Transportation Research Congress 2016: Innovations in Transportation Research Infrastructure

According to surface energy theory and adhesion-peeling model, Wilhelmy plate method and sessile drop method are respectively used to test the surface free energy parameters of asphalt and aggregates so that adhesion work and peeling work can be calculated. ER is an evaluation product based on adhesion work and peeling work, which can reflect the moisture susceptibility of asphalt mixture because of its good correlation with macroscopic index. The higher ER is, the better the mixture performs. Results show that short-term aging, contrary to long-term aging, improves the moisture susceptibility of asphalt mixture; soaking will decrease the anti-stripping ability; freezing has no effect on moisture susceptibility, but additional high temperature thawing process will reduce the resistance to water damage. Anti-stripping ability of asphalt mixture is improved with the increasing of surface roughness; an increase in surface water and clay content is detrimental to moisture susceptibility.

To analyze the effect of moist aggregate and multiple freeze-thaw cycles on moisture susceptibility of warm mix asphalt (WMA) containing organic wax additive (Sasobit), different target moisture contents (1%, 2%, 3%) of aggregates (limestone and basalt) are simulated using the bucket-mixer heating method in lab. The moisture susceptibility of WMA that composed of 3% Sasobit modified asphalt binder (by weight of SK-90 asphalt binder) and different types of dry/moist aggregates in one/two freeze-thaw cycles are test using the modified Lottman test. The test results show the moisture susceptibility of WMA linearly decreases significantly with the increase of moisture content and freeze-thaw cycle number. The moisture susceptibility of WMA made with moist aggregate cannot meet the current specification in China. However, under identical conditions (same moisture content and freeze-thaw cycle number), the moisture susceptibility of WMA made with basalt is better than that of WMA made with limestone.

The gradation of 100 groups of lateritic gravel along the Barcelona Highway in The Republic of Mali is studied by the means of grain size analysis and the typical grading was determined. The compaction property is studied by heavy compaction test and vibration platform method and the mechanical property is evaluated through California bearing ratio (CBR) test. The results showed that: 1) the gradation of natural lateritic gravel is generally poor. It holds a high percentage of coarse grain soils and lacks sandy soils. The proportion of fine grained soil is also high. 2) The fine grained soil belongs to low liquid-limit clay, which cannot meet the domestic requirements of natural gravel material used as base and subbase filling. 3) The heavy compaction method can achieve more desirable compactness. 4) The CBR values are closed to 80% in the degree of compaction of 96% or more, which can be used as bottom subbase of all highways in the West Africa. Lastly, the performance evaluation indices of lateritic gravel subbase are given through domestic and foreign regulatory requirements and existing experience in engineering practice.

To research the effect of material composition parameters on pavement concrete, parameters such as the amount of cement, water-cement ratio, ratio of coarse and fine aggregate, mortar volume component, and air content are tested by rotating cutter method. Recommended ranges of material composition parameters are given on this basis. The result shows that the abrasion loss only decreases by 8% by increasing the amount of cement under the condition of the same water-cement ratio, but it decreases by 50% when to decrease the dosage of water. When the water-cement ratio is at a quite small value, the abrasion loss can decrease by 60% by increasing mortar volume component. Abrasion loss increases 56% when the ratio of coarse and fine aggregate is at a quite low value. It increases by more than 30% when the air content is bigger than 4%.

Asphalt concrete (AC) exhibits significant inherent anisotropic behavior due to the preferential orientation of internal aggregates. In previous work, the inherent anisotropy of compacted AC sample was quantified by using the inclination angles of internal aggregate particles. However, limited attention has been devoted to study how to predict the inherent anisotropy degree of AC through the aggregate geometric parameter before AC specimen compaction. Moreover, the relationships between the inherent anisotropy of AC and geometric parameters of aggregate particles have not been established. In this paper, four types of AC specimens were prepared using the Marshall compaction and wheel rolling method. The modified vector magnitude developed in previous work was validated in this paper and used to quantify the inherent anisotropy of the four types of AC. The cross sections of each specimen were scanned to measure the inclination angle, surface area, and aspect ratio of the aggregates, which were then employed to calculate the modified vector magnitude. The geometric parameters of aggregate particles (>2.36 mm) in each AC specimen was measured using digital image processing before specimen compaction. The relationships between the geometric parameters of different-sized aggregate particles and the modified vector magnitude of compacted AC specimen were developed for each type of AC. Results show that the modified vector magnitude is capable of quantifying the inherent anisotropy of AC. The contribution to the inherent anisotropy of each size aggregate is quite different. Aggregates with the size of 9.5~13.2 mm make the greatest contribution to the inherent anisotropy of AC with the nominal maximum particle size (NMPS) of 13.2 mm.

Rejuvenator is widely used for aged SBS modified asphalt recycling. The objective of this research is to develop a procedure to evaluate rejuvenator on the soften ability, toughening ability, and diffusion ability for aged SBS modified asphalt. Four kinds of rejuvenator and two kinds of self-made SBS modified asphalt were selected. First, penetration grade tests and SHRP asphalt tests were taken for lab-aged SBS modified asphalt whose SBS content was 15%. Second, infrared spectrum experiment and toughness test were taken. Third, a new diffusion test was designed to evaluate permeability of four different kinds of rejuvenator. The test data included penetration, soften point, ductility, G*/sinδ, BBR stiffness S, BBR slope m, viscosity, and toughness. The test results showed that with the aging time increase, the C=C bond rupture gradually. Rejuvenator B was best on toughness ability and diffusion ability for lab-aged SBS modified asphalt. The diffusion ability of rejuvenator could be evaluated by the designed diffusion test.

Due to the research of Marshall test method in anti-cracking material, application is inadequate, in accordance with results of gyratory compaction test, different number of Marshall compaction test has been carried out. With porosity as the evaluation index, two-sided compaction 75 times can be used as the Marshall test optimum compaction times of anti-cracking layer material. Through the regression of gyratory compaction test and Marshall test results, and combined with the characteristics of anti-cracking material and related technical specification, the technical requirements for Marshall test on anti-cracking layer material were determined, and the optimal asphalt content was 7.5% which was close to gyratory compaction test result 7.6%. Those experimental results showed that the research of Marshall test evaluation method for anti-cracking material was definitely accurate and reliable. Study results can provide an important reference for determining the optimal asphalt content of anti-cracking material and the popularization and application of anti-cracking material in road reconstruction projects.

