Experimental Study On Tensile Properties Of Basalt Fiber Reinforced Cement Stabilized Soil

Cement soil is widely used in practical engineering because of its low price,easy mixing and local materials.The most common is that the cement soil mixing pile is mainly used in the soft soil foundation treatment engineering.For example,the Baishan control project area of the diversion line from Yangtze River to Huaihe River uses the cement soil mixing pile to strengthen the soft soil embankment along the river.However,the eccentric compression of the cement soil mixing pile often leads to tensile stress in some structures,and the low tensile strength and insufficient ductility of the cement soil often lead to the failure of the cement soil.Aiming at the limitations of low tensile strength and insufficient ductility of cement soil,this paper explores the method of adding basalt fiber into cement soil to enhance its tensile strength and the mechanism of basalt fiber strengthening the tensile strength of cement soil by using the advantages of high tensile strength,large elastic modulus and low price of basalt fiber.The main research contents and achievements of this paper are as follows:(1)Through the self-developed uniaxial tensile equipment to carry out the tensile test,and using the orthogonal experiment and extremum difference analysis,it is concluded that the primary and secondary order of the three factors(length,diameter,dosage)of single BF to enhance the tensile strength of cement soil is: length,dosage,diameter.It is also concluded that the optimal mix proportion in this paper is length 9mm,dosage 1.5%,diameter 17μm.The stress-strain curve of BF cement soil is normalized and analyzed.The influence of BF length and dosage on the tensile peak strength and residual peak strength of cement soil is discussed.The addition of BF has greatly improved the toughness and ductility of cement soil,which is mainly reflected in the fact that the BF cement soil becomes "cracked and continuous" when it is damaged by tension.(2)Through the unconfined compression test,it is found that the addition of BF can improve the peak compressive strength and residual strength of cement soil,and delay the stress loss rate of cement soil specimen after reaching the peak strength,and the improvement effect of BF on residual strength is more obvious.The influence of basalt fiber length and content on the compressive strength and residual strength of cement soil is analyzed,and the relationship of tension compression ratio is obtained.(3)Based on the SEM observation of the specimens after compressive failure,and combined with the tensile and compressive test results,the strengthening mechanism of basalt fiber on the tensile strength of cement soil is explained from two aspects of friction constraint and additional equivalent confining pressure.(4)Through the uniaxial tensile test of three kinds of basalt fiber mixing combinations,it is found that 9mm : 12 mm = 3 : 1 is the optimal fiber mixing parameter,which is also the optimal fiber parameter for the peak tensile strength of basalt fiber reinforced cement soil in this paper.The tensile strength and residual strength of the experimental group increased by 2.5% and10.5% respectively compared with the optimal group of 9mm(1.5%).