Geo-China 2016: Advances in Pavement Engineering and Ground Improvement

One of the viaducts of the high speed railway in Taiwan has suffered significant structural cracks in its piers. This has raised serious public concern. The damage was conjectured to have resulted from ground settlement due to regional water pumping. The paper proposed a practical methodology to investigate the downdrag behavior of the pile foundations of the viaduct. A fictitious settlement controlled layer beneath the pile foundation was used to control the ground surface settlement due to deep water pumping. A three-dimensional finite difference mesh including the soil profile and the pile foundation was established with the geotechnical investigation report and design data. By varying the ground surface settlement, the variations of the pile settlement, ground settlement, and downdrag force with depth for each pile can be reasonably simulated. The results show an obvious pile group effect, which shows the minimum downdrag force in the interior pile and maximum force in the corner pile. There also exists a critical surface ground settlement at which the drag force reaches the maximum value. The simulated differential settlement was close to the measured value, however this was not enough to have caused the structural cracks in the piers. The cracks are more likely caused by other engineering events.

A physical model for expressway foundation with cement mixing piles was established according to the similarity theory. The effect of pile length, area replacement ratio and surcharge load on foundation settlement was studied. The pile length was varied from 40 cm to 100 cm while the area replacement ratio was changed from 0.023 to 0.093. Test results show that the foundation settlement will decrease as the increase of pile length at the same area replacement ratio and surcharge load. As the surcharge load increases, the settlement difference between foundation with longer pile and shorter pile will also increase. When the pile length is certain, bigger area replacement ratio will lead to smaller foundation settlement.

It is quite often geotechnical engineers suggest the use of concentrated loads in order to suppress the swelling under foundation for areas known of expansion. The swelling pressure obtained using constant volume apparatus and/or oedometers are certainly not simulating actual field conditions. The minimum applied dead load suggested based on these tests may be too high and may be associated with excessive settlement or exceeds the bearing capacity of the substrata. The difference between bearing capacity and minimum dead load required to suppress expansion can be very small. In this case careful computations for the settlement and swelling pressure shall be performed. A site in Khartoum showed typical problem and the choice of the appropriate geotechnical design parameters were to be studied. Seventeen boreholes were drilled in order to ascertain the subsurface condition and its ability to sustain infrastructure facilities. Swelling pressure obtained in a constant volume or oedometer in a constrained testing shall be corrected based on actual relaxation that occurs in the field due to immediate and/or consolidation settlement. A methodology for evaluating short and long term settlement was conducted to predict the downward movement of the substrata during the lifetime of the proposed structures. The design of the foundation system in such soil should exert downward loads greater than the corrected swelling pressure and without causing excessive settlement beyond the permissible limits.

Based on the establishment of the wall model with fixed orientation and date by ABAQUS finite element numerical analysis software, this paper studied the surface temperature change rule of the concrete retaining wall with different deep, high and thick defects. To the concrete retaining wall with different defect depth, if defect depth was relative shallow, the wall surface temperature corresponding defect area rose sharply, while the temperature influence of the non-defective area was lesser; with the depth increasing, the wall surface temperature and temperature difference corresponding defect area decreased, and the temperature curve became smooth. To the concrete retaining wall with different defect height, at the beginning stage, the temperature difference was small between the inner surface and the outer surface of the wall; after a steady state analysis, the thermal resistance corresponding defect area was larger than non-defect area; with solar radiation increasing, surface temperature difference was rising between defect area and non-defect area. To the concrete retaining wall with different defect thickness, if the defect thickness was thin (≤6c), the defect thickness had great influence on the maximum temperature difference of the wall surface; but with the defect thickness increasing, the temperature difference of the wall surface became consistent. This will contributed to the analysis to find out the distribution of the defect location, the defect size and the defect depth, and also provide theoretical basis for infrared thermal imaging technology in the application of the concrete retaining wall detection.

Highly plastic, compressible organic Ibese shale with high swelling potential and expected to pose field compaction problems was treated with agricultural waste materials with the aim of improving its geotechnical properties while promoting waste disposal through reuse. 2 to 20% by weight of rice husk ash (RHA) and coconut husk ash (CHA) mixed with shale and compacted at the modified AASHTO energy was subjected to consistency limits and unconfined compressive strength (UCS) tests. Between 35% and 73% reduction in plasticity index respectively at optimum content between 6% and 10% with RHA and CHA was observed giving an indication of improvement in cosistency and workability. Addition of 14% RHA and CHA resulted respectively, in 645% and 529% increase in UCS thus contributing to strength development but with RHA considered as the more effective additive.

Road material compaction is achieved through the application of various types of rollers to the pavement layer. The use of vibration compaction is quite prevalent, where the vibration frequency and amplitude can be optimized to obtain optimum density for the material that is being compacted. In this paper the vibrations measured in the field during vibratory compaction of pavement layers consisting of different materials are compared to the results of vibration table compaction in the laboratory at a range of frequencies to determine the effect of frequency on the optimum densities for the different materials, and the relationship between the applied roller frequencies and the densities achieved. The frequencies inside the material and on the roller drum are monitored and compared with the frequencies applied in the laboratory on the vibration table, and the resultant densities achieved or three different base layer materials. The data indicate the importance of selecting appropriate frequencies for different types of road building material to enable optimal compaction.