The amount of spent fluid catalytic cracking (FCC) catalyst is nearly 80 kt~90 kt annually in China, which damages the environment seriously and causes great waste of resources. How to deal with the spent catalyst is an emergency to be solved. This research explored the possibility of using this material in the asphalt binder. Two kinds of spent catalysts from different sources were selected. First, the properties of the two spent catalysts were characterized in terms of the particle size distribution, crystalline phase, chemical compositions, BET specific surface area, and surface microstructure. Then, the influences of the catalysts on the conventional properties, viscosity, storage stability, as well as the short term aging of asphalt binder containing the spent catalyst, were studied. And the blending mechanism was also investigated using Fourier transform infrared (FTIR) spectroscopy. It was found that the average diameter of catalyst A is 28.5 μm and for B the average diameter is 64.9 μm. X-ray diffractiometer (XRD) results indicated that the spent catalysts contain Al₂O₃, SiO₂, and Y zeolite. X-ray fluorescence (XRF) data presented that the two spent catalysts are mainly made up of Al₂O₃ and SiO₂. Also, the specific surface areas for the two catalysts are more than 100 m²·g-1. The scanning electron microscope images showed that A and B are spherical granules, and there are pores on the surface. Regarding the asphalt properties, it was found that the penetration and the ductility were dropped, while the softening point and the viscosity were improved with the increase of the spent catalyst dosage. And the asphalt binders containing catalyst with smaller size showed better performance due to the good dispersion in the asphalt binder as proposed. Asphalts with spent catalyst A presented good storage stability at all condition periods. However, asphalts with catalyst B did not show this property once its loading level is 8% and the conditioning time is 12 h or longer. The spent catalyst A and B illustrated the similar influences on the short aging properties of asphalt binder. FTIR spectrum indicated that this blending process was a physical mixing, and there is no chemical reaction occurred between asphalt and spent catalysts.

The pressure aging vessel (PAV) is an aging procedure proposed by the Strategic Highway Research Project (SHRP) to simulate long-term field oxidative aging of asphalt. While the thin film oven test (TFOT) is used to simulate short-term thermal aging, which is referred to the aging of mixing process. The objective of this study is to find the law and corresponding relationship between TFOT and PAV. A laboratory study was conducted to evaluate the performance of three representative kinds of matrix asphalt through TFOT and PAV tests by viscosity, penetration, softening point, and ductility. Test results showed that the increased aging time led to viscosity increase, penetration decrease, and softening point increase in both TFOT and PAV tests. The viscosity test results indicated that the viscosity-temperature property of asphalt after TFOT (5 h)+PAV (20 h) was very close to that of TFOT (15 h) for different kinds of asphalt, but tests of TFOT and PAV did not change the temperature sensitivity of asphalt. Penetration and softening point test results showed that as for one kind of asphalt, penetration and softening point of asphalt after TFOT (5 h)+PAV (20 h) were corresponding to that of the almost same specific time of TFOT, but different kinds of asphalt had different corresponding time. The findings would enhance the cognition of laboratory simulation aging of asphalt.

With the development of civil engineering, the new materials are applied to solidify and modify the material of civil engineering such as concrete and soil. The study on improving the engineering properties of concrete or soil is one of the hot topics now. As the new type of materials, nanomaterials have four special effects which are the small size effect, quantum effect, surface effect, and interface effect, compared with the traditional materials, they have some particular properties. The nanomaterials improve the properties of concrete and soil that has been paid more attention by scholars in the modified field of civil engineering materials, some useful explorations and researches are carried out. In this paper, an overview on the progress of the nanomaterials applications for civil engineering in recent years is done. The prospect of development direction for nanotechnology in the civil engineering in the future is made at end.

The manufacturing and construction temperatures of foamed warm-mix asphalt are lower than those of hot-mix asphalt, which has favorable for aging-resistance properties of asphalt. In this study, the foamed warm-mix asphalts with different foaming water content were prepared by foaming machine in laboratory. The foamed warm-mix asphalt samples were treated by rotating thin film oven test (RTFOT) and pressure aging vessel (PAV). And then, the conventional properties, rheological properties, and fatigue resistance of foamed warm-mix asphalt were investigated by conventional tests and dynamic shear rheometer (DSR) tests. The results show that the foaming water could prevent the aging degree for asphalt and improve the aging-resistance, while foaming water compromises the fatigue resistance of asphalt. Compared to non-foamed asphalt, foamed warm-mix asphalt provides better high temperature performance and worse fatigue resistance performance. With the increase of foaming water content, the softening point and viscosity of foamed warm-mix asphalt increase at first and then decrease, while the fatigue resistance of foamed warm-mix asphalt decrease.

Cement asphalt materials are nowadays widely used in the area of transportation. This paper adopted DMA method to test cement asphalt mastic of five different A/C at different temperatures. According to time-temperature superposition principle, viscoelastic parameters master curves were obtained. Through comparison of CAM model fitting results, cement asphalt mastic working performance was evaluated in three aspects of deformation resistance, temperature sensibility, and vibration reducing. Combined with microstructure analysis, mechanism of mechanical performance variation was explained. Results show that CAM model has a high fitting degree especially for A/C≥0.8 mastic. Increase of A/C obviously reduces resistance to deforming at high temperatures but has little effect on low temperatures. Temperature sensibility increases with A/C increase especially for temperatures between 0 °C ~40 °C. Increase of A/C enhances vibration reducing performance. A/C variation from 0.4 to 0.8 leads to mastic skeleton structure changing which is the fundamental cause to various mechanical properties of different A/C.

Swell-shrinking damage caused by expansive soil in China leads to about 15 billion dollars economic loss every year, and it will be valuable in engineering to improve the characteristic of the expansive soil. The expansive soil in the area of Lishui, Nanjing, is used as the example to study the improvement characteristic in this paper. First, the maximum dry density and the relationship between the optimum moisture content and lime content were analyzed by liquid-plastic limit test and standard compaction test. Then through the triaxial compression test, the relationship between the mechanical property of the improved expansive soil with the lime and fiber content were studied. The result turned out that the strength of the improved soil of 6% lime content was three folds of that of plain soil, while fiber had a better ductility improvement and less strength improvement. At last, it was observed by using unconfined compressive strength test that the improved expansive soil (6% lime content and 0.3% fiber content) is 5.7 folds than plain soil in strength.

This paper introduces one fatty acid based biobinder and two kinds of waste tire rubber to matrix asphalt as additives, and studies properties of biobinder rubber modified asphalt. Penetration test, softening point test, ductility test, and viscosity test were used to evaluate physical properties of asphalt binder. Afterward, rheological properties of biobinder-rubber modified asphalt were characterized by dynamic shear rheometer (DSR) and bending beam rheometer (BBR) tests. Furthermore, Fourier transform infrared (FT-IR) was employed to analyze the chemical property of biobinder-rubber modified asphalt. It was found that physical properties and rheological properties of rubber asphalt improved when biobinder was added at low dosages. However, rubber modified asphalt would be softened when blended with high concentrations of biobinder (>5%, specifically). FT-IR test result indicated that biobinder would enhance the interaction between rubber and asphalt matrix. Through this research, it is concluded that biobinder can be incorporated into rubber modified asphalt as a kind of practical additive which in turn can enhance rubber modified asphalt’s pavement performance.

Asphalt mastic is treated as a two-phase composite with asphalt matrix and embedded-matrix coated mineral filler. A micromechanical model was established to predict the dynamic shear modulus of asphalt mastic, as used the generalized Maxwell model and elastic-viscoelastic correspondence principle, based on the simplified Christensen-Lo model solutions. The DSR tests for asphalt mastic were conducted to verify the proposed model, and the model parameters affecting the predicted moduli were also discussed using the derived predictive model. The results showed that the predicted modulus exhibited a acceptable precision for asphalt mastic with 10% filler volumes fractions, as compared to the measured ones; however, the predicted moduli indicated a decrease at 20% and 30% volumes fractions of fillers, the discrepancy mainly resulted from the interaction between filler particles with higher percentage, the percolation theory was then introduced to develop a newly modified model, the predicted moduli obtained by the modified model agreed well with the measured ones, the elastic modulus of fillers showed a slight effect on the predicted moduli, and the increased volumes fractions of fillers lead to the increased predicted moduli.

