Excavation failure during micro-tunneling in fine sands: A case study

Partly funded by the World Bank, a new gravity sewer line is currently being constructed in Anzali, Iran using micro-tunneling methods. The project includes the installation of 2551 m reinforced concrete pipes with diameter ranging from 600 to 1000 mm at an average depth of 5 m below surface. Micro-tunnel Boring Machine (MTBM) and hydraulic pipejacking have been used to install the sewer line. Pipejacking in saturated highly porous sandy soil poses various challenges during construction including the risk of face failure, possibility of shaft collapse, massive rush of groundwater (in this case from the Caspian Sea) and surface subsidence. This paper provides an overview of the project and summarizes the challenges faced and the techniques used to handle the difficulties encountered during construction.     

Air leakage measurement and analysis in duct systems

Air ducts and related equipments are used in a large number of buildings having thermal comfort. In this study, energy loss related with air leakage is studied. The leakage measurement setup was produced according to NEN-EN standards and the evaluation of data have been conducted by using power law model. The measurements were made on 300 and 1000 mm diameter single circular ducts, 300 mm × 250 mm and 1000 mm × 500 mm flanged joint rectangular ducts, 300 and 630 mm diameter circular beaded slip joint ducts, 300 mm × 200 mm and 500 mm × 300 mm rectangular flanged and drive slip joint ducts, and an branched air distribution system having different diameters for positive internal pressures. Test results have showed that the most of air leakage is from the joints. The seam contribution to air leakage is relatively lower than the joints. Using sealing gaskets help to improve the air leakage by about 50%.     

Experimental investigation of ultimate capacity of wired mesh-reinforced cementitious slabs

Experimental tests conducted on 27 square cementitious slabs of 490 × 490 mm simply supported on four edges and subjected to patch load are presented. The slabs had a clear span of 400 × 400 mm and provided with a 445 × 445 mm closed frame of 8 mm diameter steel bar to hold the reinforcement in place and to act as a line support. The test variables were the wire mesh volume fraction: four expanded and two square types; slab thickness: 40, 45, 50 and 60 mm; and the patch load pattern: square and rectangular. The test results showed that as the volume fraction increased the punching strength of the slabs was also increased. Adding a wire mesh to ordinary reinforcement increases significantly the punching resistance at column stub. Moreover, as the loaded area size increases both ductility and stiffness increases and the bridging effect due to the difference in the reinforcement ratio in orthogonal directions was clearly noticed. More research was needed to identify the volume fraction ratio at which the mode of failure alter from flexure to punching.     

Maximum surface settlement based classification of shallow tunnels in soft ground

Prediction of the maximum surface settlement due to shallow tunnelling in soft grounds is a valuable metrics in ensuring safe operations, particularly in urban areas. Although numerous researches have been devoted to this issue, due to the complexity and a large number of the effective parameters, no comprehensive solution to the problem is available. In this study, a shallow tunnel classification system (STCS), based on maximum settlement, is proposed. The STCS holds on the results of several tunnelling projects around the world. The classifier categorises a tunnel based on geometry, ground, and performance characteristics. A decision tree classification method, after training with 20 cases, was successful to predict the maximum settlement for 14 tunnelling projects. The maximum surface settlement predictions were in the form of assigning a class label to each tunnel. Four tunnel classes were defined as follow: (i) class A (maximum settlement < 9.9 mm), (ii) class “B” (10 ⩽ maximum settlement < 19.9 mm), (iii) class “C” (20 ⩽ maximum settlement < 29.9 mm), and (iv) class “D” (maximum settlement ⩾ 30 mm). The most explanatory independent variables were selected, by the STCS, as follow: tunnel depth, diameter, volume loss, and normalised volume loss. The proposed classification scheme can be employed as a decision making aid in settlement prediction/prevention in shallow tunnelling in soft grounds. The STCS is proposed as a supplemental tool to the observational methods, and it is not expected to be a stand-alone measure for settlement.     

Permeability of high-performance concrete subjected to elevated temperature (600 °C)

Permeability is one of the most important parameters to quantify the durability of high-performance concrete. Permeability is closely related with the spalling phenomenon in concrete at elevated temperature. This parameter is commonly measured on non-thermally damaged specimens. This paper presents the results of an experimental investigation carried out to study the effect of elevated temperature on the permeability of high-performance concrete. For this purpose, three types of concrete mixtures were prepared: (i) control high-performance concrete; (ii) high-performance concrete incorporating polypropylene fibres; and (iii) high-performance concrete made with lightweight aggregates. A heating–cooling cycle was applied on 160 × 320 mm, 110 × 220 mm, and 150 × 300 mm cylindrical specimens. The maximum test temperature was kept as either 200 or 600 °C. After the thermal treatment, 65 mm thick slices were cut from each cylinder and dried prior to being subjected to permeability test. Results of thermal gradients in the concrete specimens during the heating–cooling cycles, compressive strength, and splitting tensile strength of concrete mixtures are also presented here. A relationship between the thermal damage indicators and permeability is presented.     

