Abstract:To study the horizontal bearing capacity of pile with cap under the existing vertical load, two groups of PIV model test were carried out. The effects of different vertical loads on the horizontal displacement, bending moment of pile and soil displacement field around pile are analyzed. The influential mechanism of vertical load on pile-soil interaction under pile with cap is studied. The results show that the existing vertical load decreases the horizontal displacement, weakens the bending moment of pile under the same horizontal load. In the process of horizontal loading, the main region of pile-soil action is the middle and upper region of the soil around the pile. The application of the vertical load on the pile top will mobilize the soil around the pile, form a larger soil disturbance area. The soil densification effect caused by vertical load will reduce the horizontal displacement and bending moment of pile and increase the horizontal bearing capacity of cap pile. Meanwhile, this densification phenomenon also reduces the uplift and collapse area of pile side soil.

Abstract:In order to study the stability of GFRP lined recycled composite pipe under bending moment, a finite element analysis software was used to establish the finite element model of GFRP lined recycled composite pipe based on the bilinear constitutive relationship between layers, and the influences of the corrosion degree of outer pipe and the thickness of inner layer on the stability of GFRP lined composite pipes was analyzed. The stress cloud diagram of the composite pipe under bending action was obtained and the curve of bending moment-center point displacement of the pipe was extracted. The results show that the interlayer force between the outer pipe wall and the GFRP lining layer limits the rapid development of pipeline deformation to a certain extent, and improves the ultimate bending moment of the composite pipe and the anti-deformation ability of the pipe before buckling. The deformation and stress of the composite pipe with corrosion pit are mainly concentrated around the deepest part of the corrosion pit. With the increase of corrosion depth, the extreme value of bending moment gradually decreases.

Abstract:The pile-soil interaction mechanism of h-type retaining structures is complicated. As a result, a reasonable engineering design method has not been developed yet. The deflection differential equations of the front and rear piles are established on the basis of the Euler-Bernoulli beam theory and a series of soil springs around piles. It ensures the deformation compatibility of pile at sliding surface, a matrix equation set using the finite difference method was conducted to evaluate the internal force and deformation of h-type retaining structure. A finite element model was established based an h-type retaining structure engineering in Keku landslide. The two methods are used for evaluating the internal force and deformation of piles, the difference in the maximum bending moment and shear force between the finite difference method and FEA method is less than 5%, which indicates that the proposed method is reasonable for evaluating the h-type retaining structure in slope design engineering.

Abstract:In order to study the mechanical performance of the connection nodes of double web I-beam GFRP waist beam in deep foundation support, two sleeve type connection methods of GFRP waist beams were tested with two points of symmetric loading footage, and the three-dimensional numerical models of the two connection methods were established with the help of ABAQUS finite element simulation software to analyze the force performance of GFRP waist beams with different connection methods, and the span section of waist beam was taken as the object of study to reveal the transverse deformation law of the connection. The transverse deformation law between the sleeve and the GFRP waist beam is studied, and the limit states and damage forms of the GFRP waist beam members with different connection methods are mastered. The results show that the double web I-beam GFRP waist beams have high bearing capacity and good stability of the members; the use of built-in steel sleeves to connect the members has less deformation, higher node bearing capacity, easy installation on site, and can realize the recycling of waist beam members in foundation pit support, which is a reasonable connection method for GFRP waist beam construction on site.

Abstract:In order to realize the real-time settlement analysis of interlaction process between miscellaneous fill and soft soil foundation and explore the effect of coarse particle content of soft soil on the interbedded settlement and the consolidation settlement of soft soil, with the help of self-developed interbedded test instrument of miscellaneous fill and soft soil, the interbedded settlement and consolidation settlement of soft soil were quantitatively distinguished through laboratory tests. Orthogonal experimental groups were designed to analyze the settlement development rule of two kinds of miscellaneous fill particles (5 mm, 10 mm) and five kinds of coarse particle content soft soil (0, 3%, 6%, 9%, 12%) under a certain load, and to summarize the differences of final settlement and instantaneous settlement of total settlement, interbedded settlement, and consolidation settlement of soft soil. The experimental results show that when coarse particles exist in soft soil, the total settlement and interbedded settlement increases more and develops faster than that those without coarse particles in each stage, and the total settlement and interbedded settlement reach a maximum value when coarse particles content is 6%. Besides, the influence of the coarse particles content on consolidation settlement of soft soil is not obvious.

Abstract:Due to the special cross section of H-shaped piles, the characteristics of soil compaction effect caused by pile driving cannot be simply replaced by the soil compaction law of pipe piles. Therefore, based on the field test data of Hujiashen Phase II project, this paper studies the laws of excess pore water pressure and soil displacement caused by pile sinking. Based on the modified circular hole expansion model, a calculation formula for rectangular hole expansion suitable for H-shaped piles is derived considering the particularity of H-shaped piles during hole expansion. The formula is used to calculate the excess pore pressure and soil displacement caused by pile driving, and compared with other methods. The results show that the modified expanded hole model fully considers the linear variation of pore water pressure along depth in calculating the excess pore pressure and soil displacement of H-shaped piles, and the results are closer to the measured data.

