The study proposes a framework combining machine learning (ML) models into a logical hierarchical system which evaluates the stability of the sheet wall before other predictions. The study uses the hardening soil (HS) model to develop a 200-sample finite element analysis (FEA) database, to develop the ML models. Consequently, a system containing three trained ML models is proposed to first predict the stability status (random forest classification, RFC) followed by 1) the cantilever top horizontal displacement of sheet wall (artificial neural network regression models, RANN1) and 2) vertical settlement of soil (RANN2). The uncertainty of this data-driven system is partially investigated by developing 1000 RFC models, based on the application of random sampling technique in the data splitting process. Investigation on the distribution of the evaluation metrics reveals negative skewed data toward the 1.0000 value. This implies a high performance of RFC on the database with medians of accuracy, precision, and recall, on test set are 1.0000, 1.0000, and 0.92857, respectively. The regression ANN models have coefficient of determinations on test set, as high as 0.9521 for RANN1, and 0.9988 for RANN2, respectively. The parametric study for these regressions is also provided to evaluate the relative insight influence of inputs to output.

This paper presents a study of closely spaced double tunnels in Taizhou, China. One is Xiabei Mountain No. 2 four-line super-span high-speed railway tunnel (HRT), and the other is Xiabei Mountain double-line large-span subway tunnel (ST). The excavation spans of HRT and ST are 26.3 and 14 m, respectively. The two tunnels are located at different levels, and their separating distance is 17.2 m. Due to the short construction period, the HRT excavation was completed earlier than ST. The structural design of the HRT, taking account of the disturbance by the ST construction, was analyzed by a numerical simulation. It was found that the “yielding principle” design was more feasible than the “resistance principle” design when considering the safety and durability of the HRT secondary lining. The mechanical responses of the HRT during ST construction were comprehensively monitored and analyzed, including the vault settlement, horizontal convergence, surrounding rock pressure, and the internal stress in shotcrete and steel arch. Results show that the longitudinal influence range of the ST construction on the HRT was approximately 0.6–1.1 times the ST outer diameter; the disturbance was mainly generated in the ST upper bench excavation; and the final axial force of the HRT shotcrete was approximately 9–16 times that of the steel arch, which indicated that the shotcrete was the main bearing structure. The safety status of the HRT was assessed based on the monitoring data, and the minimum safety factors of the HRT shotcrete and steel arch were 1.61 and 1.89, respectively. Parametric studies were performed to show how the lining stress of HRT was affected by the relative angle, pillar width, ST excavation method and excavation footage. Finally, the design and construction optimization were proposed according to the monitoring data and parameter analysis results. This study might provide practical reference for similar projects.

In the present study, a comparison between the new shallow tunneling method (STM) and the traditional pile and rib method (PRM) was conducted to excavate and construct subway stations in the geological conditions of Tehran. First, by selecting Station Z6 located in the Tehran Subway Line 6 as a case study, the construction process was analyzed by PRM. The maximum ground settlement of 29.84 mm obtained from this method was related to the station axis, and it was within the allowable settlement limit of 30 mm. The acceptable agreement between the results of numerical modeling and instrumentation data indicated the confirmation and accuracy of the excavation and construction process of Station Z6 by PRM. In the next stage, based on the numerical model validated by instrumentation data, the value of the ground surface settlement was investigated during the station excavation and construction by STM. The results obtained from STM showed a significant reduction in the ground surface settlement compared to PRM. The maximum settlement obtained from STM was 6.09 mm as related to the front of the excavation face. Also, the sensitivity analysis results denoted that in addition to controlling the surface settlement by STM, it is possible to optimize some critical geometric parameters of the support system during the station excavation and construction.

The horizontal stiffness of the isolated layer is reduced substantially by a friction pendulum bearing (FPB) toprotectthe structure from potential damages caused by earthquakes. However, horizontal stiffness is essential to progressive collapse resistance of structures. This paper presents a simplified model to assess the progressive collapse response of beam-pier substructure isolated by FPB. Progressive collapse resistance by flexural action of the beam and additional resistance owing to the horizontal restraining force was achieved. The influences of the equivalent radius and friction coefficient of the FPB, the applied axial force on the FPB, and span-depth ratio of the beam on the additional resistance were investigated. Simulations were conducted to verify the proposed model. The results show that progressive collapse resistance provided by horizontal restraining can be reduced as large as 46% and 88% during compressive arching action (CAA) and catenary action (CA), respectively. The equivalent radius of the FPB shows limited effect on the progressive collapse response of FPB isolated structures, but friction coefficient and applied axial force, as well as depth ratio of the beam, show significant influences on the additional progressive collapse resistance capacity. Finite element method (FEM) results are in good agreement with the result obtained by the proposed method.

Three-point bending tests were carried out on nineteen Reinforced Concrete (RC) beams strengthened with FRP in the form of completely wrapping. The strip width to spacing ratios, FRP type, shear span to effective depth ratios, the number of FRP layers in shear, and the effect of stirrups spacing were the parameters investigated in the experimental study. The FRP contribution to strength on beams having the same strip width to spacing ratios could be affected by the shear span to effective depth ratios and stirrups spacing. The FRP contributions to strength were less on beams with stirrups in comparison to the tested beams without stirrups. Strengthening RC beams using FRP could change the failure modes of the beams compared to the reference beam. In addition to the experimental study, a number of equations used to predict the FRP contribution to the shear strength of the strengthened RC beams were assessed by using a limited number of beams available in the literature. The effective FRP strain is predicted by using test results, and this prediction is used to calculate the FRP contribution to shear strength in ACI 440.2R (2017) equation. Based on the statistical values of the data, the proposed equation has the lowest coefficient of variation (COV) value than the other equations.

