UNIVERSITI TUN HUSSEIN ONN MALAYSIACENTER OF DIPLOMA STUDYASSIGNMENTS(LATEST TECHNOLOGY IN SOIL IMPROVEMENT USING PREFABRICATED VERTICAL DRAINAGE METHOD)

SUBJECT CODE: DAB 20702 AMALAN TEKNOLOGI SUBSTRUKTUR DAN CERUN

GROUP: 1MEMBERS:NAMENO. MATRIC

AKASHAH BIN RIDZUAN AA130936

AMIRUL DANIAL BIN SAMSUDIN AA130190

FARAH HANI BINTI MD SIDEKAA130008

FATIN HAZWANI BT MOHD ZULKIFLIAA130098

LECTURER: EN. AHMAD HAKIMI

1. IntroductionPrefabricated Vertical Drains (PVD) and Vertical Strip Drains (VSD) also known as Wick drains, are a ground improvement technique that provides drainage paths for pore water in soft compressible soil, using prefabricated geotextile filter-wrapped plastic strips with molded channels. A hollow mandrel is mounted on an excavator or crane mast. The wick drain material, contained on a spool, is fed down through the mandrel and connected to an expendable anchor plate at the bottom of the mandrel. A vibratory hammer or static method is used to insert the mandrel to design depth. The mandrel is then extracted leaving the wick drain in place. The wick drain is then cut at the ground surface, a new anchor plate is connected to it and the mandrel moved to the next location. A pattern of installed vertical wick drains provides short drainage paths for pore water, thereby accelerating the consolidation process and the construction schedule.The use of prefabricated vertical drains with preloading is now common practice and is proving to be one of the most effective ground improvement techniques known. The factors affecting its performance, such as the smear zone, the drain influence zone, and drain unsaturation, are discussed in this paper. In order to evaluate these effects a large scale consolidation test was conducted and it was found that the proposed Cavity Expansion Theory could be used to predict the characteristics of the smear zone based on the soil properties available. Moreover, the procedure for converting an equivalent 2-D plane strain multi-drain analysis that considers the smear zone and vacuum pressure are also described. The conversion procedure was incorporated into finite element codes using a modified Cam-clay theory. Numerical analysis was conducted to predict excess pore pressure and lateral and vertical displacement. Three case histories are analysed and discussed, including the sites of Muar clay (Malaysia), the Second Bangkok International Airport (Thailand), and the Sandgate railway line (Australia). The predictions were then compared with the available field data, and they include settlement, excess pore pressure, and lateral displacement. The findings verified that smear and well resistance can significantly affect soil consolidation, which means that these aspects must be simulated appropriately to reliably predict consolidation using a selected numerical approach. Further findings verified that smear, drain unsaturation, and vacuum distribution can significantly influence consolidation so they must be modelled appropriately in any numerical analysis to obtain reliable predictionsPreloading is the application of surcharge load on the site prior to construction of the permanent structure, until most of the primary settlement has occurred. Since compressible soils are usually characterized by very low permeability, the time needed for the desired consolidation can be very long, even with very high surcharge load. Therefore, the application of preloading alone may not be feasible with tight construction schedules and hence, a system of vertical drains is often introduced to achieve accelerated radial drainage and consolidation by reducing the length of the drainage paths.2. Litreture review

2.1 Theory of Vertical Drains The basic theory of radial consolidation around a vertical drain system is an extension of the classical one-dimensional consolidation theory. Barron (1948) studied the two extreme cases of free strain and equal strain and showed that the average consolidation obtained in both cases are nearly the same. The free stain hypothesis assumes that the load is uniform over a circular zone of influence for each vertical drain, and that the differential settlements occurring over this zone have no effect on the redistribution of stresses by arching of the fill load. The equal strain hypothesis on the other hand assumes that the load applied is rigid and equal vertical displacement in enforced at the surface, i.e. horizontal sections remain horizontal. The solution for the second case is considerably simpler (Barron 1948)

2.2 Properties of the filter In general, the drain material of a sand drain and the filter jacket of a prefabricated drain have to perform two basic but contrasting requirements, which are retaining the soil particles and at the same time allowing the pore water to pass through. According to Hansbo (1979, 1994), the filter has to meet the following requirements: the permeability of the filter should be high enough not to influence the discharge capacity of the drain system, on the contrary, the permeability of the filter should be low enough to retain fine soil particles. The soil particles might penetrate through the filter into the core, which eventually might be filled with soil and get clogged, the filter needs to be strong enough to withstand high lateral pressure in order not to be squeezed into channel system of the core the filter should be strong enough not to break during installation, and the filter should not deteriorate with time because this would reduce the discharge capacity of the drain

