All existing mathematical models for predicting deformation-dependent lateral earth pressure assume the at-rest state as the turning point for the relationship between lateral earth pressure and soil deformation. However, this assumption lacks rigorous consideration of the physical meaning of the turning point. In this study, the physical implications of the turning point in a general relationship between lateral earth pressure and soil deformation are analyzed. A simple hyperbolic model is subsequently developed and then validated using experimental results from plane strain loading tests. It is found that it is more appropriate to take the isotropic stress state as the turning point, because the principal stress orientation begins to rotate at this point. This finding is helpful and constructive for developing mathematical models that predict deformation-dependent lateral earth pressure. The proposed simple hyperbolic model can be used to describe well the measured nonlinear relationship between lateral earth pressure and soil deformation.

Negative skin friction (NSF) of piles in recent filling or soft area is an important effect factor of pile bearing capacity. Since field experiments on NSF are time consuming and it is difficult to large surcharge loads in experimental research, a unified calculation method of pile positive/negative skin friction was established based on the effective stress method for investigation. The closed-form analytical solutions for calculating the pile skin friction corresponding to the plastic and elastic state were derived respectively. Meanwhile, the axial load of a single pile under different distribution forms of the pile skin friction was deduced. The calculation method was verified by comparing with an in-situ test. Furthermore, a computer model, which was established by the finite element method, was used to study the effect of the friction coefficient, consolidation time, consolidation pressure, drainage condition, and pressure ratio on the distribution of NSF and the location of neutral point. The results show that the effect of the friction coefficient, consolidation time, and pressure ratio on the NSF were significant. The friction coefficient increased from 0.05 to 0.4, the position of the neutral point rose by 22%, and the drag load of pile shaft was obviously increased. The effect of consolidation pressure and drainage conditions on the neutral point were relatively less, but they had a great influence on the distribution and magnitude of NSF. Furthermore, under different consolidation pressures, the normalized maximum axial load, F_max/p, of the pile shaft had a good linear relationship with the pressure ratio, n, and the slopes were the same.

Image edge detection in virtual reality scenes is one of the most important technologies in the field of image processing and computer vision. It occupies an important position in the image processing system and is a key factor that affects the performance of the entire system. The quality of the algorithm directly affects the performance of the computer’s visual system. This paper briefly describes the basic theoretical methods of image edge detection. The basic theory and processing flow of image edge detection are analyzed, and several commonly used edge detection preprocessing methods and their basic principles are elaborated in detail. The existing traditional edge detection methods are briefly introduced, and the traditional edge detection methods are compared. This paper studies the adaptive multi-scale edge detection method based on Canny algorithm, and through theoretical analysis, compares the advantages and disadvantages of various algorithms in image edge detection. In the process of acquiring image edges, the local maximum value of the modulus is calculated along the gradient direction and the threshold is adaptively selected based on the image blocking principle. Comparing with the traditional modulus maximum edge detection method, this algorithm overcomes the contradiction that can suppress the interference of noise and obtain better edge detection effect to a certain extent. Experiments show that the method in this paper not only suppresses the interference of impulsive noise to the image edge detection, but also greatly reduces the possibility of false edges, and obtains a satisfactory accurate binary edge image.

Foam concrete, as an important construction and building material, mainly consists of small inner pores (produced by preformed foam) and foam walls (i.e., the concrete surrounding the small inner pores). The effect of density and air volume quantity on compressive strength has been investigated in many previous studies. However, the findings on the relationship between compressive strength and water-to-cement ratio (R_wc) are controversial from different studies. The possible reason may be the effect of sand-to-cement ratio (R_sc), which has not been considered in pervious studies. In this study, a series of compressive tests on foam concrete with various R_wc and R_sc were conducted at a fixed air volume quantity. The results show that when R_wc was 0.5–1.0, the compressive strength increased along R_wc, different from the change of the concrete without foam. The enhance effect from the foam walls was dominant. When R_wc was larger than 1, the slurry was too thin to preserve the bubble for the R_sc of 2. However, for the R_sc of 5, the slurry performed well and its compressive strength remained constant, which was different from the increase stage with R_wc of 0.5–1.0. It was because of the enhanced effect caused by the decrease in the number of small holes, which almost offset the weakening effect for the R_wc on the strength. The enhance effect due to the decrease in the number of small holes can be normalized by the water-to-solid ratio (R_ws). Except the results in the constant stage, the compressive strength increased with the increase of R_ws, irrelevant to the R_sc. It indicates that the sand and cement had the same function on the decrease in the number of small holes. In order to get the same compressive strength, the cement can be replaced by the sand in the increase stage. The research results are expected to improve the quality control and the engineering efficiency of foam concrete.