丹霞山顺层洞穴风化特征的试验研究

doi:10.13249/j.cnki.sgs.2014.04.454

摘要/Abstract

摘要：

以丹霞盆地丹霞组2段顺层洞穴为研究对象,探讨不同岩性红层抗风化能力的差异,重点关注软岩夹层的风化特征及其对顺层洞穴发育的影响。在野外考察的基础上,选择3个典型顺层洞穴为案例,采集了洞穴剖面不同岩性红层的岩样及夹层水样品,进行一系列的岩矿理化测试和水样分析实验。结果表明：洞穴剖面岩性的不均一性及软岩夹层的风化凹进是形成丹霞山顺层洞穴的主要原因。顺层洞穴发育的软岩夹层一般是粉砂质泥岩,粘土矿物含量高,以泥质胶结为主,吸水性较强,开型空隙率较大,抗压强度小,易于风化破碎;上下岩层主要是砂岩和砂砾岩,以钙质和铁质胶结为主,吸水性较弱,开型孔隙率较小,抗压强度较大,风化速度较慢。在洞穴岩层风化过程中,粘土矿物的胀缩、钙质胶结物的溶解, 及铁质胶结物的水化作用等是导致岩体结构破坏的重要因素,但促使不同岩性红层风化的主导因素有所差别。粉砂质泥岩的风化以粘土矿物的胀缩作用为主,砂岩和砂砾岩的风化则以钙质胶结物的溶解作用为主。此外,酸性雨水渗入岩体后与各种矿物进行的一系列离子交换作用也促进了顺层洞穴岩层的风化。

关键词: 丹霞地貌, 顺层洞穴, 软岩夹层, 风化特征

Abstract:

This study focuses on the bedding caves developed in the 2^nd Member of the Danxia Formation at Danxia Basin. Investigations of differential weathering of red bed rocks were conducted, especially the weathering features of soft interlaid rock layers and how this weathering effects the development of the bedding caves. Based on field investigations, three bedding caves were selected as study cases, followed by a collection of rock samples with different lithologies, as well as interlayer ground water samples, for laboratory test and analysis. The data reveals that primary factors for bedding cave formation at Mt. Danxiashan are the different lithological characters of rock layers in the cave wall and the rapid weathering and erosion of soft interlaid rock layers. Soft interlaid rocks between layers generally belong to silty mudstone with high content of clay minerals and argillaceous cements. Due to strong absorbability, high porosity and low compressive strength, these soft rocks are vulnerable to weathering and easily broken into smaller pieces. The overlying and underlying rock layers are more resistant sandstones or sandy conglomerates, cemented mainly by calcite and iron oxides, with low porosity and higher compressive strength. During the weathering process of rock layers in bedding caves, factors that are responsible for the disintegration of rocks include the expansion and contraction of clay minerals, dissolution of calcareous cements, and hydration of iron oxides. However, the dominant factors contributes rock decay vary in different lithotypes. For silty mudstones, the repeated expansion and contraction of clays is a significant cause of weathering. As for the weathering of sandstones and sandy conglomerates, the dissolution of calcareous cements plays a more important role. In addition, the infiltration of acid rainwater can also accelerate the weathering processes by ion displacement with minerals in red bed rocks.

Key words: Danxia landform, bedding caves, soft interlaid rock layers, weathering features

中图分类号:

彭华, 邱卓炜, 潘志新. 丹霞山顺层洞穴风化特征的试验研究[J]. 地理科学, 2014, 34(4): 454-463.

Hua PENG, Zhuo-wei QIU, Zhi-xin PAN. Experimental Study on the Weathering Features of Bedding Caves at Mt. Danxiashan[J]. SCIENTIA GEOGRAPHICA SINICA, 2014, 34(4): 454-463.

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岩样编号	粒径(mm)	主要矿物	主要胶结物	镜下图片编号
HY0	0.2~3	石英、泥硅质岩屑、长石	钙质	Fig. 5-1
HY1	0.05~0.15	石英、斜长石、泥硅质岩屑、方解石	钙质、泥质	Fig. 5-2
HY2	0.02~0.09	石英、云母、粘土矿物、方解石	钙质、泥质	Fig. 5-3
HY3	0.03~0.15	石英、硅质岩屑、长石、方解石	钙质	Fig. 5-4
LQ1	0.03~0.1	石英、长石、硅质岩屑	铁质、泥质	Fig. 5-5
LQ2	0.02~0.5	石英、方解石、长石、硅质岩屑	铁质、泥质	Fig. 5-6
LQ3	0.05~0.21	石英、斜长石、方解石、硅质岩屑、泥质岩屑	铁质、泥质	Fig. 5-7
WX1	0.01~0.08	粘土矿物、石英、云母	泥质、铁质	Fig. 5-8
WX2	0.04~0.1	石英、长石、云母、方解石	钙质	Fig. 5-9
WX3	0.01~ 0.02	粘土矿物、石英、云母	泥质	Fig. 5-10
WX4	0.04~0.12	石英、方解石、长石、硅质岩屑,	钙质	Fig. 5-11
WX5	0.03~0.1	石英、长石、方解石、云母、铁质岩屑	铁质、泥质	Fig. 5-12
WX6	0.08~0.2	石英、长石、方解石、硅质岩屑	铁质	Fig. 5-13