Parametrical static analysis on group studs with typical push-out tests

Group studs are known as shear connectors in steel and concrete composite structures. By now, many composite bridges have been characterized by long lateral cantilevers. The shear studs are actually under biaxial action consisting of shear force and action in light of lateral bending moment on concrete slab induced by long cantilever and passing by moving loads. Moreover, lateral bending moment may even lead to the initiation of bending-induced concrete cracks. These two situations can both affect mechanical performance of group studs. Thus, a parametrical FEM analysis was carried out, in which damage plasticity was introduced to simulate material nonlinear behavior. In the analysis, lateral bending moments respectively inducing maximum concrete crack widths of 0.1 mm and 0.2 mm, shank diameters of 13 mm, 16 mm, 19 mm and 22 mm and stud heights including 80 mm and 100 mm were parameters. It was found that mechanical behavior of group studs with large shank diameter would be less affected by biaxial action and initial bending-induced concrete cracks seemed unfavorable to stud shear stiffness. On the other hand, typical push-out tests were executed to investigate reductions of shear stiffness and shear capacity of group studs. The reliability of FEM analysis was also verified based on the tests. In addition, stud shear capacity evaluations according to several design specifications were presented. It indicated shear capacity evaluation of Eurocode 4 got a relatively large safety factor. Moreover, the applicability of these specifications for group studs on shear capacity evaluation was also discussed.     

Study on the graphite and carbon fiber modified asphalt concrete

The mechanical and electrical properties of graphite and carbon fiber modified asphalt concrete were measured in this paper through the indirect tensile test. The experimental results indicate that the mechanical properties of asphalt mixture are influenced by the addition of conductive component like graphite and carbon fiber, When the graphite content increased from 0 to 22 vol.%, Marshall stability decreased from 12.8 kN to 9.43 kN and residual stability from 91.1% to 87.2%. Rutting dynamic stability decreased from 3318 times/mm to 2619 times/mm. After adding the carbon fiber, when the carbon fiber content increased from 0 to 2 vol.%, their Marshall stability and residual stability increased from 12.8 kN to 13.5 kN and residual stability from 91.1% to 92.7%. Rutting dynamic stability increased from 3318 times/mm to 3403 times/mm. When modified through combination effect of graphite and carbon fiber mixed fillers, the mechanical performance and electrical property were improved greatly, their Marshall stability and residual stability has increased from 9.43 kN to 12.1 kN and residual stability from 87.2% to 89.2%. Rutting dynamic stability increased from 2619 times/mm to 3292 times/mm. Furthermore, the resilient modulus is influenced by the addition of graphite, the value of resilient modulus is as much as that of the original, it is 90% when graphite is 30 vol.% and is 70% when graphite is 45 vol.%. The electrical resistance increases reversibly with increasing tensile strain either under dynamic indirect tensile testing or static indirect tensile testing, graphite and carbon fiber modified asphalt concretes are effective for the self-monitoring of strain. It is foreseen that the strain–stress self monitoring is valuable for weighing, traffic monitoring, border monitoring and structural vibration control.     

Nanostructured zonolite–cementitious surface compounds for thermal insulation

This paper investigates the effect of zonolite loadings on the thermal resistivity and indirect tensile strength of nanostructured cementitious compounds. The main objective of this research is to develop a structural lightweight compound that can be used on building skins and cores for pre fabricated structural insulated panels (SIPs). The application of this compound is intended to improve the thermal resistivity of the building envelope with suitable mechanical performances. The zonolite dosage was added to the cement-nano clay blend at different dosages up to 40% by weight. The nano clay reinforcement used is montmorillonite clay (Hydrated sodium calcium aluminum silicate). The mixes were prepared using water of consistence. The wet compounds were molded in PVC cylindrical molds, having 50 mm inside diameter and 27 mm height, and left for 24 h, then demolded and cured in humid air (20 ± 1 °C&100% RH) for 28 days. The samples were then dried at 105 ± 5 °C for 24 h before testing using a forced convection oven. The thermal resistivity and indirect tensile strength of the different compounds were evaluated. Results demonstrate that the thermal resistivity at 40% zonolite loading enhanced by about 2.9 folds compared to the control samples. An increase of more than 30% in the indirect tensile strength was also achieved when a 0.5% by weight of polycarboxylate superplasticizer was used.     

