② On October 30, 2018, the Plaintiff sent the content-certified mail to Defendant B to claim construction cost for bad soil treatment. Accordingly, Defendant B sent the content-certified mail to the Plaintiff on November 8, 2018. Defendant B acknowledged the fact that the content-certified mail sent the content-certified mail to the Plaintiff.

③ On March 30, 2018, the Plaintiff submitted to Defendant B a letter of performance stating that “The Plaintiff will lawfully transport and dispose of defective soil and sand, and will assume all legal responsibilities when it would cause illegal reclamation or civil criminal problems in the course of the disposal of soil.”

④ Defendant B, by day, prepared a survey sheet on the shipment of defective soil by day (Evidence A7).

⑤ On May 9, 2019, the Plaintiff sent a text message to Defendant B’s representative director L, stating that “Istop: 10,372*5,500 = 3,8283,00 designated sand: 3,8283,00 = 11,484,00 + total amount of 69,080,000 supply price,” and issued an electronic tax invoice (hereinafter “electronic tax invoice of this case”) on May 14, 2018.

④ On June 18, 2018, Defendant C sent to Defendant C a letter stating that “Around April 2018, Defendant C’s Field Director M had ordered the Plaintiff to dispose of defective soil, but the Plaintiff completed construction machinery at the instant new construction site as the unit price was not determined up to now. As such, the construction was suspended due to the suspension of construction, it shall be promptly taken and changed.”

In light of the above official text, Defendant C’s on-site director’s order to treat bad soil around April 2018 is deemed to have been given to the Plaintiff. However, there are various types of contractual relationships between the prime contractor and the subcontractor at a construction site, and such cases also exist.