Metal Transport Parameters of a Gneiss Saprolitic Silty Soil for Liner Design

Diffusion coefficients and retardation factors of two metal cations (Cd2+ and Pb2+) were measured for a compacted Brazilian saprolitic soil derived from gneiss, aiming to assess its geoenvironmental performance as a liner for waste disposal sites. This soil occurs extensively all over the country in very thick layers, but has not been used in liners because of its hydraulic conductivity, higher than 10?9?m/s when compacted at optimum water content of standard Proctor energy, but which can be reduced by means of appropriate compaction techniques or additives. Batch, column, and diffusion tests were carried out with monospecies synthetic solutions at pH 1, 3, and 5.5. Measured diffusion coefficients varied between 0.5 and 4×10?10?m2/s. Retardation factors show that cadmium, a very mobile cation, is not adsorbed at pH 1 but is significantly retained at pH 3 and pH 5.5, whereas lead is retained at all tested pH values though slightly at pH 1. Estimated retardation factors from batch tests were 1.3–2.3 times those resulting from column tests and at its highest when obtained by diffusion tests; whereas batch tests allow a more complete exposure of the soil grains to the solution, time-dependent nonspecific adsorption may take longer to occur. The importance of contact time was observed and should be considered in further investigations. Its significant retention of metals suggests a promising utilization of this soil as a bottom liner for wastes landfills.     

Improvements in Frost Heave Laboratory Testing of Fine-Grained Soils

We present a laboratory system designed for studying frost heave in fine-grained soil. The system consists of: a modified refrigerator, a frost heave test cell, a laser for measuring heave, a differential pressure transducer for measuring water intake, and platinum resistance temperature detectors for measuring pedestal temperatures. The frost heave cell allows for visual observation of the sample, and accommodates pretest sample consolidation, freezing tests using a variety of freezing methods, triaxial tests on frozen soil, and thaw consolidation tests. The modified refrigerator maintains the specified temperature ±0.5°C during the full length of the test. Test results indicate repeatability of frost heave ratios ξ to within ±7%, and average heave rates to within ±0.05?mm/h. Results from frost heave tests conducted on five fine-grained soils indicate that: (1) a soil removed of its colloidal organic content becomes less frost susceptible; (2) the geomorphologic history of a “regional” soil is a critical factor influencing its frost susceptibility; and (3) ξ is dependent on overall clay content and is most sensitive to chlorite content.     

Evaluation of Cyclic Shear Strength of Two Cemented Calcareous Soils

The mechanism controlling the cyclic shear strength of cemented calcareous soils was investigated based on the results obtained from monotonic and cyclic triaxial tests on two different types of calcareous soil. Undrained cyclic triaxial tests performed on artificially cemented calcareous soils with different loading combinations showed that the effective stress path moved towards or away from the origin, due to the generation or dissipation of pore pressure with progressive cycles. Previous investigations have shown that the Peak Strength Envelope or the State Boundary Surface or the Critical State Line forms a boundary beyond which effective stress paths during cyclic loading cannot exist. However, in this study it was observed that the maximum stress ratio (ηmax) obtained from monotonic tests defined the boundary for the cyclic tests. Based on the information obtained from this study, an approach for evaluating the cyclic shear strength is proposed. It was observed that the modified normalized cyclic shear strength had a strong linear relationship with the logarithm of the number of cyclic to failure irrespective of confining pressure, type of consolidation and stress reversal.     

香港交通政策及其启示

香港交通运输系统的高效运转，得益于完善合理的交通政策。通过对其交通政策的详细介绍．希望可以对其他城市的交通建设提供可以借鉴的方面。     

Key Parameters for Strength Control of Artificially Cemented Soils

Often, the use of traditional techniques in geotechnical engineering faces obstacles of economical and environmental nature. The addition of cement becomes an attractive technique when the project requires improvement of the local soil. The treatment of soils with cement finds application, for instance, in the construction of pavement base layers, in slope protection of earth dams, and as a support layer for shallow foundations. However, there are no dosage methodologies based on rational criteria as exist in the case of the concrete technology, where the water/cement ratio plays a fundamental role in the assessment of the target strength. This study therefore aims to quantify the influence of the amount of cement, the porosity and the moisture content on the strength of a sandy soil artificially cemented, as well as to evaluate the use of a water/cement ratio and a voids/cement ratio to assess its unconfined compression strength. A number of unconfined compression tests, triaxial compression tests, and measurements of matric suction were carried out. The results show that the unconfined compression strength increased linearly with the increase in the cement content and exponentially with the reduction in porosity of the compacted mixture. The change in moisture content also has a marked effect on the unconfined compression strength of mixtures compacted at the same dry density. It was shown that, for the soil-cement mixture in an unsaturated state (which is usual for compacted fills), the water/cement ratio is not a good parameter for the assessment of unconfined compression strength. In contrast, the voids/cement ratio, defined as the ratio between the porosity of the compacted mixture and the volumetric cement content, is demonstrated to be the most appropriate parameter to assess the unconfined compression strength of the soil-cement mixture studied.     

Play therapy in Hong Kong: Opportunities and challenges.

