纤维底渣混合土循环剪切性能研究

生活垃圾焚烧底渣作为常见的固体废弃物之一,可与纤维混合提高其强度和稳定性。对生活垃圾焚烧底渣–黏土–聚丙烯纤维按一定比例混合,进行循环前大型直剪、循环剪切和循环后直剪试验,研究不同竖向应力、不同剪切位移幅值、不同压实度对纤维加筋底渣混合黏土循环剪切特性及循环后单调直剪特性。试验结果表明:循环前直剪试验中,剪切位移与剪应力曲线呈现弱硬化现象;施加循环荷载后的单调直剪试验,剪切位移与剪应力曲线则呈现明显软化现象。循环剪切试验过程中土样在不同竖向应力、不同剪切位移幅值下均出现循环剪切硬化和剪缩现象。随循环次数增加,硬化程度和剪缩量逐渐减小。随压实度增加,试样由明显的硬化型向软化型发展,压实度越大,沉降量越少,剪缩量越小。对比循环剪切后试样的单调直剪试验与未循环剪切单调直剪试验结果发现,循环剪切后的土样抗剪强度明显增大,黏聚力和摩擦角都相应增加。聚丙烯纤维的加入可以与底渣混合土形成空间网络骨架,从而增加试样抵抗变形能力,减小竖向沉降,增强稳定性。

Cyclic shear performance of fiber bottom ash mixed soils

As one of the common solid wastes,municipal solid waste incineration(MSWI) bottom ash can be mixed with fibers to improve its strength and stability. In this paper,in order to investigate the characteristics of fiber-reinforced bottom ash mixed clay soil under different vertical stresses,different shear displacement amplitudes and different degrees of compaction,large direct shear tests before and after cyclic shear and cyclic shear tests were carried out on the mixture of MSWI-clay-polypropylene fiber at a certain ratio. The test results show that the shear displacement and shear stress curves in the monotonic direct shear tests present weak hardening phenomenon while that the shear stress-displacement curves present obvious softening in the monotonic direct shear tests after cyclic shear. During the cyclic shear process,the soil samples show cyclic shear hardening and shear shrinkage under different vertical stresses and different shear displacement amplitudes. As the number of cycles increases,the degree of hardening and the amount of shear shrinkage gradually decrease. With increasing the degree of compaction,the specimen develops from a clear hardened type to a softened type. The greater the degree of compaction,the less the amount of settlement and the smaller the amount of shear shrinkage.Comparing the results of cyclic monotonic direct shear test after cyclic shear and non-cyclic monotonic direct shear test,it is found that the shear strength of the soil sample after cyclic shear increases significantly,and the cohesion and friction angle increase accordingly. The addition of polypropylene fibers can form a spatial network skeleton with the bottom ash mixed soil,thereby increasing the resistance of the sample against deformation,improving stability and reducing vertical settlement.