Preliminary experimental investigation of the fatigue bond behavior of CFRP confined RC beams

This paper presents the results of the first phase of a study on the effect of the confinement provided by transverse carbon fiber reinforced polymer (CFRP) sheets on the fatigue bond strength of steel reinforcing bars in concrete beams. Reinforced concrete bond-beams 150 × 250 × 2000 mm were tested. The variables examined were the area of the CFRP sheets (none or one U-wrap CFRP sheet), the reinforcing bar diameter (20 or 25 mm) and the load range applied to the specimens. The results showed that increasing the bar diameter increased the fatigue bond strength for the unwrapped beams. The CFRP sheets increased the bond strength of the bond-beams with 20 mm bars. However, for the beams with 25 mm steel bars the failure mode changed from a bond splitting failure for the unwrapped beams to a diagonal shear failure for the CFRP wrapped beams, and there was little increase in fatigue strength. Finally, the bond failure mechanism for repeated loading is described.     

Effect of crumb rubber modifiers on high temperature susceptibility of wearing course mixtures

This paper investigates the effects of different sizes of crumb rubber modifier (CRM) on the high temperature susceptibility of three gradations (AC-10, AC-20 and PA) of wearing course mixtures. A wet process and 10% CRM by total weight of binders were used in these studies and the control variables for these studies included three CRMs of sizes 0.15 mm, 0.30 mm and 0.60 mm. The evaluations were twofold. Firstly, a comparison of the properties of those modified and unmodified binders at a wide range of testing temperatures and ageing conditions was conducted. Secondary, a comparison of the rutting resistance of the CRM and conventional mixtures was made. The results show that all the CRMs have overall contributed to better performance of both binders and mixtures at high temperatures. In addition, among these three CRM sizes, mixtures modified with 0.15 mm CRM exhibited the best effect on the dense-graded mixture (AC-10 and AC-20) whereas mixtures modified with 0.60 mm CRM exhibited the best effect on the open-graded mixture of porous asphalt (PA).     

Composite tubes as an alternative to steel spirals for concrete members in bending and shear

Glass fibre-reinforced polymer (GFRP) tubes are compared to steel spiral reinforcement in circular concrete members with longitudinal reinforcement and prestressing, using six beam tests. Two 324 mm diameter and 4.2 m long prestressed specimens were tested in bending. Four 219 mm diameter reinforced specimens were also tested, including two 2.43 m long beams tested in bending and two 0.6 m long beams tested in shear. In each set, one specimen was essentially a concrete-filled GFRP tube, while the other control specimen included steel spiral reinforcement of comparable hoop stiffness to that of GFRP tube. The strength of control specimens was governed by crushing and spalling of concrete cover. Unlike spiral reinforcement, GFRP tubes confined larger concrete areas and also contributed as longitudinal reinforcement, leading to increases in flexural and shear strengths, up to 113% and 69%, respectively.     

Extinguishing characteristics of a diffusion flame with water vapor produced from a water droplet impacting onto a heated plate

In this study, we have investigated an extinguishing method of a diffusion flame with water vapor produced from a water droplet impacting onto a headed plate, which is called as indirect fire attack. In order to clarify the extinguishing characteristics, the extinguishing experiments of a methane-air diffusion flame have been performed by using a pure water droplet with the diameter of 3.2 mm. The droplet dropped from the height of 400 mm. The wall superheat and the burner height were varied from 0 K to 330 K and from 32 mm to 102 mm, respectively. As a result, under certain wall-heat conditions, the water-vapor vortex ring is formed and visualized by the white water fog. At wall superheat of 150 K, the formation probability of the vortex ring is unity and the extinguishing probability always shows the peak values regardless of the burner height. As a result, it can be said in our study that the wall superheat of 150 K is the most effective value for the indirect extinguishing method.     

