Journal of Performance of Constructed Facilities

The seismic performance of reinforced concrete in a saline soil environment has attracted great attention from the scientific community. This study aims to effectively predict the seismic yield strength of RC at different moments in a saline soil environment. After an electrochemical rapid corrosion test of 12 RC bridge pier column specimens, low-cycle repeated-loading tests were conducted. The corrosion rates and axial compression ratios are the primary research parameters. The seismic yield strength of the pier column was determined using the energy method. A calculation model of the seismic yield strength of the RC pier column in a saline soil environment is developed by considering the time-dependent model of the longitudinal strength yield in the saline soil environment. The results show that for the specimens studied in this research, the seismic yield strength of the pier column increased with an increase in the axial compression ratio when the corrosion rate was constant and the axial compression ratio is within a certain range. When the axial compression ratio was constant, the seismic yield strength of the pier column decreased with an increase in the corrosion rate. The calculation results of the seismic yield strength of RC pier columns were compared with the experimental results, and there was a high consistency. This model can provide a strong reference for the seismic design of pier columns in saline soil environments.

The polymer curing agent was used in the slope and the external-soil grass-planting was then carried out. It was found that this new ecological protection technique can effectively prevent, weaken, or slow down the softening of weak rock slope. Its waterproofness, hydrophobicity, and surface structure with good greening effect were thus improved. The effectiveness of polymer curing agent used in the weak rock slope was evaluated and verified by testing its workability, adhesion, waterproofness, and hydrophobicity. The safety factors of slope stability under three conditions, including not setting curing agent layer, setting curing agent layer, and setting curing agent layer with 25% rock bolt reduced, were calculated by using the Slide software version 5.014. They are 1.199, 1.281, and 1.238, respectively. It was indicated that the safety factor of weak rock slope setting polymer curing agent layer was 6.84% higher than that without the setting polymer curing agent layer. Based on the preceding research, the polymer curing agent as a new ecological protection technique was verified and summarized through the practical engineering projects, which could be expected to be applied in the weak rock slope protection engineering.

Important buildings located in high seismic zones of many developing countries are sometimes designed without paying much attention to the earthquake risk in the area. Such buildings are prone to severe damage during earthquakes and need immediate strengthening using techniques that should not only be economical but also should not interfere with the functioning of the building. The present study focuses on the assessment of the seismic vulnerability of a publicly funded reinforced concrete building (New Market building) in Imphal, India, that suffered severe damage during January 4, 2016, earthquake. It is further intended to suggest a suitable strengthening strategy for improving the lateral-load performance of the large building used by hundreds of local vendors. A detailed investigation of the damaged building was first carried out visually as well as using nondestructive tools and by collecting concrete core samples from various members of the building. Demand to capacity ratios (DCRs) were obtained using nonlinear static and dynamic analyses to determine the adequacy of the column sections of the building. Local seismic strengthening in the form of reinforced concrete jacketing was applied to the weaker columns ($\mathrm{DCR}>1$) based on several trials to achieve the required global strength and ductility. After retrofitting, yielding of most of the column members is substantially delayed. In addition, the peak story displacement and acceleration are found to be remarkably reduced for both the orthogonal directions. The seismic vulnerability assessment of the original building suggests that most of the column sections do not satisfy the allowable code-specified drift limits; however, the vulnerability reduced substantially after implementing the suggested strengthening scheme.

