Multi-Effects of Tunneling and Basement Excavation on Existing Pile Group

Tunnels and foundation pits are two separate types of excavation that are frequently used in urban settings. Excavating tunnels and foundation pits sequentially around existing pile foundations is becoming more and more prevalent as urban underground space utilization rates increase. The deformation and load transfer mechanisms of the pile group foundation under two asymmetric excavation conditions of “first tunnel, then foundation pit” and “first foundation pit, then tunnel” are studied from the perspective of the relative positions of the tunnel–pile–foundation pit based on the constant gravity model test and 3D numerical simulation. The result shows: The pile settlement of the front pile (closer to the tunnel) caused by the excavation condition of the “first foundation pit-then tunnel” is relatively larger, while the pile settlement of the rear pile (closer to the foundation pit) caused by the excavation condition of “first tunnel-then pit” is larger. The transverse tilting of the pile group caused by the excavation of the “first foundation pit-then tunnel” is relatively larger. For the front pile, the pile tip resistance generated by “first excavation-then tunnel” is about 10% greater than it was before the initial excavation, which is greater than the result of “first tunnel-then foundation pit”. For the rear pile, the pile tip resistance generated by “first excavation-then tunnel” is about 85% greater than it was before the initial excavation, which is smaller than the result of “first tunnel-then foundation pit”. The multiple excavation sequence of “tunnel first-then foundation pit” leads to a larger induced bending moment for the front pile, whereas a larger induced bending moment for the rear pile results from the multiple excavation sequence “first foundation pit-then tunnel”

Experimental Study and Extended Finite Element Simulation of Fracture of Self-Compacting Rubberized Concrete

Self-compacting rubberized concrete (SCRC) is a high-performance concrete that can achieve compacting effect by self-gravity without vibration during pouring. Because of its excellent fluidity, homogeneity, and stability, the application of self-compacting concrete in engineering can improve work efficiency and reduce project cost. The effects of loading rate on the fracture behavior of self-compacting concrete were studied in this paper. Three-point bend (TPB) tests were carried out at five loading rates of 1, 0.1, 0.001, 0.0001, and 0.00001 mm/s. The dimensions of the specimens were 100  mm × 100 mm × 400 mm. A precast crack was set in the middle of the specimen with a notch-depth ratio of 0.4. The experimental results show that the peak load on the load-CMOD (crack mouth opening displacement) curve gradually increases with the increase of the loading rate. Although the fracture energy a presented greater dispersion under the loading rate of 1 mm/s, the overall changes were still rising with the increase of the loading rate. Besides studying the softening characteristics of the self-compacting concrete, the constitutive softening curve of the self-compacting concrete was obtained using the bilinear model. Finally, curved three-point bending beams were simulated by using the extended finite element method based on ABAQUS. The fracture process of the self-compacting concrete under different loading conditions was analyzed more intuitively. The simulation results were compared with the experimental results, and the same conclusions were obtained

Analysis of Rubberized Self-Compacting Concrete under Uniaxial Tension by 3D Mesoscale Models

Damage and failure of rubberized self-compacting concrete (RSCC) are studied by mesostructural models. The models include six phases: mortar, aggregates, rubber particles, aggregate-mortar interfacial transaction zones (A-M ITZs), rubber-mortar interfacial transaction zones (R-M ITZs), and voids. Thin layers between mortars and aggregates and between mortars and rubber particles represent A-M ITZs and R-M ITZs, , respectively. Aggregates and rubber particles are modeled with linear elastic, while mortars, A-M ITZs, and R-M ITZs are with different damage-plasticity behaviors. The mesoscale models are validated by the comparison of numerical results and experimental results. The effects of essential phase parameters on the composite’s strength are evaluated, and empirical laws for these effects are established by data regression. It is demonstrated that the effect of porosity, size, and content of rubber particles affect strength and toughness, which provides guidance to the design of such composites for practical applications

Multi-Effects of Tunneling and Basement Excavation on Existing Pile Group

Tunnels and foundation pits are two separate types of excavation that are frequently used in urban settings. Excavating tunnels and foundation pits sequentially around existing pile foundations is becoming more and more prevalent as urban underground space utilization rates increase. The deformation and load transfer mechanisms of the pile group foundation under two asymmetric excavation conditions of “first tunnel, then foundation pit” and “first foundation pit, then tunnel” are studied from the perspective of the relative positions of the tunnel–pile–foundation pit based on the constant gravity model test and 3D numerical simulation. The result shows: The pile settlement of the front pile (closer to the tunnel) caused by the excavation condition of the “first foundation pit-then tunnel” is relatively larger, while the pile settlement of the rear pile (closer to the foundation pit) caused by the excavation condition of “first tunnel-then pit” is larger. The transverse tilting of the pile group caused by the excavation of the “first foundation pit-then tunnel” is relatively larger. For the front pile, the pile tip resistance generated by “first excavation-then tunnel” is about 10% greater than it was before the initial excavation, which is greater than the result of “first tunnel-then foundation pit”. For the rear pile, the pile tip resistance generated by “first excavation-then tunnel” is about 85% greater than it was before the initial excavation, which is smaller than the result of “first tunnel-then foundation pit”. The multiple excavation sequence of “tunnel first-then foundation pit” leads to a larger induced bending moment for the front pile, whereas a larger induced bending moment for the rear pile results from the multiple excavation sequence “first foundation pit-then tunnel”

