Chek Lap Kok Airport (Southern Runway and Taxiways)
Chek Lap Kok Airport was built on an airport platform (12.5 km²) with 75% of the area on reclaimed land with the remaining 25% formed by excavating two existing granitic islands. The construction comprised the placement of approximately 197 million m³ with 70 million m³ of that being hydraulically placed dredged sand fill. The placed fill thickness varied from 10 to 25m.
The capping materials to sub-grade level on the southern runway and taxiway areas were predominantly dredged marine sands. The balance of the capping materials consisted of decomposed granite with variable quantities of rock fragments. The southern runway area had a compressible in-situ marine deposit below the dredged fill. The consolidation settlement was less than the anticipated settlement resulting in inadequate compaction in the upper reclaimed levels.
Landpac was engaged to carry out Impact Compaction of the in-situ sub-grade materials as an alternative to the costly removal to the required depth and backfilling in layers with conventional roller compaction.
Monitoring & Verification/QA
The subgrade dredged sands contained variable amounts of coarse grained, finer grained plastic materials and shell fragments. Due to the variability of the subgrade material plate load tests were used to verify the compaction requirements. A 200T Porter Super Compactor was initially used to proof roll the subgrade after Impact Compaction. As the Impact Compactor also provided an onerous proof roll of the subgrade use of the Porter Super Compactor was discontinued.
Client: Hong Kong Provisional Airport Authority
Principal Contractor: Downer-Paul Y-McAlpine JV
Ground Improvement Contractor (Top 3 metres): Landpac
Port Botany Container Terminal Expansion
The project consisted of the reclamation of 63Ha with 8 million m³ of dredged Sand. The project infrastructure includes a new container terminal and almost 2km of extra berth length. The new berth structure required the construction of counterfort walls up to 21m high. The project also included the reclamation of a 2Ha area for a public boat ramp and car parking area.
The borrow areas consisted of fine to medium grained marine Sands with lenses containing organic and clay. The specification for the dredged Sands used for the reclamation required less than 10% fines passing the 75µm sieve. The project specification called for compaction to 75% Density Index to 2m below the reclamation level and 70% Density Index from 2-3m depth in the new terminal areas. For reclamation material below the Mean Low Water Neaps and 4 metres below the existing in-situ surface levels in the new terminal areas and boat ramp area a CPT cone resistance value (Qc) greater than 5MPa for a minimum of 90% of the cone profile was specified.
To achieve the required compaction in the hydraulically placed dredged fill to 16m depth or so, Dynamic Compaction or Vibro-Floatation was used. The upper 3m of the soil profile with the use of Dynamic Compaction or Vibro-floatation techniques on a non-cohesive soil tend to be loose. Impact Compaction provided an economical means of compacting the upper loose soil profile to the required compaction levels after the Dynamic Compaction or Vibro-floatation had been applied.
Monitoring & Verification/QA
The impact compaction works were monitored with Landpac’s (CIR) soil response and (CIS) continuous induced settlement monitoring systems. The compaction requirements were verified with Density testing to 1.8m depth and CPT (Cone Penetrometer) geotechnical testing. The CIR and geotechnical test results have shown that the sub-grade was uniform and that the required compaction specification was achieved consistently.
New Terminal Density Test Results (Average)
Client: Sydney Ports
Principal Contractor: Baulderstone-Jan de Nul JV
Ground Improvement Contractor (Top 3 metres): Landpac
Kooragang Island Coal Export Terminal
The proposed capacity of the NCIG Kooragang Island . CET was increased to 30 Mtpa of coal throughput. The project involved dredging of three berths in the south arm of the Hunter River to construct a serviceable port for the export of coal. Dredging was carried out by a joint venture between Dredeco and Boskalis Australia. The 3.5 million m³ of Dredged Sands was re-used as construction fill.