Improving the cracking resistance of steel-normal concrete (NC) composite beams in the negative moment region is one of the main tasks in designing continuous composite beam (CCB) bridges due to the low tensile strength of the NC deck at pier supports. This study proposed an innovative structural configuration for the negative bending moment region in a steel-concrete CCB bridge with the aid of ultrahigh performance concrete (UHPC) layer. In order to investigate the feasibility and effectiveness of this new UHPC jointed structure in the negative bending moment region, field load testing was conducted on a newly built full-scale bridge. The newly designed structural configuration was described in detail regarding the structural characteristics (cracking resistance, economy, durability, and constructability). In the field investigation, strains on the surface of the concrete bridge deck, rebar, and steel beam in the negative bending moment region, as well as mid-span deflection, were measured under different load cases. Also, a finite element model for the four-span superstructure of the full-scale bridge was established and validated by the field test results. The simulated results in terms of strains and mid-span deflection showed moderate consistency with the test results. This field test and the finite element model results demonstrated that the new configuration with the UHPC layer provided an effective alternative for the negative bending moment region of the composite beam.

The stress state of the built-in corridor in core rock-fill dam on thick overburden is extremely complex, which may produce cracking and damage. The purpose of this paper was to investigate the effect of thick overburden on the stress and deformation of the built-in corridor in a rock-fill dam, and ascertain the damage causes of the corridor. The rationality of the analysis method for corridor with similar structure is another focus. The approach is based on finite-element method and the calculation result accuracy is verified by the field monitoring data. The improved analysis method for corridors with similar structure is proposed by comparing various corridor load calculation methods and concrete constitutive models. Results demonstrate that the damage causes of the corridor are the deformability difference between the overburden and concrete and the special structural form. And the calculation model considering dam construction process, contact between concrete and surrounding soil, and concrete damage plasticity can reasonably reflect the mechanical behavior of the corridor. The research conclusions may have a reference significance for the analysis of tunnels similar to built-in corridors.

Experimental evaluations were conducted to determine the water sorptivity, setting time, and resistance to a highly acidic environment, of mortar with alkali-activated ground granulated blast furnace slag (GBS) binder and also of combinations of fly ash and GBS binders. Binders were activated using mixtures of NaOH and Na₂SiO₃ solutions. The molarity of NaOH in the mixtures ranged from 10 mol·L⁻¹ to 16 mol·L⁻¹, and the Na₂SiO₃/NaOH ratio was varied from 1.5 to 2.5. Mortar samples were produced using three binder combinations: 1) GBS as the only binder; 2) blended binder with a slag-to-fly ash ratio of 3:1; and 3) mixed binder with 1:1 ratio of slag to fly ash. Mortar samples were mixed and cured at (22 ± 2) °C till the day of the test. The impact of activator solution alkalinity, activator ratio Na₂SiO₃/NaOH, GBS content on the rate of water absorption were evaluated. After 7, 28, and 90 d of immersion in a 10% sulfuric acid solution, the resistance of a geopolymer matrix to degradation was assessed by measuring the change in sample weight. The influence of solution alkalinity and relative fly ash content on setting times was investigated. Alkali-activated mortar with a slag-to-fly ash ratio of 3:1 had the least sorptivity compared to the two other binder combinations, at each curing age, and for mortars made with each of the NaOH alkaline activator concentrations. Mortar sorptivity decreased with age and sodium hydroxide concentrations, suggesting the production of geopolymerization products. No reduction in weight of sample occurred after immersion in the strong acid H₂SO₄ solution for three months, regardless of binder combination. This was due to the synthesis of hydration and geopolymerization products in the presence of curing water, which outweighed the degradation of the geopolymer matrix caused by sulfuric acid.

Polyethylene terephthalate bottles production has drastically increased year after year due to high versatility of polyethylene terephthalate plastics and considerable consumption of beverages. In tandem with that increase, the major concern of society has been the improper disposal of this non-biodegradable material to the environment. To deal with this concern, recycled polyethylene terephthalate bottles were incorporated in concrete as fibre reinforcements in this study. The objective of this research is to evaluate the mechanical properties of recycled polyethylene terephthalate fibre reinforced concrete (RPFRC) in comparison with control concrete without fibres. polyethylene terephthalate fibres with three different diameters (0.45, 0.65, and 1.0 mm) and two lengths (20 and 30 mm) were added at various proportions (0.5%, 1.0%, 1.5% and 2.0%) by volume of concrete in order to determine the effect of fibres initially on compressive, flexural and splitting tensile strengths of concrete. The results revealed that none of the fibres have detrimental effects up to 1% volume fraction, however further addition caused slight reductions on mechanical properties in some conditions. Plastic shrinkage resistance and impact resistance tests were also performed according to related standards. Polyethylene terephthalate fibres were observed to have marked improvements on those properties. Such a good performance could be attributed primarily to the bridging effect of fibres.