advanced drainage system - Polypipe

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General Structural Design 3.2 Pipe structural performance Pipes are typically categorised as rigid or flexible, depending upon the material from which they are manufactured. Rigid pipes, such as concrete, have a high inherent strength and resist applied loading by a bending action within the pipe walls. They are generally stiffer than Compressible Board the pipe surround material, Compressible in Board particular the sidefill, and consequently Trench Trench Support Support support a higher load than the sidefill material. For design purposes, they are generally assumed to support the entire Compressible Board Compressible Board vertical load transmitted through the backfill material placed above the level of the pipe crown (Figure 1B)*. Failure of rigid pipes occurs when the vertical 100mm loading exceeds its load capacity and causes fracture of the pipe wall 150mm (Figure 150mm 2B*). In order to perform satisfactorily the pipe must therefore be strong enough to support the design loading, in addition to being laid on a stiff bedding material, 150mm 150mm 150mm which must ultimately support the 200mm 200mm 200mm loads transmitted through the pipes. 150mm 150mm The bedding must not allow differential settlement of the pipeline to occur, since this 100mm would result in stress concentrations in the pipe 150mm 150mm 150mm wall and result in failure. 1ess than 1.2m Minimum 150mm 150mm 1ess than 1.2m 1ess than 1.2m Minimum 150mm 150mm 150mm 150mm 150mm 150mm Compared with rigid pipes, flexible pipes 100mm are versatile and have important structural performance advantages. Unlike rigid pipes, flexible pipes have excellent resistance to differential settlement. Plastic pipes, when overloaded, will simply deform (Figure 2A) further to generate 150mm greater passive earth pressures until the system 200mm regains equilibrium. In contrast, overloaded rigid Concrete Concrete Grade 150mm C20 150mm Grade C20 pipes are subject to fracture that can result in catastrophic failure of the system. 100mm 150mm 1ess than 1.2m 150mm 150mm 150mm A. Flexible B. Rigid A. A. Flexible B. B. Rigid Rigid A. Flexible B. Rigid Figure 1* - Illustration of performance mechanisms Figure 2* - Illustration of overloading effect As a consequence of the differing performance mechanisms, flexible pipes have structural performance advantages over rigid pipe systems. • Flexible pipes offer excellent resistance to differential settlement and ground movement. • When overloaded, rigid pipes are subject to fracture and failure of the system. Plastic pipes, when overloaded, will deflect further to generate greater passive earth pressures until the system regains equilibrium. 48 Pipe deformation The deformation of flexible pipes under load results in the ovalisation of the pipe (a reduction in the vertical diameter and an increase in the horizontal diameter). As the horizontal diameter of the pipe increases, it derives support from the sidefill and trench wall. This passive earth pressure increases as the pipe deforms further until the pipe-soil system comes into equilibrium. Further deformation will not occur thereafter unless a higher vertical load is applied to the pipe-soil system or consolidation (or creep) of the materials occurs over a long period of time. It is internationally recognised that when a pipe is installed in accordance with an appropriate code of practice, increases in deflection virtually stops after a short period of time. The duration of time is dependent on soil and installation conditions but generally does not exceed two years. Serviceability limits Deformation of flexible pipes must occur if the pipe-soil system is to reach equilibrium. Therefore deformation is not detrimental, but a natural action allowed for in flexible pipe design. European research on flexible pipes has shown that pipe deformations of more than 30% have occurred in practice without signs of structural failure. However, it is accepted that a limit on vertical deformation is necessary to ensure adequate long term pipe performance. Appropriate deflection (serviceability) limits should be set on a case by case basis. For example, greater limits may be allowable in a deep landfill installation compared to a pipe buried at a shallow depth under a road. Deflection limits within the UK varies, depending on the relevant adopting authority. For design purposes the Highways Agency specifies a maximum allowable deformation of 5% for thermoplastic structured walled pipes, while the water industry tends to specify 6%.