The objective of this research is to investigate the deformation instability intrinsic rules about asphalt mixture at high temperature from the shear fatigue damage perspective. Firstly, the shearing strength parameters and the shear stress value in the damaged surface about the test material were determined by conducting unconfined compressive strength tests and uniaxial penetration tests, and then characteristics of the cumulative deformation instability in asphalt mixture at high temperature were obtained using uniaxial compressive dynamic creep tests. In addition, the curves of the creep deformation versus cycles can be obtained under different loading levels, respectively, so that the rheological cycles and the corresponding value as an instability point were defined. Finally, the relationship between the shear stress level and the rheological cycle, namely, the fatigue equation was established by analyzing testing results. The effect of shear fatigue obviously exists during the rutting development process, and the rutting instability in the third stage of the creep curve is the macroscopic phenomena of the cumulative deformation under the shear fatigue effect.

Compressive strength is one of the main mechanical performances of hardened concrete which is important for the concrete quality development for service. The strength detection and monitoring technology of concrete is a very important element to civil engineering. The study of concrete compressive strength using non-destructive technology has a very important practical significance. In the paper, a new method based on piezoelectric smart aggregate is proposed for non-destructive monitoring and forecasting early strength of concrete. The piezoelectric smart aggregate sensors are embedded in the concrete specimens of different specimen size and strength grade. The monitoring system based on compact RIO embedded platform is used in the test and keeps monitoring the concrete early-age (0-28 d) strength and extracting the signal parameters value within 28 d. Meanwhile, the concrete standard destructive test for standard concrete test blocks under the same curing conditions is conducted by a universal compression testing machine to obtain the compressive strength value for validation. And, the test data are normalized to two comprehensive indexes including energy ratio and strength percentage. The results show that the detection signal energy value in the monitoring test and strength development of concrete are basically synchronous, indicating that the proposed monitoring method can reveal the strength development trends. Finally, through the linear fitting for the monitoring data index and the analysis of the relationship between fitting results and the different concrete strength grade and specimen size, the strength monitoring formula and methods for common grade of concrete was deduced.

Dealing with reclaimed asphalt pavement (RAP) becomes more and more important in the development of road industry. Hot in-plant recycling technology are widely used to solve RAP. This paper mainly studies the influence of mixing temperature on the performance of hot in-plant recycled asphalt mixture. Several conclusion can be drew as follow through the study. The performance of hot in-plant recycled asphalt mixture can meet the specifications’ requirements. The proportion of RAP influences mixing temperature greatly, and, it’s main influencing factor of the mixture’s performance. The strength, high-temperature stability, and water stability of recycled mixture increase with the proportion of RAP improving. Mixing temperature has little effect on the performance of mixture. It is necessary to choose higher RAP temperature when the proportion of RAP is high. Otherwise the temperature of mixture cannot meet the requirements.

Asphalt mixture is a multi-phase complex composite of coarse aggregate, asphalt binder, air voids, and asphalt-aggregate interface. Failures often start from interface, which is often considered as the weakest link in asphalt mixture with respect to its formation, strength, and durability. This article introduces the current research on asphalt-aggregate interface failures mechanism and its effect factors, focus on experiments and constitutive models related to interface bond strength and stress analysis, and interface mechanical behavior under different loading modes was also discussed. Diseases related to interface degradation, such as fatigue failure, moisture damage, as well as interface imperfect bonding were summarized. The researches show that current interface models ignore some special loading and extreme adverse conditions, which make asphalt-aggregate interface mechanical properties difficult to be perceived. Therefore, models account for complex variable conditions, viscoelastic behaviors, mixed-mode damage, and dynamic loading would be an urgent task in the industry, which will provide a theoretical and scientific support for the optimization of asphalt mixture design.

The properties of fine steel slag (0-5 mm) and slag power produced by the roller technology in BaoSteel Group were investigated, and they were used to replace the miner power and fine aggregate of asphalt mixture. The mix design, volume expansion property, high-temperature performance, low-temperature performance, and water stability of the steel slag asphalt mixture were experimental studied. The results indicated that the fine steel slag and slag power had larger density than ordinary aggregates and were porous and shown the relatively stronger ability to absorb the asphalt. For the suitable volume parameters of asphalt mixture, the asphalt content of the steel slag asphalt mixture was higher than that of conventional asphalt mixture, and the grading curve of the steel slag asphalt mixture was beyond the gradation range of conventional asphalt mixture. But the volume expansion of asphalt mixture caused by steel slag powder and fine steel slag was little, and compared with the common asphalt mixture, the routine pavement performances of the steel slag asphalt mixture were significantly improved.

Waterborne polyurethane (WPU) has the advantages of high mechanical strength, strong adhesion, good flexibility, and so forth, which can significantly enhance the mechanical properties and durability of emulsified asphalt and micro-surfacing mixture. This study provides a preparation method of WPU modified emulsified asphalt, and its microstructure, tensile mechanical property, and rheological property were investigated. The results showed that the tensile strength and elongation at break increase greatly when the content of WPU was more than 10 wt%. However, phase transformation occurred when the content of WPU exceeds 30 wt%. The results of temperature sweep test indicate that the complex shear modulus (G*) of asphalt improved obviously and the phase angle (δ) decreased with the increase of WPU content, which shows that both the high and low temperature performance of WPU modified emulsified asphalt have enhanced. The relationship between the loss modulus, storage modulus, phase angle, and load frequency in frequency sweep test shows that the viscosity and elasticity of the asphalt enhance with the increase of WPU content, especially at low frequency and high temperature.

In order to alleviate the present issue of construction waste piling up, this paper studied the mechanical properties of cement stabilized aggregate constructed with construction waste composite powder material (hereinafter referred to as CWCPM). Analyzed the microcosmic improvement mechanism of CWCPM on the performance of cement stabilized aggregate through DSC-TG test. The results show: CWCPM improves the 28 d unconfined compressive strength and 90 d flexural strength of the specimens; an appropriate dosage of CWCPM improves the compression resilient modulus of the specimens. The CWCPM has good filling effect and volcano ash effect, which perfect the cement hydration products and reduce the content of Ca(OH)₂, finally improve the compactness of cement-based materials.

The micro-texture of pavement layer aggregate has a direct influence on the skid resistance of pavement. In this paper, the 3D coordinate data of three kinds of aggregates surface is collected based on the surface profiler. Using the box counting method, the MATLAB program is compiled and the 3D fractal dimension of the rock surface is calculated. The results show that the method has good effect on describing the 3D microstructure of the aggregate surface. After that, the difference analysis of fractal dimension of three kinds of different aggregate is carried out. The significant level of microstructure difference between different aggregates is obtained. The results show that there is a significant difference between the surface microstructure of basalt and the other two aggregates. And, there is no significant difference between the surface microstructure of limestone and red sandstone aggregate.

