| As a special property of loess,the collapsibility of loess,which often causes a series of serious consequences such as uneven settlement of building foundation and cracking of buildings,has a serious harm in the field of construction engineering.Therefore,it is particularly important to solve the problems caused by the collapsibility of loess.For the grouting method to deal with the collapsibility of loess,cement grouting material is mainly used as grouting material in actual engineering at present,and the price of cement material is relatively high,resulting in the increase of engineering cost.The industrial wastes,such as fly ash and slag,can be activated by alkali and have cementation ability.Their solid particles are smaller than ordinary cement particles and can be used as grouting materials.This kind of materials can not only meet the requirements of strengthening soft soil foundation,but also play a unique role in environmental protection and waste utilization,and meet the requirements of sustainable development and green development in China.In this paper,the undisturbed loess in Xining area was taken as the research object,and various physical and mechanical parameters of undisturbed loess were obtained through various performance tests of industrial waste grouting materials,indoor immersion compression test?collapsible test?,conventional triaxial test,permeability test and microscopic sem test,etc.Using a set of small indoor homemade grouting equipment,the indoor grouting test was conducted to obtain the soil after grouting reinforcement and then the above tests were conducted to compare with the undisturbed soil,so as to study the mechanism of industrial waste grouting reinforcement collapsible loess.The main contents of the research are as follows:?1?Testing the properties of fly ash cement and slag cement under different conditions by setting different curing ages and different water-cement ratios,so as to find the optimal mixing ratio of industrial waste grouting materials.?2?Using triaxial shear permeameter,the unconsolidated undrained triaxial shear test was carried out on the soil before and after grouting,so as to obtain the shear strength of the soil before and after grouting.?3?A consolidation instrument and a triaxial shear osmotic instrument were used to conduct the collapsibility test and osmotic test of soil before and after grouting so as to study the changes of soil's collapsibility coefficient and osmotic coefficient after grouting.?4?Scanning electron microscope?SEM?and particle crack image recognition and analysis system?PCAS?were used to analyze the soil before and after grouting,and the changes of soil micro-pore structure before and after grouting were obtained.The main conclusions of the study are as follows:?1?Through the performance tests of grouting materials with different curing ages and ratios,it can be seen that the strength of slag cement in each curing age decreases significantly in the process of increasing the slag content,so it is not suitable for slag cement to serve as a kind of grouting materials.The strength of fly ash cement is higher than that of slag cement,meanwhile,fly ash cement has a better injectability.?2?By comparing the shear strength indexes of the soil before and after grouting,it can be seen that the internal friction angle of the soil before and after grouting is not significant.The higher the cement content in grouting material,the smaller the internal friction angle of the soil.However,the change of cohesive force is significant,and the change law is closely related to the age of the soil after grouting.The longer the age,the greater the cohesive force,and the value is also significantly related to the cement content in the grouting material.The higher the cement content,the greater the cohesive force.?3?By comparing the collapsibility coefficient and permeability coefficient of soil before and after grouting,it can be seen that the collapsibility coefficient of soil after grouting is reduced by more than 75% compared with the undisturbed loess,while the permeability coefficient changes more significantly,from 10-4cm/s to 10-7cm/s.?4?The micro test results of soil before and after grouting show that the obvious reasons for the changes of soil strength,collapsibility coefficient and permeability coefficient lie in the huge changes of micro pore structure in the soil,which changes from the macro pore structure to the dense structure filled by various cement hydration products and produces a large strength,and it explains the macro mechanical test phenomenon well from the micro point of view. |
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