Research On The Vertical Bearing Mechanism Of Bottomed Piles In Red Mudstone

Red beds,as a weak engineering rock mass,widely exists in Sichuan Province.With the country’s strong support for the economic construction of Sichuan,the infrastructure construction requirements of Sichuan area will be higher and higher,the upper building load will be larger and larger,the foundation depth will be deeper and deeper.All kinds of large-scale building foundations will surely penetrate into red mudstone in order to achieve greater bearing capacity.In order to obtain higher single pile bearing capacity,the expanded pile will be a more excellent pile foundation form in the red mudstone area.At present,the related research on the red mudstone pile contact surface indicates that the frictional resistance of the mudstone-concrete interface has a displacement softening phenomenon.Due to the irregular shape of the expanded pile,the mechanism of friction and end resistance is complicated.In order to safely,economically and efficiently utilize the bearing capacity of the expanded pile,it is necessary to clearly understand the vertical bearing mechanism of the belled pile in red mudstone.Therefore,in this paper,by carrying out the indoor test direct shear test,the numerical simulation and theoretical analysis of the red mud mudstone bottom pile,the vertical bearing mechanism of the red mudstone rock bottom pile under the softening condition of the side friction is studied.The research content and achievements mainly includes the following aspects:(1)Carry out the direct shear experiment of the red mudstone pile-rock contact surface,and got the softening law of frictional displacement and displacement:using the collected weathered mudstone to carry out the direct shear test of the mudstone-concrete interface under different normal stresses,and obtain the mudstone-concrete displacement-Shear stress softening characteristics of the contact surface.Based on the three-fold linear displacement softening constitutive,the three-fold linear displacement softening constitutive of the frictional contact surface of the red mudstone pile rock is established by reducing the shear strength parameters.(2)Based on the obtained displacement softening law,a numerical contact surface constitutive model which can consider the softening of the side friction resistance is established:The softening constitutive model of the friction resistance is compiled into the FLAC3D software by the fish language,and the three-fold linear displacement softening contact of the FLAC3D software is prepared.Facial constitutive.The correctness and applicability of the three-fold line displacement softening contact surface constitutive of FLAC3D software were tested by numerical direct shear experiment.(3)Establishing a numerical model of red-soil mudstone expanded piles and analyzing its vertical bearing characteristics:Based on the compiled softening constitutive model of contact surface,the vertical bearing capacity model of red mudstone belled pile is established,and the load transfer characteristics of red mudstone belled pile under pile top load are obtained.That is,the lateral friction of equal section section is exerted firstly,after the lateral friction of equal section is fully exerted,the inclined plane pulls apart,the lateral friction of inclined plane is reduced to 0,and the end resistance participates in the sharing of pile top load.(4)Analyze the influence of softening resistance and expansion head on the bearing capacity of pile foundation:The numerical models of side friction softening expanded bottom pile,non-softening expanded bottom pile,softening straight pile and non-softening straight pile in red mudstone are established.Comparing the side friction softening with the non-softening pile foundation,it is concluded that the side friction softening will degrade the side friction of the pile body and accelerate the downward load transfer.Compared with the straight pile,the ultimate bearing capacity of the red mudstone expanded bottom pile is 40%higher than that of the red mudstone pile.(5)Analyze the influence of various factors on the vertical bearing capacity of red mudstone expansive piles,and establish the calculation method of red mudstone expansive piles under different parameter values:The vertical bearing capacity of red mudstone bottom-enlarged piles under different parameters was calculated.The sensitivity of each factor to the vertical bearing capacity of red mudstone bottom-enlarged piles was obtained as follows:cohesion of contact surface>Poisson’s ratio of mudstone>standard compressive strength of pile body material>friction angle in contact surface>elastic modulus of mudstone.