Contemporary Topics on Testing, Modeling, and Case Studies of Geomaterials, Pavements, and Tunnels

Red clay is a typical particular soil in China, whose particular engineering properties are concerned in the engineering. Based on the laboratory test results of undisturbed samples from different depths, physico-mechanical properties of structural red clay can be investigated. Structural character of soil is analyzed combining the plat load test. It is investigated that there are three factors effecting on the structure of red clay. The results are presented for different drained triaxial tests on different depth soils specimens under different consolidated stress states. Simulating the process of stress changes and stress states, some conclusions of mechanic properties of red clay under different stress level can be drawn. It is discussed that some factors influence the strength and deformation of structural red clay, such as structure, stress level, stress paths and so on.

The nondestructive mapping of anomalies and voids under roadway pavements is critical to highway authorities because of the potential safety hazards caused by the loss of support. A 400 MHz Ground Coupled Penetrating Radar (GCPR) was utilized in this study to characterize subsurface voids. To enhance the understanding of the data collection and interpretation, different thicknesses of calibration concrete slabs with different depths of voids were designed and constructed. In addition, a field study using the GCPR was also conducted on US-290 with visible settlement. The extents of the anomalies in the horizontal and vertical directions were accurately identified from the GCPR images. Coring was performed to verify the extent of the subsurface void conditions. Fortunately, the voids near the drainpipes were detected by GCPR in time. Otherwise, the void would have been progressed in size, and that could have led to a severe hazard to the general public. This study has successfully demonstrated that the GCPR is able to identify anomalies and voids. Engineers can utilize the information from GCPR to undertake remedial actions with confidence.

Layers moduli are very crucial parameters for pavement design and evaluation with a mechanistic-empirical method. Falling Weight Deflectometer (FWD), as a nondestructive testing technology, is an effective tool to determine asphalt pavement layer moduli. The objective of this study was to establish a method to predict structural layer moduli of cement treated base (CTB) asphalt pavements by using FWD deflection basin parameter (DBP) indicators. Firstly, a general dynamic finite element model of CTB asphalt pavements was established and a synthetic database of dynamic DBP indicators corresponding with material properties of structural layers was generated. Secondly, the relationship between DBP indicators and structural layer moduli was discussed by the related coefficient, then the optimal regression function was established to predict structural layer moduli. Finally, the presented method was applied to predict structural layer moduli of the existing CTB asphalt pavement of Shanghai A11 Expressway and its validity was verified by the fitting degree between the measured deflection basin and the theoretical deflection basin. The research results provide a technology supports to popularize FWD testing technology applied in evaluating structural performance of CTB asphalt pavements.

A united anisotropic strength criterion is proposed for soils. Based on the linear combination of Matsuoka-Nakai and the Lade-Duncan criteria, functions and loci of this new strength criterion are presented on the octahedral plane. The influences of model parameters on the size and shape of the failure surface are also discussed. The proposed criterion is also used to capture the experimental results of the true triaxial tests on mud and sand. The comparisons between the predictions and experimental results show that this strength criterion is capable to capture the anisotropic strength behaviors of soils.

According to radar wave propagation characteristics in pavement structures, the impacts of depth of multiform voids upon radar reflected signals are studied by establishing the model of GPR electromagnetic wave propagation in rigid pavement with voids. Meanwhile, the method of determining the depth of voids beneath rigid pavement slabs is presented. This paper provides an important technical support for identifying the depth of voids beneath slabs in rigid pavement based on the Ground Penetrating Radar(GPR) reflected signals.

