Formation Mechanism and Engineering Characteristics of Sandy Dolomite in Wuhan Tianxingzhou Carbonate Rock Belt
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摘要: 武汉市碳酸盐岩天兴洲条带，发育一套巨厚层砂化白云岩.为查明该岩层的成因及工程特性，采用构造调查、薄片鉴定、X射线衍射试验（X-ray diffraction，XRD）、X射线荧光光谱分析试验（X-ray fluorescence，XRF）、颗粒分析试验、饱和单轴抗压强度试验等多种方法，对砂化白云岩成因及其工程特性进行深入研究.结果表明：研究区位于3条断裂之间，且地层出现倒转现象，表明该区域在印支期所受的挤压应力及燕山期所受的张拉应力非常强烈，区域构造特征及显微镜下照片也佐证了这一观点；砂化程度越强烈，白云石矿物含量就越低，而石英石及黏土矿物含量则越高；CaO、MgO等主量化学成分迁移演化特征与白云岩砂化过程呈一定的负相关性，而SiO2、Al2O3、Fe2O3等主量化学成分则与之呈一定的正相关性.综上所述，研究区内砂化白云岩及其不均性特征的成因机理可以从“宏观构造动力作用”、“细观矿物结构组成”和“微观化学成分变迁”3个层面予以概括.砂化程度对白云岩饱和单轴抗压强度影响极大，其在砂化阶段“微-弱、微-中、微-强”的降幅分别可达38.6%、68.1%、90.0%，且呈幂函数关系；由此，拟合得到⑤1全砂化极破碎白云岩的饱和单轴抗压强度标准值为1.3 MPa，解决了全砂化白云岩难以制作标准岩样进行室内试验获取岩体力学参数的工程难题.
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关键词:
- 武汉市碳酸盐岩天兴洲条带 /
- 砂化白云岩 /
- 成因机理 /
- 工程特性 /
- 工程地质
Abstract: The Tianxingzhou carbonate rock belt in Wuhan has developed an exceptionally thick sandstone dolomite formation. To elucidate the genesis and engineering characteristics of this rock formation, a comprehensive study was undertaken employing various methods, including structural surveys, thin section analysis, X-ray diffraction (XRD), X-ray fluorescence (XRF), particle analysis, and saturated uniaxial compressive strength tests. The results indicate that the study area is situated between three faults, and the strata are inverted, suggesting that the region experienced intense compressive stress during the Indosinian period and tensile stress during the Yanshan period. Regional structural features and microscopic observations corroborate this interpretation. Notably, the higher the degree of sandstone, the lower the dolomite mineral content, and the higher the quartz and clay mineral content. The migration and evolution characteristics of major chemical components, such as CaO and MgO, exhibit a negative correlation with the dolomite sandstone process, while components like SiO2, Al2O3 and Fe2O3 display a positive correlation. In summary, the primary causes of the dolomite sandstone and its heterogeneous characteristics in the study area can be attributed to three distinct scales: "macroscopic structural dynamics", "microscopic mineral structure composition", and "microscopic chemical composition evolution". The degree of sandstone significantly influences the saturated uniaxialcompressive strength of dolomite. The reduction amplitudes for the "micro-weak", "micro-medium", and "micro-strong" sandstone stages can reach 38.6%, 68.1%, and 90.0%, respectively, exhibiting a power function relationship. Consequently, the standard value of the saturated uniaxial compressive strength for the fully sandstone and extremely broken dolomite in ⑤1 layer was fitted to be 1.3 MPa, resolving the engineering challenge of obtaining rock mechanics parameters for fully sandstone dolomite through indoor testing of standard rock samples. -
图 1 武汉市碳酸盐岩条带分布图(底图据中国地质调查局武汉地质调查中心, 2019)
Fig. 1. Distribution map of carbonate rock belt in Wuhan (after Wuhan Center of China Geological Survey, 2019)
图 3 砂化白云岩主层岩心照片及钻孔柱状图
a.⑤1全砂化白云岩；b.⑤2弱砂化白云；c.钻孔柱状图
Fig. 3. Core detail photos and column chart of sanding dolomite main layer
图 4 白云岩矿物成分含量实测
