Where the sub base is laid in two layers as upper sub base and lower sub base the thickness of each layer shall not be less than 150 mm. If the traffice is less than 1015 vpd, single layer base course should sufice 1. Granularsubbase is often used as subbase layer of the pavement. In both layers, the ability to redistribute loads needs to be replicated in any reinstatement. Icqa3051 granular pavement base and subbase materials. The details and results of this specific portion of the study have been the subject of a previous technical paper 4 and only a brief summary is presented here. Personnel of 30 highway departments were interviewed by project personnel. Subbase and subgrade performance investigation and design. The granular subbase is supposed to be a lower quality material than the granular base. In order to do this, an investigation of the factors affecting mr was undertaken. These quarries provide the sub base material for road construction in ibague city located in colombia. Granular material, compacted to a thickness of 100 mm minimum. Farm roads carriageway 3500 shoulder 500 shoulder 500 ldrain 600 sub base 140mm base course 120mm hard shoulder compacted granular soil soling farm road subgrade cbr 7% note. This specification is written as a provincialoriented specification.
When the source of material for a granular subbase has. Road construction method statement method statement hq. Granular bases and subbases industrial resources council. Mechanistically, this configuration provides a stronger reaction platform than unbound subgrades or sub bases, allowing increased granular base compaction during construction, and it also has the potential to take advantage of the compressive stresses induced in the granular aggregate base owing to the presence of the stiff underlying layer. If unstable material is to be excavated from the embankment or other specialized procedures.
Unless specified otherwise in section 01001 supplemental conditions, shown on the drawings or directed by the engineer, base course granular material shall be a base. This simple procedure consisted of coring out approximately a 411 diameter hole to a depth of 45, filling the hole with 1 liter of water, and timing how long it took to drain from the hole. Granular subbase gsbspecification and construction procedure. Testing and evaluation of reclaimed materials as aggregate. Reclmmed concrete material user guidelme granular base. The material should be tested for cbr at the dry density and. The completed sub base courses will be tested for the required thickness and surface before acceptance. How to calculate the quantity, compaction factor value and loose thickness of gsb. The sub base aggregate or sub base mix in place on the road during and after spreading and compacting. Pdf the main purpose of providing granular subbase gsb in highway pavements is to serve stability and drainage functions. Granular soils granular soils range in particle size from.
Subbase is an important layer in flexible pavement which functions as a secondary load spreading layer, drainage layer and as a preparatory platform for the construction of road base. May 15, 2018 however, it is well known that the gradation of granular materials has a dramatic impact on its performance. Providing and laying granular subbase course gsb to. If unstable material is to be excavated from the embankment or other specialized procedures are required, the work will be paid for on the basis of extra work. Granular subbase is also known as road rock, road stone, base stone, class a road stone, class a road rock, shoulder stone, surfacing stone, modified subbase, and granular subbase. Used in roads, parking lots, and driveway construction. Materials and research department manual of materials and tests mrdtm and all. Annex a4 new table added for principal to nominate use of macadam materials. Recommended grading bands for compactable granular materials are shown in fig. In present study drainage characteristics are to be determined interms of permeability characteristics of gsb mix by preparing specimens fulfilling the required gradation of granular sub base layer. The sub base thickness will depend on loading and on the strength of the subgrade. In the present study recycled aggregate are used in granular sub base gsb.
Section 6f1 pavement subbase design and construction. The surface of the formation for a width of subbase, which. Sub grade preparation of sub grade by excavating earth to depth. This report is brought to you for free and open access by the institute for. Laboratory studies on strength and bearing capacity of gsb. Some soils or degrees of gradient may not be suitable for permeable paving. Granular sub base bluemetal aggregate is often the main loadbearing layer of the pavement. In a pavement structure, the granular base and subbase are compacted aggregate layers between the asphalt concrete or the portland cement concrete pavement layers and the underlying subgrade material. Design guide for subgrades and subbases iowa state university. Granular sub base raja44 civilenvironmental 28 sep 02 08. Granular subbase base gsb quantity compaction factor. Comparison of permeability characteristics of granular sub. Granular subbase gsbspecification and construction.
Geocellular box systems incorporate a greater storage capacity and may reduce the required depth of the granular sub base. Subbases may be constructed of granular materials, cementtreated. Characteristics sand and gravel obtain maximum density in either a fully dry or saturated state. Granular sub base codes and standards general discussion. Sub base selection and placement the sub base must be wellgraded, compactable and for permanent works, capable of transporting rising water and resistant to longterm degradation. Granular soils are known for their waterdraining properties. Superior quality ordovician dolomitic limestone road rock base stone roadrock is comprised of various fractured pieces of limestone, and isblended with a specified amount of limestone fines. Pdf the main purpose of providing granular sub base gsb in highway pavements is to serve stability and drainage functions.