In order to improve the stability and deformation resistance capacity of permeable open-graded friction course (OGFC) asphalt mixture, a kind of flocculent special basalt fiber with good performance is used as a reinforced stabilizer. By selecting different mixing contents of the basalt fiber, the mixture ratios of OGFC-13 were designed, then various pavement performances of the OGFC-13 mixtures under the optimum asphalt aggregate ratios were tested. The results show that the special basalt fiber can adsorb asphalt very well to bond the coarse aggregate skeleton into a solid whole; then, all the pavement performances of basalt fiber reinforced OGFC-13, including high temperature, low temperature and water stability, etc., are obviously improved. However, when the mixing content of basalt fiber is too high, a part of basalt fiber reinforced asphalt mortar will distribute in the connected voids of OGFC-13 to cause the reduction of void ratio, and a few basalt fiber with uneven dispersion is easy to form the weak points in the mixture structure, so as to influence the mixture pavement performances. Therefore, the suitable range of mixing content of the special basalt fiber is determined as 0.3%~0.5%, and the optimum mixing content is 0.4%. The results can provide references for the engineering application of permeable noise reduction asphalt pavement.

Micro-surfacing mixture has been widely used in pavement maintenance due to its several advantages, including water proofing, anti-skidding, and wear resistance. However, micro-surfacing pavement produces more noise than common pavement. It is difficult to measure this kind of noise with existing indoor test practices. A mineral aggregate gradation of low-noise micro-surfacing was proposed along with a novel test method. The addition of fiber was useful for decreasing the aggregate size and reducing the noise produced. The brush test for emulsified asphalt cold recycling mixture was used to measure the indoor noise of the micro-surfacing mixture, and micro-surfacing mixtures with different levels of gradation were tested. Results showed that the indoor noise is related to both speed and aggregate size, and noise is reduced by the addition of fiber and decreased structural depth. The indoor noise was reduced by increasing the sieve size to 7.2 mm pores and increasing the amount of fine aggregate.

Hydrated cement concrete is one of the most commonly used materials in civil engineering. Hydrated cement concrete is heterogeneous, consisting of aggregates, sands, hydrated cement paste, and chemical additives, etc. The compositions have different spatial size, ranging from centimeter to micrometer. Mechanical failures of hydrated cement concrete originate from atomic-bond breakage into micro-voids and micro-cracks and then propagate to macro-cracks. To better understand fundamental mechanism of mechanical failures, there have been a lot of laboratory experiments and numerical simulations. However, the wide spatial variations in hydrated cement concrete make mechanical analysis using simulation techniques at multiple scales very challenging. This study reviews available methods of multiscale mechanical modeling for hydrated cement concrete. In addition, problems in this field are discussed, and suggestions are made at the end to better apply multiscale mechanical modeling methods to improving field performances of hydrated cement concrete.

The polish resistance performance of aggregate is closely related to the skid resistance performance of asphalt pavement, while the mineral composition significantly determines the physical and mechanical properties of aggregate; however, there is very few research on the relationship between mineral composition and properties of aggregate. In this paper, the polishing effect on aggregate is simulated by Wehner/Schulze test, the slope of linearized polished stone value (PSV) tendency is proposed as the index of polish resistance performance, while the mineral composition of three types of aggregate is obtained based on X-ray diffraction test. The relationship between aggregate mineral compositions and polish resistance performance is analyzed based on gray relevance theory. Result shows that calcium and magnesium group mineral has a high correlation with the polish resistance performance of aggregates, the aggregate properties of polish resistance is significantly affected by these minerals.

Preventive maintenance decision making has the characteristics of multi-objective and multi-attribute. And the influencing factors of the decision making process have certain fuzziness. This paper sets up a fuzzy comprehensive evaluation model on the basis of the analysis of asphalt pavement preventive maintenance technology at home and abroad, comprehensively applying analytic hierarchy process and vague mathematics. Take one highway in Beijing as example, the preventive maintenance measures are listed in order of excellence by the method above, and it shows that the method recommended in the paper is feasible and effective. This method has a certain practical application value.

Short trip, including joint mode of long trip, plays an important role in daily traveling. As the modes of public transit, there is a competitive relation among public bicycle, bus, and mass transit in short trip. When choosing the public transit mode, the effect of weather on comfort and conveniences is an important consideration besides time and monetary cost. But fewer utility model researches focus on this aspect. This paper firstly investigates the choice behavior of short trip in a subtropical city, Guangzhou, and gets the choice results influenced by time, money, and weather. Secondly, temperature and precipitation are selected and analyzed as sensitive weather factors. The impact mechanism shows that the selection probability of public bicycle reaches the peak at a temperature range of 18~23 °C. Then, synthesize time cost, monetary cost, and comfort level influenced by weather and build the public transit choice behavior model of short trip. Finally, this paper applies the model to a case study.

Non-slip and noise reduction asphalt pavement is a new type of asphalt pavement. As its good resistance to sliding, reducing the noise, inhibiting driving water on a rainy day and reducing the “glare” when drive at night, non-slip and noise reduction asphalt pavement is becoming more and more popular in domestic. This paper mainly analyzes the long term performance of non-slip and noise reduction asphalt pavement in the southern rainy, humid, and hot climates. This pavement has been followed up and observed for one year. The change rules of drainage performance, roughness, noise reduction, anti-sliding performance are concluded, which could provide technical guidance for estimating the engineering application of non-slip and noise reduction asphalt pavement.

The intelligent transportation system (ITS) in traffic and transportation engineering is becoming more and more popular among pavement engineers. In order to solve the road related problems, find the optimal approach, an integration of multi-disciplinary research and technology on the ITS was introduced in this paper. The current ITS function, further application, and development were also introduced. The key technologies and difficulties in ITS were analyzed.

Stone mastic asphalt (SMA) is an asphalt mixture composed of asphalt, fiber stabilizer, filler, and a small amount of fine material of with gap grade. Due to its high temperature stability, low temperature crack resistance, anti-sliding performance, waterproofing performance, good durability, and excellent road performance, SMA has been widely used in highway constructions all over the world. In this paper, the history of introduction and application of stone mastic asphalt (SMA) in China has been briefly reviewed. One case study is also conducted to reveal the advantages of SMA.

For quantifying the energy consumption and carbon emission of maintenance activities during the asphalt pavement operation phase, a calculation method based on the life cycle assessment theory was proposed. Two asphalt pavement maintenance strategies, traditional maintenance strategy including rehabilitation and reconstruction treatments, and active maintenance strategy including rehabilitation, reconstruction, and several preventive maintenance treatments were compared in a 40 year cycle analysis period. The results showed that active pavement maintenance strategy compared with the traditional maintenance strategy, it was more environmentally friendly. The environmental burden like energy consumption and carbon emission were much less under active pavement maintenance strategy.

Basalt fiber reinforced polymer (BFRP) has become a promising alternative to the steel counterpart for its high strength, durability, insulation, non-magnetism, and resistance to corrosion, especially in specific circumstances such as ports, mining areas, and high speed railway structures. Continuously reinforced concrete pavement (CRCP) with BFRPs has been used in such circumstances for its outstanding properties. To point out the specific mechanical characteristics, a finite element model based on property tests is established by ABAQUS. Influences of crack width, BFRP modulus, reinforcement ratio as well as void under the pavement are analyzed. Results have been elicited that crack width and distance between cracks increased when using BFRP bars instead of steel bars; crack width and void beneath pavement show conspicuous influence on both mechanical state and load transfer efficiency; concrete lose the ability to transfer load when crack width surplus 1.1 mm; BFRP modulus and reinforcement ratio show little effect on neither mechanical property nor load transfer efficiency in constant state, but calculation shows their efficiency in controlling crack width. The paper provides practical guidelines for the design of CRCP reinforced by BFRP.