a.⑤1全砂化白云岩；b. ⑤2弱砂化白云岩
Fig. 4. Measured map of dolomite mineral composition
图 6 主要化学成分含量随砂化程度变化
Fig. 6. Content of main chemical components varying with sanding degree
图 8 不同砂化程度白云岩饱和单轴抗压强度试验值分布
Fig. 8. Saturation uniaxial compressive value distribution of dolomite in different sanding degrees
图 9 饱和单轴抗压强度与砂化等级的关系
Fig. 9. Relation between saturated uniaxial compressive strength and sanding grade
表 1 ⑤ 2层白云岩显微镜下照片及其特征
Table 1. Microscopically photographs of ⑤2 dolomite and its characteristics
BP1-1 BP2-2 BP3-2 
角砾状结构，形成大小不等的孔洞和裂隙，被白云岩、硅质岩碎屑及粒间岩石矿物碎粒、碎粉填充(起胶结作用)，低级区域变质 碎裂结构，形成大小不等的孔洞和裂隙，被碎粒、碎粉或石英充填；动力变质 角砾状结构，形成大小不等的孔洞和裂隙，局部充填破碎的岩粒并发生褐铁矿化，岩石角砾含量较低区域，多为微晶白云石与硅质物质；动力变质 BP4-1 BP5-1 BP6-2 
微晶结构，裂隙发育，其宽度窄、延伸长，内部充填碳酸盐矿物，少量被硅质矿物充填，也有中空者；生物碎屑灰岩被白云石交代，动力变质 角砾状结构，形成大小不等的白云岩碎屑，周围为岩石或矿物碎粒、碎粉，有贯穿裂隙；动力变质 角砾状结构，形成大小不等的孔洞和裂隙，岩石角砾周围裂隙内见无色硅质填充；动力变质 
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表 2 各砂化程度时白云岩矿物成分含量(%)
Table 2. The contents of dolomite mineral composition in different sanding degrees (%)
层号及名称 白云石含量 铁白云石含量 石英石含量 高岭土含量 ⑤1全砂化 49.79 24.59 10.46 15.17 ⑤1a强砂化 55.58 22.88 11.54 10.01 ⑤2a中砂化 42.65 37.76 11.85 7.73 ⑤2弱砂化 47.66 39.51 12.83 0.00 ⑤2b微砂化 82.78 13.63 2.84 0.75
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表 3 各砂化程度时白云岩化学成分含量(%)
Table 3. Statistical analysis of dolomite chemical components in different sanding degree (%)
层号及名称 SiO2 Al2O3 Fe2O3 MgO CaO Na2O K2O MnO 其他 烧失量 ⑤1全砂化 43.69 10.90 2.11 3.24 11.69 0.06 2.04 3.01 0.28 23.00 ⑤1a强砂化 17.44 0.14 0.26 7.52 34.65 0.05 0.01 0.03 0.00 39.90 ⑤2a中砂化 14.59 0.26 0.27 8.04 35.60 0.05 0.00 0.06 0.10 41.03 ⑤2弱砂化 10.43 0.17 0.33 8.87 36.43 0.06 0.01 0.07 0.00 43.63 ⑤2b微砂化 8.54 0.56 1.41 13.90 36.79 0.06 0.05 0.04 0.59 38.06 最大值 43.69 10.90 2.11 13.90 36.79 0.06 2.04 3.01 0.59 43.63 最小值 8.54 0.14 0.26 3.24 11.69 0.05 0.00 0.03 0.00 23.00 平均值 18.94 2.41 0.88 8.31 31.03 0.06 0.42 0.64 0.19 37.12
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表 4 白云岩砂化程度分级
Table 4. Classification table of sandy dolomite
对应层号 ⑤1 ⑤1a ⑤2a ⑤2 ⑤2b 砂化程度 全砂化 强砂化 中砂化 弱砂化 微砂化 砂化等级 1 2 3 4 5 岩石类别 极软岩 软岩 较软岩 较硬岩 坚硬岩 岩体完整程度 极破碎 破碎 较破碎 较完整 完整 frk范围(MPa) (0, 5] (5, 15] (15, 30] (30, 60] > 60 标准值(MPa) 拟合值1.3 7.0 22.5 43.3 70.5
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表 5 白云岩砂颗分试验统计
Table 5. Particle test statistics of dolomite sand
样品号 取样深度(m) 颗粒级配占比 定名 10.00~5.00 mm 5.00~0.00 mm 0.00~1.00 mm 1.00~0.50 mm 0.50~0.25 mm 0.250~0.075 mm < 0.075 mm RD1 30.5~30.7 1.46% 34.02% 16.69% 25.71% 7.55% 3.04% 11.54% 粗砂 RD2 33.0~33.2 0.13% 14.23% 9.58% 40.72% 20.09% 8.26% 7.00% 粗砂 RD3 33.5~33.7 1.09% 40.32% 11.42% 29.61% 10.37% 3.15% 4.04% 粗砂 RD4 34.0~34.2 0.20% 18.21% 8.16% 32.40% 20.73% 8.94% 11.36% 粗砂 最大值 - 1.46% 40.32% 16.69% 40.72% 20.73% 8.94% 11.54% - 最小值 - 0.13% 14.23% 8.16% 25.71% 7.55% 3.04% 4.04% - 平均值 - 0.75% 26.89% 11.78% 32.48% 14.50% 5.90% 8.25% -
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表 6 白云岩砂颗粒级配曲线
Table 6. Particle grading curves of dolomite sand
RD1 RD2 RD3 RD4 
d60=1.64，d30=0.62，d10=0.04，
Cu=41.00，Cc=5.8d60=0.76，d30=0.42，d10=0.12，
Cu=6.33，Cc=1.93d60=2.06，d30=0.67，d10=0.30，
Cu=6.87，Cc=0.73d60=0.74，d30=0.35，d10=0.06，
Cu=12.33，Cc=2.76
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