Master Plan of LAPSSET Highway
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Study for LAPSSET Corridor FS & Lamu Port MP & DD JPC & BAC/GKA JV ------------------------------------------------------------------------------------------------------------------------------------------------------- 25. Master Plan of LAPSSET Highway 25.1 Highway Planning and Design Considerations 25.1.1 Highway Alignment The general route of the corridor was selected and is described in Chapter 23 of this report. The alignment of the highway (both horizontal and vertical) was designed based on existing 1:50,000 or 1:100,000 together with aerial mapping terrain data and is part of the preliminary design. Figure 25.1-1 Highway Alignment Plan Source: JPC Final FS & MP Report (Vol. III) 25.1 - 1 May, 2011 Study for LAPSSET Corridor FS & Lamu Port MP & DD JPC & BAC/GKA JV ------------------------------------------------------------------------------------------------------------------------------------------------------- 25.1.2 Design Standards The highway design guidelines are shown in Table 25.1-1 below. Table 25.1-1 Design Guidelines Description Design Standard Reference 140 km/hr (except in mountainous Design Speed areas) Design Vehicle WB -15 (semi-trailer) AASHTO (RDM) Superelevation Max e = 6 % RDM Rate of change of Max ∆s = 0.5 % RDM /AASHTO superelevation Min ∆s = 0.3 % Cross fall 2.5 % RDM Horizontal Curve Min radius (R) = 1,400m RDM Stopping = 350 m Sight Distance RDM Passing = 775 m Max grade (g) = 3 % Grade AASHTO/RDM Min grade (g) = 0.5% Stopping sight distance on crest K value = 186 Vertical Curve AASHTO Stopping sight distance on sag K value = 92 Source: JPC The design standards of the Ministry of Roads Design Manuals (RDM) are given higher precedence as they are customised for local conditions with the AASHTO manuals being used in instances where the local manuals are inadequate in regard to urban sections and modern interchanges. 25.1.3 Cross Section Currently, traffic data on the existing segments of the highway are insufficient to make meaningful traffic forecasts. Results of economic analysis indicate that a 2-way single carriageway will adequately cater for traffic generated as a result of construction of Lamu Port up to the year 2030. Table 25.1-2 shows the cargo forecast for the critical section between Lamu and Garissa. Table 25.1-2 Cargo Forecast for Lamu-Garissa Section Unit: million tonnes Description Year 2020 (ton/yr) Year 2030 (ton/yr) Imports 2.9 4.3 Exports 2.8 5.2 TOTAL 5.7 9.5 Source: JPC Using a conversion factor of 3.5 the traffic volume at the year 2030 will be 7,120 pcu/day. According to RDM 3 a dual carriage should be considered when traffic volumes exceed 8,000 pcu/day. Based on the projected traffic at year 2030 it will be necessary to expand the Lamu-Garissa section into a dual carriage (4-lane 2-way). A typical 2-lane single carriageway is shown in Figures 25.1-2, 25.1-3 below. In urban centres along the corridor urban design standards shall apply with the provision of appropriate service lanes, Non- Motorized Transport facilities and lighting. Final FS & MP Report (Vol. III) 25.1 - 2 May, 2011 Study for LAPSSET Corridor FS & Lamu Port MP & DD JPC & BAC/GKA JV ------------------------------------------------------------------------------------------------------------------------------------------------------- Figure 25.1-2 Typical Single Carriageway Cross-section (Fill) Source: JPC Figure 25.1-3 Typical Single Carriageway Cross-section (Cut) Source: JPC Cut and embankment slopes may vary depending on particular site conditions. 25.1.4 Junctions It is inevitable that the highway will cut through different classes of roads and therefore the need for junctions. All the junctions are planned to be at-grade with the exception of Lamu Metropolis where it is proposed to construct interchanges on two locations in the year 2030. 25.1.5 Bridges and Major Drainage Structures An inventory was carried out using the acquired aerial photography of the selected route. From the analysis it is noted that 56 bridges will be required, with spans ranging between 30m and 140m. Construction of more than 160 box culverts will also be required in addition to installation of pipe culverts. Majority of these structures will be located on the rugged section between Isiolo and Lokichokio. The choice between use of bridges or culverts shall be determined by the hydrology and geology at each site. Typical bridge and culvert sections are shown in Figure 25.1-4 below. CL ROAD FILL MATERIAL 300.0 300.0 WINGWALL 2000.0 SCOUR PROTECTION TOE BEAM SCOUR PROTECTION 300 CROSSSECTION SECTION Final FS & MP Report (Vol. III) 25.1 - 3 May, 2011 Study for LAPSSET Corridor FS & Lamu Port MP & DD JPC & BAC/GKA JV ------------------------------------------------------------------------------------------------------------------------------------------------------- CL CULVERT FINISHED ROAD LEVEL FILL MATERIAL ELEVATIONSECTION C C C L ABUTMENT L PIER L ABUTMENT 3000.0 3000.0 3000.0 2000.0 2000.0 2000.0 2000.0 2000.0 2000.0 2000.0 2000.0 2000.0 2000.0 2000.0 2000.0 3000.0 3000.0 3000.0 EXTEND DETERMINED ON