Phosphogypsum,as one of the industrial solid wastes,can enhance the soil strength but also increase the brittleness while the fiber reinforcement technique can improve the soil plasticity.The synergy between the two materials(phosphogypsum and fiber)can play a complementary role in improving the mechanical properties of soils.The loess from Yangling,Shaanxi Province,was used to explore the optimal mix ratio of phosphogyp-sum in the loess by unconfined compressive strength(UCS)tests.Then,the optimal mix ratio of fiber in the mixture of phosphogypsum and loess was investigated by the direct shear test based on the mixture ratio above.Finally,the microscopic mechanisms of loess improvement with phosphogypsum and polypropylene fibers were examined through scanning electron microscopy(SEM).The results showed that the loess UCS increases first and then decreases with an increase in the phosphogypsum mass when the phosphogypsum is mixed with the loess for reinforcement,and the optimal mix mass ratio of phosphogypsum in the loess is 12% in this study.The polypropylene fibers were then mixed into the mixture of phosphogypsum and loess based on the optimal mix mass ratio of phosphogypsum in the loess.It can be found that the peak strength,cohesion,and residual strength of the mixture sample increase first and then decrease,while the internal friction angle increases,with an increase in the polypropylene fiber content.The microscopic test results also indicated that the phosphogyp-sum-improved loess and phosphogypsum-polypropylene fiber-improved loess both significantly enhance the cementation and fill the voids among soil particles.Polypropylene fibers in loess can form fiber clumps to wrap the soil particles,thereby providing tensile stress and improving the plasticity for the soil sample.
Cables are the main force-transfer components of cable-stay bridges,and the safety and durability of the bridges will be threatened when the cables are seriously corroded.In this study,artificial accelerated corrosion,three-dimensional topography scanning and mechanical properties testing were carried out to explore the mechanism of the influence of additional zinc wire on corrosion expansion characteristics and mechanical properties degradation of the cables.Firstly,high-strength steel wire cable specimens with zinc wire and without zinc wire(control group)were prepared,and the artificial accelerated corrosion was carried out for 4,8,and 12 weeks by spraying droplets through the annular openings set up in the sheaths to simulate the damage of the sheaths.Secondly,the Holon 3DX+non-contact scanner was used to construct the point cloud model of the cable,and the influence of zinc wire on the corrosion expansion of high-strength steel wires was analyzed.Finally,the MTS testing machine was utilized to conduct static tensile tests on high-strength steel wires with varying degrees of corrosion.A correlation model between the cross section loss rate and the mechanical properties of the corroded high-strength steel wires was established,and the load-bearing performance of the cable was evaluated.The results show that after 4,8,and 12 weeks of accelerated corrosion,the average values of the maximum section loss rate of the steel wire at the sheath opening of the zinc-added wires were reduced by 47.14%,62.68%,and 38.70%,respectively,compared with those of the zinc-free wires;the average values of the ultimate strength of the steel wires at the sheath openings and the average values of the yield strength were increased compared with those of the cables without zinc wire by 0.17%,6.12%,5.55%,and-0.31%,8.54%,and 6.24%,respectively;and the residual load carrying capacity of the cable was increased by 0.16%,5.41%,and 4.83%,respectively.
The present study investigates the dynamic response characteristics during the shield cutting pile process.The dynamic response induced by shield cutting pile impact load was solved by combining numerical simulation and theoretical analysis with the background of the shield crossing group pile project of Nanjing Metro Line 10.Concurrently,vibration sensors were installed on the cutterhead to monitor the dynamic response of the shield cutting pile.The results of the study indicate that:(1)When the shield cuts the reinforced concrete pile foundation at a low speed of approximately 5 mm/s,the thrust and torque changes are small,and the thrust and torque show obvious hysteresis because the pile foundation is cylindrical and the cutting section increases slowly.The peak thrust and torque are about 1.3 times and 1.25 times the initial value.(2)As demonstrated by the simulation results,the rebar incision presents a compression-tension fracture under the action of multiple cuts by the cutter.Under the impact loading,multiple dynamic response waveforms appear at the cutterhead bearing position with peaks close to 0.6g.(3)The measured data show that under the impact load,the time domain curve of cutterhead vibration acceleration shows several consecutive peaks with an interval of about 0.1 s and an amplitude of 0.5g.The measured impact response waveform is highly consistent with the theoretical solution and they verify each other.The waveform can be used as a typical characteristic of continuous cutting of steel bars by multiple cutters.(4)During the whole pile cutting process,the acceleration response and peak value are significantly higher,and the maximum intensity is about twice as high as when cutting clay ground.After this,the response will undergo a rapid decline.
Both calcium source and admixture have an impact on the reinforcement effect of microbial induced calcium carbonate precipitation(MICP).In order to explore the effects of different concentrations of the admix-ture(AlCl3∙6H2O)and calcium sources on the curing effect of MICP,the sand column test and aqueous solution test were carried out,and different concentrations of AlCl3∙6H2O were added to the cementing solution for perfu-sion test,and the unconfined compressive strength(UCS)and calcium carbonate content after reinforcement were measured.The MICP reinforcement effects of calcium chloride and calcium acetate were analyzed,and the improvement of MICP reinforcement effect under different concentrations of AlCl3∙6H2O for the two calcium sources was analyzed.The effect of aluminum ions on the composition and morphology of calcium carbonate was analyzed with SEM.The results showed that calcium acetate as a calcium source had a better curing effect.After the addition of aluminum ions,the strength optimization effect of calcium chloride as a calcium source was more obvious.Among them,the concentration of AlCl3∙6H2O at 6 mmol/L was the optimal concentration,which was conducive to reduce the number of perfusions,saving raw materials and reducing economic costs.Aluminum ions contribute to the formation of calcium carbonate crystals,enhance the adsorption of sand parti-cles,and improve the curing strength.The concentration of aluminum chloride has a significant effect on the cur-ing effect of MICP with different calcium sources,which is of great significance for engineering practice.
Exploring the mechanical properties of soft-hard interbedded rock mass with different initial damages is crucial for assessing the stability of post-seismic damaged rock masses under cyclic drying and wetting condi-tions.Taking the interbedded rock mass of metasandstone and phyllite as a research object,the samples with dif-ferent initial damage degrees were prepared through cyclic loading and unloading tests followed by cyclic drying and wetting tests.Subsequently,uniaxial compression tests were conducted to investigate the deformation and failure characteristics,crack evolution process,and strength degradation laws of samples with different initial damage degrees,to explore the precursor information of sample failure,and to reveal the damage degradation mechanism from a micro perspective.The results indicate that the deformation difference coefficient can quantify the discrepancies in deformation across different areas of the sample surface.The propagation of transcrystalline cracks and intercrystalline cracks extends throughout the loading process,with tensile fracturing being the prima-ry mode of failure.The increase in the proportion of shear fractures will cause an increase in the coefficient of variation(Cv)of the RA/AF values.When the Cv reaches 6.5,the sample is approaching failure.The shear fail-ure mode of the sample is primarily governed by the structural features of the rock mass,while initial damage in-fluences the type of failure and the development of cracks.Initial damage leads to a decrease in elastic modulus,compressive strength,and failure displacement.The increase in microcracks and the weakening of interparticle bonding are the fundamental causes of the deterioration of the rock mass's macroscopic mechanical properties.