This paper presents the results of an experimental study investigating the mechanical behavior of corroded beams strengthened by three different strengthening schemes, and the influence of further corrosion on the structural performance of strengthened corroded beams. Eight rectangular reinforced-concrete (RC) beams were tested through a three-point bending system. The experimental results showed that the failure modes of the strengthened corroded beams were diagonal tensile failure, flexural failure, and support crush failure, respectively. The increases in ultimate load capacity and rigidity of the corroded beams strengthened with combined strengthening were up to 39.44% and 127.57%, respectively, compared with those of the corroded beams. The ductility of the tested beams strengthened with a single U-shaped steel strip was 16.97% greater than that of the corroded beams, while the ductility of the corroded beams strengthened with flexure strengthening and combined strengthening was, respectively, 4.6% and 28.8% lower than that of the corroded beams due to brittle failure. Compared with the strengthened corroded beams, the ductility and ultimate load capacity of all strengthened beams subjected to further corrosion (5% average corrosion loss of the cross section of the tensile steel bar) increased from 53.14% to 73.39% and from 37.37% to 53.13%, respectively. It was found that further corrosion had a small influence on the rigidity of tested beams strengthened by flexure strengthening and combined strengthening as opposed to the beams strengthened by shear strengthening.

Real-time monitoring of underwater construction is important for structural stability. To prevent tunnel disasters, an integrated analysis framework for tunnel stability evaluation was proposed using real-time monitoring and statistical analysis. A typical underwater shield tunnel, located in the Yangtze River, China, was selected as a case study. A structural health monitoring system (SHMS) was developed to implement real-time monitoring of the water pressure, temperature, and strain during the service period. An analytical model was developed to investigate the mechanical behaviors of the structure based on the monitoring data obtained from the SHMS. To calibrate the model parameters, numerical simulations were carried out using the finite element method with parameters based on the geological conditions for the study site. Consequently, the results indicate that (1) the numerical results agreed well with the analytical results, which showed that the response of the segment strain varied with position and the maximum strain occurred in the arch crown; (2) the segment strain increased with decreasing water pressure, and the maximum value was $4.118\times {10}^{-7}$ when the water pressure changed by 1 kPa; and (3) the strain variation and temperature were proportional, and the maximum value was $13.492\times {10}^{-6}$ when the temperature changed by 1°C. As a potential application, the proposed method was used to predict future behaviors of the structure, which is crucial for preventing disasters, and provides a reference for underwater construction.

Being exposed to weather directly or indirectly for more than 100 years, ancient timber buildings have experienced different levels of mechanical degradation. Especially the mortise-tenon joints, which play a crucial role in resisting various loads for these buildings, have suffered from severe deformations and damages, resulting in a significant reduction in the structural safety for the ancient timber buildings. In this study, a method is proposed to quantitatively describe the destruction of one-way straight mortise–tenon (OWSMT) joints, and the impact of joint damage on the seismic performance of the ancient timber structure was studied. The deterioration of the mortise-tenon joints was simulated by changing the size of the mortise, and controlling the width of the mortise compression zone and the gap between the tenon and the mortise. Low-cyclic loading tests were carried out on 23 groups of OWSMT joint specimens. The structural performance in terms of $M\text{-}\theta$ skeleton curves, stiffness degradation, and equivalent viscous damping of the OWSMT joints were obtained. Through the comparative analysis of the experimental and numerical simulation results, this paper further analyzes the seismic performance of the damaged timber joints.

Limited data exists on how construction activities physically impact construction workers. This research explores the use of physiological status monitors (PSMs) to assess the impact of construction activities, individual characteristics, and environmental factors on construction worker physiology. The fundamental objective of the study is to explore the potential for and effectiveness of using off-the-shelf devices and software to measure physical indicators related to heart rate, breathing rate, core temperature, and physiological and mechanical loads to assess construction worker physical status and wellbeing. The secondary objective to demonstrate various opportunities for decision makers to use such a system to analytically and visually evaluate the health and productivity of individuals performing various construction activities. The research was completed in three phases and compares data from individuals of varying experience performing four construction activities. While findings may or may not be generalizable, they suggest that fitness impacts the physical stress experienced by construction workers; findings also suggest that stress varies considerably across individuals and construction activity. Such findings highlight significant opportunities and potential strategies for monitoring and assessing construction worker health and productivity. Specifically, the contribution of the research is to describe and document the innovative capabilities of a monitoring system, which collects construction worker instantaneous and cumulative physiological measures.

