Kent Design - Technical Appendix - Kent County Council

highways specification and construction
total cost incurred for any temporary traffic diversion order.
The Developer shall take particular care with the siting of all hoardings,
huts, plant, equipment, materials, stacks or heaps within the site, in
order that no danger or obstruction of visibility splays will be caused.
The Developer's agent and deputy shall be direct employees and shall
be entirely responsible for all liaison with the Engineer and where
specified, with the Police and local residents, in connection with any
traffic management system.
The Developer shall supply to the Engineer and the Police, the name and
telephone number of the Agent and a responsible person to act as
Deputy, one of whom must be available at all times in case of emergency.
The Developer shall allow for the installation and removal of any
traffic system involving restrictions or diversions to be carried out
under the direction of the Police.
The Developer shall not alter the layout of any traffic system without
the prior approval or direction of the Engineer.
3.2 CARRIAGEWAY PRELIMINARIES
3.2.1.1 GENERAL
The road/s shall be designed and constructed in accordance with the
approved plan/s and the requirements of this document.
Wherever possible the carriageway designs submitted should include
alternative construction thicknesses which make the maximum use of
the material available on the site for capping layer, sub-base or
roadbase by using permitted binders as described in this Section. In
addition the use of construction materials from sources which
maximise the amount of recycled materials is strongly encouraged,
the information to be supplied is stated in Section 1.3.
A pavement construction may need to satisfy 4 structural functions
• to provide a construction access route for the building works
• to provide a layer of sufficient stiffness so that subsequent
layers can be compacted properly
• to ensure that the traffic loads during the life of the
carriageway do not exceed the capability of the
construction to resist them without rutting or cracking.
• to provide adequate protection to frost susceptible soils
where necessary.
Alternatives are provided to assist the designer to select the
appropriate construction to satisfy all these requirements - see clause
3.3 (long and short term conditions).
Where the road is to be used as a short term construction access route
for the carriageway construction itself and/or the dwellings on the site,
the construction shall be organised to ensure that the subgrade and
paving materials are not overloaded, this will be evidenced by surface
rutting. This will require knowledge of the strength of the existing
subgrade (road foundation) at the time of construction.
Long term strength of the subgrade may be considerably different
from that pertaining at the time of construction. In summer it is likely
to be higher, at other times possibly lower. The long term strength of
the subgrade is evaluated using the equilibrium CBR or Stiffness
modulus. This is estimated in the Laboratory from the properties of
the subgrade soils.
It will be necessary to carry out carriageway designs for the construction
phase and for the long term condition and choose the more conservative
thickness of carriageway construction materials to be provided.
3.2.1.2 SOIL INVESTIGATION
Before any proposals are submitted a geotechnical investigation
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Kent
Design
should be carried out in order to assess a number of design issues
including the following:
Disposal of Surface Water Run-off
• depth to water table/perched water tables
• chemical contamination risk assessment
• suitability of strata for soakaway discharges in accordance
with Kent County Council’s ‘The Soakaway Design
Guide’
• consultation with the EA
• impact on adjacent developments, landslips, slopes etc
Sub-soil Drainage
• depth to water table/perched water table
• chemical attack on concrete pipes
• control of piping of fined grained soils
• treatment of solution features below drainage runs
• impact on adjacent developments, landslips, slopes etc
Earthworks
• cutting/embankment fill sideslopes
• frequency and treatment of solution features in cutting
slopes
• limits for earthworks acceptability/recycling on-site materials
• chemical contamination risk assessment
• need for ground improvement of foundation soils
• impact on adjacent developments
• geotechnical certification for strengthened
embankments/reinforced structures
Road Pavement Thickness
• short term/construction subgrade strength (see Kent
Pavement Design Guide)
• long term/equilibrium subgrade strength (see Kent
Pavement Design Guide)
• frost susceptibility of subgrade
• frequency and treatment of subgrade/soft spots features
underground/caves etc
• differential settlement risks/need for ground improvement
• suitability of subgrade soils for in-situ lime/cement
stabilisation (if required)
• shrinkage/swelling potential of over consolidated clays
(particularly when trees are removed)
The site investigation shall be carried out in accordance with the
Association of Geotechnical Specialists (AGS) Guidelines for Good
Practice in Site Investigation. The scale of the investigation will be
dependent upon the scale of the project but should typically
comprise a Desk Study followed by a ground investigation.
A Desk Study is beneficial for even small schemes with valuable data
readily available from Well Records, published records, geological
maps and memoirs, aerial photographs, local libraries, local authority
landfill databases, Speleological Society records and aquifer
protection maps. This literature search will help to optimise and
accelerate the planning of the ground investigation and the
subsequent design and construction process.