| 摘要: |
| 北方某土坝工程拟建场地的地质条件复杂，地基为淤泥质黏土层上覆硬土层，软土层最大埋深约为17m, 并具有含水率高、压缩性大、排水固结性能差等特点。设计采用无砂垫层真空联合堆载预压方案，但在高寒区缺少真空预压施工经验和参考案例，工程面临有如下难题：(1)坝基淤泥质粘土层上覆硬土层，传统插板工艺的施工效率和地层适应性不确定；（2）坝基表面的土层透水透气性大，场地的侧向密封措施对保证膜下真空度至关重要；（3）坝体填筑荷载大，直接在密封膜表面填筑坝体，施工过程中密封膜存在破损风险；（4）冬季气温低至-30℃，冻结力可能会损坏饱水的密封和排水系统进而影响第二年的真空预压排水效果。为此选取先导试验段，分别开展了塑料排水板插板工艺试验，密封墙成墙试验、密封膜保护试验和坝基防冻试验。研究结果表明：履带式振动插板工艺能有效穿透上覆硬壳层，其施工效率优于引孔+振动插板工艺；采用1.2m双排泥浆搅拌墙方案能起到良好的负压密封效果；在密封膜表面铺设无纺布、编织布，过渡层采用轻型压实能有效保护真空密封膜。在土坝上层和坡脚填筑2m的防冻层，可有效防止地基土层和排水系统冻结，冬歇期后真空排水系统可正常运行。 |
| 关键词: 寒区筑坝工程 真空联合堆载预压 复杂地质条件 软土地基 |
| DOI： |
| 分类号: |
| 基金项目:国家自然科学基金项目（面上项目，重点项目，重大项目） |
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| Application of vacuum combined preloading method on dam construction in cold regions |
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zhanxinjie, Yang Shouhua
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Nanjing Hydraulic Institute
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| Abstract: |
| The geological conditions of the proposed site of an earth dam project in the north area are complex. The soft soil layer of the foundation is silty clay, overlying by a hard soil layer and the maximum burial depth of the soft soil layer is about 17m, and has the characteristics of high water content, high compressibility and poor drainage consolidation performance. Vacuum combined surcharge preloading was selected as ground improvement method, but the local area lack of construction experience and reference cases. The project faced the following difficulties:(1) The construction efficiency and stratigraphic adaptability of the conventional PVD installation process remained uncertain for the hard soil layer overlying the silty clay layer.(2) The soil layer on the surface of the dam foundation is highly permeable, and lateral sealing effect is essential to ensure the vacuum pressure under the membrane. (3)The filling load of the dam was large, and filling the dam material directly on the surface of the sealing membrane lead to the risk of breakage during construction. (4)The temperature in winter is as low as -30℃, The freezing force may damage the saturated sealing and drainage system and thus affecting the drainage effect of vacuum preloading in the second year. For this purpose, a pilot test section was selected and installation test of prefabricated vertical drains, formation test of the sealing wall, protection test of sealing membrane and anti-freezing test of the dam foundation were carried out. The test results showed that the crawler type vibratory installation process could effectively penetrate the overlying hard soil layer, and its construction efficiency was better than “pilot hole + vibratory installation process”. The 1.2m double-row mud mixing wall could play a good sealing effect. Non-woven cloth and woven cloth were laid on the surface of the sealing membrane, and the lightly compacted transition layer can effectively protect the sealing membrane. A 2m anti-freezing layer on the upper layer and the foot of the earth dam can effectively protect the foundation soil layer and drainage system from freezing, and the drainage system can operate normally after the winter period. |
| Key words: Dam construction in cold areas vacuum combined preloading Complex geological conditions soft soil foundation |