3.0 Method procedure3.1 Sequence of vertical drainage wick installation

Fig. 6.1 Installation equipment for wick drains

All vertical drainage wicks will go to maximum allowable/anchor able depths or until refusal as per following method:-a) Thread the vertical drainage wick off the wick roll/spool, up the wick tube, and over the top wick roller and down through the mandrel.b) Place the drainage wick through or around the anchoring device and tuck the loose end of the wick up into the mandrel about 6 to 8 inches (150 to200 mm). Pull the drainage wicksexcess slack tight through the mandrel and vertical drainage wick tube by reversing the verticaldrainage wick rollbyhand. By reversing the vertical drainage wick spool or wick roll, the anchoring device will retract up tight against the bottom tip of the mandrel. This will prevent dirt or mud from entering the mandrel during the insertion of the mandrel into the ground.c) Move the machine/mandrel to the specified vertical drainage wick locationand insert themandrel with anchoringdevice in place using static force(and /or vibratory force if necessary) into the ground to the desired depth.d) Extract the mandrel, leaving the anchoring device and the completed or installed vertical drainage wick in place, uncontaminated and the properdepth.e) Cut the vertical drainage wick off the contract-specified length above the working surfaces)Check the vertical drainage wick installation machine mast to make sure it is plumb. Use hydraulic controls to correct if not with the specification

Fig. 6.2 Installation of drain.3.2 Splicing vertical drainage wickVertical drainage wick is supplied on wick rolls. Each wick roll will hold about1000 ft. of drain or 305 m. Once the wick roll is used off, a splice is necessary to add thenext wick roll. To splice, cut the end of the previous wick roll at an angle and stuff it insidethe end of the new wick roll. Then staple them both together as shown in figure.

Fig. 6.3 Splicing of wick drains

4.0 Discussion on the method A vertical drainage system can be installed in order to accelerate the consolidationprocessandhelptoimprovedischargeofexcessporepressureinthesubsoil. Inthisway, a stable situation is reached more quickly, thus shortening the filling time dramatically. At the same time, the settlement process is accelerated to such an extent that earthwork finishing off processes can be started earlier. All of these results in a substantially shorter construction time which may be important both economically and socially. The installation of vertical PVC drains is usually done with the aid of a dragline fitted with tams along which the lance can move up and down vertically. The length of drain to beinstalled determines the minimumlength both of the equipmentandofthe lance. The drains are wrapped around a coil which is placed in housing in the rig. From there, the drain passes over a travel roller until it feeds into the top of the rig and then via second travel roller through the lance downwards. Beneath the lance, a small anchor platies secured to the drain. The lance is then installed to the desired depth either by vibration or with the help of a static pressure and tensioner. Any solid layer encountered can be pre-jetted. The anchor plate ensures that the drain, once to depth, remains at that depth whilstthe lance is being withdrawn. The drain is then clipped off above ground level, after which the entire procedure can be repeated all over again at the next drain location. Depending upon soil conditions, the length & width of the drain strip, an output of 2000 to 6000linear m per eight hour work day per rig can be achieved.

5.0 CONLUSION

Each and every project is unique due to its features, geographical locations and importance; hence while adopting one variety amongst various available alternatives, precautions should be kept in view. In addition, while deciding the method to be adopted for enhancing the process of consolidation, the economy aspect, time available for construction and availability of various materials should be considered. The need of the method depends upon the time frame for completion of project. If project is to be completed early; the stage construction cannot be employed. For such cases, the methods for quick consolidation of sub-soil have to be adopted using PVC vertical drainage system. In case, when no time constraint is there, installation of sand drains with stage construction after proper design can be adoptedThe technology surrounding the use and application of prefabricated vertical drain is continually growing. The concept of vertical drainage utilizing prefabricated fdrains has been applied to many non-traditional applications

6.0 References https://www.academia.edu/5418048/Pre-fabricated_Vertical_Drains_MLMCE_1_Civil_Engineering http://www.docstoc.com/docs/73459057/PRE-FABRICATED-VERTICAL--DRAIN--(PVD) http://www.americandrainagesystems.com/images/wick_drain_installation.htm http://www.uswickdrain.com/ http://www.wicks.nl/vertical-drainage

7.0 Appendices

1 Machines installing the wick drain

2 Water come out from land through fabricated drainage

3Area of land installed with fabricated wick drain