Geophysical testing has been used to monitor CO₂ injection into a test well in the Citronelle Oil Field in Alabama. The Citronelle Oil Field is the largest oil producer in Alabama and is currently in the tertiary oil production stage. This research is part of a project to evaluate the Rodessa Formation (depth at 11,500 ft) for its potential to recover additional oil through enhanced oil recovery (EOR) using CO₂, as well as its CO₂ sequestration potential. A total of 15,000 tons of CO₂ will be injected. The goal of the Geophysical testing is to determine if seismic measurements are capable of detecting changes in the geologic formation and the migration of CO₂ during and after the injection. A Derivative of Refractive Microtremor (DoReMi) method using wireless sensor has been used for the Geophysical testing. The success of the Geophysical testing in monitoring CO₂ migration in the oil field can help prevent possible leakage of CO₂ back into the atmosphere, hence reduce its environmental impacts, which may have significant implications in reducing greenhouse effects. Monitoring results, before and during injections, show possible correlation to the stressing of the oil field strata during CO₂ injection.

Inverse analysis is widely used in geotechnical problems, among others, to search a set of input parameters that best fits the observations of a certain model. However, the solutions of an inverse problem are always affected by uncertainties associated with parameter determination, which should be considered simultaneously to the variability of geotechnical data. This paper focuses on the uncertainty analysis of material properties on the responses of Falling Weight Deflectometer tests. A dynamic backcalculation model and a number of sensitivity indices based on Monte Carlo simulation techniques (i.e. Fourier amplitude sensitivity test, FAST) are presented. The dynamic backcalculation is carried-out in the time domain and the inverse procedure is solved by minimizing a relative absolute objective function that involves the peak deflections. Although focus is placed on uncertainties in subgrade material properties, the methodology presented in the paper can be used to quantify uncertainties associated with other layer properties and pavement responses.

The efficiency of track foundation material gradually decreases due to insufficient lateral confinement, ballast fouling, and loss of the shear strength of soil due to local liquefaction and clay pumping. This paper presents characterization of rail track subsurface to identify ballast fouling and subsurface layers (capping layer, sub grade) strength using seismic refraction survey. Seismic refraction survey of multichannel analysis of surface wave analysis (MASW) has been carried out in model track and field track. Shear wave velocity obtained from MASW was used to identify the fouling character of track ballast, there by to evaluate track conditions. The shear velocity of fouled ballast increases with fouling percentage and reaches a maximum value then decreases. This character is used to define optimum and critical fouling points of fouled ballast. This article also highlights ballast gradation followed in India and comparison of Indian ballast gradation with international gradation standards. The ballast gradation followed by Indian railways is poorly graded and more favorable for drainage.

Limited financial capability of governments for road rehabilitation in developed countries and technical constraints of laboratory tests in assessing pavement quality highlight the need to develop an innovative technique in pavement evaluation. The performance of the Spectral-Analysis-of-Surface-Wave (SASW) method to evaluate the dynamic parameters on the existing road pavements is presented herein. The aim of this paper is to propose a coupled analyses procedure for calculating elastic modulus and damping ratio of soil subgrade layer in pavement. The dynamic elastic modulus was obtained from the shear wave velocity produced from the inversion of an experimental dispersion curve. To validate the modulus obtained from the SASW method, the falling weight deflectometer (FWD) test was used to determine the subgrade modulus at same sites. In this study, a damping ratio of soil layer was also obtained using attenuation coefficient from the modified Bornitz equation. Good agreements were also obtained between the attenuation coefficients from this study and previous studies. The SASW method is able to characterize adequately the in-situ pavement stiffness which can be potentially developed as an innovative evaluation device.

A quick and efficient of the spectral analysis of surface wave (SASW) has been developed to non-destructively measure the stiffness of PCC slabs. However, in layered PCC slab with strong stiffness contrast, several wave groups were observed due to the refraction and reflections of stress waves at the layer boundaries. As a result, the phase spectrum affected by these different wave groups is to be complicated. In this study, a time-frequency analysis of wavelet transform was then employed to impulse response analysis to overcome identification problem of the non-stationary wave groups and spectral characteristics of phase spectrum. Time-frequency wavelet spectrogram was utilized to select the interested response spectrum from wave groups. A time-frequency wavelet filtering was then used to remove the interference of unnecessary wave groups or background noise based on simple concept of wavelet filtering. Consequently, the phase spectrum was reconstructed from denoised impulse response by inverse wavelet transform. Results showed that the wavelet analysis of impulse response can be used to improve the phase spectrum and reconstruct better phase velocity dispersion curve. A good agreement was also established between the PCC stiffness from SASW measurements compared to ACI formulation.

