Roads and Driveways
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Junctions to main roads - Council will generally advise or provide conditions to a development application when specific design of junctions to main roads are required. These may inculude
BAL /BAR - a basic left turn and basic right turn
AUL/AUR - Auxilliary
CH - Channelised
The Roads and Traffic Authority (RTA) will generally review road designs. For major junctions eg to the Princes highway or the Monaro highway a more extensive process with RTA approvals required along with the developer entering into a WAD.
Driveways - There are usually council geometric requirements on residential driveways such as the maximum slope. Bega Valley Shire Council has standard details on drawings 1691 and 1692
Road Design
Horizontal Alignment
Vertical Alignment
Cross section
Safety Barriers
Compaction
Soils can be compacted by processes such as rolling and vibration. The level of compaction is measured by its increase in density. Moisture is an important part of the compaction process and a particular type of soil will have a particular Optimum Moisture Content (OMC). In general density will increase with increasing moisture content until it reaches its OMC and then will decrease with further moisture. Optimum Moisture Content by definition gives the highest density but this is not necesarily at the highest soil strength.
The highest density is called the Maximum Dry Density (MDD).
In construction it is generally the aim to compact at OMC to have an efficient process. Compaction though can be achieved by compacting at other moisture contents and most of the time it isn't important how the compaction was achieved but that it was achieved. For example the compaction might be achieved with 4 passes of a roller at OMC or with 6 passes of a roller at a moisture content above or below optimum.
Different materials have different compaction curves. For example a Sandy Clay may achieve a dry density of 1750 kg/m^3 when compacted at an OMC of 17% whereas a heavy clay may achieve only 1650kg/m^3 at an OMC of 22%.
Compaction Vs Consolidation
Compaction is a process where air is removed from soil without significantly altering the moisture content. This is typically by tamping , rolling , impact or vibration.
Consolidation is a process where primarily water is removed from soil due to an imposed long term static stress.
Earthworks specifications would refer to compaction only and not to consolidation.
There are two basic types of compaction control tests destructive and non destructive.
Sand replacement is a destructive method of measuring compaction. It involves excavation and removal of some of the fill material. Once the hole is excavated the weight and moisture content of the material removed is determined. The volume of the hole is then determined by pouring in sand. The total density and relative compaction can then be calculated.
Nuclear techniques are non destructive and require calibration against materials of a known density.
Australian Standard AS3798 Guidelines on Earthworks for commercial and residential developments although proposing minimum relative compaction for pavements of 98% does state in its scope (clause 1.1) that it is 'not intended to be used for pavements, major roadworks or water-retaining structures'.
Modified Vs Standard Compaction Tests
The Standard proctor compaction test developed in the 1930's is a laboratory test which uses a 2.7kg hammer mass to impart 596 kJ/m^3 of compaction energy to the sample. The Modified compaction test is a later development designed to account for heavier equipment. It imparts 2703 kJ/m^3 of compaction energy to the sample.
There are some instances where the modified test should be avoided.
There is generally no direct relationship between Standard and Modified compaction since the material itself is a siginificant variable. A relationship might only hold for a single material.
Degree Of Saturation (DOS)
DOS = volume of water / volume of voids When DOS = 100% voids are completely filled with water (no air)
California Bearing Ratio (CBR)
CBR as the name suggests was developed in California. It is widely used in pavement design. It is a quasi-static bearing capacity test and is a ratio to an ideal specimen. It is not a fundamental engineering property apart from empirical correlations.
CBR's can be tested soaked or unsoaked. Soaking will produce a lower CBR value. Soaked CBR testing should be undertaken when the pavement pavement being designed is within a wet area such as a floodway, where there is a high water table, where there is poor drainage or seepage likely. Unsoaked values would only be used in situations where dry conditions are a certainty. An area which has <500mm median annual rainfall and has excellent drainage may be a candidate for the use of unsoaked CBRs.
Proof Rolling
The objective of proof rolling is to identify and correct problem areas prior to the placement and compaction of stronger , more expensive materials.
Proof Rolling equipment as given in AS3798
Static smooth drum roller with minimum mass 12t and 6t/m width of wheel
Pneumatic tyre roller with minimum mass 20t and 450kPa / tyre
Truck with minimum mass 8t rear axle and 550 kPa / tyre
A full water truck could be used for this test (with 2/3 = 8t of load on rear axle).
Road and Earthworks Design
Tasman engineering consultants use the Autodesk product 'Civil 3D' to model and design roads, intersections and earthworks. Utilising this product road alignments, cross sections and long sections can be quickly and easily produced.