Overlapped subway shield tunnels are subjected to the dynamic impacts caused by running trains and are damaged during their long-term service life. In this paper, the dynamic response and cumulative damage evolution of the overlapped shield tunnels were numerically studied. The numerical simulation takes into account the uniaxial constitutive concrete model and the fatigue damage constitutive model of steel-reinforced concrete that is able to simulate any number of loading (cycling) times. For simplicity, only the case of a train running in the upper tunnel is considered in this study. The fatigue life of the overlapped tunnel section is numerically computed. The results indicate that the fatigue life meets the design requirements. The maximum principal stress is mainly concentrated at the bottom arch in the upper tunnel as the train runs in the upper tunnel. The lower tunnel is subjected to smaller damage than the upper tunnel. The tunnel structure undergoes greater tensile damage than the compressive damage in terms of damage amplitude and range. The failure of the structure is mainly associated with tensile damage. The cumulative damage of overlapped shield tunnels indicates a two-stage feature: the rapid increase stage (0–6.85 years) and the slow development stage (6.85–102.74 years). The steel spring floating slab can greatly reduce the cumulative compressive and tensile damage of the bottom arch at the upper tunnel.

To enhance the durability of side-by-side box girder bridges, a common source of maintenance issues can be eliminated using the jointless bridge concept. Accurate estimation of the average effective bridge temperature range is a key issue. A deck-extension bridge containing side-by-side box girders was chosen as case study. The temperature distribution on the bridge cross section and the longitudinal thermal movement of the superstructure were monitored. Finite-element models of the bridge superstructure were developed, which indicated close agreement with measured temperature responses. The average effective temperature of girder cross sections could accurately predict the longitudinal thermal movement of the superstructure. The highest and lowest average effective bridge temperatures for side-by-side box girders were estimated for 12 cities in 4 climatic regions in China under historically extreme temperature conditions. For most cities, the difference between the highest and lowest average effective bridge temperatures exceeded the design temperature range. The Chinese-code design procedures may overestimate the allowable length of deck-extension bridges, because the code underpredicts the change in the average effective bridge temperature.

Over a bridge’s service life, physical damage, such as material deterioration, accidental impact, and overloading, can decrease its load-carrying capacity. To assess the integrity and serviceability of in-service bridges, accurate and efficient structural health monitoring is required for as frequent intervals as feasible. In this study, an integrated decision-making protocol is proposed to continuously postprocess collected dynamic-response data of a bridge to notify the bridge owners of any noticeable change in the in-service condition of the structure, at system level, and to more fully understand the in situ performance of the bridge for triggering smart inspection techniques (e.g., visual inspection, modal identification methods). This is done to determine the location and severity of damage and calculate the bridge load-carrying capacity based on the given damaged component(s). The study for this protocol is an instrumented vertical-lift truss bridge subjected to four simulated damage scenarios. For both the healthy and simulated damage conditions, a verified structural model is used as a baseline to determine the structural system response for damage detection using a wavelet-based energy rate index and to investigate the bridge load-carrying capacity according to current standards for load resistance factor-rating approach due to likely damage scenarios.

In 2004, during ordinary maintenance work, consisting of waterproofing a building located in the south of Italy, the long-span (14.5 m) in situ RC roof partially collapsed. The building, constructed in 1950, was in service as a cinema until 1967 and then utilized as a school until 1985. Lastly, it was a hotel until 2000. In 2004, when the building was not in service and was undergoing maintenance work, it partially collapsed under dead load. After the collapse, which involved a large portion of the roof, several beams, and two columns, the Italian court nominated an official technical consultant to investigate the direct and related causes of the failure. After the main causes were identified, the building was repaired and the roof was reconstructed with a light steel structure. This article is focused on the behavior of the collapsed structure considering the original design choices, the construction details adopted, and the material properties, including the effect of concrete and steel degradation. The influences of these aspects on the collapse are examined, with particular emphasis on concrete carbonation, steel bar corrosion, and design mistakes. The lessons learned from the case study could help professional engineers to be aware of the main peculiarities and structural deficiencies of structural systems affected by material degradation and the importance of in situ periodic checks and monitoring during the life of the structures.