Influence of corrosion crack patterns on the rate of crack widening of RC beams

Corrosion crack widths are often used by structural engineers in the field to predict level of steel corrosion as well as residual load-bearing capacities of corroding RC structures. This paper presents further work on this matter but with focus on corrosion crack patterns and how they affect rate of crack widening. It is based on results from a research where 17 quasi-full-scale (153 × 254 × 3000 mm) RC beams were corroded under various levels of sustained loads. The rate of widening of corrosion crack widths was found to be very much dependent on crack patterns. Deformation of cover concrete under each crack pattern was discussed. It was found that at maximum crack widths below 0.6 mm, the majority of beams exhibited nearly similar crack patterns as well as rate of widening of corrosion cracks. A mass loss of steel of 1% corresponded to a maximum crack width between 0.14 and 0.22 mm. At large crack widths (>0.6 mm), various beams exhibited very different rates of crack widening. It was shown that at crack widths above 0.6 mm, to be conservative an increase in mass loss of steel of 1% corresponded to corrosion crack widening of 0.02 mm.     

Non-destructive evaluation of the grouted ratio of a pipe roof support system in tunneling

The pipe roof system is widely used in the New Austrian Tunneling Method (NATM) as the main support system. Thus, the integrity of the pipe roof system influences the tunnel stability. The purpose of this study is to evaluate the grouted ratio of a pipe roof system using a non-destructive method in the laboratory and in the field. In the laboratory tests, four specimens embedded in soils and five non-embedded specimens are prepared with different grouted ratios of 0%, 25%, 50%, 75%, and 100%. The steel pipes are 6 m in length, 60.5 mm in external diameter, and 3.8 mm in thickness. Field tests are conducted with two fully grouted pipes with dimensions of 12 m in length, 60.5 mm in external diameter, and 3.8 mm in thickness. The reflection method of guided waves, which are generated by a hammer impact and are measured using an acoustic emission sensor, is used for the non-destructive testing. Experimental studies demonstrate that the group velocities and the main frequencies of the guided waves decrease as the grouted ratio increases for embedded and non-embedded specimen in soils. The variation of the main frequency, however, is more significant than the variation of the group velocity. In addition, the group velocities and main frequencies of the field specimens are lower than those of the embedded specimens. This study demonstrates that the variations of the group velocity and main frequency may be used effectively to estimate the grout ratio of a pipe roof system in tunneling.     

Damage to surface structures due to blast vibration

This paper describes effect of blast produced ground vibration on damage potential to residential structures to determine safe levels of ground vibration for the residential structures and other buildings in mining areas. Impacts of 341 blasts detonated at two mines were monitored at the test structures and 1871 blast vibrations signatures were recorded on or near the test structures. Cosmetic cracks in a native brick-mud-cement house were detected at peak particle velocities (PPV) between 51.6 and 56.3 mm/s. The reinforced concrete and cement mortar (RCC) structure experienced cosmetic cracks at PPVs of 68.6–71.3 mm/s at the first floor, whereas at second floor it was detected at PPV levels of 71.2–72.2 mm/s. Minor damage in brick-mud-cement house was recorded at PPV levels of 81.0–89.7 mm/s. The RCC structure at first and second floors experienced minor damage at PPV levels of 104 and 98.3–118 mm/s, respectively. The brick-mud-cement house experienced major damage at PPV level of 99.6–113.0 mm/s, while major damage was recorded in RCC structure on first floor at PPV of 122 mm/s, the second floor at PPV levels of 128.9–161 mm/s. Recommended threshold limits of vibrations for the different type of structures is based on these measurements and observations.     

Strength,durability, and micro-structural properties of concrete made with used-foundry sand (UFS)

This paper presents the design of concrete mixes made with used-foundry (UFS) sand as partial replacement of fine aggregates. Various mechanical properties are evaluated (compressive strength, and split-tensile strength). Durability of the concrete regarding resistance to chloride penetration, and carbonation is also evaluated. Test results indicate that industrial by-products can produce concrete with sufficient strength and durability to replace normal concrete. Compressive strength, and split-tensile strength, was determined at 28, 90 and 365 days along with carbonation and rapid chloride penetration resistance at 90 and 365 days. Comparative strength development of foundry sand mixes in relation to the control mix i.e. mix without foundry sand was observed. The maximum carbonation depth in natural environment, for mixes containing foundry sand never exceeded 2.5 mm at 90 days and 5 mm at 365 days. The RCPT values, as per ASTM C 1202-97, were less than 750 coulombs at 90 days and 500 coulombs at 365 days which comes under very low category. Thereby, indicating effective use of foundry sand as an alternate material, as partial replacement of fine aggregates in concrete. Micro-structural investigations of control mix and mixes with various percentages of foundry sand were also performed using XRD and SEM techniques. The micro-structural investigations shed some light on the nature of variation in strength at the different replacements of fine aggregates with foundry sand, in concrete.     

