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The proposed Colombo Katunayake Expressway, which is approximately 24.6 km long, traverses from Peliyagoda area to Katunayake, predominantly over the flood plains of Kelani  river and canals of the area. The terrain encountered along the said alignment is predominantly marshy land comprising compressible soils at or near ground surface.

Investigation work of this project was comprised field as well as laboratory work. Field investigations, consisting of wash boring, rotary core drilling, hand auguring and field vane shear testing, along with sampling. The samples collected during field operations were used for classification tests and obtaining consolidation and strength parameters, in the laboratory.

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The design of ground improvement measures and  road embankments for the Colombo Katunayake Expressway Project – Phase I was undertaken by the Geotechnical Engineering Division of NBRO. The road trace traverses predominantly marshy and water logged areas. the road embankment is to be constructed using sea harvested sand. About three-quarters of the length of the proposed expressway are laid on soft and compressible sub-soils where the construction of the embankment will require ground improvement measures. The thickness of soft, highly compressible layers encountered varies from about 1m to 12m.

 the consultancy services performed by NBRO consist of: the detailed design of ground improvement, road embankments, and toe protection measures, the preparation of technical specifications, bills of quantities and a construction sequence for the ground improvement and road embankment construction.

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Road Development Authority has entrusted NBRO to conduct additional geotechnical investigations at the locations where proposed interchanges and overpasses of CKE. RDA established the field test locations. There are mainly at ; Northern approach to New Kelani bridge, Peliyagoda interchange to connect Al, A3 and CKE, Ja-ela interchange, Ktunayake interchange and Overpasses at Telangapatha road, Wanawasala, Welikadamulla, Mabole (CH. 7+135), Naiduwa road (CH. 7+500), Gunasekara Mawatha, Thotupola road, Kandana-Uswetikiyawa road, Kalaeliya (CH. 13+400) and Tudella-Pamunugama road.

These investigations were consisting of 74 wash boring, 31 core drilling, 98 augur boring in the field and index tests, consolidation tests, triaxial tests (UU, CU), uniaxial compressive tests (for rocks) and chemical tests in the laboratory. The NBRO laboratory handled the entire laboratory testing of this investigation programme.

Geotechnical Investigations for in Colombo Katunayake Expressway

The Government of Sri Lanka has awarded the design and construction of Colombo – Katunayake Expressway to Deawoo to Keangnam J/V and they entrusted NBRO to conduct the Geo-technical Investigation along the main carriageway, the access roads, interchange and structures.

The scope of the Geotechnical Investigation was to review of preliminary information on the surface and subsurface geotechnical condition by implementation of additional investigation, selection of geotechnical parameters to access ground improvement, embankment stability and for structural designs. Also establishment of general guidelines for design and construction of the CKE was done.

The investigation was consisting of 62 boreholes in the main road, 15 boreholes in Peliyagoda interchange, 58 (35+additial 23) rotary core drilling at bridge locations and 57 static cone penetration tests (SCPT) for soft ground. In the laboratory, index tests, consolidation tests (UU, CU), uniaxial compressive tests,(for rocks) and chemical tests were conducted. The NBRO laboratory handled the entire laboratory testing of this investigation programme.       

Geotechnical Investigations for CKE have been carried out in three stages previously and some of the embankments were partially constructed. The objective of this investigation is to asses the improvements of the previous soft ground treatment, confirm the existing information and obtain any missing information.

This investigation includes drilling programme by core drilling and non core drilling, field tests such as Standard Penetration Test, field vane shear Test, Pocket Penetrometer test, Static cone penetration test and field permeability tests.

 In the laboratory classification tests, shear strength tests, oedometer tests, rock strength tests and chemical tests in soil were performed. The entire fieldwork was carried out under the direct supervision of NBRO and our laboratory handled the entire laboratory testing programme.

The project has been identified as vitally important to improve the transportation system between capital city Colombo and the Southern province. NBRO conducted the investigations along the proposed road alignment to assess the engineering geological conditions and to obtain mechanical, physical and engineering properties of the subsoil, which shall be used to detailed design of the highway and its components.

The initial investigations comprised of auger boring and dynamic cone penetration tests (DCPT). The detailed programme comprised of case boring for major cuts, high embankments or embankments on soft foundations and for structures. These borings were supplimented by dynamic cone sounding (firm subsoil strata) and static cone sounding (soft strata). Also test pits were excavated in cut areas to obtain bulk samples of fill mateials tests.

 For boring, classifications testing were carried out in out areas, bloch soil samples were collected from the test pits and drained shear strengths were determined. And consolidation testing of soil cohesive strata was carried out at high embankment locations. Strength properties of materials from cuts will be determined from CBR testing, and the possible use of these materials sub-base was investigated with lime stabilization. The suitably of the rock  excavated from cuts will be confirmed by compressive strength, soundness and LA abrasion testing on representative core samples or bulk samples taken local quarries.

