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Armfield Instruction Manual

10

Permeable Membranes

Curved Permeable Membrane

Straight Permeable Membrane

Two straight and one curved membrane are supplied with S1. Both membranes are
formed from perforated sheet metal that is covered with fine woven material with
perforations small enough to prevent the passage of sand particles. Rubber strips on
the sides seal the membranes to the vertical front and rear walls of the sand tank.
The ‘V’ shaped straight membrane can be located adjacent to the outlets inside the
sand tank to allow variation of the water depth without the sand affecting the height
adjustment.

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Summary of Contents for S1

Page 1: ...Drainage and Seepage Tank Instruction Manual S1 ISSUE 16 June 2013 ...

Page 2: ...eable Medium Sand 8 Accessories supplied 9 Dye Injection Unit 9 Permeable Membranes 10 Impermeable Membranes for Pressure Measurement 11 Tile Drain 12 Installation 13 Advisory 13 Electrical Supply 13 Installing the Equipment 14 Commissioning 14 Choice of Sand 14 Operation 15 Operating the Equipment 15 Equipment Specifications 16 Overall Dimensions 16 Equipment Location 16 Electromagnetic Compatibi...

Page 3: ...aining Effect of a Tile Line 31 Exercise D Draining Effect of an Open Trench 33 Exercise E Uplift Pressure on Foundation of Structures 34 Exercise F Changing Uplift Pressure by Changing Length of Flow Lines 35 Exercise G Reduction of Uplift Pressure by Draining 36 Exercise H Reduction of Lateral Thrust on a Retaining Wall by Draining 37 Exercise J Quicksand 39 Exercise K Stability of an Earth Dam ...

Page 4: ......

Page 5: ... Customer Support helpdesk Monday to Thursday 0830 1730 and Friday 0830 1300 UK time Contact details are as follows United Kingdom International 0 1425 478781 calls charged at local rate 44 0 1425 478781 international rates apply Email support armfield co uk Fax 44 0 1425 470916 Copyright and Trademarks Copyright 2013 Armfield Limited All rights reserved Any technical documentation made available ...

Page 6: ...own they can be altered using drains cut offs sheet pile walls and other means to change the flow pattern Similar problems arise in other engineering structures built from or on soil As examples we can mention levees road and railway embankments canals navigation locks foundations of buildings bridges harbour walls and similar structures Another engineering field where good understanding of water ...

Page 7: ...e physical properties of the medium and characteristics of flow are found To further simplify the problem we usually restrict ourselves to a two dimensional flow investigating conditions in a vertical cross section along the horizontal direction of the moving water mass The Armfield Drainage and Seepage Tank Model S1 is specifically designed to permit the simulation in the laboratory of such verti...

Page 8: ...4 Equipment Diagrams Figure 1 Front View of S1 Drainage and Seepage Tank Shown with impermeable baffle fitted but not filled with sand ...

Page 9: ...Equipment Diagrams 5 Figure 2 Side View of S1 Drainage and Seepage Tank ...

Page 10: ...pply with a reliable earth connection so that the equipment is adequately earthed The equipment must only be operated using a fused electricity supply Details of required fuse ratings can be found on page 10 The equipment must not be operated with any of the panels removed To give increased operator protection the unit incorporates a Residual Current Device RCD alternatively called an Earth Leakag...

Page 11: ...xample of the need for cleanliness Under the COSHH regulations the following precautions must be observed Any water contained within the product must not be allowed to stagnate ie the water must be changed regularly Any rust sludge scale or algae on which micro organisms can feed must be removed regularly i e the equipment must be cleaned regularly Where practicable the water should be maintained ...

Page 12: ...it different demonstrations Water is returned to the sump tank by the overflows Each overflow incorporates a plug of open cell foam material to prevent particles of sand from washing into the sump tank Two aluminium rails along the top edges of the sand tank provide location for an adjustable clamp 5 for an impermeable baffle plate 4 or lateral pressure plate described later when required The rail...