Subgrade is the base of highway structures, so to evaluate its construction quality accurately is very important to ensure the required strength of the whole highway. Several subgrade segments under construction of Tai-Ao highway in China were selected as engineering examples, the point-to-point test mode was adopted, and then the deflections, dielectric values and compaction degrees were in-situ tested with the new and traditional NDT (Non-destructive testing) devices or control methods such as FWD (dynamic falling weight deflectometer), BB (static Benkenlman beam), PFWD (portable falling weight deflectometer), GPR (ground penetrating radar), special dielectric constant device, and sand cone method, and FWD, PFWD and GPR are proved to be the rapid and precise devices for quality control of the highway subgrade.

In engineering practices, sand-cone tests were performed to access the compaction quality of backfilled materials of highway embankments or earth dams. However, performing a sand-cone test is time consuming and can only obtain the physical but not the engineering properties of backfills. The objective of this paper is to establish a systematic procedure based on stress wave propagation velocities to evaluate the quality and engineering properties of compacted backfills for the quality control of earth works. To achieve this goal, a low plasticity material used in the earth dam of the Hushan Reservoir was collected. Laboratory tests were performed on compacted samples of this material to obtain the calibration curves for the relationship between moisture content, dry density and stress wave velocities. Results of these tests indicate that there is a good correlation between the moisture content, dry density, CBR and the shear (S) wave velocity. Comparing with values measured in the field using traditional sand-cone test, the proposed method underestimates the moisture content and overestimates the dry density. However, the resulting error is less than 10%. It is thus concluded that the proposed method is a tool with high potential for the evaluation of the compaction quality of backfills.

Though there are lots of test and detection methods for bearing capacity of foundation, choosing test detection methods was chaotic in construction due to lack of systemic occupation standards. Because test methods and quoted standards were adopted wrongly in construction, construction quality problems and potential dangers in engineering for highway subgrade appeared frequently. Aimed on the soft soil foundation in Zhangjiajie-Huayuan Expressway, the Boussinesq elasticity solution was introduced to calculate bearing capacity of foundation corresponding to different embankment height. Furthermore, slab loading test method and light dynamic penetration method were adopted to verify weaken foundation in-situ tests in Zhangjiajie-Huayuan Expressway. The relation between number of dynamic penetration blows and bearing capacity from slab loading test was obtained by linear fitting and logarithmic fitting respectively. Linear fitting results showed that both of methods had good correlation because the correlation coefficient R² exceeded 0.961 and 0.873 respectively for light dynamic penetration and Dutch light dynamic penetration. The fitting formula may provide a fast and convenient method for dynamic penetration to determine depth of removing silt. Moreover it is important to insure subgrade construction quality.

A new kind of electronic miniature cone penetrometer is developed for miniature cone penetration test (MCPT), with which the cone penetration resistance and penetration depth can be acquired automatically. In order to form homogeneous soil specimens for MCPT, a new experimental facility is designed. A series of MCPTs in silty soil are carried out and it is found that, for silty soil, the curves of the penetration resistance vs. the depth have no correlation with the cone angles. For MCPTs in silty clay, the initial segment of the penetration curve is straight and the cone tip resistance tends to be stable when the cone is intruded into a certain depth, i.e. the critical depth. For silty clay, the critical depth effect of the cone tip resistance is related with the different failure mechanism of soil under different confining pressure. The relation between the characteristic values of the penetration curve and soil strength parameters is analyzed. The cone resistance factor is linear with the tangent of the internal friction angle of soil. The ultimate cone penetration resistance is found to be closely related to the critical depth.

