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| An equivalent area method for evaluating the point load strength of#br#
irregular soft phyllite |
| ZHU Jiangjiang1，LUO Qiang1，ZHAN Xueqi2，JIANG Liangwei1，FANG Dong1 |
(1. School of Civil Engineering，Southwest Jiaotong University，Chengdu，Sichuan 610031，China；
2. China Railway Siyuan Survey and Design Group Co.，Ltd.，Wuhan，Hubei 430063，China) |
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Abstract For soft rocks，point load test is often used as an effective method to evaluate the strength quickly and easily due to that it is difficult to obtain complete cylindrical standard specimens. Based on the mechanical essence of the point load strength，the difference between the calculation models of load spacing method and equivalent diameter method was analyzed. By introducing the width ratio of the actual breaking section to the minimum section，the unified expression of the equivalent area method with taking the minimum section area as the basic parameter was constructed. The samples of irregular soft phyllite were adopted to discuss the variation characteristics of the ratio with different weathering degrees and to investigate the influence of the shape factor and the loading point space on the point strength index. Test results show that the distribution of the ratio is highly skewed，and that，with increasing the weathering degree，the characteristic value increases slightly between 1.40 and 1.46，which is not only larger than 0.3–1.0 of the“load spacing method” but also greater than 4/π of the“equivalent diameter method”. Consequently，1.43 is suggested as the characteristic value for soft phyllite. The point load strength decreases with increasing the shape factor or the loading point space. With increasing the weathering degree，the sensitivity of the influence of the shape factor on the point load strength reduces gradually. While the relative deviation of the point load strength is less than 40%，for strongly，weak and slightly weathered samples，the shape factors are not less than 0.4，0.5 and 0.6 respectively and the loading point spaces are 35–80 mm.
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2018, Vol. 37 