Reinforcement cage length has a significant impact on the bearing capacity of bored piles. Accurate measurement of the cage length provides an important guideline for judging pile quality. Currently, the electric method has been widely used in detecting reinforcement cage length. However, the precision of detection results requires further improvements. This paper presents an electric potential difference method for length detection based on theoretical analyses and formula derivations. Against the numerical calculation it can be observed that detection accuracy increased along with increases in the actual skeleton length and decrease of the pile-to-borehole distance, electrode spacing, and moving step size of electrodes. Parameter preferences of length detection were recommended as follows: (1) the electric potential difference method was recommended to complete the detection when the designed length of the pile was more than 8 m; (2) the pile-to-borehole distance was suggested to be less than one-fifth of the designed cage length; (3) the electrode spacing should be no more than a hundredth of the designed cage length; (4) the moving step size was limited to less than one-tenth of the designed skeleton length, and the length was an integral multiple of the step size. Moreover, the results and recommendations were verified by physical model experiments and engineering practices.

The Xi’an City Wall (XCW) is a typical ancient building in Xi’an that is well known for its history and culture. The Xi’an Metro crosses below the XCW at various locations, which may pose hazards of cracking or collapsing the XCW due to the irregular settlement of the wall foundation during tunneling and vibrations induced by train operation. To minimize the effect of the metro on the XCW, the authors exhibit different mitigation measures in this paper, mainly including route optimization, active control technology during tunneling, foundation reinforcement, building reinforcement, and floating slab technology for damping train vibrations. Meanwhile, the case studies about the construction stage in Line 4 of the Xi’an Metro near the Heping Gate and the vibration effect during the metro operation stage were conducted. After employing the suitable countermeasures, the maximum foundation settlement and the maximum vibration velocity of the XCW could be controlled effectively within the guideline values.

A multicriteria and multilevel seismic risk management framework is presented to ensure an acceptable and consistent level of risk for existing buildings in Canada with a focus on minimizing threats to life safety. The framework consists of three levels: (1) Level 1: preliminary seismic-risk screening tool (PST); (2) Level 2: semiquantitative seismic-risk screening tool (SQST); and (3) Level 3: seismic evaluation guidelines (SEG). Level 1 (PST) was developed based on a number of key criteria (seismicity, benchmark code edition, consequences of failure, and remaining occupancy time) to assist in exempting existing buildings from further assessment without the need for a site visit. Level 2 (SQST) consists of three key components: (1) structural scoring system that quantitatively assesses the structural seismic risk based on the probability of collapse; (2) nonstructural components scoring system that qualitatively evaluates the seismic risk of nonstructural components based on the seismic demand of critical nonstructural components; and (3) ranking procedure that prioritizes buildings with potentially unacceptable seismic risk for the Level 3 (SEG) based on structural and nonstructural components priority indices. The Level 3 (SEG) aims to identify the building deficiencies that lead to unacceptable seismic risk for existing buildings.

In this article, a new measurement method for human comfort assessment levels for stadiums is proposed and demonstrated. The method is based on a specific computer vision and image processing algorithm called optical flow. The motion of the structure can be tracked and well-known human comfort index measures RMS and Vibration Dose Value (VDV) can be computed accordingly. The implementation was carried out using simple off-the-shelf cameras and the results were compared with conventional accelerometers. The analyses from tracking structural elements return similar results as accelerometers. The proposed methods and algorithms along with the computer vision technologies can be employed for practical human comfort assessment of structures.