Pavement materials, including unbound layers and asphalt concrete (AC) have been recognized cross-anisotropic materials. This research is conducted to investigate the effects of road materials cross-anisotropy on mechanical response of AC overlay over asphalt pavement with or without cracking existing in the underlying layer. To facilitate this study, series of three-dimensional (3D) finite element model (FEM) of cross-anisotropic asphalt pavement with AC overlay are developed. The FEM simulations are applied to analyze and compare the surface deflection as well as critical stress and strain on AC overlay in different levels of cross-anisotropy. The numerical results reveal that cross-anisotropic properties of road materials have important effects on the mechanical response of AC overlay: the cross-anisotropic structure has more potential to suffer from failure, which has been currently neglected. It’s indicated that cross-anisotropic properties of road materials should be considered in asphalt pavement overlay design.

In last few years, a great progress has been achieved in the highway development in China. Consequently, on one hand, the highway network scale expands rapidly which brings a huge highway maintenance task. On another hand, the available maintenance fund is limited; meanwhile, the policy of energy conservation and emission reduction is implemented effectively, and as a result, the requirements both on maintenance efficiency and environmental impact are relatively high. Under this background, this research focused on the asphalt pavement maintenance decision making methodology based on the life cycle science consisting of life cycle assessment (LCA) and life cycle cost analysis (LCCA). The pavement performance as well as life cycle cost and environmental impact were taken into consideration when the decision making index system was built, including benefit cost ratio (BCR), benefit energy consumption ratio (BER), and benefit greenhouse gas emission (GHG) ratio (BGR). The decision making models of project-level and network-level pavement maintenance as well as the optimal maintenance timing were developed. Finally, the decision making and optimization methods were applied in factual highway maintenance projects in Jiangsu province with case studies. Research results show that, considering the cost and environmental impacts of road users, when milling and repaving (M&R) and hot in-place recycling (HIR) are compared as for maintenance measures selection, the benefit is associated with traffic volume. M&R has higher BCR, BER, and BGR than HIR at a low traffic condition, but when the traffic grows to a certain degree, the HIR has a higher BCR instead. There exists an optimal maintenance trigger value where the comprehensive benefit is the most. For the maintenance timing optimization, the maintenance triggered level should be improved to keep the pavement a good performance level at a high traffic condition, so that the life cycle cost can be reduced as well as energy consumption and GHG emission. The multi-purpose optimization method for network can be used to solve the maintenance decision making problems under some constraints.

The long-term performance of long life pavement with flexible base and the traditional pavement with semi-rigid base which has the same other layers were evaluated and compared depend on the indexes of pavement deflection, damage, and rutting based on the construction and maintenance engineering of Hu-Ning Highway, Yan-Jiang Highway, and Zhen-Li Highway in Jiangsu Province, China. In addition, the economic benefit of both kinds of pavements was analyzed by present value cost (PVC) method. A result showed that, at the beginning, the performance of the traditional asphalt pavement with semi-rigid was better. Later, the durability and economic benefit of the long life pavement with flexible base was better.

The soil base of low embankment highways is greatly affected by external changes in temperature and humidity, as well as traffic loads. 41 types of soil bases from operational roads were subjected to dynamic, repeated triaxial tests indoors. Non-linear statistical regression was applied to recalibrate the parameters for the Chai-Muria prediction model for permanent strain. This established the quantitative relationships between permanent deformation of soil bases and the plasticity index, moisture content, compactness, and traffic loads. The quasi-static method was used to convert traffic loads to the equivalent static distributed force exerting long-term repeated effects. Next, the additional dynamic stress that traffic loads imposed on soil bases was computed using the theory of elastic multi-layered systems. The calibrated model for predicting permanent strain and the itemize and layerwise summation method were combined to compute permanent deformation of soil bases under various factors. The results were then used to analyze variations in such deformations and ranking of the factors involved. The findings indicated that permanent deformations had a U-shaped distribution curve and was directly proportional to the plasticity index, moisture content, and traffic load, but inversely proportional to the compactness. The ranking of the factors are: plasticity index > moisture content > excess traffic loads > compactness.

The purpose of this paper is to develop a PZT based transducer which can harvest considerable energy from vehicle load. By reviewing the mode of vehicle load and theoretically deducing the energy conversion mechanism of piezoelectric effect, a prototype model of pile-type transducer is proposed. The mechanism response under vehicle load with different number and shape of supporting piles was simulated via finite element analysis, and it is concluded that transducer of four and more round-piles and are more reliable. By the calculation under condition of structural stability constraint, the mechanism of energy conversion limit under different supporting modes is studied, and it is concluded that the value of energy harvested potential decreases with the increasing of the number of supporting piles. So PZT transducer with four-round-piles is preferable to harvest energy from vehicle load. The designed pile-type transducer can harvest 7.85 J under one time of traffic load. The potential of energy harvest is determined by the properties of PZT (d₃₃, ε_r^T, E₀, and σ₀), vehicle load (F), supporting mode (n), and pile shape (r, t).

Temperature segregation control is of great importance to improve the quality of asphalt pavement construction. In this paper, the real-time collection method of paving temperature was studied, and compared with other temperature monitoring methods. It is proven that the method in this study has its own advantages on temperature monitoring of segregation. Based on the infrared temperature sensors array which was evenly arranged on the paving section and distance sensor, the real-time acquisition device of asphalt pavement temperature was developed. Through the interpolation algorithm, the temperature data of discrete points collected by the device mentioned above were expanded into the surface temperature data. In addition, software was developed to draw the paving temperature cloud chart. A new evaluation method of temperature uniformity was put forward in this paper to extend the temperature statistics method which is mentioned in current studies from points to area. Based on the method, the non-uniformities paving areas were quantified, and could be visually displayed on the cloud chart, to provide additional support for the construction management. Finally, a remote monitoring platform was developed to store and process the real-time data received from paving sites, to achieve construction site remote monitoring and real-time early warning.

Subgrade soil is nonlinear elastic-plastic material; its modulus has the stress dependence, which varies with the soil moisture and density. In normal use, subgrade is subjected to the cycling effect of traffic load and the natural environment, which lead to a depression in carrying capacity, settlement deformation and sliding failure, etc. So, the authors studied the variety range of the modulus of elasticity and moisture of subgrade, under the influence of various environmental factors (climate, temperature, water flow, etc.), explored the variation of subgrade humidity and elastic modulus under different humidity conditions, dry-wet conditions and freezing thawing cycles, analyzed the relationships of modulus and humidity between the construction status and balance moisture condition, which has far-reaching implications for subgrade performance design.

In order to compare the difference of loading mode between the RLWT (rotary loaded wheel tester) and the APA, the specimens were compacted using the same gradation under different compaction times, the rutting tests were conducted using RLWT and the APA. Moreover, the images of specimens profile were processed with digital image technology, and the equivalent diameters of coarse aggregates were extracted and analyzed. The results show that the angle between the long axis of coarse aggregate and X-axis increases gradually for RLWT, oppositely, the angle between the long axis of coarse aggregate and X-axis decreases gradually for APA, which is agree with the movement direction of aggregates in the open traffic pavement. The study indicates that it exist great difference of loading mode between the RLWT and the APA, the research for the extensive promotion of RLWT should be further conducted.