Page 13: ...ted on a metal rod clamped to the top rail of the sand tank as shown below 6mm internal diameter flexible tubing and T pieces are used to form four outlets from the dye reservoir each outlet incorporating a pinch valve to vary the flow of dye and a hypodermic needle at the end to inject the dye into the sand The length of each flexible tube can be varied to locate the injectors at different positi...

Page 14: ...d sheet metal that is covered with fine woven material with perforations small enough to prevent the passage of sand particles Rubber strips on the sides seal the membranes to the vertical front and rear walls of the sand tank The V shaped straight membrane can be located adjacent to the outlets inside the sand tank to allow variation of the water depth without the sand affecting the height adjust...

Page 15: ...ips along the edges The foundation pressure plate is 610mm long with 5 Perspex tubes 210mm long normal to the surface as standpipes The lateral pressure plate is 720mm long with longitudinal reinforcement and five standpipes cranked through 90 Each impermeable plate incorporates filters over the connections to the standpipes on the inlet face to prevent sand from entering the tubes ...

Page 16: ... copper tube with one end closed and having a pattern of eighteen holes drilled along its 150mm length The open end is connected to a clean PVC tube 500mm long Fine woven material is fastened around the copper tube to act as a filter These tile drains can be screwed into any of the six tappings in the aluminium plate at the rear of the tank having removed the appropriate sealing plug Each tapping ...

Page 17: ... 1 AMP Electrical Supply for Version S1 B The equipment requires connection to a single phase fused electrical supply The standard electrical supply for this equipment is 120 V 50 Hz Check that the voltage and frequency of the electrical supply agree with the label attached to the supply cable on the equipment Connection should be made to the supply cable as follows GREEN YELLOW EARTH BROWN LIVE H...

Page 18: ...D The RCD must trip Switch on the RCD again 8 Close the flow control valve 14 then check the operation of the centrifugal pump by operating the mains switch Gradually open the flow control valve and confirm that water is supplied to the sand tank 9 Raise both overflow pipes 7 16 to maximum height and fill the sand tank with water to check for any leaks Tighten the clamp strip fixing screws if nece...

Page 19: ...15 Operation Operating the Equipment See the Laboratory Teaching Exercises for details on operating the equipment ...

Page 20: ...nt The equipment is a self contained unit and needs only a temporary supply of cold water for the initial filling of the sump tank and for cleaning flushing purposes Electromagnetic Compatibility This apparatus is classified as Education and Training Equipment under the Electromagnetic Compatibility Amendment Regulations 1994 Use of the apparatus outside the classroom laboratory or similar such pl...

Page 21: ...uations up to 10 of the nominal voltage f Transient over voltages typically present on the MAINS supply Note The normal level of transient over voltages is impulse withstand over voltage category II of IEC 60364 4 443 g Pollution degree 2 Normally only nonconductive pollution occurs Temporary conductivity caused by condensation is to be expected Typical of an office or laboratory environment ...

Page 22: ...n Any build up of sand in the sump tank should be removed to avoid damage to the circulating pump 3 After use the tile drains and permeable membranes should be washed thoroughly to remove any particles that may be blocking the filter material 4 After prolonged use scale may build up on the inside of the glass panel preventing a clear view of the water levels inside the sand tank To clean the glass...

Page 23: ...ed However any number of other practical investigations can be made which will add to general knowledge and enrich the experience of the experimenter Several basic rules should be followed in order to obtain good results First of all great care is needed in sealing the areas of contact between the membranes and the tank walls To achieve a well sealed contact requires clean sand free tank walls and...

Page 24: ...oss L length of the flow path A more usual statement of Darcy s Law however in terms of velocity of flow Since velocity is given as 2 division of equation 1 by A leads to the familiar statement of Darcy s Law 3 Since the ratio which is called hydraulic gradient and is analogous to slope is dimensionless the coefficient of permeability K must have the dimensions of velocity for equation 3 to be val...