Very little data exists on the live-load behavior of twin-girder bridges despite their unique configuration and minimal redundancy. To investigate the live-load behavior of twin girder bridges, the State Highway 52 Bridge over the Snake River was instrumented and studied. The live-load response was monitored by attaching 62 strain gauges on girders, stringers, and intermediate diaphragms at nine cross-sectional locations. The live-load was applied with two trucks that were driven along three predetermined load paths. A finite-element model of the bridge was calibrated with the measured response from the live-load tests. The calibrated finite-element model was used to quantify moment distribution factors and load ratings for the bridge. The finite-element distribution factors were compared with those calculated according to methods provided in the AASHTO standard and LRFD specifications. The distribution factors from both specifications were found to be unconservative for the girders and overly conservative for the stringers. The model also was used to quantify the effect of the transverse diaphragm members on the live-load distribution. Distribution factors were calculated with and without the diaphragm members. The diaphragms were found to increase the distribution of moments by over 20% for both positive and negative moments.

This study aimed to assess the defect liability system for repairing various defects during residential buildings’ defect liability period using the loss distribution approach (LDA). It examined 6,087 defect cases from 48 residential buildings in the Republic of Korea between 2008 and 2017 for which defect disputes occurred. The analysis confirmed that damage and water problems were found to be serious defects in the reinforced concrete work, while relatively varied serious defects occurred in the finish work. Specifically, the structure and finish show high-severity/high-frequency characteristics; thus, attention must be paid to their quality control. Deriving the defect cost ratio’s distribution for each defect liability period showed that defect liability bonds must be increased to cover the 2- and 10-year defect liability periods and must be decreased for the 3- and 5-year defect liability periods. A defect classification matrix suitable for different defect liability periods for each country and a defect liability system evaluated using the LDA-based model can provide a basis for reasonably adjusting defect costs among the parties involved in defect disputes.

One of the largest items in the bridge inventory for many states is culverts, and cast-in-place reinforced concrete box culverts constitute a sizeable portion of the overall culvert inventory. In Louisiana, most of these culverts were constructed using old standard details. Following current load rating procedures for these culverts often yields unacceptable load rating factors, even though their performance is acceptable with no signs of distress. The discrepancy between calculated load rating and observed performance of the culverts is investigated for eight selected culverts by field live load testing and finite element modeling. Each culvert was instrumented using a 48-sensor structural health monitoring system before a loaded truck was driven on the culvert along three different load paths to collect field data. Three-dimensional (3D) finite element (FE) models were calibrated using the recorded field data, and an HL-93 design truck and 10 legal trucks such as Type 3-3 were used to load the calibrated FE models to obtain culvert specific load rating factors. Acceptable rating factors were obtained for all eight culverts. The rating methodology, rating factors, and recommendations for rating culverts are presented in this paper.

This paper presents an assessment of the lateral load capacity and ductility of a 21-year-old reinforced concrete (RC) structure situated in a marine environment and affected by rebar corrosion. Nonlinear pushover analysis is carried out for the structure by modeling the hinges. The consequence of corrosion is accounted for in the moment rotation characteristics of the hinges by considering the reduction in bond strength, loss of rebar diameter, and reduction in the mechanical properties of steel. The basic bond stress–slip relationship from an internationally established model code is modified to account for corrosion using a bond model. This bond model is used to obtain the hinge properties of the corroded rebar. The simplified beam macromodel developed considering these modified hinge properties due to corrosion is validated with four-point bending tests carried out on beams and similar experiments from the literature. Moreover, a simulation is also carried out using a two-dimensional finite element micromodel of a beam using the modified bond model for the rebar affected by corrosion. The load deflection characteristics of the micro and macromodels are found to agree well for the four-point bending load for different levels of corrosion. The proposed beam model, considering the effect of rebar corrosion, is used for evaluation of performance of the 21-year-old corroded RC structure for the design basis earthquake load. Subsequently, a seismic assessment methodology is proposed for corroded RC structures.