With the improvement of computer-communication technology, wireless sensors and network are used in the intelligent monitoring system of road transportation because of its small size, high integration, low maintenance cost, and less installation time. However, the wireless sensor is very easy to fail due to the high exhaustion of power and the disconnection of network. To solve these problems, a self-powered intelligent monitoring system of road transportation with low power consumption is designed and introduced in the paper. The innovative new system can significantly reduce the node communication and energy consumption of data processing; piezoelectric energy and solar energy are used for sensing node and gateway node, respectively. The real-time data collection, processing, analyzing real-time display of monitoring data at mobile terminal, user and project management can be obtained based on this innovative new system.

High grades and sharp curves are the major features for highway geometry in mountainous regions. Excessive lateral stress, which is associated with rollover, may occur at sharp curves. Therefore, understanding the relationship between speed and curve radius is necessary to recommend suitable ranges of curve radius in terms of speed limit. In this paper, the safety model was developed based on vehicle-road coupling principles. The model, which considers two critical scenarios, including sideslip and rollover, was validated by software simulation. The recommended values for curves in mountainous region were provided based on both simulation and theoretical results. The results may also provide reference for the mountainous highway geometry design.

Tunneling in weak and broken rock mass will inevitably disturb surrounding rock mass, which results in instability failure due to the excessive deformation or the high stress generated in rock mass. Therefore, anchor bolts are always used as early support in practical engineering. In this paper, the weak and broken rock mass of grade IV according to Chinese codes is taken as the reference prototype. Subsequently, the trapdoor model test was carried out to simulate tunnel excavation in such type of rock mass, for the purpose of studying the progressive failure characteristics, the failure mode, and the bolt anchoring effect. The test results show that tunneling will inevitably form a disturbed zone around the tunnel, but only part of the rock mass in this zone collapses into tunnel arch shape. Secondly, due the support effect of bolt, the rock mass above tunnel crown presents the trend of damaging in partition. Thirdly, the damage zone mainly concentrated in a fan-shaped region, and the angle between this zone boundary and the horizontal plane is about 45°+ϕ/2. Finally, after the tunnel excavation, an arch-shaped bearing belt with high tangential stress will appear in the rock mass, about 1.0 to 1.25 B away from the tunnel crown.

It is extremely sensitive to do excavation of super pit in central business districts, and the continuous wall construction is a key factor to the success of pit construction. Taking the large excavation of North Huaqiang Station of Shenzhen Metro Line 7 as the engineering background, the construction mechanical response of the pit and surrounding buildings in different wall embedded depths were analyzed using of numerical simulation software FLAC^3D. By contrasting the results of stratum subsidence, foundation lateral displacement, and uneven subsidence in surrounding buildings, it is put forward that the continuous wall of complex embedded reasonable depth in super pit underground formations in different environmental conditions.

With the aim to present the effect of seasonal temperature change on circle beam supporting systems, the monitoring data of a typical excavation engineering in soft clay area has been analyzed. Relationships between seasonal temperature change and pit-retaining structure displacement, circle beam supporting load, the surroundings, are presented in this paper. The analyzed results indicate that the horizontal displacement of the retaining structure increased 15.67 mm to 21.45 mm due to temperature descending from 16 °C to -2 °C, accounting for 50% to 152% of the initial value and there was approximate a linear relationship between the horizontal displacement increment of pile top and the temperature change. Supporting axial force of the circle beam fluctuates with the fluctuation of temperature and the change trend is consistent. The increase of horizontal displacement of the retaining structure further aggravate the soil settlement outside the pit, causing adverse effects on the whole deformation of excavation and the surrounding environment. Using general finite element software ABAQUS to make a numerical simulation, calculation results is better in line with monitoring results. The simulation results show that the bending moment of the circle beam increases with the temperature decreasing and there is an approximately linear relation between them, which is obviously detrimental to the support mainly subjected to axial load. And the maximum settlement increment reached 21 mm with the temperature descending from 16 °C to -2 °C. In addition, the effect of rising temperature on the soil pressure behind retaining wall is great while the temperature reduction has less impact on it.

At present, the effect of deep excavation on piles about the force and deformation had been paid more and more attention, but the mechanism of deep excavation on load transfer and settlement of pile was not very clear. Using ABAQUS software, a two-dimensional axisymmetric finite element model, considering pile length, excavation depth, and over consolidation, was modeling under three different conditions to analyze the influence of unloading effect and rebound effect on the engineering piles stiffness. Comparative analysis showed that vertical stiffness loss of pile was mainly caused by rebound effect before reaching inflection point load and the rule was all the same as pile length changed. Then, unloading effect gradually becomes the main cause of vertical stiffness loss. In addition, when the size of pit reached certain limit value, continuing to increase the size had less influence on the stiffness and ultimate bearing capacity of pile. The over consolidated effect significantly increased the vertical stiffness of pile.

Based on geographic and regional geological study to karst area of Baise District in southwest of Guangxi Province where a 100 km long motorway would be built, the development law and characteristics of karst flaws were deeply revealed. Physiognomy, mineral ingredients of strata, evolution history of geology, and tectonics, local base level of erosion were taken into consideration to judge the possible nature, size, position, and shape of karst flaws largely. The conclusions were regulated by face geology investigation while tunneling. This is significant in two ways, for one thing, the right exploration method of geophysics would be chosen, for another, the survey data may be interpreted more accurately. For some possibilities could be excluded based on reasoning. This geology analyses predominated method assisted with geophysical exploration proved to be more effective and exact in detecting karst faults.

The failure mechanism of geosynthetic-encased stone columns (GECs) in soft clay under embankment is still far from clear. In this study, centrifuge modeling was performed on two different stiffness GECs under embankment. The soft clay used in the tests was made of sodium bentonite powder and glycerin with a 1:1 mixture ratio by mass. The undrained shear strength of the man-made clay is only 5.6 kPa. Two polymers with 123.4 and 13.6 kN/m stiffness were used in the tests. The test results show that the encased stone columns under embankment slope are bended outwards at approximately half depth of foundation. As it can be seen, the bending of the columns encased with low stiffness polymer was more apparent compared to the columns encased with high stiffness polymer. However, the failure mechanism of the GECs is different from that of the GECs in relatively stiff clay revealed by the authors before. In the authors’ previous physical tests, the top of the encased columns in Kaolin clay under embankment bended outwards the largest. It can be concluded that the stiffness of soils between the columns may influence the failure modes of the GECs.

Aiming at existing problems in the maintenance technology of the subgrade frost heaving in the discontinuous frozen ground area, the replacement processing technology can be used. Instead of using traditional replacement materials to reduce the influence of high volume traffic, this paper presents two newly introduced packing with good insulating performance, property of rapid hardening, and easy for construction. The controlled low strength material (CLSM) was mixed with foam particles due to the CLSM properties of high mobility, self-filling, and self-compacting. The optimum volume ratio in filling material of foam particles is 1% obtained from compressive strength test, coefficient of thermal conductivity test and freezing-thawing resisting cycling test based on two proportions. From the perspective of technology and economy, the treatment approaches are suggested as followed: adopting the full thickness of replacement in small subsidence sections and XPS board and CLSM replacement repair in large subsidence region. According to the implementation of the test section results, the new materials that dedicating to the subgrade replacement in the existing discontinuous permafrost zone can meet the requirements of practical engineering projects.