General Structural Design 3.2 Methods of flexible pipe design Numerous methods of pipeline design have been developed, influenced by the prevailing conditions in the country in which the development occurred. The most established method of design for flexible pipes is that produced by Spangler. Although originally developed for large diameter thin-walled corrugated steel culverts under embankment conditions, the method has been adopted in much of the world for all types of flexible pipes. This design method is recommended for the UK in BS EN 1295: Part 1 and forms the basis of this section. Prediction of long term pipe deformation BS EN 1295-1:1998; “Structural design of buried pipelines under various conditions of loading.”; is the standard used within the UK in assessing pipeline design. The various different types of pipe systems available are differentiated according to cross-sectional behaviour as rigid, semi-rigid or flexible. For design purposes, the flexible calculation procedure is normally used for pipes manufactured from steel, thermoplastic and GRP. The following procedure is extracted from BS EN 1295-1, Clause NA.6: Ovalization, Kx [(DLPe)+Ps] = (Clause NA.6.2.4; BS EN 1295-1) D (8EI/D 3 )+ (0.061E’) Where: = Pipe deflection D = Pipe diameter Pe = Vertical Soil Pressure = H PS = Surcharge pressure, due to vehicle wheels (Figure NA. 6; BS EN 1295-1) DL Kx ∝ = Deflection lag factor = 1 (Non pressure application) (Table NA. 6; BS EN 1295-1) = Deflection Co-efficient = 0.083 (Based on a Class S1 embedment) (Table NA. 6; BS EN 1295-1) EI/D 3 = Product modulus (Polypipe Civils Technical Data) E’ = Overall soil modulus Overall Soil Modulus, E’ = E’2 CL Where: E’2 = Bed & surround soil modulus (Table NA. 6; BS EN 1295-1) CL = Soil modulus adjustment factor Soil modulus adjustment factor, CL = 0.985 + (0.544 Bd/Bc) [1.985-0.456 (Bd/Bc)] (E’2/E’3) - [1-(Bd/Bc)] (Clause NA.6.2.4; BS EN 1295-1) Where: Bc = Pipe O.D Bd = Trench width = Bc + 300mm E’3 = Native Soil Modulus (Table NA.1; BS EN 1295-1) 49
Page 1 and 2: Uniclass G581 C1/SfB (52.3) October
Page 3 and 4: Contents Company Introduction 3 Str
Page 5 and 6: CONTACTS Polypipe Civils Division P
Page 7 and 8: Ridgidrain introduction 1.1 Ridgidr
Page 9 and 10: BBA BRITISH BOARD OF Ridgidrain AGR
Page 11 and 12: Ridgidrain Pipe Dimensions 1.2 90°
Page 13 and 14: Ridgidrain Pipe Dimensions 1.2 90°
Page 15 and 16: Pipe detail specifications Ridgidra
Page 17 and 18: Ridgidrain Pipe Design Properties 1
Page 19 and 20: Ridgidrain Installation 1.5 Standar
Page 21 and 22: Ridgidrain Installation 1.5 Midi-gu
Page 23 and 24: Ridgidrain Installation 1.5 Special
Page 25 and 26: Ridgidrain Model Specification Clau
Page 27 and 28: Ridgisewer and Polysewer Introducti
Page 29 and 30: BBA BRITISH BOARD OF AGRÉMENT CERT
Page 31 and 32: Polysewer Pipe Dimensions 2.2 45°
Page 33 and 34: Ridgisewer Pipe Dimensions 2.2 Plai
Page 35 and 36: Ridgisewer Pipe Dimensions 2.2 90°
Page 37 and 38: Ridgisewer Pipe Dimensions 2.2 11.2
Page 39 and 40: Ridgisewer Pipe Dimensions 2.2 Rock
Page 41 and 42: Ridgisewer Pipe Specification 2.3 S
Page 43 and 44: 1ess than 1.2m Road Construction St
Page 45 and 46: Ridgisewer Installation 2.5 Concret
Page 47: General Introduction and Cover Dept
Page 51 and 52: General Structural Design 3.2 Figur
Page 53 and 54: General Structural Design 3.2 Figur
Page 55 and 56: General Structural Design 3.2 It sh
Page 57 and 58: General Structural Design 3.2 Table
Page 59 and 60: General Hydraulic Design 3.3 Hydrau
Page 61 and 62: 750 500 450 375 150 100 General Hyd
Page 63 and 64: General Properties 3.4 Urban draina
Page 65 and 66: General Properties 3.4 Abrasion Res
Page 67 and 68: General Properties 3.4 Chemical Res
Page 69 and 70: General Site Instructions 3.5 Gener
Page 71 and 72: General Site Instructions 3.5 Joint
Page 73 and 74: General Site Instructions 3.5 Recom
Page 75 and 76: General Maintenance 3.6 Maintenance
Page 77 and 78: FAQ Section 3.8 What special requir
Page 79 and 80: FAQ Section 3.8 Q. How are pre-fabr
Page 81 and 82: FAQ Section 3.8 b) Spigot and socke
Page 83 and 84: References 3.9 British Standards In

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