Hurricanes produce high winds and heavy precipitation, causing widespread damage to infrastructure in coastal areas. Throughout low-lying coastal cities such as New Orleans, Louisiana, a network of constructed waterway systems is maintained to mitigate flooding effects during hurricane events. However, for any waterway vessels (e.g., barges) located within the waterway network, hurricane winds and storm surges can propel the vessels into nearby protection structures. In the event that such impacts lead to failure (localized breaches or overturning), catastrophic flooding can occur to the surrounding area. Presented in this paper is a framework for assessing the risk associated with barge impacts on floodwall protection structures. Components of the framework bring together findings from forensic, experimental, and numerical modeling investigations, which collectively allow for both probability of failure and consequence of failure assessments. Use of the framework is demonstrated for critical floodwall infrastructure located throughout New Orleans, leading to recommendations for improved design of hurricane and storm damage risk reduction systems.

It is well recognized that debris flow is a threatening natural hazard that can apply a large impact force on building structures. To increase structural safety, it is imperative to understand the structural performance under the debris flow impact. This paper proposes a method of using foamed aluminum to improve the capacity of buildings to resist debris flow, and validates its effectiveness through a series of impact tests. The results show that the frame structure strengthened with foamed aluminum is effective to resist the debris flow impact. The proposed method has a double protection mechanism. When the impact load is relatively small, the foamed aluminum can fully absorb the impact energy; when the impact energy is large enough, the hardened foamed aluminum can, after repeated loadings, restrain the concrete and further enhance the bearing capacity of the column. Under the step-loading cases, the traditional frame column is not only damaged at an earlier stage than the strengthened one, but also has a greater deflection after failure. This indicates that the main deformation of the structure is concentrated on the impacted column. Using the foamed aluminum to strengthen the frame column, the impact resistance of the overall structure is noticeably improved because of the buffer effect. In addition, the novel strengthened frame structure has a more efficient force transmission mechanism, making full use of other structural components to dissipate the impact energy. This study would be helpful in the design of buildings in debris flow–prone areas.

To mitigate the limitations in traditional concrete crack-measuring methods such as low degree in automation and high cost, this study aims to develop a novel method with standard operational procedures (SOP) for nondestructive inspection and automeasure on bridge concrete cracks based on monocular vision and the Harris algorithm. Through experiments in four scenarios using commercially available software as the programming and imaging-processing interface, a novel method, named Mono-Harris, with high automation, high detection speed, and high precision for nondestructive inspection and automeasure of bridge concrete cracks based on monocular vision and the Harris algorithm was developed. There were three main criteria in the experiments, including the shooting angle (parallel and not parallel), shooting distance (far and near), and checkerboard target positioning. Results revealed positively that the combination of monocular vision and image processing technique could effectively measure bridge concrete cracks and the Mono-Harris method developed in this study was efficient and effective.

This research first proposed a conceptual hybrid performance measurement model of elevators (HPMME) that consisted of three latent constructs involving three key performance indicators (KPIs) (condition of equipment, level of service, and risks) and 34 observed variables based on a comprehensive literature review and three rounds of brainstorming sessions with elevator experts. After that, a questionnaire survey was carried out to evaluate the relative importance of the three KPIs and their observed variables. Then, exploratory factor analysis of the survey data was conducted to identify the latent constructs representing the KPIs and their observed variables to validate the conceptual HPMME, and structural equation modeling was done to modify and improve the HPMME. Finally, the HPMME was further validated by experts. With the clearly defined relative significance of each KPI and each observed variable, the HPMME can act as a tool to quantitatively measure the performance of elevators, which would enable the relevant authorities in important decisions that include but are not limited to the prioritization of elevators for modernization and the allocation of manpower and other resources. Using the HPMME, maintenance contractors can identify the critical areas of performance improvement leading toward end-user satisfaction.

In the present research effort, the topic of service life prediction is revisited, using external paint finishes on rendered facades as a case study. A statistically robust approach to develop ordinary linear regression models is proposed, covering the identification of the explanatory variables to include in the model and the identification of outliers. The application of this approach to the analyzed case study improved the determination coefficient (${\mathrm{R}}^2$) up to 0.84, from the 0.74 obtained in the original research in which the data set was presented. In addition to the increase in accuracy, the novel approach proposed enabled the identification of four factors having a statistically significant influence on the degradation rate of the paint finishes: (1) the urbanization density; (2) the humidity level; (3) the type of surface finishing; and (4) the facade orientation. Finally, to enable the development of a hybrid model, a novel approach is suggested whereby the model uncertainty is used to combine statistical and expert inputs. The hybrid modeling approach was proposed to allow tuning the model performance in situations in which experts can identify specific characteristics or conditions affecting the service life not taken into account by the statistical model.

