Influence Mechanism Of Pebbly Silty Clay's Creep On Lattice Beam Adopted In The Qiaotoubei Slope

Pebbly silty clay accumulation of the Q iaotoubei slope is in creep.There are cracks founded through on-site investigation on multiple parts of the lattice beams without anchor rods used in landslide correction.Even some longitudinal beams and transverse beams were broken.In order to clarify the influence mechanism of the creep of pebbly silty clay on the deformation and failure of lattice beams,Pebbly silty clay accumulation of the slope is taken as the study subject,In view of the shortcomings of the traditional one-dimensional compression creep test that does not allow lateral deformation of the sample,the test method has been improved,and the modified high-pressure consolidation instrument is used to conduct the compression creep test of the pebbly silty clay.Based on the test data,a creep constitutive model suitable for describing the creep characteristics of pebbly silty clay with gravel is selected by regression analysis,FLAC3 D software is used to simulate t he stress and deformation process of the structure beam during the creep process of the landslide accumulation body.Based on the above research results,the internal mechanism of the deformation and failure of the lattice beam without anchor bolt caused b y the creep of the silty clay with gravel in the accumulation body is discussed.The results are as follows(1)The compression creep test with the loading area smaller than the upper surface of the cylinder specimen can overcome the disadvantage that the specimen transverse deformation is not allowed in the traditional one-dimensional compression test.The test results show that the smaller the loading area under the same load,the larger the final creep of the specimen,the greater the creep rate,the longer the creep stability time,and the greater the load,the more significant this phenomenon.In this paper,the size of the pebbly silty clay with a size of 220 mm × 300 mm is used.Under the load of the maximum first-order load of 250 k Pa,the final creep o f the sample with a loading surface diameter of 150 mm is reduced by 39% compared with the diameter of 70 mm.Stabilization time is reduced by 24h;The test results with a loading surface diameter of 100 mm and 70 mm are basically the same,indicating that the loading surface diameter of 70 mm can greatly reduce the lateral deformation limit of the sample.Therefore,for the undisturbed soil sample with a diameter of 220 mm,the 70 mm diameter is used for loading The test data is more accurate.(2)The pebbly silty clay has obvious attenuation creep characteristics under the load of 50 ? 250 k Pa,and has not entered the stage of constant velocity creep.The least square method is used to fit the creep test curve.Both the generalized Kelvin model and the Burgers model can approximately express the creep law of the soil,and the correlation coefficients are both greater than 0.95.However,because the Burgers model cannot accurately describe the deformation characteristics of the sample at the end of loading,the creep rate tends to zero,so the generalized Kelvin model can better describe the creep characteristics of the crushed silty clay containing the research object in this paper.(3)The numerical simulation results show that under the influence of a single factor of the creep of the accumulation body,when the creep time is 90 days,a tensile stress of 2.2MPa appears at the junction of the first row of beams and longitudinal beams on the top of the slope;Under the influence of the creep of the accumulation body and the soil under the rain-washed beam,the tensile stress of 1.8MPa appeared at the connection between the first beam and the longitudinal beam at the top of the slope during the 60 days of creep.This shows that the creep of the accumulation body is enough to generate tensile stresses beyond the tensile strength of the C25 concrete inside the lattice beam,and rainwater erosion will accelerate the destruction of the lattice beam.(4)For the lattice beams of the square frame structure without anchor rod used for the slope protection of the Q iaotoubei slope,During the creeping process of the upper layer of landslide,the crossbeam bear the thrust of the upper soil body and are transmitted to the stringers.Stringers are compression members and their defor mation is small,so the two ends of the crossbeam can be regarded as fixed constraints.Its stress state is similar to that of statically indeterminate beams subjected to vertical and downward uniformly distributed loads and fixed constraints at both ends.With the increase of the creep deformation of the accumulation body,the soil thrust above the beam will continue to increase,and a large bending moment will be caused at both ends and the center of the beam,resulting in the tensile stress exceeding the concrete tensile strength at the connection between the beam and the longitudinal beam and the central position of the beam,resulting in the tensile fracture.Because the rain erosion of the soil under the crossbeam will lead to the loss of the support force of the soil under the crossbeam,making the crossbeam under the same size of the upper soil thrust deformation is larger,more prone to damage.