Cambodia National Highway No.5 Rehabilitation Project Team
【Obayashi Corporation】
Representative：Hideaki Kamimura（Obayashi Corporation, Asia Pacific Regional
Head Quarter, Civil Engineering Construction Department, GeneralManager）
No. of Member：１２（Obayashi Corporation１２）
National Highway No. 5 (Asian Highway No. 1), which connects the capital of theKingdom of Cambodia, Phnom Penh, with neighboring Thailand, is also part of theSouthern Economic Corridor, an economic artery that connects ASEAN by road, andis an important trunk road that is essential for the economic development ofCambodia. Obayashi Corporation has overseen the construction of 47 km of theexisting National Highway No. 5 between Pursat and Prey Svay since 2019, out of the366 km of four-lane renovation work that has been underway since 2017 with loan
assistance from the Japan International Cooperation Agency (JICA).
The challenge in advancing the construction was the process management, wheredelays had become apparent in the preceding construction section. The problems
with process management included 1) the difficulty of managing construction over along distance, 2) the tropical monsoon climate with a rainy and dry season, 3)
securing embankment materials (borrowing pits), 4) the process management levelof local contractors, and 5) the difficulty of maintaining the detours in theconstruction section.
In the Obayashi section, the construction policy was to start construction on eight
bridges early (including design changes) and 57 cross drainage ditches in the firstdry season, and to focus on construction in four urban areas (5.2 km in total) whereconstruction efficiency would decrease in the second dry season, with an emphasison continuous construction as much as possible.
To secure the embankment materials required for earthwork, detailed priorinvestigations and planning were conducted from the bidding period in 2018,shortening the lead time (unexploded ordnance detection was essential), andearthwork was started promptly after construction began.
However, one year after the start of earthwork, a three-month delay occurred, so
the six-km section was switched to direct construction without sub-contractor andthe site management system was strengthened accordingly. Japanese engineers withextensive experiences in road construction were always stationed to check the daily
construction procedures, and a PDCA cycle was established so that Cambodian
engineers could see the site from the same perspective as Japanese engineers andpractice quality and schedule management.
Throughout the construction period, the quality of the key earthworks (Embankmentand Subgrade) was thoroughly controlled, including checking the basement of theroad, replacing necessary areas, and carefully selecting embankment materials,
because even a quality defect of one meter can lead to a delay in the process.
Amidst this, the construction work was carried out under even more severe
conditions due to the recovery from the flood damage that occurred in October 2020
and the COVID-19 pandemic.
Cambodia also has a country risk in that the traffic accident mortality rate is about
five times that of Japan (statistics for 2022). Most of these accidents were caused by
motorbikes. Under these circumstances, the detours for general traffic diversions andtemporary bridges set up beside existing national highways, and the maintenanceand management of safety equipment along the construction route and dust
prevention measures were meticulously continued day and night to thoroughly
eliminate the risk of third-party accidents. Led by the top management, basic

guidance was continued to ensure that staff, heavy equipment operators, and eachworker understood and acted on the principle of "avoiding accidents and not causing
accidents. What should we do to achieve this?". The special caution of Obayashi’s site
engineer was emphasized on management of dump truck drivers (230 trucks at peak)under the considerable risk of traffic accidents involving dump trucks transporting
materials (soil and crushed stone).
With the understanding and cooperation of local government agencies and residents,
these risk management measures were implemented one after another, andconstruction was prevented from being halted due to serious accidents orenvironmental issues, which resulted in the recovery of the schedule.
In the eight sections including Japanese companies, only Obayashi completed theproject within original contract period. As a result, the road was opened one month
before the end of the construction period, contributing to improved logistics functions
and reduced travel times.
Furthermore, dedicated maintenance was conducted as a trade-off for quality control
during the defect liability period, which often causes a problem in developing
countries, contributing to extending the road's lifespan.
Due to the above outstanding achievements and future developments, this casedeserves an award in the field of international contributions.

Completed Road Bridge

Completed Road (Rural Area)