During the construction of interval tunnel from the Tianqiao Station to the outside of Yongdingmen Station of Metro Line 8 in Beijing City, the shield machine will have to pass beneath an existing bridge. On top of the bridge, it is the Beijing-Tianjin intercity railway and the Beijing-Shanghai high-speed railway. At the project worksite, sand and gravel is the main component of ground formation. The stratum is a typical unstable one, so it is easy to induce the excavation face instability and ground subsidence or even collapse during the process of shield tunneling, which will inevitably affect the safe operation of the above railway bridge as the high-speed train has extremely strict requirements on track smoothness. Therefore, the risk of shield crossing construction is rather high. In this paper, the impact of tunnel excavation on the stress and deformation of the bridge structure as well as ground settlement, distribution of pore water pressure caused by shield tunneling were analyzed by means of three-dimensional numerical simulation. Furthermore, a series of countermeasures and monitoring schemes were proposed to ensure the safe operation of bridge before and after the shield crossing construction. The research results can not only guide the construction of this project, but also provide some reference for other similar issues.

Drill-blasting method is used in subway tunnel excavation, when the tunnel located in soil-stone assorted strata. However, the study on pipeline next to subway tunnel is not enough now, when drill-blasting excavation is used in subway tunnel construction. The stress and displacement of pipeline is studied, when blasting load is considered in FLAC3D software in subway tunnel excavation. In the study, pipeline characters have been considered. It shows that: (1) Because of the physico-mechanical parameters of pipeline and of soil stratum, when the position of pipeline and tunnel is vertical, displacement of pipeline less than when is horizontal. When the position is vertical, tension and compression stress of pipeline is bigger than that is horizontal. (2) During the excavation, the factors that affect on the stress of pipeline remarkably include diameters, thickness, materials, and joints. (3) The factors that affect on the displacement of pipeline significantly include diameter of pipeline, depth of pipeline, and joints.

Sand liquefaction is affected by many factors. In order to investigate the dynamic characteristics of saturated sand and the influence of the dry density on liquefaction, DDS-70 microcomputer-controlled electromagnetic vibration triaxial testing system was used in this study. The liquefaction strength of saturated sand determined was conducted using this system. Through the curve fitting results between the liquefaction shear stress of saturated sand and vibration frequency, it shows that the power function fitting has good correlation. A number of dynamic triaxial tests on saturated sand of different dry density are also analyzed; the influence of dry density on the dynamic strength characteristics of saturated sand are discussed. It is found that the power function model parameters have a strong correlation with the dry density, which increases gradually as the dry density increases. The model parameter b is in the range between -0.20~0.00.

Nowadays, most transfer MTR stations are located in the bustling commercial district. In order to ensure the safety of surrounding buildings and existing stations, more strict rules for deformation control and technical requirements are put forward during construction. When the diaphragm wall of transfer station was demolished, a three-dimensional numerical simulation with ANSYS was adopted to analyze the behavior and deformation characteristics of existing station structure in Huaxin transfer station in Line 7 and Line 3 in Shenzhen. According to the calculation results, a diaphragm wall demolition scheme that sublevel interval demolition and temporary supporting was proposed. So it can effectively improve the stress condition and guarantee the safety of the existing station, and the conclusions can provide reference for the construction of similar projects in the future.

The existence of the defects of filled layer in inverted arch leads to a more complicated stress state of the deep-buried and heavy-haul railway tunnel structures, which can easily cause the structural cracking and directly affect the safety of the tunnel structures. Based on deep-buried and heavy-haul railway Wuyanhe Tunnel in South Central Shanxi, the numerical simulation is used to analyze the effect of the defects of filled layer in inverted arch on the lining structure and the effect of anchor pile in inverted arch for this filling defect. The results show that: (1) The main stress of the filling layer is mainly controlled by the dynamic load of the train and the ground load has small impact on the filling layer. But when the second lining failure occurs, the filling layer begins to bear the ground load and may be destroyed. (2) The structural damage of the filling layer is not controlled by the dynamic displacement but the tensile break. (3) It is feasible to adopt the method of anchor pile reinforcement to reduce the stress level of the second lining and filling layer. The research results have some reference value for the design and disposal defect of deep-buried and heavy-haul railway tunnel in the future.

The soil settlement or heave of shield tunnel caused by tunneling excavation is a three dimensional problem. Based on the previous research results, this paper proposed a three dimensional unified equation to calculate the vertical soil displacement induced by ground loss under non-synchronous construction for double-tube shield tunnels. The equation takes into account the lag time of construction and the effect of soil consolidation. Analyzed results showed that the following vertical soil displacement can be obtained simultaneously through the equation: (a) at ground surface and any depth of ground, (b) along transversal and longitudinal direction, (c) under non-synchronous and synchronous construction, and (d) for single-tube tunnel and double-tube tunnels. Meanwhile, the equation can be applied to illustrate the two-dimensional and three-dimensional curves of vertical soil displacement. Compared with the monitoring data of shield tunnel section between Zaoying Station and Dongfeng Beiqiao Station in Beijing Metro Line 14, the rationality and applicability of the proposed equation were verified. The influencing factors and changing tendency of vertical soil displacement for shield tunnel were investigated by adopting the equation.

With the rapid development of urban rail transit, the existence of the fault and fracture zone usually bring greater difficulty to the shield tunnel construction. Taking the engineering of shield tunnel crossing the fault fracture zone in Shenzhen Metro Line 7 Project for example, using the numerical simulation method to analyze the mechanical characteristics of shield tunnel crossing the fault fracture zone construction, and optimize different stratum reinforcement scheme. In the longitudinal direction, the fault fracture zone has great influence on the surface subsidence within a scope 9 m in front of and behind the fault; the effect magnitude on the stratum deformation is about 23.2% (increase). After comparing different reinforcement schemes, it shows that the range of strength within 2~5 times harder than the surrounding strata is the reasonable reinforcement strength scope for the fault fracture zone; and in the transverse direction, the area contained by the boundary of 6m from the center of the tunnel is reasonable; in the longitudinal direction, the area contained by the boundary of 6~9 m front and behind the fault is reasonable.

There are diverse stratigraphic classifications in tunneling, which played a vital role in engineering practice. Current rock classifications were basically developed for mining method tunnel where the ground stability was the main evaluation index. However, in shield tunneling, we paid more attention to the boreability of strata, the wear of cutters, the stability of heading face, as well as the ground movement. What’s more, the current classifications failed to take the complex strata into account, but this factor might have the major impact on shield tunneling, and sometimes even played the decisive role. So the ordinary classifications had certain limitations when were applied in shield tunneling. In order to classify the strata based on the difficulty of shield tunneling, four evaluation factors were selected, including drivage efficiency, cutter wear, heading face stability, as well as ground loss and displacement. According to the difficulty of cutting and deformation control, the ground was divided into four categories, including easy to cut and easy to control, easy to cut and hard to control, hard to cut and easy to control, hard to cut and hard to control as well, and corresponding suggestions for each category were put forward in the end. This stratigraphic classification can make up for the limitations of the current classification and provide practical references for control measures in shield tunneling.