Abstract:When the structure generates large local deformation under blast loading, the single degree of freedom (SDOF) method will have large errors or even mistakes to calculate the overall displacement of structure. In order to solve this problem, based on the SDOF theory, study on I-shaped steel beam, after analyzing the influence of local deformation of flange on the overall displacement of steel beam, the bending resistance function is improved based on the proposed simplified deformation model of steel beam section. An improved single degree of freedom (ISDOF) method for blast resistance analysis of steel beams is proposed. Finally, the dynamic displacement response and failure characteristics of steel beams under different blast loading are numerically simulated by the finite element software ABAQUS. The results are compared with those of the SDOF model and the ISDOF model, and the displacement and failure differences of steel beams under different calculation models are studied. The results show that compared with the finite element simulation results, the larger the local deformation of the steel beam flange is, the smaller the SDOF model calculation result is. The calculation results of ISDOF model are better, ISDOF model can be better applied to the simplified displacement calculation of blast resistance analysis of steel beams.

Abstract:Based on the upper bound limit analysis and random field theory, this paper investigates the reliability of excavated slopes in undrained conditions within the framework of Monte Carlo simulation. The soil undrained shear strength is simulated as random fields. The effects of degree of non-stationarity and coefficient of variation on the slope stability are highlighted in the parametric sensitivity analysis. The results indicate that the slope reliability index increases with the increase of degree of non-stationarity and reduces as the coefficient of variation increases. Meanwhile, the soil spatial variability affects significantly the failure mechanism of slopes. Under the combination of random parameters considered in this paper, the failure mode is mainly of deep failure. With the increase of degree of non-stationarity and coefficient of variation, the probability of occurrence for the deep failure mode gradually reduces and the probability of occurrence for the toe failure and deep toe failure modes increase accordingly.

Abstract:To further understand the fracture damage process of complex fractures, this paper uses PFC2D software to conduct numerical tests on rock masses with different number of fractures based on the fracture mechanics theory, and analyses the influence of fracture dip angle, surrounding pressure and other factors on the strength and fracture expansion of rock masses. The study shows that the peak stress and initiation stress of single fracture decrease and then increase as the fracture inclination angle increases, and the peak stress increases from 120 MPa to 160 MPa when the surrounding pressure increases from 2 MPa to 8 MPa. In cases of 60° and 90°, the fracture inclination is mainly coplanar secondary fractures, and the peak stress of multiple fractures decreases significantly with the increase of the number of prefabricated fractures at different surrounding pressures. The research results can provide reference for further exploration of the destabilization damage law of fractured rock masses.

Abstract:In view of the poor durability of traditional cement solidified soil, the unconfined compressive strength test, dry-wet cycle test, dry shrinkage test and SEM electron microscope scanning test were carried out on the cement solidified sand with three different water absorption properties of polyacrylamide (PAM). The strength, durability and microscopic mechanism of PAM with different water absorption properties to improve cement solidified soil were studied and analyzed. The test results show that the incorporation of PAM can effectively improve the strength of cement solidified soil, and the different water absorption properties of PAM will lead to a certain regular change in the strength of cement solidified soil. The incorporation of PAM can effectively improve the durability of cement stabilized soil. Relatively speaking, the strong water absorption PAM shows a better impact on the durability of cement stabilized soil. After PAM is mixed with cement solidified soil, the overall cementation structure of PAM-cement stone-soil particles is formed, which enhances the strength and dry shrinkage cracking resistance of cement solidified soil.

Abstract:The use of stainless steel slag in alkali-activated cement plays an important role in its resource utilization. Calcium oxide, sodium carbonate and water glass are used as composite activators, and the total alkali equivalent is fixed at 6% (the alkali equivalent of calcium oxide and sodium carbonate is 4%, the alkali equivalent of water glass is 2%). The effect of stainless steel slag content (0%、10%、20%、30% and 40%, the effect of the mass ratio of stainless steel slag to the summation of slag and stainless steel slag) on the compressive strength, flexural strength, splitting tensile strength, strain of interior steel ring, circumferential tensile stress and cracking resistance of alkali-activated slag-stainless steel slag mortar (ASLm) is investigated, and the crack resistance of ASLm was characterized by crack resistance evaluation index A_cr (t). The study found that with the increase of stainless steel slag content from 0% to 40%, the compressive strength, flexural strength, splitting tensile strength, strain of interior steel ring and circumferential tensile stress decrease, while the cracking resistance first increases and then decreases. When the content of stainless steel slag is 30%, the A_cr (t) of ASLm reaches the largest, i.e., the crack resistance is the best.