Geotechnical Investigations for the Southern Highway between Kottawa to  Kurundugahahetekma & Rehabilitationof A4 & B5 Road.

The proposed southern highway project has been identified as vitally important to improve the transportation system between capital city Colombo and the Southern Province. NBRO was entrusted to conduct geotechnical investigations along this section from Kottawa to  Kurundugahahetekma & Rehabilitationof A4 & B5 Roads.

This section between Kottawa to Kurundugahahetekma is approximately 70km long. The rehabilitation of A4 and B5 roads are approximately 30km in total. The proposed highway traverses across the hilly terrain, paddy fields, floodplain of major rivers and three major river crossing.

The field investigations comprised of test pits, augur boring, cased boring (wash boring and core drilling), standard penetration test (SPT), dynamic cone penetration test, field vane shear test, and field permeability test. laboratory tests included soil classification and index tests such as natural moisture content, specific gravity, Atterberg limits and grain size analysis, strength tests including triaxial tests (UU & CU), consolidation for soft soil samples and material testing including CBR and standard Proctor compaction.

Southern Transport Development Project – Kahatuduwa to Arakagoda Sta. 5+ 000 to Sta. 19+000.

These soil investigations of subsurface condition along road trace from Kahatuduwa to Arakagoda is carried out to establish the engineering geological conditions along the road trace to determine the foundation conditions for embankments and to asses ripability of bed rock for excavation in cuts and to establish the geotechnical parameters of various soil types that require for design of road embankment to determine post construction consolidation settlement and to ensure the stability of side slopes.

The investigations along the proposed road alignment consist of augur borings, case boring, in situ vane shear test and laboratory tests. Cased borings were made either by wash boring or rotary core drilling techniques and samples were taken in each soil layer or at maximum 1.0m depth intervals. In cohesive soils, undisturbed soil samples were taken. In-situ vane shear tests also were carried out cohesive soils. In granular soils, SPT sampling was made at 1.0m depth intervals. For all borings, classification tests were carried out on representative soil  samples and consolidation tests on soft cohesive strata were carried out to determine the settlement characteristics.

Rocks samples obtained from quarry at Arakagoda area was tested for Point Load Index., Soundness and Los Angeles Abrasion value.

Additional Geotechnical Investigations for the Southern Highway between Kurundugahahetekma to Matara (Construction Stage).

 Additional Geotechnical Investigations in the construction stage for the section from Kurundugahahetekma to Matara of the proposed Southern Transport Development Project was carried out by NBRO to asses the soil profile and the shear strength of the soft soils along the proposed expressway.

Field investigations were comprised field Vane shear tests, CPT and hand auguring. Laboratory tests include soil classification and index tests such as Natural moisture Content, Specific gravity, Atterberg Limits, Grain Size Distribution and Consolidation tests and also the chemical tests on soil such as Organic Content, Ash Content, pH, Chloride Content and Sulphate Content.

Design and Construction Supervision of Japan–Sri Lanka  Frienship Road.

The Design and Construction Supervision of 2.3km length Japan-Sri Lanka Friendship road was under taken by the NBRO. The existence of the considerable thickness of soft soil underneath had to be considered in designing of road embankment, Planning and execution of Geotechnical investigation required for the embankment design, ground improvement design to improve the underneath soft soil, construction supervision together with  field  instrumentation and field monitoring program was carried out by the NBRO in this project.

Rotary Core Drilling plant (Diamond bit), wash boring units and hand auguring units were used for the investigation and 03 core drilling locations, 15 wash boring holes and 20 hand auguring locations were drilled in order to obtain the sub soil profile. Also, 10 field vane shear tests were performed to obtain the in-situ strength of the soft soil underneath.

For the ground improvement design soil parameters were obtained by performing mainly 8 Nos. of undrained tri- axial tests, 5 Nos. of consolidation tests, 15 Nos. of standard proctor tests in the NBRO laboratory and 10Nos. of field vane shear tests.

Consultancy Services for the Construction of Access Road to IT Park at  Malabe.

NBRO carried out the consultancy services for earth work  for the construction of proposed two lanes, 2.4km long and 15m wide access road and by roads to IT Park at Malabe.

Due to the presence of soft soil underneath the proposed road embankment a comprehensive improvement to the ground with proper quality control is required. The NBRO was acted as an advisory consultant for the entire earthwork/ground improvement for the period of 12 months.

NBRO has undertaken following tasks. Reviewing the ground improvement, road embankment designs, toe protection, technical specification and construction sequence of the earthwork. Planning additional investigation/laboratory for precise estimation of consolidation characteristics and strength properties of soft soil with respect to the ground improvement measures and embankment design. Quality control of borrow materials and earth filling work. Review and Interpretation of instrumentation data to estimate the rate of primary consolidation settlement to facilitate the construction programme. Establishment of general guidelines / specification for the entire work. Proved design concept for the foundation for the extension of existing culverts and new culverts. Review and reporting comments on the ground improvement design report of CECB.