SITE EXTEND DETERMINED ON SITE FINISHED ROAD LEVEL END DIAPHRAM BEAM END DIAPHRAM BEAM FILL MATERIAL FIXED BEARINGS MAIN BEAMS H.F.L FREE BEARING FILL MATERIAL PRESTRESSED EXISTING GROUND LEVEL EXISTING GROUND LEVEL ABUTMENT WALL ABUTMENT WALL WEEP HOLES WEEP HOLES RIVER BED BRIDGEBRIDGE ELEVATION ELEVATION GI PIPE HANDRAIL GI PIPE HANDRAIL 50MM DIAMETER 50MM DIAMETER FLEXBEAM CL BRIDGE FLEXBEAM GUARDRAIL GUARDRAIL WALKWAY WALKWAY 2.5% 2.5% DRAIN PIPE DRAIN PIPE BRIDGEBRIDGE DECK ELEVATION ELEVATION Figure 25.1-4 Typical Box Culvert and RC Bridge Source: JPC 25.1.6 Preliminary Sub-grade Classification The LAPSSET corridor study does not cover the investigation of engineering characteristics of in situ soil or pavement construction materials. However to be able to generate preliminary cost estimates, a conceptual pavement design has been carried out using data generated from previous studies carried out by the geological and agricultural sectors such as the exploratory soil map of Kenya carried out in 1980 by the ministry of agriculture and the geological Mapping of Kenya as done by the Geological department in 1962. Although the proposed corridor traverses different geological areas from Lamu to the two border crossings of Nakodok and Moyale, broad distinctions can be made of the areas that are likely to bear the same characteristics in terms of in situ soil and material availability. The Segment between Isiolo and Moyale is currently being upgraded and is under various stages of design or construction. This study has broadly adopted the design standards for this segment and shall only consider the Lamu to Southern Sudan section. The section between Lamu and Isiolo can be taken as being homogenous with the remaining segment to Nadapal having two discernable geological regions as follows Isiolo to Lokori, Lokori to Nakodok. Table 25.1-3 Preliminary Subgrade Classification Section Geological Classification 1 Lamu to Isiolo Quaternary Sediments 2 Isiolo to Lokori Tertiary Volcanic 3 Lokori to Nakodok Quaternary Sediments Source: JPC Final FS & MP Report (Vol. III) 25.1 - 4 May, 2011 Study for LAPSSET Corridor FS & Lamu Port MP & DD JPC & BAC/GKA JV ------------------------------------------------------------------------------------------------------------------------------------------------------- Road development projects have been undertaken in the recent years which lie in the same regions as outlined above, in which intensive soil investigation was carried out and thus the engineering characteristics are likely to be similar to what is encountered along the corridor. These projects are outlined below. Table 25.1-4 Soil Investigations from other Projects Geological Subgrade Project Year Soil Type Classification Classification 1 Lamu – Witu - 2008 Silty sand Quaternary Average CBR is 13; S3 Kiunga1 Sediments 2 Loruk- Tot (B4) 2009 Clay soils Tertiary Volcanic Average CBR is 8; S2 Road2 Source: JPC For the preliminary designs, the subgrade classes for the three segments are thus assumed as shown in Table 25.1-3 and Table 25.1-4 above. Pavement Material Similar to the subgrade material, material sources for pavement layers are also distributed according to the geology of the area. In the Lamu -Witu - Kiunga road, the most readily available construction material was sand as no hard stone or gravel sites could be located. However suitable gravel sites can be located along the corridor from Garissa to Nakodok. The corridor also traverses regions that have no major permanent rivers to provide construction water. To this end, proper construction planning should enable damming of some seasonal rivers during the rainy season as well as sinking of boreholes. 25.1.7 Pavement Structure (1) Traffic Classification The table below illustrates the division of traffic classes’ in Kenya. Table 25.1-5 Traffic Class Traffic Class Cumulative No. of Standard Axles *ESA/day in year 1 T1 25 million-60 million 2,500-6,000 T2 10 million-25 million 1,000-2,500 T3 3 million-10 million 300-1,000 T4 1 million-3 million 100-300 T5 0.25 million-1 million 25-100 Source: RDM Part 3; 2.5.2 *ESA: Equivalent Standard Axle The cumulative standard axles, T, is obtained from the relationship. Where; t1, average daily number of standard axles in the first year after opening i = annual growth rate expressed as a decimal fraction N = Design period 1 Final Preliminary Design Engineering Report, Howard Humphreys and Stewart Scott, 2008. 2 Final Material Report Loruk-Tot, Abdul Associates, 2009. Final FS & MP Report (Vol. III) 25.1 - 5 May, 2011 Study for LAPSSET Corridor FS & Lamu Port MP & DD JPC & BAC/GKA JV ------------------------------------------------------------------------------------------------------------------------------------------------------- For the proposed LAPSSET highway, the damage is taken to be from Heavy Goods Vehicles (HGV) and Medium Goods Vehicles (MGV) only. Freight forecasts for the first year of opening are 3 million tons between Lamu and Garissa and 400,000 tons from Garissa northwards. It is thus proposed to use two pavement designs for the two sections as the loading is significantly varied.