Design Method and Verification of Electroosmosis-Vacuum Preloading Method for Sand-Interlayered Soft Foundation

The design method of electroosmosis-vacuum preloading for soft foundation treatment is not systematic and complete, thereby restricting the application of the technology in engineering. A design method for the electroosmosis-vacuum preloading treatment of sand-interlayered soft foundation is therefore presented. A compressible electrical prefabricated vertical drain is developed, and a vacuum sealing and draining system is designed for the application of the electroosmosis-vacuum preloading in sand-interlayered soft foundation. Calculation formulas of site resistance considering the interlayer and interface resistivity of the electrode are established to design the power supply and electrical circuit. A simple numerical simulation method is proposed to predict the ground settlement treated by electroosmosis-vacuum preloading. A field test of electroosmosis-vacuum preloading is designed using the suggested method, and comparison tests between the electroosmosis-vacuum preloading and the vacuum preloading are performed to verify the proposed technique. The test results show that the proposed design method is reasonable for the design of electroosmosis-vacuum preloading in engineering

Lateral Deformation Characteristics and Control Methods of Foundation Pits Subjected to Asymmetric Loads

Using the foundation pit at the Jianye Road Station of Hangzhou Metro Line 6 as a case study, the deformation characteristics of a foundation pit subjected to asymmetric loads is investigated in this paper using PLAXIS 3D numerical simulation software. The influence of active pressure zone reinforcement, passive pressure zone reinforcement, and increased thickness of the diaphragm wall at the loaded side on the maximum lateral displacement of diaphragm wall retaining structure of foundation pit is also systematically analyzed. The results show that the deformation of the diaphragm walls on both sides of the foundation pit is strongly inconsistent when subjected to asymmetric loads and is affected by the asymmetric load value and its distance to the foundation pit. In order to reduce the lateral deformations of foundation pit subjected to asymmetric load, two displacement control methods are adopted in the numerical simulations. It is shown that reinforcing the active pressure zone can reduce the maximum lateral displacement of the diaphragm wall on the loaded side to a certain extent but the reinforcement should have a certain depth, resulting in poor efficiency. On the other hand, reinforcing the passive pressure zone can effectively reduce the difference in lateral deformation between the two sides of the foundation pit by increasing the depth and width of the reinforcement zones. It is also observed that the increase in the thickness of the diaphragm wall can reduce the adverse effect of asymmetric loads on the foundation pit. The research results can provide reference for using measures to reduce the influence of asymmetric loads

Modeling Test and Numerical Simulation of Vertical Bearing Performance for Rigid-Flexible Composite Pouch Piles with Expanded Bottom (RFCPPEB)

Rigid-flexible composite pouch piles with expanded bottom (RFCPPEB) are generally considered as new symmetrical piles in practical engineering, but their bearing characteristics and design method are still not completely understood. The objective of this study is to investigate the vertical bearing performance and the optimal design scheme of RFCPPEB. Hence, laboratory modeling tests for this symmetric structure and an ABAQUS three-dimensional (3D) numerical simulation analysis were used to study the vertical bearing characteristics on bottom-expanded piles and rigid-flexible composite piles with expanded bottom. The vertical bearing capacity, shaft resistance, pile tip resistance distribution rule, and load sharing ratio of RFCPPEB were analyzed and verified using different bottom expansion dimensions and cemented soil thicknesses. The results revealed that the optimal bottom expansion ratio of rigid bottom-expanded piles was 1.8 when the ratio of pile body to bottom-expanded pile head was 9:1. When the bottom expansion ratio (D/d) was increased, the bearing capacity of bottom-expanded piles was significantly increased at D/d = 1.4 and D/d = 1.8 compared to that of D/d = 1.0, reaching 1.67 and 2.29 times, respectively, while for D/d = 1.6 and D/d = 2.0, the ultimate bearing capacity remained unchanged. Besides, shaft resistance played an important role in the bearing process of the rigid bottom-expanded piles and RFCPPEB. When the shaft resistance was increased, the ultimate bearing capacity of the pile foundation was significantly improved. The shaft resistance of RFCPPEB was increased with increasing cemented soil thickness. The increases in the shaft resistance and thickness of the cemented soil showed a nonlinear growth, and the maximum shaft resistance was approximately 75 cm from the pile top. When the diameter of the expanded head was 1.8 times the diameter of the pipe pile and slightly larger than the thickness of the cemented soil (0.5 times the diameter of the pipe pile), the optimal amount of concrete 425.5 kN/m3 required for per unit volume around piles was obtained, with the RFCPPEB ultimate bearing capacity of 7.5 kN. For RFCPPEB, the soil pressure at the pile tip was directly proportional to the pile top load under small load and was decreased in the form of a half quadric curve under large load. It reached the most reasonable position where the slope of the quadric curve was the largest when the thickness of the cemented soil was larger than 0.5 times the diameter of the pipe pile

