For example, the uniaxial compressive strength of a project in Dehua is 6 1.5mpa, which is described as broken and moderately weathered tuff dissolution by field investigation and appraisal. According to the former judgment, the rock stratum should belong to hard rock, and according to the foundation specification, the characteristic value of its rock bearing capacity can be taken as fa=0. 1. 61.5mpa = 6.15mpa = 6150kpa, but according to the field appraisal, the rock can only be relatively soft, and the maximum bearing capacity of the rock foundation can only be 0. 1? 30 MPa =3 MPa = 3000 kPa. The difference of bearing capacity between the two foundations is more than one time, which brings great confusion to foundation designers, because the width of foundation section of the latter is twice that of the former. For such a question, the investigation report should have the correct answer. To this end, some members of the basic professional group and structural professional group of the expert Committee of the association held another seminar in the conference room of the association on April 29, 2006 to discuss this issue. After heated discussions among the participating experts, the participating experts reached the following consensus on the expression of bearing capacity of rock foundation, which is now compiled and published for the reference of survey and design units: 1. The characteristic value of bearing capacity of rock foundation should be determined scientifically and reasonably on the basis of rock classification. Rock classification can be divided into geological classification and engineering classification. Geological classification is the basic classification of rocks. According to geological origin, mineral composition, structure and weathering degree, it can be expressed by geological name and weathering degree, such as moderately weathered granite and slightly weathered sandstone. Engineering classification is to further distinguish the hardness of rocks on the basis of geological classification. The hardness of rocks can be divided into five types: hard rock, hard rock, soft rock, soft rock and extremely soft rock. Only by accurately identifying the geological classification of the site can it be possible to qualitatively determine the hardness of the rock. For example, according to the qualitative classification in Table A.0. 1 in Appendix A of the Foundation Code, weathered to slightly weathered granite belongs to hard rock, and weathered to slightly weathered granite belongs to hard rock. Therefore, geological classification is the basis of engineering classification. Engineering classification can also be divided into hard rock and soft rock according to the uniaxial saturated compressive strength of core. Take 30mpa as the dividing line of quantitative area, hard rock ≥30mpa, soft rock ≤30mpa. For rocks that can be sampled and tested (such as complete, relatively complete or relatively broken rocks), the hardness of rocks should be determined by quantitative methods as far as possible. For the broken and extremely broken rocks that cannot be sampled and tested, the hardness of the rocks can be determined by the qualitative method in Appendix A of the Foundation Code through integrity. Because geological classification is the basic classification, when there is a contradiction between qualitative classification and quantitative classification, qualitative classification should be the main one. For example, the tuff dissolved rock of the above Dehua project belongs to hard rock, but it should be classified as relatively soft rock after moderate weathering and crushing. 2. With regard to the selection of characteristic values of bearing capacity of rock foundation (pile tip), in the absence of load test of rock foundation, if the investigation unit can conduct sampling test according to the requirements of geotechnical engineering investigation specifications, it can directly put forward the results of uniaxial saturation test and the description of rock stratum integrity (the adoption rate should generally reach more than 80%, and it should reach more than 65% in the case of crushing, with no less than 6 groups of samples). According to the relevant provisions in Articles 5.2.6 and 8.5.5 of the Foundation Code (GB50007-2002), the foundation designer should determine the characteristic value of the bearing capacity of the rock foundation, and the exploration unit does not need to provide the standard value of the ultimate bearing capacity to avoid unnecessary contradictions and misleading. Used for crushing, extremely crushing and soft rock. If it is impossible to sample and detect, the exploration unit should first classify the geology according to the on-site identification, and then make a comprehensive judgment by plate test or other in-situ tests combined with regional experience, and provide the characteristic value or limit standard value of bearing capacity for designers to use. Three. Regarding complete and relatively complete hard rock, whether to distinguish the characteristic value of foundation bearing capacity from the characteristic value of rock bearing capacity at pile tip should be based on the relevant provisions and explanations in Articles 5.2.4, 5.2.6 and 8.5.5 of the Foundation Code. For complete and relatively complete hard rocks, the mechanical mechanism of shallow foundation and deep foundation is the same, so the bearing capacity characteristic values of the two should be the same and should not be distinguished. This is a typical difference from the bearing capacity of geotechnical foundation. It should be pointed out that the bearing capacity of soil foundation should be revised in depth and width, while the complete and relatively complete rock foundation above moderate weathering should not be revised in depth and width (see Note 5.2.4 in Table 5.2.4 of Foundation Specification). Four. What formula is suitable for estimating the bearing capacity of rock-socketed piles in complete and relatively complete hard rocks? The estimation formula and foundation specification of complete and relatively complete rock-socketed piles in hard rock adopt simplified formula, that is, only the pile end resistance is considered, while the geotechnical engineering survey high gauge considers not only the end resistance but also the side resistance. It is considered that the simplified formula of foundation code is applicable because the strength of rock-socketed pile is much higher than the strength of pile body and the bearing capacity of pile. For soft rock, the reduction of uniaxial compressive strength may be lower than the strength of pile material, and designers should take a low value to control it. Note: 1. The expert members attending this seminar are: Ma Shidong, Wang, Xie Yongming, Zhou, Huang, Yan Nansheng, He Yaotang, Lin Lizhen, Li Qiumu, Wang, Li and Li Demin. Comrade Li Demin, Chairman of the Expert Committee, is responsible for sorting out the opinions of this seminar. 3. If you have different opinions or amendments to this arrangement, you can send them to the expert committee of the Association, or publish them directly through the website or publication of the Association for further discussion. May 2, 2006