What is the ruling on making up Dhuhr and Asr prayers outside their prescribed times due to the nature of strenuous work for long hours?

You must employ the means that aid in waking for prayer. If you do not wake, there is no sin upon you, and you should pray it upon waking, maintaining the order of the prayers. If the time for prayer begins while you are awake, and you know that sleeping will cause you to miss the prayer, then you must pray before sleeping. If waking for Dhuhr prayer is extremely difficult, you may delay both prayers until the end of the optional time for Asr and pray them as a combined late prayer (jama' ta'khir) if the hardship is significant.