Modeling Test and Numerical Simulation of Vertical Bearing Performance for Rigid-Flexible Composite Pouch Piles with Expanded Bottom (RFCPPEB)

Rigid-flexible composite pouch piles with expanded bottom (RFCPPEB) are generally considered as new symmetrical piles in practical engineering, but their bearing characteristics and design method are still not completely understood. The objective of this study is to investigate the vertical bearing performance and the optimal design scheme of RFCPPEB. Hence, laboratory modeling tests for this symmetric structure and an ABAQUS three-dimensional (3D) numerical simulation analysis were used to study the vertical bearing characteristics on bottom-expanded piles and rigid-flexible composite piles with expanded bottom. The vertical bearing capacity, shaft resistance, pile tip resistance distribution rule, and load sharing ratio of RFCPPEB were analyzed and verified using different bottom expansion dimensions and cemented soil thicknesses. The results revealed that the optimal bottom expansion ratio of rigid bottom-expanded piles was 1.8 when the ratio of pile body to bottom-expanded pile head was 9:1. When the bottom expansion ratio (D/d) was increased, the bearing capacity of bottom-expanded piles was significantly increased at D/d = 1.4 and D/d = 1.8 compared to that of D/d = 1.0, reaching 1.67 and 2.29 times, respectively, while for D/d = 1.6 and D/d = 2.0, the ultimate bearing capacity remained unchanged. Besides, shaft resistance played an important role in the bearing process of the rigid bottom-expanded piles and RFCPPEB. When the shaft resistance was increased, the ultimate bearing capacity of the pile foundation was significantly improved. The shaft resistance of RFCPPEB was increased with increasing cemented soil thickness. The increases in the shaft resistance and thickness of the cemented soil showed a nonlinear growth, and the maximum shaft resistance was approximately 75 cm from the pile top. When the diameter of the expanded head was 1.8 times the diameter of the pipe pile and slightly larger than the thickness of the cemented soil (0.5 times the diameter of the pipe pile), the optimal amount of concrete 425.5 kN/m3 required for per unit volume around piles was obtained, with the RFCPPEB ultimate bearing capacity of 7.5 kN. For RFCPPEB, the soil pressure at the pile tip was directly proportional to the pile top load under small load and was decreased in the form of a half quadric curve under large load. It reached the most reasonable position where the slope of the quadric curve was the largest when the thickness of the cemented soil was larger than 0.5 times the diameter of the pipe pile

Full-Scale Experimental Study on Prefabricated Greening Ecological Retaining Walls

Prefabricated walls are frequently utilized as retaining structures in different applications. A new type of prefabricated greening ecological retaining wall (PGERW) is proposed in this research. Full-scale tests and numerical simulations were conducted to investigate the stress characteristics of the PGERW. To this end, the load–stress relationship, load–displacement relationship, and crack development of the retaining wall columns were carefully evaluated. It was found that when the load acting on the 3 m high column reached the ultimate load-bearing capacity (about 150 kN), an “arc + 7”-shaped crack pattern emerged. A V-shaped crack composed of bolt–chamfer cracks formed when the load applied to a 2.5 m high column reached the ultimate load-bearing capacity (about 335 kN). The design of hollow thin-walled columns can effectively reduce the amount of concrete used and, as a consequence, reduce its carbon emissions, while meeting the design strength requirements of the retaining wall. The PGERW addresses the challenges of improving the extent of greening and drainage performance of traditional prefabricated retaining walls. It has excellent applicability to highway slope construction and therefore can be applied in several contexts

Influence of Scour Protection on the Vertical Bearing Behaviour of Monopiles in Sand

Extensive studies have been performed on the effectiveness of scour protection against scour erosion progression. But there is little research to date evaluating the effect of scour protection on vertical resistance behaviour of monopile foundations. This paper investigates the influence of scour protection on the vertical loading behaviour of monopiles installed in sand using centrifuge tests and finite element analysis (FEA). Four scour protection widths (1D, 2D, 3D, 4D; where D is the pile diameter) and three scour protection thicknesses (1 m, 2 m, 3 m) were modelled on a pile with a slenderness ratio (L/D) of five. In the FEA, the scour protection mechanism was modelled using two strategies, namely the ‘stress method’ by applying stress and the ‘material method’ by applying virtual material on the seabed surface around the pile. Outcomes between these two strategies were compared, and the contact coefficient δ used in the ‘material method’ for describing the contact effectiveness of the overlaying scour protection material with the pile structure was introduced, providing a more scientific and accurate calculation reference for engineering applications. The results indicated that the vertical capacity of monopiles could be increased by 5% to 23% by adopting the scour protection measure, depending on the scour protection width and scour protection thickness.Geo-engineerin