Abstract:In order to study the ductility behavior of steel box-section piers with T-shaped stiffeners subjected to a constant vertical load and lateral cyclic loading, the accuracy of the finite element analysis method is firstly verified by comparing with the test results. Then, a series of parametric studies is carried out to investigate the effect of the normalized flange width-thickness ratio, normalized pier’s slenderness ratio, normalized stiffener’s slenderness ratio and axial load ratio on the maximum strength and ductility behavior of steel box-section piers with T-shaped stiffeners. Finally, the formulas for predicting the maximum strength and ductility ratio of steel piers are proposed on the basis of parametric analysis results. The research results show that the ductility behavior of steel piers is significantly improved with the decrease of the normalized flange width-thickness ratio, normalized pier’s slenderness ratio, normalized stiffener’s slenderness ratio and axial load ratio.

Abstract:In order to study the aerodynamic effect of high-speed trains passing through underground stations, it provides a reference for the design of underground high-speed railway stations. Based on the background of an underground high-speed railway station, a numerical model of tunnel-underground station-train was established by numerical simulations. The calculation method of sliding mesh was used to simulate the train running through the underground station. The train speed was selected at 200 km/h, 250 km/h, 300 km/h and 350 km/h, and 25 measuring points were arranged on the platform for monitoring. The influences of the train speed and platform position on the aerodynamic wind field on the platform was studied. The results show that: (1) The aerodynamic effect on the platform changes more with the increase of train speed; (2) After the train passes through the underground platform, it will also produce coda waves that cannot be ignored; (3) The highest fluctuation value of the aerodynamic wind field on the platform is at the entrance of the platform.

Abstract:Based on the actual project of a multi arch tunnel in Northern Shaanxi, to study the deformation characteristics of surrounding rock during the construction of shallow buried multi arch tunnel with weak and broken surrounding rock, the long-term tests of vault settlement and surrounding rock deformation were carried out by laying certain monitoring instrument on site, while the laws of vault settlement and surrounding rock radial deformation during the construction process were obtained. The results show that: the surface settlement is similar to peck settlement curve. The closer to the center of the tunnel, the greater the surface settlement is. The maximum settlement value is about 12.1 mm after the excavation of the left tunnel, and the variation of vault settlement along the longitudinal direction of tunnel is as follows: middle pilot tunnel > main tunnel > left and right pilot tunnel. The middle pilot tunnel shows a vault settlement, while the side pilot tunnel shows a horizontal convergence. The convergence deformation of the upper step construction is significantly greater than that of the lower step construction because of no temporary invert bottom sealing. With the increase of the distance from the tunnel wall, the cumulative deformation of the measuring point decreases gradually. The surrounding rock loose area of K21+970 test section is about 2 m, and the loose area of K21+970 test section is more than 4 m due to the limitation of the layout of the measuring line.

Abstract:The side contraction of the water behind the gates is more serious and the water flow diffuses longitudinally, resulting in a more complex flow pattern, when the plane gate of the deep-hole pressure tunnel operates with small opening. Therefore, some engineering measures need to be taken to improve the flow pattern behind the gates. Based on the physical model experiment and the theoretical analysis, the hydraulic characteristics behind the gate under different heights of diversion ridge are studied in this paper. The results show that the side contraction of the water behind the gate decreases with the increase of the height of the diversion ridge, the height and length of the tongue of the water behind the gate decrease significantly and the negative pressure of the bottom plate basically disappears, and the pressure distribution tends to be uniform. However, the increase of the height of the diversion ridge in the gate chamber has a certain influence on the flow capacity. Compared with the plane bottom gate chamber, the flow capacity under the gate decreases with the increase of the height of the diversion ridge. In order to avoid affecting the flow capacity, the height of the diversion ridge should not be too high.

Abstract:In order to study the hydrogeological conditions and main engineering hydrogeological problems of the major project from western Bomi to Nyingchi section in eastern Tibet, On the basis of the previous research results, the relevant research work of key borehole core geological cataloging and field hydrogeological investigation.The results show that there are four types of hydrogeological problems along the route, such as high cold, high steepness, high seismic intensity, high ground stress, high ground temperature and high water pressure. There are mainly four types of hydrogeological problems, such as high water pressure water inrush in deep-buried long tunnel, high pressure water inrush in fracture zone bedrock, thermal damage caused by high temperature hot water, and the influence of tunnel drainage on ecological environment. The predicted water pressure outside the Yigong tunnel is between 0.80 and 3.47 MPa, the predicted maximum water inflow of the Yigong Tunnel and Sejilashan tunnel is close to or over 100 000 m³/d, and the measured bottom temperature of 25 boreholes along the Lanyue tunnel is between 12.5 ℃ and 93.5 ℃.