木质素纤维-高钙粉煤灰复合改良膨胀土试验研究

Experimental study on expansive soil improved by lignin fiber-high calcium fly ash composite

为改进单一方法改良膨胀土存在的不足,选用木质素纤维和粉煤灰复合改良膨胀土,提升改良土强度和破坏韧性,抑制膨胀变形。分别开展了自由膨胀率、有荷膨胀率(50 kPa)、无侧限抗压强度试验、低应力直剪试验获得单掺粉煤灰时的最优掺量,再掺入木质素纤维进行力学强度试验、水稳试验和微观试验,以力学特性变化结合微观结构特征分析复合改良效果。结果表明:单掺粉煤灰能够抑制膨胀土的膨胀特性,提升改良土强度,最佳粉煤灰掺量为20%;加入木质素纤维进行复合改良能够进一步提升土体强度,增强破坏韧性,水稳性也大大增强,20%粉煤灰和1.0%木质素纤维复合改良效果最好;复合改良能够很好地改善孔隙分布,抑制土体裂缝延伸,增强土体密实度。

To improve the shortcomings of a single method to improve expansive soil,this paper adopts the method of composite improvement,and selects lignin fiber and fly ash(high calcium)to improve expansive soil.Based on the reuse of production waste,it is used in the improvement project of expansive soil in Mengzi,Yunnan to inhibit the expansion deformation of soil and improve the strength,failure toughness and water stability of improved soil.The optimal dosage of fly ash is obtained by free expansion rate,loaded expansion rate(50 kPa),unconfined compressive strength test,and low-stress direct shear test of improved soil.The mechanical strength test,water stability test,and micro test are carried out by adding lignin fiber,and the composite improvement effect is analyzed by mechanical properties and microstructure characteristics.The test shows that:(1)When fly ash is added alone,the expansion characteristics of the improved expansive soil are inhibited,the expansion rate is greatly reduced,the unconfined compressive strength and shear strength are improved,and the cohesion changes significantly;(2)With the increase of curing age,the unconfined compressive strength of the improved soil can be significantly improved,the failure mode of the sample is improved,the existence of the fiber increases the failure toughness,and the water stability is also greatly enhanced.The composite improvement effect of 20% fly ash and 1.0% lignin fiber is the best.(3)There are tiny pores in the plain expansive soil,and cracks are developed.After the improvement,the pore distribution in the soil is improved,and the large pores become small pores.The generated cemented particles fill the cracks,and the particles gather together to enhance the compactness of the soil.Fiber incorporation inhibits the extension of soil cracks and contributes some strength to the soil‘s resistance to external forces.