#$9909$ While designing civil engineering projects, it's essential to consider various factors, such as soil mechanics, structural integrity, and environmental impact. With this in mind, let's delve into a theoretical scenario: Suppose you're tasked with designing a bridge spanning a wide river in a seismic zone. Discuss the challenges you would face in terms of selecting suitable materials and structural configurations to ensure the bridge's stability during both normal conditions and seismic events. Additionally, address how you would account for potential soil liquefaction and dynamic loads caused by seismic activity. Finally, propose a comprehensive risk mitigation strategy that includes measures for both pre$-$construction planning and post$-$construction monitoring to ensure the safety and longevity of the bridge. Your response should demonstrate a thorough understanding of civil engineering principles, structural dynamics, and risk management strategies.