Experimental Investigation On Reinforcement Of Defective TuLou By Microbe

Fujian Tulou is located on the southeast coast of China.Due to its own materials and the erosion of the southern wind and rain,it has caused a large number of cracks in the wall of Tulou,and will further expand under the infiltration of rainwater,affecting the safety of Tulou.Microbial grouting reinforcement is a method of in-situ filling particles in cracks as the framework of the reinforcement structure under the condition that the structure is not suitable for using traditional grouting materials such as cement,epoxy resin and lime.At the same time,microorganisms and nutrient solution are injected to induce the formation of calcium carbonate in the pore of filling particles and gel filling particles to make them have a certain strength.Relevant research shows that the application of this technology in the reinforcement of masonry cultural relics and concrete cracks has obvious effect.For Fujian Tulou,the strength of rammed earth wall determines the safety of Tulou,and the continuous expansion of wall cracks will seriously affect the safety of Tulou.This paper is the first attempt to apply microbial grouting technology to repair the cracks in rammed earth wall,and take a new step for the reinforcement technology of Fujian Tulou.The main contents of this paper are as follows:Firstly,the selection of microorganisms,the growth curve of microorganisms and the optimum culture temperature and PH were measured,and then the microorganisms were preserved.Secondly,the effects of microbial concentration,Ca₂⁺concentration,urea concentration and NH₄⁺concentration on urease activity and the concentration of both microbial and nutrient solutions on calcium carbonate yield were studied.The results showed that the higher the microbial concentration,urea concentration and NH₄⁺concentration,the higher the urease activity,and the higher Ca₂⁺concentration the lower the urease activity.When the concentration of nutrient solution was 1.0 mol/L,the inhibition of urease activity by Ca₂⁺concentration in nutrient solution could be reduced under the condition of guaranteeing the yield of calcium carbonate.Then,the site investigation of Tulou in Yongding District of Fujian Province is carried out,and the main diseases and causes of the rammed earth walls are summarized.The basic physical properties of the soil samples of the local abandoned Tulou are determined,and the preparation and maintenance of rammed soil sample are completed.Then,by using the optimal bacterial concentration and nutrient solution concentration obtained from the study,the controllable grouting parameters such as particle size,soil content and grouting times were optimized through cementing experiments to form microbial sand columns with certain strength.The unconfined compressive strength,SEM and XRD tests of these microbial sand columns were carried out,and the compressive strength,stress-strain curve,failure mode and micro-structure were analyzed.According to the structure and crystal type of calcium carbonate,the uniaxial compressive strength increases with the increase of grouting times,and the compressive strength of sand column is the highest when the filling particle is full-graded sand:soil（3:2）.Finally,using the optimal bacterial concentration,nutrient solution concentration and filling particles obtained from the study,microbial grouting was used to repair the tamped soil specimens damaged by bending and shearing.The cracks were set at 5,10 and 15 mm.The repaired rammed soil samples were re-tested for bending and shear strength,and the static contact angle of the surface of the soil samples at the cracks was tested.The repairing rate of flexural and shear strength,failure mode and contact angle of soil surface after repairing are analyzed.It is concluded that the rate of bending and shear repair decreases with the increase of crack width.And with the increase of cracks,the water resistance of soil samples decreases,but the decrease is not obvious,and the water resistance of soil samples at cracks is significantly higher than that of Rammed Soil Samples itself.