Page 25: ...eepage or leakage below a dam or through an earth dam the uplift pressure caused by the water on the base of a concrete dam or say a harbour wall and the danger of a quick or liquefaction condition at points where seepage water comes to the ground surface The path which a particle of water follows in its course of seepage through a saturated soil mass is called a flow line In isotropic soil flow f...

Page 26: ...have the same potential at the points of entry and similarly they will have the same potential when eventually reaching the bottom of basin II This follows from the fact that the water tables in both basins I and II are horizontal as well as their bottoms So the pressure is constant along the whole bottom of each basin Now we pick two of the unlimited number of possible flow lines and denote them ...

Page 27: ...een the two equipotential lines can be shown to be the shortest distance between the two lines at the point in question Hence the gradient will be maximum along that chord However by definition the two lines are infinitely close together at that point So the difference in length between the arc and the chord is infinitely small Hence at that point the gradient along the arc is equal to the gradien...

Page 28: ...ip between the two flow lines into a sequence of such squares we can use their number n for calculating the potential drop dh between two successive equipotential lines Since all the values of dh must be the same according to equation 8 we have 9 Knowing dh we can finally determine from equation 5 the discharge per unit length through the area between two flow lines Although it is advantageous to ...

Page 29: ...ions exist for some types of boundary conditions Nor is it necessary to seek the correct flow line pattern experimentally There are however many cases of seepage where boundary conditions are not so clearly defined as in part b Flow Nets above A typical such case is seepage through an earth dam shown above Here the upstream slope of the dam represents an equipotential line the head h consists of t...

Page 30: ...r until the solution becomes a semi transparent opal like liquid of orange greenish colour Fill the tank with pure sand to a level of about 300mm above the bottom of the tank Adjust the upstream overflow so that its top is about 100mm below the top of the tank and the downstream overflow so that its top is about 25mm above the surface of the sand bed Adjust the impermeable screen at the middle of ...

Page 31: ...ing dye container until dye surface is about 50mm below water level in pool Let the flow lines wash away Do not take out the needles before the dye input has been shut off as indicated Otherwise dye will get into water in the pool while needles are being removed ii Flow Net Construction Trace the flow line pattern and the boundary conditions the perimeter of the cross section of the body of sand i...

Page 32: ... to avoid this is to set up a separate rectangular flow net in each of the two boundary channels This can be done by appropriately changing the position of some equipotential lines iii Seepage Rate First the pressure drop dh is determined from equation 9 Then the seepage rate in each flow channel is determined using equation 5 in case of a square network or equation 10 in case of a rectangular net...

Page 33: ...boundary conditions are not completely specified by the geometry as they are in problems similar to that of seepage under a sheet pile wall The objectives of the experiment are as follows 1 To determine the position and shape of the flow line representing the uppermost free water surface inside the body of the dam 2 To visualise the flow lines system and to show each flow line starts perpendicular...

Page 34: ...illed The rate of filling should be slow Otherwise the dam segment can easily collapse When the upstream water level is stabilised needles with dye are inserted along the upstream slope next to the transparent side of the tank the first being fixed immediately at the water surface The procedure to be followed in visualising the flow lines construction of equipotential lines and calculation of seep...

Page 35: ...medium obstructing the water movement and or b by making the head difference between an upper pool and the desired end points of flow lines greater than the original A tile line a trench or a well accomplishes the first effect automatically The second is achieved only by maintaining a tail water level at a lower elevation than the original tail water This is usually done by pumping or by draining ...

Page 36: ...about 450mm The overflows are set with their tops about 25mm above sand level before water is poured slowly into the space around the upstream overflow After steady flow conditions have been achieved dye is introduced in the usual manner at different points along the sand surface and also along the edge of the upstream membrane ...

Page 37: ...all will be considered to be vertical and will be simulated by a perforated metal sheet just like that used in Exercise C Draining Effect of a Tile Line to separate the upper pool from the body of sand In this experiment one sheet supported by the downstream overflow pipe separates the sand body from the downstream pool representing half of the trench cross section while the other separates the sa...

