Experimental Study On The Influence Of Humus And Polypropylene Fibers On The Strength Features Of Cement Mixing Satuated Loess

When the railway constructed in loess areas of poor engineering properties，it hasencountered some technical challenges in many aspects, such as subgrade settlement causedby collapse deformation for collapseible loess and the bearing capacity of foundation.Cement-soil mixing pile is a method commonly used to improve soft clay, in terms of thecurrent railway embankment reinforcement of saturated loess foundation, it is less using thesoil-cement mixing pile, and this method lacks accumulated experience;meanwhile,whencement-soil mixing pile is used for improving railway subgrade of saturated loess, it willinevitably encounter humus and plant roots and twigs and other debris.This paper willresearch the strength variation of cement mixing saturated loess containing humus and treebranches and other debris, and the influence of polypropylene fiber reinforced cement mixingsaturated loess role.On the study of humus affect the strength of the cement mixing soil,humus content of saturated loess were1%,3%,5%,7%,9%, cement and fly ash mixturecontent were12%,15%,18%and20%,and testing the unconfined compressive strengthafter cured in water for7d,28d,90d;on the study of plant roots affect the strength of thecement mixing soil, plant roots content of saturated loess were different, cement and fly ashmixture content were12%,15%and20%,and testing the unconfined compressive strengthafter cured in water for28d,90d; on the study of polypropylene fiber affect the strength of thecement mixing soil, cement and fly ash mixture content were12%,15%and20%, in eachgroup of cement mixing soil with the same cement and fly ash mixture content, mixed withdifferent contents of polypropylene fibers, and testing the unconfined compressive strengthafter cured in water for28d,90d; when using FLAC3D numerical simulation softwaresimulation of cement mixing pile composite foundation, studied the bearing behavior ofcement-soil mixing pile and the settlement characteristics of pile groups composite foundationduring the roadbed construction process and construction is completed.The study found that:(1) Cement mixing soil which contains humus, it’s unconfinedcompressive strength will decreasing when humus content increasing, while it’s moisturecontent corresponding increase. This means cement mixing soil which contains humus willinhibit the hydrolysis and hydration reaction, the product of hydrolysis and hydration reactionwill reduce, which inhibiting the growth of cement mixing soil strength,and the residualmoisture in the soil increased.(2) Cement mixing soil which contains plant roots, it’sunconfined compressive strength will increasing when cement and fly ash mixture contentincreasing, and it’s strength higher than the strength of ordinary cement mixing soil;when thecement and fly ash mixture content is same, it’s unconfined compressive strength willdecreasing when plant roots content increasing. On the one hand, cement mixing soil which contains plant roots will reduce the contact surface of the cement and water will inhibit thehydrolysis and hydration reaction, inhibiting the growth of cement mixing soil strength, onthe other hand, plant roots which in the cement mixing soil will produce friction or adhesionaround soil, thereby increasing the strength of cement mixing soil.(3) Cement mixing soilwhich contains polypropylene fiber, it’s unconfined compressive strength will increasingwhen cement and fly ash mixture content increasing, and it’s strength higher than the strengthof ordinary cement mixing soil; when the length of polypropylene fiber is shorter, while thestrength increased obviously. The study suggests that there are two aspect of polypropylenefiber affect mechanism: physical strengthening effect and chemical inhibition effect. Physicalstrengthening effect is divided into friction or adhesion, equivalent confining pressure effectand anchor function; chemical inhibition effect is inhibiting the hydrolysis and hydrationreaction.(4) The result of cement mixing pile composite for numerical simulation analysis is:during the roadbed construction process, the pile is closer to the center line,the axial force isgreater, and the settlement is greater too; the pile is farther to the center line,the axial force issmaller, and the settlement is smaller too.