A circular area of radius 'R' on the surface of a semi-infinite soil mass is uniformly loaded with a loading intensity of 'q'. The vertical stress z directly below its centre at a depth 'z', is given by

• A. <img src="/_files/images/civil-engineering/upsc-civil-service-exam-questions/03-623-1.png">
• B. <img src="/_files/images/civil-engineering/upsc-civil-service-exam-questions/03-623-2.png">
• C. <img src="/_files/images/civil-engineering/upsc-civil-service-exam-questions/03-623-3.png">
• D. <img src="/_files/images/civil-engineering/upsc-civil-service-exam-questions/03-623-4.png">