This paper investigates the parameters affecting the saturated hydraulic conductivity of lime-treated expansive clays. The experimental program accounted for lime content (0%, 4%, and 6%), curing period (7 and 28 days) and confining pressures (15, 30, and 45 kPa). In addition, the effect of accelerating curing on the saturated hydraulic conductivity of lime-treated clay was investigated. Experimental results indicated that the addition of lime resulted in a significant increase in hydraulic conductivity as compared to untreated specimens. Furthermore, the saturated hydraulic conductivity values showed less notable change for specimens with curing period greater than 7 days. Mercury intrusion porosimetry conducted as part of this study provided a clear insight and explanation to experimental observations.

Recently, the use of controlled modulus columns (CMC) has gained popularity in the support of rail and road bridge approach embankments on soft soils. If the columns are extended into a competent firm soil, and designed to take nearly all the vertical loads, they become rigid inclusions. The advantage of this design approach is that settlement will be controlled, but the drawback is that the columns will attract greater load, including bending moment and shear force in situations where non-uniform loading or ground conditions exist. The load on the composite soil-CMC is uniformly distributed by the upper layer of granular load transfer platform (LTP). In this paper, the effect of CMC length on the load transfer mechanism is numerically investigated. Coupled flow-deformation analysis has been performed for a long period to understand the system response in the long term, while interface elements capable of simulating gapping and sliding between CMC and the surrounding soil are considered. A geosynthetic reinforcement layer has been simulated using the inbuilt FLAC^3D geogrid element. The force in the reinforcement layer has been evaluated, and in particular, a clear comparison is made between the stresses in CMC and the ground settlement with floating and end-bearing columns.

Increased traffic volume has made it necessary to increase highway capacities by widening embankments and pavements. Differential settlement may develop between and within the new and existing portions of the embankment, especially over soft soils. A multi-column composite foundation is used a benefit concept utilizing different column types with varying lengths and diameters to support the embankment fill, to mobilize the strength, and stiffness of the soil at shallow depths. This study presents the results of finite element analyses using PLAXIS code to investigate the consolidation behavior of a road embankment constructed on a multi-column composite foundation. Two-dimensional finite element software was used after the calibration of the model against a field case study and numerical analyses were conducted to investigate the deformations of the widened embankments over soft soil with or without the remediation of foundation columns. The settlement and differential settlement are presented and discussed in detail.

In this study, an ideal compaction grouting technique was designed by injecting grout into a special designed Latex balloon. In this way, the bleeding and penetration of grouts was avoided, and the extension of fractures could be limited. A large scale model test was accordingly developed to investigate the responses of the surrounding soils. After the application of an overburden pressure, pressure grouting was performed on sand samples, meanwhile, the evolution of grouting pressure, soil surface displacement, earth pressure as well as the void ratio at different distance from the injection point are monitored by various transducers. The results show that (i) the pressure grouting induced compaction effect in this study did not reach the up boundary of the model test; (ii) the earth pressure is obvious larger for the soil closer to the injection point; (iii) the densification effect decreases as the distance from the injection point increase, presenting clearly the density gradient around the injection point.

This paper presents the use of recycled waste expanded polystyrene (EPS) foams, as a lightweight material with a Nigerian standard sand (Igbokoda sand). Thermally modified waste EPS tagged modified expanded polystyrene (MEPS) was used. The influence of MEPS on compaction characteristics such as the maximum dry density (MDD) and the optimum moisture content was investigated with three different compaction energies: (standard proctor, modified proctor and West African compaction method). MEPS was added to the Igbokoda sand at 1%, 2%, 3%, 4% and 5% by dry weight of soil. The unconfined compressive strength increased from 95.0 kPa to 128.0 kPa, which shows about 34.7% increase in strength with the addition of 5% MEPS. The 5% MEPS content at standard proctor compaction is recommended for sand-MEPS utilization as light weight construction material since it has the lowest MDD, the highest increase in strength and a high value of co-efficient of determination (R² = 0.976). The sand-MEPS mixture can be offered as a potential geotechnical construction material as lightweight backfill for retaining walls, fill in embankments, road sub-base over compressible soil to minimize settlement and simultaneously solving the environmental problem by the beneficial reuse of municipal solid waste (MSW).

Severe damages can occur on civil engineering structures and infrastructure including roads, channels, houses, sidewalks, and driveways if built on expansive soils. In this study to limit the expansive soil impacts on roads, quicklime and class F fly ash were employed as potential stabilisers in enhancing the engineering properties of expansive soils. The samples were prepared by integrating artificial soils combined with a mixture of quicklime-fly ash at a ratio of 1:3. Various contents of quicklime-fly ash were applied on soil samples, composed of 40% bentonite (B) and 60% kaolin (K). Sample properties were measured at 3, 7, and 28 days of curing time. Moreover, another set of soil samples were prepared containing 20% B and 80% K to study the effect of bentonite content on the soil mechanical properties of the stabilised soil.