In China there are no clear prescriptions to the compaction degree of the subsoil around guardrail posts in the current highway safety specification. So the bearing capacity of guardrail posts can not satisfy the actual requirement due to the presence of the plant soil in the central separate belt. A series of laterally loading tests of posts embedding in the silty clay are carried out. The linear relation is found between the critical load representing lateral bearing capacity of posts and the limit cone tip resistance of the miniature penetrometer representing soil strength in the miniature cone penetration test (MCPT). Assuming that the soil reaction on the post is related directly to the cone limit penetration resistance, a model of soil reaction distribution corresponding to the critical load is put forward and the unknown parameter in model is calculated inversely by test data. According to this model and the embedding conditions of posts in situ, an effective method of using one steel plate to reinforce the post is presented and verified by tests. Now this reinforcement method has been applied to guardrail posts of some expressways of China.

Since the "5.12" WenChuan Earthquake occurred in China, evaluation of the ultimate aseismic capacity has been a crucial issue for seismic safety design of high core rock-fill dams. However, reasonable evaluation of the ultimate aseismic capacity of high rock-fill dams still confuses the hydraulic engineers. Thus an original approach to evaluate the ultimate aseismic capacity is proposed. In this approach, the ultimate peak acceleration of input motion which the dam could tolerate is taken as an important index to evaluate the ultimate aseismic capacity. The ultimate peak acceleration can be directly achieved on the basis of `Specifications for seismic design of hydraulic structures' instead of trial and error method. Then, the proposed method is adopted to evaluate the ultimate aseismic capacity of the 240m ChangHe high rock-fill dam. In addition, comprehensive studies on the dynamic response and potential failure mode as the rock-fill dam subjected to the ultimate tolerable input motion, that is, the rock-fill dam is at verge of failure, are presented. Consequently, the corresponding reinforced design for the high rock-fill dams can be carried out effectively on the basis of the dynamic analysis as the dam reach the ultimate limit equilibrium state.

This paper presents a method that measures an impact process of a spherical object colliding with on a testing material and, through analytical techniques based on Hertz's theory of impact, deduces the elastic modulus of the tested material. Furthermore, by distinguishing the compress and rebound phrases, and by accounting for the plastic deformation characteristics of the tested material, this method can measure the compressive modulus and rebound modulus simultaneously. This method is suitable for testing various materials, such as steel, concrete, and geomaterials including cement-treated soils. Various deformation parameters can be deduced from this method, including compressive modulus, subgrade soil modulus K₃₀, California Bearing Ratio (CBR) value, and Benkelman Beam Deflection value. This method is shown to be very accurate in a large number of validation tests performed by the authors. Its advantages include broad applicability, high efficiency, and relatively large strain (thus also capable of evaluate material strength). Results from field implementation in actual civil projects show that this method has great potential in many applications, particularly real-time fill materials quality assurance and construction optimization.

This paper presents a rapid geomaterial strength testing method that measures the impact process of a spherical object colliding with a test material. This method is based on Vesic (1977) cavity expansion theory and combines with the technology developed for measuring deformation characteristics (in a companion paper by the authors). In this new method, a geomaterial's strength parameters including its internal friction angle φ and cohesion c are directly calculated. Results from validation tests demonstrated satisfactory testing accuracy of this method and its unique advantages comparing with conventional laboratory strength tests.

Use of geophysical methods for geotechnical site characterization is increasing with the development of user friendly and efficient geophysical equipment. Electrical resistivity is one of the geophysical techniques of soil investigation; two latest pieces of electrical resistivity equipment, i.e., Super Sting Digital Resistivity Meter and Nilsson 400 Soil Resistance Meter, were used to characterize a site in the vicinity of Islamabad, Pakistan. The research not only provided an opportunity to validate the geotechnical application of electrical resistivity testing, but also endowed with a good practical log-on the use of these two new pieces of equipment for the field and laboratory resistivity. Field resitivity testing with Super Sting Digital Resistivity Meter and extensive laboratory resistivity of undisturbed soil samples at different moisture content and densities with Nilsson 400 Soil Resistance Meter, has proved the efficiency and versatility of these gears. This paper discusses practical aspects of these state of the art equipments in geotechnical site characterization.