The authors analyzed the results of a number of standard granular laboratory tests and concluded that, with proper quality control practices during crushing and manufacturing, rca is a viable and economical solution for conserving. Oct 24, 2019 granular sub base is often used as subbase layer of the pavement. High performance granular base and subbase materials incorporating reclaimed asphalt concrete pavement author. Granular base equivalency or granular base equivalence gbe is a measure of total pavement thickness.
Use of materials like brick material, kankar and crushed concrete shall be permitted in the lower sub base. From the relatively large data base that was generated from the study, the following specific objectives were studied in the project. Gbe translates the thickness of different road layers to a number using a set of coe. The main role of this layer is to spread evenly the load over the subgrade. The benefits of this form of construction are also discussed. Calcium manual published by the chief inspector of explosive of india. Timber used shall be well seasoned, free from loose knots, projecting nails, splits or.
The report notes that few of these design manuals produce savings in pavement thickness from the use of stabilised sub bases even though they are frequently recognised to have higher strengths than unbound granular materials. Bases and subbases for concrete pavement federal highway. The sub base layer is often the main loadbearing layer of a pavement. If i refer to the 1993 aashto guide for design of pavement structures to obtain the layer coefficients, i get the following. Granular sub base gsb materials shall be free from organic or other deleterious constituents. Best value granular material for road foundations january 2012 6. Use of recycled aggregate is not very common in india and other developing. It shall be free from organic or other deleterious materials. Technical specification road work granular subbase gsb. The most common types of sub base are a crushed miscellaneous base cmb, a class ii road base, or a decomposed granite dg. The base course is often a layer of granular material, innnediately below the surface course, whose function is to distribute intense surface loads over a large area of the subgrade. Granular sub base material typically underlaying granular a.
Chapter three granular base and subbase construction practices. Improvement of granular base course materials with portland. Technical specifications for granular sub base gsb civil4m. The quality of subbase is very important for the useful life of the road.
It shall confirm the grading requirements as per morth v table 4001. This purpose is fulfilled by using a machine known as aggregate distributor. Introduction and terminology page 1 key point page every foundation for a concrete pavement structure should be free from abrupt. Jul 02, 1991 permeability of a granular subbase material, a procedure was developed to obtain a relative idea of the permeability of the material. Posted by pattison website staff comments off on granular subbase ordovician dolomitic limestone granular subbase ordovician dolomitic limestone.
Aggregate or granular subbase as shown on the drawings. Just a few centimetres of the right type of material, compacted in the right way, can turn an unreliable, rutprone sub grade into a surface capable of carrying cars and other vehicles. Specifically, a region can be partitioned into a covering of sub regions, with each sub region containing both solid and void. Granular materialsubbase course materials engineering. Pdf evaluation of subbase materials for mechanistic. Trbs national cooperative highway research program nchrp. The loadbearing function and capacity of even a 100mm sub base should not be underestimated. The development of a performance specification for granular. The materials functionality is a result of its quality, designed gradation, thickness, and method of placement. This work shall consist of laying and compacting well graded material on prepared subgrade in accordance with the. Granular sub base gsb sub base gsb the full form of gsb is granular sub base. The material quality requirements for a subbase are not as strict as those for a base since. The work shall consist of laying and compacting of wellgraded materials. Material layer coefficients of unbound granular materials.
Free draining daylighted subbases are the reasonable alternative to rapidly draining. If a geogrid is not used, the total granular sub base layer thickness must be increased by minimum 50%. This specification covers the requirements for granular aggregate materials for use in subgrade, subbase, base, gravel surface course, shouldering and bedding and backfill to sewers, culverts, and other structures. It can be seen that the granular material achieves its densest state at 0% moisture. Read chapter chapter three granular base and subbase construction practices. The materials used may be either unbound granular, or cementbound. The subgrade, the layer of soil on which the subbase or pavement is built. Sri guru enterprises offering gray granular sub base gsb, for construction at rs 32cubic feet in chennai, tamil nadu. The use of the geogrid will therefore greatly reduce the aggregate costs. Pdf design charts for drainage capacities of granular subbases. The basics forecasting with financial accounts, analyzing with labor and equipment activity actuals. Sieve per cent by weight passing the sieve grading iv grading v grading vi 75 mm 100 53 mm 100 80100 100 26. The sub base material shall be hard, durable and clean.