Determination of smoldering time and thermal characteristics of firebrands under laboratory conditions

The laboratory experiment was conducted to simulate the transfer of smouldering particles produced in forest wildfires by a heated gas flow. The pine bark pieces with the linear dimensions L=(15; 20; 30) mm and a thickness of h=(4−5) mm were selected as model particles. The rate and temperature of the incident flow varied in the range of 1–3 m/s and 80–85 °C, respectively. The temperature of the samples was recorded using a thermal imager. To determine the minimum smouldering temperature of pine bark, the thermal analysis was conducted. The minimum smouldering temperature of pine bark was found to be 190 °C. This temperature will cause thermal decomposition of bark only at the first stage (oxidation of resinous components). In the study the smouldering time, the temperature and the weight of samples were obtained and analyzed under various experimental conditions. The data analysis shows that the increase in the particle size leads to the decrease in their mass loss, and the rate change of the incident flow does not practically influence the mass change. For particles with the linear dimensions of 10 mm and 20 mm, the mass varies from 6% to 25%. The maximum mass loss is observed for the flows with a rate of 1 and 2 m/s. The results have shown that the increase in the particle size leads to the increase in the smouldering time. The position of the particle plays an important role, the effect of which increases with increasing the particle size. The calculations showed that the smouldering time of bark samples is long enough for the particles to serve as new sources of spot fires. The particles were found to be transported to a distance of 218 m from the fire line which can certainly influence the propagation of the fire front.     

Experimental evaluation of the flexural behavior of corroded P/C beams

Corrosion phenomena and related effects, such as size reduction in both rebars and strands, bond decay at steel–concrete interface, and cracking in the surrounding concrete, are particularly critical in prestressed-concrete members, not only for safety reasons, but also for their huge potential socio-economic effects. As a matter of fact, this technique has been used for the last 50 years in the majority of viaducts and bridges built in many countries like Italy.In order to evaluate the influence of the corrosion on prestressed pretensioned beams, a number of tests has been carried out in the Laboratory of the University of Rome “Tor Vergata”.Nine prestressed beams (section size 200 × 300; total length 3000 mm; clear span 2700 mm) were first subjected to artificial corrosion, to obtain different damage levels, and then were tested in four-point bending.The results clearly show the sizable effects that corrosion has on the ultimate capacity (that is significantly reduced), on the failure mode and on the structural response, that turns from ductile to brittle.     

Impact resistance of steel fibrous concrete containing fibres of mixed aspect ratio

The paper presents results of an investigation conducted to study the impact resistance of steel fibre reinforced concrete containing fibres of mixed aspect ratio. An experimental investigation was planned in which 108 plain concrete and SFRC beam specimens of size 100 × 100 × 500 mm were tested under impact loading. The specimen incorporated three different volume fractions i.e. 1.0%, 1.5% and 2.0% of corrugated steel fibres. Each volume fraction incorporated mixed steel fibres of size 0.6 × 2.0 × 25 mm and 0.6 × 2.0 × 50 mm in different proportions. The drop weight type impact tests were conducted on the test specimens and the number of blows of the hammer required to induce first visible crack and ultimate failure of the specimen were recorded. The results are presented in terms of number of blows required as well as impact energy at first crack and ultimate failure. It has been observed that concrete containing 100% long fibres at 2.0% volume fraction gave the best performance under impact loading.     

Stress-dependence of the permeability and porosity of sandstone and shale from TCDP Hole-A

We utilize an integrated permeability and porosity measurement system to measure the stress dependent permeability and porosity of Pliocene to Pleistocene sedimentary rocks from a 2000 m borehole. Experiments were conducted by first gradually increasing the confining pressure from 3 to 120 MPa and then subsequently reducing it back to 3 MPa. The permeability of the sandstone remained within a narrow range (10^?14–10^?13 m²). The permeability of the shale was more sensitive to the effective confining pressure (varying by two to three orders of magnitude) than the sandstone, possibly due to the existence of microcracks in the shale. Meanwhile, the sandstone and shale showed a similar sensitivity of porosity to effective pressure, whereby porosity was reduced by about 10–20% when the confining pressure was increased from 3 to 120 MPa. The experimental results indicate that the fit of the models to the data points can be improved by using a power law instead of an exponential relationship. To extrapolate the permeability or porosity under larger confining pressure (e.g. 300 MPa) using a straight line in a log–log plot might induce unreasonable error, but might be adequate to predict the stress dependent permeability or porosity within the experimental stress range. Part of the permeability and porosity decrease observed during loading is irreversible during unloading.