Gravel formation is the most common formation in Taichung area in Taiwan, where most of the gravels are hard and having high strength having strong interlock between gravels. Methods used for underground constructions in gravel formation are still under exploration due to lack of experience. Thus, the objective of this study is to focus on investigation of Taichung base waste water outflow pipeline construction using pipe jacking method. The analyzed data during tunnel construction include attrition and repair of the machine, torque applied at the cutter face, thrust forces used to push the pipes, encountered problems, and tunnel advancing rate are synthesized and analyzed. For drive distance less than 90 m, the thrust forces used to push the pipes are around 400 to 500 tons. The frictional resistance between the pipe, the outside diameter is 2.85m, and ground is around 0.6 to 1.0 ton/m². The average advancing rate, time used to push each pipe and torque applied at the cutter head are 20.6 mm/min, 2.9 hours and 260 t-m, respectively.

This study analyzed the construction of the Ba-Guah-Shan Tunnel (length about 5km, excavated diameter about 12m) and the effects of gravel formations. Monthly excavation rate and each construction cycle time were synthesized. The data for different construction faces and sections of geological classifications were compared and analyzed. The excavation progress in gravel formations was found to be greatly affected by the groundwater. Thus, tunneling advance rate was calculated separately for portal, dry and seepage sections. The overall advance rate was 9 to 15 hr/m. In the dry section, the advance rate reached 60 m or more per month. However, tunnel construction in other sections, i.e., seepage or water inrush sections, had substantially lower advance rates. For lowering the water table, the vacuum method was more effective than the gravity method.

Deformation of tunnel may result in settlement of ground surface. Based on the characteristics of deformation of twin tunnels excavated, the paper presents a basic deformation mechanism of twin tunnels constructed close to each other and at shallow depth. The deformation is not uniform but has an oval shape, and represents the ground loss occurred during construction of the tunnels. Using the computer program FLAC^2D, certain given deformations were applied to the boundaries of the twin tunnels as the boundary conditions, and the surface settlements caused by the excavation of twin tunnels were obtained. It was found that the computed results match well with the measured field results. Further, cases are studied to analyze the ground surface deformation behaviors under different influence factors including the distance between the tunnels, the depth and the ground loss. The final results indicate that the interaction of two parallel tunnels indeed causes an increase in the ground surface displacement.

The determination of grout pressure is an important aspect for backfill grouting during shield tunneling. The grout pressure is also one of the most important control parameters for tail voids grouting, because it controls the grouting volume, which is another control parameter for backfill grouting. Besides the covering depth of tunnel, the grouting pressure is related to the advancement rate, attitude control and over-excavation of shield tunneling, especially in a curved line. Assuming the backfill grouting is Bingham fluid, the computational formula of grouting pressure is derived, which takes into account the groundwater level, plastic consistency of grouting, advancement rate of shield tunneling and filling rate of tail void. The grouting pressures and the influence factors have a linear relationship. When the plastic viscosity and initial yield stress of the grout are close to or reach 4Pa⋅s and 40Pa, respectively, and the advancement rate of shield tunneling exceeds 2.4m/hr, the calculated grouting pressure usually exceeds 0.3MPa, a value that is commonly used in shield tunneling and needs to be paid with more cautions.