Our crushing plant features compression crushing technology that limits fines generation and increase. Motor grader is a machine used to spread the sub base material to uniform thickness and specified cross slope by adjusting the blade of the grader. The granular sub base gsb layers are used in the flexible pavements to provide a stresstransmitting medium to spread the surface wheel load to a large area so as to prevent the shear and consolidation deformations. Aggregate used for aggregate subbase to be free from vegetation matter and other. Brick metal, kankar and crushed concrete is permitted in lower sub base. The base is the load bearing layer immediately below the pavement layers, and serves to provide strength and support to the overlying pavement. Nov 05, 2016 in granular sub base gsb construction, aggregates are needed to be distributed according to their sizes. Gray granular sub base gsb, for construction, rs 32 cubic. The gsb is prepared using the 20 mm fresh aggregates and recycled aggregates to evaluate the usability of recycled aggregates in pavement construction. The materials will be delivered to the site by tipper lorries and spread and leveled by means of a back pusher for the full width of the pavement. Annex a2 table modified to clarify that requirement for additional pretreatment cycles is to be nominated by principal. Recycled aggregate, granular sub base, road construction i. Chapter three granular base and subbase construction.
Comparison of permeability characteristics of granular sub base. A sub base is used to replace the expansive native soil with a nonexpansive surface which will help to ensure an artificial grass installation will continue to look good for the duration of its 15 to 20year useful life. It is designed to evenly spread the load of the paving, and any traffic thereon, to the sub grade below. If the contractor or supplier wishes to propose new unique materials for acceptance, contact pavement.
In first phase the tests are conducted on 20 mm fresh and recycled. If construction axle loads are to be greater than 6 tonne approx. Hbms can be used as an alternative to granular sub base material in the options given in the specification for the reinstatement of openings in highways. For twoproduct crushed base course structures, the lower layer is usually more free draining and coarser with a max nominal size of 50mm or 75mm. Base course granular material shall be classified on the basis of the aggregate gradation as shown in part 2. Major emphasis during the early stages of the research was placed on accumulation and analysis of information on current practices of state highway departments. Bound a bound granular material utilizes a binding agent to address deficiencies in the native granular material in order to properly perform as a base course. Of a known suitability for use in sub bases, free from excessive dust, well graded. Granular sub base is laid below the base layer and above the subgrade layer. Type 1 unbound mixture to highways agency specification for highway works, clauses 801 and 803.
It shall be granular material and shall be free from organic material, clay balls, and any other deleterious substances. Granular sub base gsb specifications, gsb grading, layer. This paper presents a laboratory study of strength of granular sub base gsb underlain by a sub grade layer in terms of cbr and. Testing curves are relatively flat so density can be. Pattison produces granular subbase in our stateoftheart, jawcone crushing plant. Granular subbase and equipments used for its construction. The subbase shall consist of a uniform mixture of granular material placed on a subgrade, uniformly moistened, shaped, and compacted, all in accordance with the contract documents. The california bearing ratio cbr test is the most widely used method of evaluating subgrade, sub base, and basecourse materials in pavements, but has many limitations, primarily because it is arbitrary.
Since pavement is composed of multiple layers with different physical properties, its total thickness is measured by gbe. The material used in sub grade is natural sand, moorum, gravel, crushed stone, crushed slag. These granular sub bases are of type sbg 38 see figures 1 and 2 according to the construction specifications for roads of invias 20 3 4. The protection of edges of granular sub base extended over the full formation as shown in the drawing shall be considered incidental to the work providing granular sub base and as such no extra payment shall be made for the same. The primary requirement for an aggregate to be used as base course material is stability, which may be defined as the ability to transfer. To determine from laboratory resilientmodulus results, typical resilientmodulus relation of granular base and subbase materials used by test ships msha, 2. Granular sub base bluemetal aggregate, packaging type. A wellconstructed sub base will aid drainage and prevent settlement and channelisation the phenomenon common on cheap installations of block paving, where two ruts develop in the paving. Introduction the recycling of aggregate is a process in which used aggregate is reused for new construction. Its role is to spread the load evenly over the subgrade. Therefore, base and subbase materials were sampled from three regions in the state and evaluated under the following performance tests. Oakdale primary school, peterborough civil engineering nbs. Granular sub base shall be measured as finished work in position in cubic meters.
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