, 633-643. 

Fig. 24.6 Geotextile used to simulate high-capacity vertical drains...

H (D + G) (CT-B), there is no significant attenuation with the number of cycles, which is consistent with a less pronounced soil stiffness degradation that may result from the combination of a full-depth densified zone (H D in Fig. 24.9) with vertical drains. 

Hird C.C., Pyrah I.C., Russell D., et al. 1995. Modeling the effect of vertical drains in two-dimensional finite element analyses of embankments on soft ground. Canadian Geotechnical Journal 32(5) 795-807. 

Universiti Tun Hussein Onn Malaysia (UTHM) sits on deep deposit of soft marine clay with low strength and high compressibility. Pre-treatment of the soil by ground improvement is necessary before construction works can commence on these grounds. Various ground improvement techniques are available in the market, such as vertical drains with surcharge, stone columns, mass replacement, stabilisation, etc. 

The main foam destabilization mechanism in freshly poured beer is vertical draining by gravity. The height of the fresh beer foam is measured to 5 cm and can be considered constant. It can be assumed that 25% of the cross-sectional area of the foam is used for vertical draining, in this initial phase, and that the foam structure remains constant and homogeneous. 

Consequently, for a full quantitative description of foam drainage one will need to consider both horizontal and vertical draining. However, such a complete analysis has not yet been undertaken. 

It can be assumed that 30% of the cross-sectional area of the foam is available for vertical draining. How much liquid can be drained vertically (in L m ) from the newly formed foam in 10 s by gravity The foam formed turns out to be rather persistent. Describe in some detail the practical (short term) solution and an underlying mechanism you would use to solve (or at least reduce) the problem ... 

The rate of vertical draining by gravity can be calculated from Equation 13.5 ... 

The volumetric flow rate of liquid from vertical draining can be calculated from the draining rate ... 

What is the average rate of vertical draining when the film is 100 and 10 nm thick, respectively ... 

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