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.

Vertical jet grouted columns by drilling holes through the embankment of busy highways are applied to mitigate the problem of excessive postconstruction settlement on the east coast of China. Short-term ground heave due to vertical jet grouted columns is focused, investigated, and analyzed via field monitoring of a construction project in Lianyungang, China. Field results show that heaves in ground surfaces were observed to be 219 mm at most. Theoretical analysis by cavity expansion was performed to investigate the soil displacement due to vertical jet grouted columns. It was found that ground surface heave decreased with smaller grout pressure, larger geostatic pressure, and a larger distance from the column center. Comparison between measured and analytical results indicated the predictability of the theoretical solution.

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.

The particle size of expanded polystyrene (EPS) has an effect on engineering properties of EPS‐clay blends. However, the effect of differences between EPS particle size groups subdivided within 1–3 mm on engineering properties is usually ignored. In this study, different particle sizes of EPS pellets have been considered to separately investigate the effect on the optimum water content (OWC), maximum dry density (MDD), unconfined compressive strength (UCS), ductility, coefficient of permeability, and compression index of EPS‐clay blends. Results show that the MDD, ductility, hydraulic conductivity, and compression index of EPS‐clay blends do not increase with the increase in the EPS particle size in the range of 0.3–3 mm, while the OWC and UCS do not decrease. For a given EPS content, among samples with the EPS particle size of 0.3–1 mm, 1‐2 mm, and 2‐3 mm, the MDD and UCS of EPS‐clay blends with 1‐2 mm in EPS particle size are the largest, while the OWC, ductility, coefficient of permeability, and compression index are the smallest. Microstructure analyses reveal that, for samples with the EPS particle size of 1‐2 mm, the pore volume is lower and the microstructure is denser, which are the main reasons why the EPS particle size can influence engineering properties of EPS‐clay blends.

Porous concrete is an energy absorption material, which has been widely used in civil engineering, traffic engineering and disaster reduction engineering. However, the effect of pore structure on the impact behavior of the porous concrete is lacked. In this study, a series of drop-weight impact tests were carried out on three typical types of porous concrete, i.e., concrete hollow brick (CHB), autoclaved aerated concrete (AAC) and foamed concrete (FC), to investigate the effect of pore structures on their impact behavior. For comparison, static load tests were also conducted as references. According to the damage to the samples, the developments of impact force, strain, contact stress–strain relationship and absorbed energy during drop-weight during the impact test were measured and analyzed. The results show that the ratio between the peak impact stress and compressive strength of CHB was 0.44, while that of AAC and FC increased to about 0.6, indicating that the small and uniform pore structure in AAC and FC had a higher resistance against impact load than the hollow cavity of CHB. In addition, the elastic recovery strain in AAC increased by about 0.2% and its strain at peak contact stress increased by about 160% for a comparison of CHB, implying that a small open pore structure could enhance ductility. Besides, the peak contact stress of FC was close to that of AAC during impact loading, while the strain at peak contact stress of FC increased by about 36% compared with AAC, revealing that the closed-pore structure could further enhance the deformation potential. Correspondingly, the energy absorption rates of CHB, AAC and FC were 85.9 kJ/s, 54.4 kJ/s and 49.7 kJ/s, respectively, where AAC decreased by about 58% compared with CHB, and FC decreased by about 10% compared with AAC.