箱隔式拦河闸的抗冻胀研究与实践

传统的中小型拦河闸受冻害破坏较普遍而严重，新型的箱隔式拦河闸通过其总体布置，结果形式本身圆满地解决了复杂的冻害问题，不需外加任何特殊的防冻措施，箱隔式闸总体布置简单，阵线集中，薄弱环节少，受冻部位及面积小，基础在一个平面上均用水保温防冻，消除了基底法向冻胀力的危害，箱隔对称水平冻胀力大部分通过箱隔传递作用而衰减或平衡。

Clathrate Methane and Global Change: A Review

Methane clathrate is one of the most important carbon pools in the shallow (<2 km) crust of the earth, containing CH 4-C up to 10 16 kg. Warming by ocean flooding to exposed continental shelves and changes in pressure at depths might destabilize clathrates under the ocean, while ice cap growth stabilizes clathrates under it. The time scales for the two shifts are asymmetrical: the time of methane clathrate fixation as a result of surface cooling is on the order of several tens of thousands of years, while the thermal destabilization of the CH 4 clathrates is set by thermal properties of sediments and on the order of thousands of years. The sensitivity of clathrates to surface changes, the time scales involved, and the large carbon pool of the clathrates indicate that methane clathrate may have played an important role in modifying the composition of the ice age atmosphere: the release of CH 4 and its subsequent oxidation may be responsible for the observed fluctuations in atmospheric CH 4 and CO 2 concentrations during glacial and interglacial periods, which induced the strong feedbacks to climatic systems and enhanced the greenhouse warming at the end of ice ages. Up to now, the clathrate CH 4 feedback mechanisms well explain the glacial-interglacial climate variations, especially the abruptness of the ice age termination and their slow build up. The warming of the arctic permafrost and subsea permafrost and clathrate CH 4 release have been possibly in progress, but the amount of release might be small at present and in the next century. The impacts of the methane clathrate on global warming are extremely complex and highly tentative due to its roughness in carbon estimation, and meditativeness in its feedback mechanisms.