A surface explosion imparts both the air pressure and ground acceleration on structures. Very little literature is available on the effect of a surface blast on structures, especially for multistory buildings. In the present study, the effect of a surface blast on multistory buildings of different heights is extensively investigated by considering the action of the air pressure and ground acceleration separately and both acting simultaneously. For this purpose, four seismically designed reinforced concrete buildings with different heights and fundamental periods are considered. The parameters varied are the standoff distance and charge weight. Responses of the buildings are obtained by the nonlinear time history analysis (NTHA) for the time histories of the air pressure and ground acceleration. The results show that the relative effects of air pressure and ground shock on the buildings depend upon the height of the building and standoff distance. For low-rise buildings, responses are governed by the air pressure effect, whereas for taller buildings, they are governed by the ground shock effect.

Dynamic messaging signs (DMS) are found in operation over freeways, expressways, and other major intersections and provide information to travelers. If the DMS structure fails, then pedestrians and motorists can be harmed. An unstudied contributor to the reduced operation life of DMS structures is yearly thermal cycles. During the winter and summer times, the thermal variations tend to be large in range, in which daily and seasonal temperature variation can contribute to cyclic-caused fatigue. The objective of this study is to analyze thermal-induced fatigue life of highway overhead support structures. Field monitoring, mathematical analysis, and finite-element modeling were employed to perform the objective. The finite-element modeling extends to two different type of connection (slotted gusset welded joints and tube-to-tube welded joints) and two different materials (structural steel and aluminum alloy). Based on the estimated fatigue life for the overhead truss structures, the structural steel slotted gusset welded connection type provides larger fatigue life than other cases.

The flexural capacity of a single micropile is small, and some additional materials need to be built into the steel pipe to increase the flexural and tensile capacity of the structure. This paper introduced a new type of carbon-fiber micropile structure, and through comparison with a traditional micropile structure with ordinary steel, the carbon-fiber micropile structure is recommended. The results show that under the same geological and load conditions, the maximum pile top displacement of the carbon-fiber composite micropile decreased by 24% compared with that of ordinary micropiles. In addition, the displacement distribution of different pile positions showed that the stress and deformation of the carbon-fiber micropile are more coordinated and the resistance to soil displacement is improved. The maximum internal stress of the carbon-fiber composite micropiles was 1.53 times that of common-material micropiles, a relative increase of 53%, and the stress intensity of the piles was significantly improved. In terms of maximum shear stress, the maximum shear stress of the carbon-fiber composite at the squeezed end of the soil was 1.6 times that of the ordinary steel pipe pile, and the local shear resistance of the pile was improved under the premise of ensuring no brittle fracture.

To solve problems concerning insufficient subgrade filler in highway construction, the feasibility of river sand and efflorescent mudstone rock (EMR) to fill subgrade with steep slope were evaluated in this study. First, the fundamental physical, compacting, and mechanical characteristics of river sand and EMR were obtained through laboratory tests. Then combining both the river sand and EMR with various subgrade heights, a total of 24 varieties of composite subgrade plans were generated. The slope stability analyses of these subgrades were conducted by the use of strength reduction method based on FLAC3D. According to the results, it can be shown that the river sand and EMR materials can be utilized to fill subgrade together for their close optimum moisture contents. On the premise of less than 8 m of the subgrade height, the safety factors of river sand subgrades with 3–4 m slope protection width (SPW) and a composite subgrade with 3-m SPW can satisfy technical requirements. The river sand embankment with 3-m SPW may be the best scheme in terms of the vertical deformation, location of potential sliding surface, and economic cost.