CLASSIFICATION AND ZONING OF MARBLE SITES - HKU Libraries

- 15 -No simple rules exist for very difficult and extremely difficult sites. The extent,nature and geological background of the problematic karst features must be known. The rockmass quality around these features should be assessed and a suitable foundation design canthen be attempted. This may be in form of deep bored piles to penetrate the zone, boredpiles underpinned by grouting or micropiles, micropiles alone, floating piles or floating raft.9. CASE EXAMPLESAppendix A illustrates the application of the classification system on a site in centralYuen Long. This is a site where piling has been completed. Appendix B is an applicationon a site in the eastern part of Yuen Long town. This case illustrates site zoning frompreliminary ground investigation results.10. SUMMARYA classification system for marble sites has been developed basing on some knowledgeof karst processes and common karst features in Yuen Long. The system utilises RQD as thebasic parameter. Five steps are involved in the application of the system.(a)(b)(c)(d)(e)Calculate the Marble Quality Designation (MQD) valuesfor sections of 5 metres according to the reduced levels.Assign the marble rock mass classes according to theMQD values.Calculate the borehole ratings according to the rockmass class patterns.Plot borehole ratings on plan to identify problem zones.Assign site classes according to the percentage area ofthe problem zone.Based on limited experience on design and construction of foundations on karst marblein the Yuen Long area, some tentative guidelines on ground investigation and foundationdesign have been associated with the site classes. This would be the immediate applicationof the classification system.11. POTENTIAL DEVELOPMENTWith some practice, engineers and geologists may use the borehole ratings to assistinterpretation of the karst morphology of the sites. This may turn out to be the real strengthof the system as illustrated by Chan & Pun (1994).As a follow up, this system will be applied to sites in the Designated Area with goodground investigation results. The system would then be reviewed for improvement.