Urban metro tunneling can cause ground movement and deformation and decrease of bearing capacity of pile foundation. This paper uses the finite element method with an elastic-plastic model and the ANSYS software to study the influence of urban metro tunneling on bearing capacity of pile foundation and on working conditions of single piles at different distance from the centerline of the tunnel. Considering pile tips that are located at three typical positions relative to the tunnel horizontal axis and different horizontal distance, the changes in bearing capacity and the influence of soil, pile and other parameters on bearing capacity of a single pile were analyzed. The results show that piles are obviously influenced when located within 0.5–1.0 times tunnel diameter, which is the primary influence area of tunneling; and bearing capacity of pile was reduced for about 20% in this area. The influence became relatively small beyond the area.

A micromechanical model based on material properties degradation law was proposed in the paper to simulate the time-dependent damage and deformation and delayed failure of rock materials in tunnels. The time-dependent degradation law of material properties, an exponential empirical relation between degradation of material properties and applied stress, is used at the scale of each element to simulate its damage. The primary and tertiary creep regimes associated respectively with a degradation and increase of the rate of strain, damage event and energy release were observed in the simulations. The time-dependent deformation and delayed failure of tunnels on the long-term under different coefficients of lateral pressure was studied to investigate the failure patterns and mechanism of tunnels. This model can reproduce rheological properties including the three creep regimes and associated damage evolution of rock in tunnels, which is of great help to investigate long-term stability of tunnels and to prevent associated rock hazards in tunneling engineering.

Zonal disintegration within rockmass around deep excavated tunnel is a scientific characteristic phenomenon which is different from failure mode of shallow tunnel. To study changing behavior of zonal disintegration configuration within rockmass around deep excavated tunnel will help provide some basis for deep tunnel design and construction. In the paper, numerical tests on three-dimensional failure process of rock samples containing semi-arched tunnel with vertical walls is carried out with RFPA-Parallel system running on Lenovo 1800 Cluster, reproducing zonal disintegration phenomenon within rockmass around deep tunnels, and changing behavior of zonal disintegration configuration within rockmass around deep excavated tunnel is analyzed. Numerical results indicate that zonal disintegration configuration including the damage extent, localized damage distribution and deformation within rockmass occur some time later after the excavation. Therefore, the effective supporting time of deep tunnel should take into account the time-lagged behavior. This research will provide some insights in further understanding the mechanism of zonal disintegration of deep tunnel and establishing new method on excavation design and safety evaluation of deep tunnel.

The mechanical behavior of four-lane tunnels with extra-large cross section and low flat-ratio are complex and the construction methods are diversified as compared with those of a normal tunnel. Based on the site monitoring of the largest rock tunnel in China (the excavation area, span and height are 241m², 21.60m and 13.58m, respectively), the time-space effects of the construction process and different stages are analyzed, and the deformation characteristics are statistically summarized using mathematical equations by fitting the measured data. It was found that, during the tunnel construction, the excavation space-effect of the upper-stage in the right drift, the lower-stage in the left drift and the core rock is obvious. The radial incidence of the excavation of the tunnel is about 0.75 to 1.0 times the drift diameter and the longitudinal incidence of step-excavation is 1.0 to 1.5 times the drift diameter. The relationship between the rock displacement and the radial depth is an "S" curve and that between the crown settlement and time is quartic polynomial. It was also found that the secondary support structure must be established on time to withstand the rheological pressures because of the distinct rheological behavior of soft and weak rock at the entrance. The results and findings presented in the paper may be useful in design, construction and research of similar tunnels.

The method of plane finite element and three-dimensional elastoplastic damage element was adopted to demonstrate the stability analysis of surrounding rock of underground powerhouses in Xiangjiaba hydro-power station in China. The effects of mechanical parameters of the surrounding rock and mechanical model on the plastic region, stress and displacement was discussed. The distribution of displacement, stress and plastic zone of surrounding rock of the cavern is reasonable without anchor support and the surrounding rock is generally stable. But if stress concentration and through plastic region forms locally, the stability will be worsened. When anchor support is adopted, the area of distribution will be reduced and the stability will be improved. The stress of anchor bolt and prestressed cable are both less than their yield stress, thus the surrounding rock is stable and global stability can be guaranteed after anchor support.