1. All of the plaintiffs' claims are dismissed.

2. The costs of lawsuit are assessed against the plaintiffs.

Basic Facts

Around June 2009, the Defendant issued a public announcement of the construction contract on the “construction works for facilities of rural and fishing village local waterworks” (hereinafter “instant construction works”) with the contents of the installation of drainage pipes, water pipe pipes, etc. in one unit, such as Jeonnam-Gun C, D, and E.

The Plaintiffs were selected as the successful bidder of the instant construction project on July 2009 by organizing a joint supply and demand organization (investment ratio: Plaintiff A 51%, Plaintiff B 49%) with the representative of Plaintiff A, participating in the bidding of the instant construction project.

On July 20, 2009, the Plaintiffs entered into the first installment contract with the Defendant on July 29, 2014 by adding the completion date of the construction work as follows with regard to the instant construction work.

공사명 : F지구 농어촌지방상수도 시설공사(1차분) 계약금액 : 742,980,000원 총공사부기금액 : 12,899,832,000원 착공연월일 : 2009. 7. 30. 준공연월일(1차분) : 2009. 7. 30.~2010. 2. 26. (착공일로부터 7개월) 총공사기간 : 2009. 7. 30.~2014. 7. 29. (착공일로부터 60개월) 연차별 계약의 체결 및 총괄계약의 변경 차수 구분(계약일) 차수 공사기간 차수 공사대금 총공사기간 총공사대금 변경 원인 비고 1차 최초계약 (2009. 7. 20.) 2009. 7. 30.~ 2010. 2. 26. 742,980,000 2009. 7. 30.~ 2014. 7. 29. 12,899,832,000 - 1차 변경계약 (2010. 2. 23.) - - 〃 12,768,833,000 ( 130,999,000) 총괄계약 변경 2차 변경계약 (2010. 4. 14.) 2009. 7. 30.~ 2010. 2. 26. 728,189,000 ( 14,791,000) - - 보험료 정산 2차 최초계약 (2010. 2. 23.) 2010. 3. 4.~ 2010. 12. 29. 1,430,130,000 2009. 7. 30.~ 2014. 7. 29. 12,768,833,000 - 1차 변경계약 (2010. 12. 17.) 〃 1,411,210,000 ( 18,920,000) 〃 12,739,833,000 ( 29,000,000) 설계 변경 총괄계약 변경 2차 변경계약 (2010. 12. 31.) 〃 1,384,659,970 ( 26,550,030) - - 보험료 사후 정산 3차 최초계약 (2011. 1. 27.) 2011. 1. 28.~ 2011. 12. 27. 1,920,900,000 2009. 7. 30.~ 2014. 7. 29. 12,739,833,000 - 1차 변경계약 (2011. 12. 20.)...