岩样编号	Na₂O(%)	MgO(%)	Al₂O₃(%)	SiO₂(%)	K₂O(%)	CaO(%)	TiO₂(%)	Fe₂O₃(%)	WO₃(%)
HY0	-	-	5.13	83.98	2.30	5.81	-	2.78	-
HY1	-	2.57	17.42	61.42	5.08	6.61	0.64	6.25	-
HY2	-	1.69	12.46	58.99	3.74	16.18	0.61	4.12	2.20
HY3	-	0.68	6.15	61.62	2.57	27.71	-	1.27	-
LQ1	-	1.50	11.72	74.72	3.43	4.52	0.39	3.72	-
LQ2	-	1.68	11.83	73.76	3.49	5.01	0.55	3.68	-
LQ3	0.49	0.47	8.15	78.94	3.93	5.83	-	2.19	-
WX1	-	2.58	18.33	64.40	5.76	1.05	0.82	7.06	-
WX2	-	1.06	9.40	72.24	3.04	10.81	0.45	3.00	-
WX3	-	2.40	18.14	62.13	5.90	2.37	0.83	8.22	-
WX4	-	1.18	8.60	56.79	2.69	27.99	-	2.75	-
WX5	-	4.88	15.98	55.61	4.27	11.47	0.68	7.12	-
WX6	-	1.00	8.41	77.75	3.34	7.46	-	2.03	-

岩样编号	颗粒密度 (g/cm³)	块体干密度 (g/cm³)	含水率 (%)	吸水率 (%)	饱和吸水率 (%)	饱水系数（j）	开型孔隙率 (%)
HY0	2.66	2.56	0.68	1.30	1.47	0.88	3.34
HY1	-	2.63	2.56	-	-	-	7.25
HY2	2.69	2.51	1.28	2.45	2.69	0.91	6.20
HY3	2.65	2.56	0.63	1.21	1.36	0.88	3.19
LQ1	2.52	2.06	10.00	6.70	8.91	0.75	13.81
LQ2	2.65	2.44	1.43	3.06	3.27	0.94	7.30
LQ3	2.63	2.45	1.48	2.61	2.76	0.95	6.51
WX1	-	2.61	2.81	-	-	-	7.27
WX2	2.67	2.51	1.40	1.46	1.99	0.73	3.71
WX3	-	2.65	2.73	-	-	-	7.13
WX4	2.67	2.55	1.14	1.92	2.03	0.94	5.06
WX5	-	2.62	2.52	-	-	-	6.43
WX6	2.56	2.26	1.23	4.46	5.74	0.78	10.10

岩样编号	垂直层面点荷载指数平均值	垂直层面点荷载强度修正值	平行层面点荷载指数平均值	平行层面点荷载强度修正值	点荷载强度各向异性指数（g）
HY1	1.27	1.25	0.67	0.63	1.98
HY2	1.36	1.40	0.68	0.68	2.06
HY3	1.88	1.91	1.81	1.89	1.01
LQ1	-	-	-	-	-
LQ2	1.38	1.59	0.66	0.71	2.24
LQ3	1.57	1.62	0.96	1.07	1.51
WX1	1.20	1.12	0.62	0.56	2.00
WX2	1.75	1.74	1.37	1.33	1.31
WX3	1.53	1.50	0.64	0.65	2.31
WX4	2.42	2.55	1.36	1.84	1.40
WX5	1.78	1.83	1.03	1.09	1.68
WX6	1.75	1.75	1.55	1.65	1.06

	阳离子（mg/L）					阴离子（mg/L）					pH平均值
	Na⁺	NH⁴⁺		K⁺	Mg²⁺	Ca²⁺	F^-	Cl^-	NO₃^-	SO₄^2-	HCO₃^-
丹霞山雨水样品	0.4329	1.8257	0.5852	0.163	1.6251	0.1218	0.4083	4.9113	7.6497	-	4.41
龙泉岩夹层水样品	1.4104	0.0836	0.6824	0.529	10.1156	0.1257	3.7794	9.3884	13.3531	9.8419	7.18