岩石产生风化裂隙与失水拉应力、吸水压应力关系的实验研究

The concepts of water-loss tension stress and water-absorption compression stress are proposed, which are additional stress derived from the non-gravitational water. They have the regularity that the nearer close to water loss or absorption surface, the higher value of stresses. Therefore, rock failure related to increase of the two stresses always presents from the outside to the inside characteristics, and the surface of fissures produced in the rock due to water loss shows perpendicular to the surface of water-loss , and the surface of fissures due to water absorption shows parallel to the surface of water-absorption (except at the edges and corners). It has never been including the action of water as the reason of rock physical weathering in geology books, the previous researchers have not yet associated the reasons of rock weathering fissures with the change of additional stress field induced by non-gravitation water loss or absorption. The applicants intend to apply experimental methods to simulate conditions of generating additional stress mentioned above, and to obtain characteristics of the stresses distribution of rock and the rule of rock failure under corresponding stress field. Besides, in order to understand deeply the generation conditions of weathering fissures under certain qualifications, the observable emergence process of weathering fissures is shortened to 1-2 years. It also conforms further, in the general natural environment, that it is the gradient of water content density rather than temperature changes that is the main factor of generating weathering fissures for the rock with hydrophilicity.

提出岩石失水拉应力和吸水压应力的概念。它们都是由岩石中非重力水作用产生的附加应力，并且具有越接近失水-吸水面应力值越高的规律。因此，与这两种应力增加有关的岩石破坏都有由表及里的特点；岩石中所产生的裂隙面与失水-吸水面呈现出大致垂直或平行的几何关系（棱角处除外）。在地质学有关风化裂隙产生原因的章节中，从未把水的这种作用作为岩石发生物理风化的原因列入其中；以前的作者也没有把岩石风化裂隙产生的原因与非重力水的得失、从而引起附加应力场的改变相联系。本项目拟用实验方法模拟上述两种附加应力产生的条件、在岩石中应力分布特点以及在相应应力场状态下岩石破坏的规律。并且在可控条件下，将岩石中可观察到的风化裂隙产生过程缩短至1-2年内，以加深对风化裂隙产生条件的认识。通过进一步研究，确认在一般自然条件下，对于亲水性较强的岩石来说，含水密度梯度大小是它们产生风化裂隙的主要因素，而不是与气温有关的温度变化。

本项目对五大连池玄武岩、桂林灰岩、北京大理岩、云冈石窟砂岩、平遥古城青砖的风化过程和风化机理进行了研究，厘清了水（及水中可溶盐）对砖石文物风化的影响，明确了水的动力冲刷和毛细水上升对砖石文物风化的影响规律，解释了岩石中风化裂隙产生原因，确定一些岩石在不均匀吸水和失水条件下能产生较大的附加应力并且可以导致岩石发生破坏。（1）对五大连池玄武岩的风化试验结果表明，淋雨、高温-低温对玄武岩的风化规律有区别。淋雨循环下试块表面粗糙度有增大-减小的趋势，但整体变小，试块劣化由表及里。高温-低温循环下试块表面粗糙度有减小-增大的趋势，但整体变大，试块内部及外部均发生劣化。（2）对桂海碑林灰岩进行淋雨循环试验，发现灰岩在动水作用下的溶蚀过程，即试块表面的方解石基质发生缓慢溶蚀，鲕粒间的方解石基质逐渐受到侵蚀，鲕粒的联结力有所削弱；鲕粒突然脱落，溶蚀速率变大；方解石基质继续缓慢溶蚀，待下一次鲕粒脱落。（3）对北京大理岩进行自然条件高温-低温循环试验，并测试样品的质量损失、三维表面形貌、波速以及单轴抗压强度等参数，证明了自然条件下的温度变化可导致白云石大理岩劣化。（4）对比了山西大同云冈石窟新鲜与风化岩样矿物成分和微观形貌，从矿物蚀变角度提出了云冈石窟砂岩风化是方解石溶蚀和方解石白云石化作用、蒙脱石伊利石化和长石高岭石化作用导致的。（5）研究了平遥古城古砖的病害类型，提出了利用测量古砖的磁性变化来测算其烧制温度，发现烧制温度会影响物理力学性质，测试了平遥古城古砖的工程地质性质及耐盐耐冻性质。根据实验测试结果和现场监测结果，认为古砖的破坏机理就是盐分在失水和/或低温时的结晶膨胀作用导致古砖表面的剥落或脱落。根据古砖的风化机理，提出“阻水、脱盐、强砖”的防治方法。以上研究对上述砖石文物风化机理和防风化具有重要的理论和现实意义。