To attain time domain figures of uneven pavement, this paper adopts periodogram method and sampling rule in time domain to simulate time domain figures for different grades of uneven roads with the use of stochastic process phase distribution and frequency domain power spectral density about pavement stochastic roughness. Directed against the accuracy of this simulation method, the response power spectral densities of vehicles are gained by inputting the data of time domain and initial frequency domain separately. Their comparison result shows that the simulating mode is reliable. Through the comparison between internal roughness index (IRI) and pavement power spectral density (PSD), the correlation of these two indexes has been deduced on the basis of simulated time domain figures. The reliability of this relational expression is checked by measured data of pavement roughness height and it’s proved to be dependable.

Stabilization using nontraditional additives has been shown to lower carbon footprints compared to traditional ones. Among other traditional and non-traditional additives, polymers have shown an efficient performance in the field and improved sustainability. Polyacrylamide (PAM) is one such additive that has demonstrated many advantages including a reduction in permeability, an increase in durability and the provision of strength characteristics. However, information about its effect on the improved geotechnical characteristics is very limited to the field performance monitoring. Therefore, a laboratory investigation was carried out to investigate the benefits of using a synthetic PAM additive on the basic and engineering properties for three types of soils. The results showed an increase in dry density and unconfined compressive strength for all the soils. The results further demonstrated an increase in unsoaked CBR and a reduction in permeability for all the stabilized samples.

This paper presents the improved strength properties of soft clay treated with fly and bottom ash added in different amounts. A series of laboratory tests were carried out on both the treated and untreated samples to determine the compaction, consolidation and unconfined compression strength (UCS) properties. The optimum dosage of both the bottom and fly ash levels which one exhibiting the maximum UCS has been determined and estimate the quantitative improvement. The UCS of samples has been tested for various curing periods up to 28 days. The coefficient of consolidation is increases and time required to cause 90% consolidation is decreases with the addition of ash additives. The maximum UCS is obtained at an optimum fly ash level of 20% added to the clay soil and further the strength is decreases. Quantitatively, the strength of soil-fly ash mixture was found to 243 kPa which is improved about 385% over the strength of clay soil.

The present study was undertaken to evaluate rutting performance of a polymer modified binder (PMB) containing three warm mix additives (WMA) additives at high performance grade temperature (i.e., 76°C) using four rheological parameters: Superpave rutting parameter (G*/sinδ), Shenoy’s parameter “G*/(1-(1/tanδsinδ))”, non-recoverable creep compliance (J_nr), and zero shear viscosity (ZSV). Three different WMA additives: wax based (Sasobit), water based (Advera) and surfactant based (Rediset) were selected in this study. It was found that the binder modified with Sasobit had a superior rutting performance followed by the binder with Advera and Rediset. Rutting performance ranking of the binders based on G*/sinδ, G*/ (1-(1/tanδsinδ)), J_nr parameters was found to be similar except ZSV which showed opposite trend for both Rediset and control PMB binders. A correlation was observed between different rheological parameters.

Moisture damage of asphalt concrete pavements is affected significantly by water permeability. Therefore, permeability specifications were developed by different states and agencies so that they can be controlled during mix design or the construction process. However, those specifications are mostly based on laboratory permeability tests on field-collected cores. This study determines whether permeability specifications based on other test results (field permeability tests on field, laboratory permeability tests on gyratory compacted samples) and correlations (permeability vs. total pores, permeability vs. permeable pores) can be developed. It is observed that the critical permeability value obtained using gyratory compacted samples is 100E-5 cm/s. The specific value obtained using laboratory permeability of field cores and total pores tests is 125E-5 cm/s. This value rises to 320E-5 cm/s if permeable pores are used instead of total pores. A critical permeability value cannot be obtained using field permeability test results. Therefore, the field permeability test is not useful to confirm permeability specification of a pavement.

In the structural pavement design based on mechanistic principles and in quality control evaluations, stiffness of the hot mix asphalt (HMA) is one of the most important input parameters. The ASTM D4123 and EN 12697-26 (Annex C) standards describe procedures for characterizing the reference modulus using the indirect tensile test (ITT) applicable to cylindrical specimens. The objectives of this paper are the: (1) to evaluate the repeatability and reproducibility of ITT performed according to Annex C of the EN 12697-26 standard through an interlaboratory comparison using two different testing devices; and (2) to validate and calibrate a model based on ITT to predict stiffness modulus for local implementation under Portuguese conditions. An extensive testing program was performed involving two types of testing equipment (NAT and MATTA), and using specimens compacted in laboratory. ISO 5725-2 standard practice was followed to determine the precision of ITT. In addition, other tests conducted on specimens drilled in existing road pavements have shown that the stiffness modulus is more sensitive to temperature and air voids. Based on the results, a model for prediction stiffness modulus was validated and calibrated for the tested materials and a good adjustment was achieved.