There was a common phenomenon appeared as severe wear of the cutter heads and cutting tools, frequent changing of the cutting tools, difficulty of muck discharge, poor adaptability of shield, and improper handling of construction problems during metro shield construction in sandy cobble stratum. In order to improve the adaptability of shield in this kind of formation, choosing the optimum type of shield, equipment configuration, and construction countermeasures are the prerequisite to guarantee the smooth completion of construction. This article took Beijing, Chengdu, and Shenyang as study objects—three typical cities where exist widespread sandy cobble stratums. Based on the comparative analysis on the key physical and mechanical parameters (content and strength of cobble, grain composition, and so on) and hydrogeological condition in sandy cobble stratums, practical engineering problems, corresponding measures, and construction effects were systematically summarized and analyzed in the process of shield construction, and then, the shield type and its configurations, as well as the heading parameters aiming at different types of sand cobble stratums were put forward. Conclusions drawn from the paper can provide practically targeted references for engineers in sandy cobble stratum.

Numerical analysis of highway tunnel fire under semi-transverse and transverse ventilation system with the CFD code FLUENT are presented. In particular, the effect of ventilating velocity is investigated. Results show that in the tunnel with semi-transverse ventilation, when there is no wind (v=0m/s) in ventilating duct, the diffusion distance of fire is limited in the both side of the fire point about 35 m range, and the diffusion distance of high-temperature smoke in tunnel space decreases with the increase of ventilating velocity, while excessive ventilating velocity will lower the exhaust efficiency of ventilating duct. The critical ventilating velocity for semi-transverse ventilation system is 5 m/s in the case of the 5 MW heat release rate. In the tunnel with transverse ventilation, the diffusion distance of high-temperature smoke increases with the decrease of ventilating velocity in supply air vent. When the ventilating velocity in supply air vent is big, the smoke would spread to the both sides of the ventilating duct which is bad for exhausting the smoke. The critical ventilating velocity for transverse ventilation system is 3 m/s in the case of the 5 MW heat release rate.

Soft ground usually has complicated geological surroundings and lacks enough carrying capability. Due to this, uneven settlement of shield tunnel is inevitable and can be fairly large even if the construction technology has improved observably. SSPC (steel segments with pre-filled concrete) segment has been developed and used for reducing ground settlement and smoothly launching and receiving shield machine in soft ground. However, a rational design method for SSPC segment can not be established because its mechanical behaviors are not clarified up to now. Therefore, the purpose of this paper is to study the mechanical behavior of SSPC segment using finite element method and groups of four-point bending tests. The failure modes of SSPC segment were also investigated through experiments and finite element analysis. Comparisons show that the proposed finite element model is suitable for SSPC segment and can predict the mechanical behaviors of SSPC segment accurately. The relevant conclusions of this study, therefore, will provide improved methodology and guidance for the design and numerical analysis of SSPC segment.

This paper provides a comprehensive introduction to the model test of full-face excavation tunneling method in soft rock based on analysis of controlled deformation in rocks and soils (ADECO-RS) including the similarity criteria of physical and mechanical parameters, preparation of similar materials for soft surrounding rock and supports. Layout of surrounding rock stress and displacement measurement points are introduced. According to the results of the model test, the change law of surrounding rock displacement is analyzed in details. A four-stage-deformation assumption is proposed and function of advanced small pipes in controlling space effect during excavation is also studied. The results can provide a reference for the advance reinforcement of tunnel face.

During the construction of quasi-rectangular shield tunnel, the pressure distribution around tunnel is important for effective synchronous grouting to support ground strata. Due to the special shape of quasi-rectangular tunnel, the grouting may silt up on the top of the segment, which influences the grouting fluxion and filling and leads to the non-uniform distribution of the grout. A large model test of quasi-rectangular tunnel was carried out to simulate the process of synchronous grouting. By measuring the grouting pressure and surveying the final grouting shape under different working cases, the pressure distribution in toroidal direction and changing law of grouting were analyzed. Finally, by measuring the displacements of different points in designated sections, the results of settlement and upheaval in different positions are analyzed. As a result, the grouting ratio of 6:4 (up:down) is the most effective one among the three cases designed in this experiment.

The formation process of filter cake in slurry shield tunneling was simulated by particle flow code in 3 dimensions (PFC^3D), and the supporting principle of filter cake for maintaining the stability of excavation face is discussed. The simulation results show that the formation of filter cake is mainly depended on the particle size distribution of slurry and the pore sizes of stratum. The well graded slurry particles can form more compact filter cake on the excavation face than the poorly graded slurry particles. The more compact filter cake can be formed on the surface of stratum with smaller pore sizes. Moreover, the thickness of filter cake decreases with the increase of pressure difference between slurry and stratum. The supporting principle of filter cake is that the sum of driving force applied by the water to the filter cake, which containing the force applied to filter cake particles by the pressure gradient and the interaction force between filter cake particles and water, provide the horizontal effective stress to balance the horizontal earth pressure in the ground. Therefore, the more compact the formed filter cake, the larger the induced pressure gradient in the filter cake, and then the bigger the resulted horizontal effective stress in the stratum for maintaining the stability of excavation face.

Stability of soil in front of tunnel excavation face should be guaranteed during shield excavation. Therefore, the corresponding equilibrium principle and appropriate pressure of shield chamber are important for practical purpose. In conventional methods, soil water pressure at the central axis of tunnel cross-section is used as standard value. However, according to investigation in this paper, it can only maintain the resultant force in an equilibrium state while making resultant moment non-zero due to the fact that unit weight of residual soil in shield chamber differs from that of in-situ soil. A new method using earth pressure at rest at the position of 2/3 times the tunnel’s diameter to the vault as reference value is formulated in this paper, in which resultant moment is ideally zero; meanwhile, the related resultant force occurs with a small value which is beneficial to control ground settlement deformation.

In order to keep bridge safe and more durable, wireless sensors have been widely applied in bridge health monitoring. It is an engineering challenge to provide inexhaustible energy to wireless sensors. In this work, we investigated piezoelectric energy harvesting from bridge's vibration due to moving vehicles. The energy harvester and the bridge are modeled as a cantilever beam and a simply-supported beam, respectively, with Euler–Bernoulli beam assumption. Vehicle moves on the bridge is modeled as a mass. The road surface irregularity was considered in calculating the response of the bridge. The resulting expressions for the coupled mechanical response and the electrical outputs are then derived using finite mode transform method. Additionally, a numerical parametric study is conducted to highlight the effects of the velocity, installing position of the harvester and circuit resistance on energy harvesting. Numerical results indicate that the velocity of the vehicle and road irregularity have a strong influence on piezoelectric energy harvesting. An appropriate designed piezoelectric energy harvester can be used to power a wireless sensor node.

With the rapid development of bridges, the traditional sensing technology is difficult to meet the needs of diversified tests. To overcome the limitations and further develop the health monitoring system of bridges, a new network concept, namely, Internet of things (IOT), which exchanges information and creates the interconnection and communication between bridge and the monitoring system, is presented in this paper. The system is designed to achieve real-time monitoring of bridge cluster health status. This system introduces the wireless acceleration transducer by wireless gateway and cloud platform to monitor the bridge health status, which can real-time monitor the bridge cluster health status, process the real-time data, and help bridge maintenance.