Page 38: ...al bottom of a submerged structure as the basis for the experiment In this special case all the pressure is uplift pressure Equipment Set Up The set up is basically the same as in Exercise B Seepage Through an Earth Dam with an additional element consisting of a simulated foundation of a structure The foundation is simulated by means of a PVC sheet about 6mm thick 460mm long and 150mm wide with bo...

Page 39: ...stretching out the flow lines This can be done with vertical or horizontal impermeable membranes aprons In most instances these are located upstream of the structure The influence of the flow line length on uplift pressure can be easily demonstrated In Exercise E Uplift Pressure on Foundation of Structures simply change the depth of penetration into the sand of the impermeable vertical screen For ...

Page 40: ...ost convenient way to do it is by using a downstream drain in the form of a tile line or a trench In this manner the flow lines are drawn downwards and the uplift pressure is reduced or even entirely eliminated This can be easily demonstrated by modifying the outlet from the downstream pool as in Exercise D Draining Effect of an Open Trench by employing the open trench principle ...

Page 41: ...by an impermeable PVC plate of the same type used in Exercise E Uplift Pressure on Foundation of Structures for simulating the foundation of a structure In this case however the plate is positioned vertically and should be at least 720mm long so that it can be fixed at the top of the tank by the special fittings provided at the mid point of the tank The wall segment is fixed vertically into the mi...

Page 42: ...ter levels in all standpipes connected to the wall segment should stabilise at the elevation of water in the upper pool This indicates that the wall is under full hydrostatic pressure In the second step remove the sealing strip from underneath the wall segment and let the water flow into the lower pool This is equivalent to draining off the toe of a retaining wall Next insert dye at several points...

Page 43: ...that the lower end of the former rests on top of the latter The contact area between the two plates should be sealed off The space downstream of the vertical plate is then filled with sand to about 75mm depth The sand rests on the perforated plate and at the far end of tank on the tank bottom The downstream overflow is adjusted to about 25mm above the sand surface while the upstream overflow is se...

Page 44: ...Armfield Instruction Manual 40 conditions of quick and if some object a concrete or steel cube for instance is placed on its top it will sink since the sand is floating and does not have any stability ...

Page 45: ...t of moist sand in the middle of the tank with slopes as steep as the material permits the overflow pipes being adjusted as in Exercise B Seepage Through an Earth Dam Water is poured into the lower pool and after it has reached the top of the overflow the input is transferred into the upper pool and maintained at a moderate rate The rising water level in the upper pool will gradually undercut the ...

Page 46: ...o its stability Downstream it acts to pull the sand more or less horizontally out of the dam The process continues gradually until the upper part of the dam loses stability and collapses Then the whole process starts again and proceeds upwards to the dam crest ...

Page 47: ...s follows not supplied 1 6mm bore PVC clear tube x 2m long 2 Positive Displacement Pump 3 Motor for Pump 4 Fine Mesh Terylene Cloth The clear PVC tube with the end covered in fine mesh Terylene cloth to prevent the ingress of soil is suspended in the centre of the tank with its covered end about 100mm from the bottom of the tank Space around the overflows is kept free by using vertical sheets of p...

Page 48: ...d the inlet feed water adjusted to give a balanced water table level around the overflow The experiment may be extended to demonstrate de watering of a site by using two adjacent wells In this instance it will be necessary to feed water to the area adjacent to the overflow at each end of the tank This will preserve the water table adjacent to the de watered site ...

Page 49: ...e West Street Ringwood Hampshire England BH24 1DY Tel 44 0 1425 478781 Fax 44 0 1425 470916 Email sales armfield co uk support armfield co uk Web http www armfield co uk US Office Armfield Inc 9 Trenton Lakewood Road Clarksburg NJ 08510 Tel Fax 609 208 2800 Email info armfieldinc com ...

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