LDCA warns of settlement
Below average rainfall and above average temperatures could lead to the settlement of trench lines, warns the LDCA
and other soil or turf damage may take place if work is carried out when there is a high water table, puddles or saturated soil conditions. All wheeled equipment should use low ground pressure tyres. When draining through
existing turf, every care should be taken to prevent contamination of the surface with soil or backfill materials. Excavation of the drainage trench should be carried out using a continuous chain trencher fitted with laser controlled grading equipment and a spoil removal conveyor to prevent contaminating the surface with subsoil. Drainage pipe should be laid on a pre-formed trench bed, and backfilled as specified using machinery specifically designed to place backfill into the trench without spillage of the backfill onto the surface.
Secondary drainage treatments
Secondary drainage, such as sand slitting or banding, may be added to a primary piped drainage system to increase surface infiltration and improve drainage of the surface and upper part of the growing medium. “Sand slitting” refers to
narrow trenches from which
the soil has been removed, usually 50mm wide and 200- 300mm deep, partly backfilled with gravel and topped with sand.
Gravel or sand banding
refers to where soil has been displaced by a knife or tine and a band of gravel or sand is placed simultaneously.
Maintaining the drainage
Settlement of drain lines may occur as a result of drier soil conditions and/or periods of dry weather. As this would affect the playing surface, it is important that topping up is carried out as this becomes apparent. Following drainage operations, regular sand top dressing of the surface is recommended.
Surface compaction and smearing, due to intensive use in wet weather, significantly reduces infiltration and can cause waterlogging. Various types of machines are available to introduce tines into the surface to relieve
compaction in the surface and topsoil layers and restore drainage infiltration.
Information on drainage and a list of contractors is available from the Land Drainage Contractors Association website
www.ldca.org and click on Members Directory. Tel: 01327 263264 Email:
secretary@ldca.org
WITH below average rainfall and above average temperatures already this year, settlement of drainage trench lines could again be a problem in 2011, as it was last year. The early signs are that, if the current dry weather continues, soil shrinkage causing settlement of drainage trench lines on sports and amenity turf is likely to be a problem in some areas.
Operators of sports facilities should be aware that the problem can occur, especially on clay soil sites. This can affect new drainage installations and possibly existing ones in severe drought conditions. Those having drainage installed should ensure that remedial measures to cater for possible trench settlement are agreed with the drainage contractor in advance. Those with an existing drainage scheme should seek advice on how best to minimise the problem, if it occurs. Prolonged periods of dry
weather can result in a phenomenon associated with soils of high plasticity and expansion related to moisture content. Shrinkage of such soils - due to soil and ground moisture deficit - can result in subsidence of buildings, cracking of roads and, in respect of trenching, settlement of trench lines. Settlement or cracking within trench lines in agricultural environments is not generally a problem and, indeed, is considered beneficial to the restructuring of consolidated or compacted soils. However, the leisure and amenity sector can suffer to varying degrees and, in some extreme cases, sports turf facilities may be rendered no longer fit for use due to the hazard caused by cracking or settled trench lines. The clay soils of the British Isles
retain soil moisture with great tenacity. Water will only be drained from a soil once field capacity has been achieved; the drainage scheme will remove surplus soil water.
A sports turf facility equipped with a drainage scheme will typically have a network of mains and lateral pipe work spaced at between 3 and 10 metre centres. The pipes are installed within excavated trenches and are backfilled with aggregate. Tri-axial shrinkage of the clay soils leads to increased trench widths allowing the backfill materials to settle, causing depressions on the
surface. In addition to primary piped
systems, secondary slit systems are often installed, offering improved surface drainage characteristics through either excavated or injected gravel or sand slits. Clay soil shrinkage promotes natural cracking of the soils; these cracks will take the line of least structural resistance - specifically trench or slit lines. Exceptionally dry conditions can cause the drying of soil profiles to unprecedented depths, with very low soil moisture content at depths exceeding 600mm. The resultant soil shrinkage and cracking could generate settlement of trench and slit lines on both newly installed and, more surprisingly, existing established schemes which have been installed for a number of years. Where trench or slit lines have grassed over, this settlement can present an unseen hazard to players on sportsturf and to horses on equestrian facilities and racecourses. Even in correctly installed drainage schemes, some settlement can occur naturally to a greater or lesser extent in most years. Once settlement has occurred, remediation measures are limited to topping up. On intensive schemes, general sand or rootzone topdressing may be an option, but deep settlement will require specific application to individual trench lines by means of specialist equipment operated by specialist contractors.
Information on drainage and a list of contractors is available from the Land Drainage Contractors Association website
www.ldca.org and click on Members Directory. Email:
secretary@ldca.org Web:
www.ldca.org
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99 |
Page 100 |
Page 101 |
Page 102 |
Page 103 |
Page 104 |
Page 105 |
Page 106 |
Page 107 |
Page 108 |
Page 109 |
Page 110 |
Page 111 |
Page 112 |
Page 113 |
Page 114 |
Page 115 |
Page 116 |
Page 117 |
Page 118 |
Page 119 |
Page 120 |
Page 121 |
Page 122 |
Page 123 |
Page 124 |
Page 125 |
Page 126 |
Page 127 |
Page 128 |
Page 129 |
Page 130 |
Page 131 |
Page 132 |
Page 133 |
Page 134 |
Page 135 |
Page 136 |
Page 137 |
Page 138 |
Page 139 |
Page 140 |
Page 141 |
Page 142 |
Page 143 |
Page 144 |
Page 145 |
Page 146 |
Page 147 |
Page 148