The proposed coal stockpile and reclaimer area is approximately 40Ha in size and is located on dredged fill placed over Quaternary fluvial, estuarine and marine sediments of variable depth and consistency. The upper alluvium comprises layers of very soft/soft clays and very loose/loose silts and sands typically 2 to 4m thick.
Dredged fill was hydraulically placed 3 to 5m depths over the Coal Stockyard area after completion on the Dynamic Replacement. The dredged fill comprised medium to coarse grained Sands.
Dredged Fill Compaction
The Dredged Fill was subject to further compaction after placement with Impact Compaction using Landpac 3-sided 25kJ (135kJ Kinetic Energy) Impact Compactors. A medium density (Approx. CPT Cone Resistance > 5 MPa) was required.
Client: Newcastle Coal Infrastructure Group
Principal Contractor: AbiGroup Construction
Ground Improvement Contractor: Landpac
Preloading was initially proposed to induce consolidation settlement. However, due to construction programme constraints, alternative ground improvement methods were used. Dynamic Replacement was used on a triangular grid with columns to around 5 to 6m depth. A crushed rock/gravel layer 300 to 500m thick was placed over the original ground level to facilitate the Dynamic Replacement.
Port Tanger Project, Morocco
The Tanger MED 2 project in Morocco required a 140ha area to be constructed, through a dredging/backfilling operation and densification and improvement of the hydraulic fills, prior to pavement construction for a planned container terminal. Up to 5 million cubic metres of “borrow material” were dredged, sourced offshore, and backfilled onto an area behind quay walls. The backfilled dredged material was Deep Vibro Compacted (DVC) to the full depth. The Cone Penetrometer Test results, from previous DVC works within the Tanger MED site, have indicated that specification is only achievable greater than 2m below ground level with DVC. A trial was conducted on site using Impact Compaction for the compaction of the upper surface materials to 2-3m depth.
The project specification required the following criteria to be achieved in the upper 2 metres, prior to pavement construction.
CPT Cone Resistance Qc ≥10MPa
Modulus Ev2 ≥100MPa, at the surface
(Ev2/Ev1) ≤ 2, at the surface
Three trial areas were selected to assess the most suitable Impact Compaction methodologies. A nominal 250mm rock layer was placed over the sand fill prior to the Impact Compaction.
Impact Compaction Test Results
The average cone resistance values of three CPT’s prior to Impact Compaction and three CPT’s after Impact Compaction are presented in the CPT curves. The post compaction values indicate that compaction exceeded the minimum project specification line CPTU ≥ 10MPa to a depth of approximately 4.5 metres.
The post compaction Plate Load test values indicate that compaction exceeded the minimum project specification.
Jebel Ali, Dubai Port
Reclamation was done behind the new Quay 4 and Berth 21 of the Jebel Ali Port, Dubai (Middle East). Dredged marine sands were backfilled to a total depth of approximately 16m. The material below sea level was initially improved by means of Vibro compaction. Cone penetration testing (CPT) results obtained after Vibro compaction, showed that compaction was generally poor down to approximately 2.0m depth, less than the specified Cone Penetration Test (CPT) cone resistance of 6 MPa. Landpac was contracted to improve the bearing characteristics of the dredged marine sands in the top 2.0m of the soil profile.
The weighted average cone resistance recorded in the top 2.0m improved to 11.6 MPa after completion of 40 passes of the impact compactor with the weighted average cone resistance over 4.8m of 13.6 MPa after impact compaction.
The London Gateway project consisted of land reclamation with dredged fill. Landpac was engaged to do the surface compaction of the upper 3m on Port 1 & 2 (16Ha) after the completion of the deep compaction.
Moin Container Terminal, Costa Rica
APM Terminals are expanding the port capacity at Limon Costa Rica, which handles 80% of the freight for Costa Rica. The terminal is being developed on a 40 Ha reclaimed area formed from dredged sand fill. Landpac has been engaged to compact the upper 3 metres to a Relative Density of 90%