Play therapy is a well-established therapeutic approach for working with children and families in the West. This article describes the current situation of play therapy in Hong Kong—a cosmopolitan city where East meets West. The strengths, weaknesses, opportunities, and threats confronting the development of play therapy as an extension of core graduate-level mental health training are analyzed. Through this process, a number of strategic issues central to the growth and development of professionalism in play therapy are identified and discussed. A path for the future development of play therapy for mental health professionals in Hong Kong over the next decade is presented. Possibilities for collaboration in research and practice among play therapists from all over the world are also suggested. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Suction-Controlled Laboratory Test on Resilient Modulus of Unsaturated Compacted Subgrade Soils

Conventionally, the resilient modulus test is conducted in the laboratory under different moisture content in which matric suction is unknown during the test. To investigate the influence of the matric suction on the resilient modulus, this study integrated the suction-controlled testing system and developed a modified testing procedure for the resilient modulus test of unsaturated subgrade soils. Based on the axis-translation technique, two cohesive soils were tested to investigate the effect of matric suction on resilient modulus. In the modified testing procedure, in order to fulfill the equilibrium in matric suction, the number of load cycles at each loading sequence of the resilient modulus test (AASHTO T 292-91) needs to be increased significantly. Experimental data indicate that matric suctions measured in the specimen after consolidation and resilient modulus tests are consistent with the matric suctions deduced from the soil-water characteristic curve corresponding to the same moisture content. In general, the resilient modulus obtained by the suction-controlled resilient modulus test appears to be reasonable. The trends of resilient modulus obtained by the suction-controlled resilient modulus test are consistent with those obtained by the conventional resilient modulus test. However, the suction-controlled resilient modulus test provides better insights that can help in interpreting the test results.     

Modeling Construction Occupational Demand: Case of Hong Kong

Appropriate training can only be developed if training needs for specific skills are carefully identified. This paper, further to an aggregate model developed previously, aims to forecast the occupational share of the aggregate manpower demand for the construction industry of Hong Kong. The forecast, based on existing manpower statistics, is divided into two levels: broad occupations and detailed occupations. The broad occupational demand forecasting model is formulated using a time-series regression analysis to derive the relationship between the occupational share and the construction output cycle, technology, and various work-mix variables; whereas exponential smoothing technique is used to forecast the share of detailed occupations. This occupational demand estimation can provide solid information to facilitate manpower planning. It enables the policymakers to foresee the trends of occupational manpower demand and formulate policies and training and retraining programs tailored to deal effectively with the industry’s human resource requirements in this critical sector of the economy. Although the study focuses on developing models for the Hong Kong construction labor market, the adopted methodology can be applied in other labor markets to develop such models for manpower planning.     

Laboratory Investigation on Reactivated Residual Strength

Recent research has outlined that mobilized in situ strength at the reactivation of displacements along a preexisting sliding surface may be slightly greater than laboratory residual strength. Although geotechnical literature explains this difference in various ways—for instance, strength gain due to soil aging—little work has been devoted to this topic. Bromhead ring shear tests were carried out on remolded samples of the Cormons flysch, a typical geological formation in northeastern Friuli-Venezia Giulia (Italy). The specimens came from the shallow weathered crust of the Cormons flysch, near the areas of Montona and Rosazzo. This experimental study aimed at highlighting the effect of a limited number of parameters on strength gain at the reactivation of displacements along aged sliding surfaces. The results of this research confirm that aging may cause a rising of reactivated shear strength above the residual value, depending on time of aging and vertical stress. The longest aging period—about a month—showed a 20% strength increase for the Rosazzo flysch, and a 30% increase for the Montona flysch. Reactivated strength increases according to a power law: Almost 50% develops over a short time, i.e., after 24?h of aging. In the long term, strength growth is characterized by a deviatoric creep rate gradually approaching zero.     

Concessionaire Selection for Build-Operate-Transfer Tunnel Projects in Hong Kong

A significant realignment of risks between project participants is a fundamental facet of the new procurement paradigm of BOT (build-operate-transfer). A BOT concessionaire assumes far more and deeper risks than a contractor. One critical contributor to the success of a BOT project is the selection of an appropriate concessionaire who has the necessary capacity to provide the best overall deal throughout the build-operate-transfer process. However, various BOT-type procurement protocols are not yet proven and are still being tried and tested. Many countries are at the lower ends of their learning curves. Therefore, there is a need to benchmark the best practices that have been emerging. The Hong Kong government has developed a well-structured concessionaire selection framework supported by the Kepner-Tregoe decision analysis technique. This paper analyzes and draws experiences and lessons from this concessionaire selection practice. Current concessionaire selection practices worldwide are also discussed with a view to improve the procurement process of regions lacking in such experiences or expertise.     

Anisotropic Elastoplastic Bounding Surface Model for Cohesive Soils

The initial stresses existing in the natural ground are anisotropic in the sense that the vertical stress is typically larger than the lateral stresses. The construction activities, such as embankments and excavation, induce anisotropy in the stress system. The stress-deformation behavior and excess pore water pressure response of soils are affected by the inherent and induced stress anisotropy. This paper presents an improved soil model based on the anisotropic critical state theory and bounding surface plasticity. The anisotropic critical state theory of Dafalias was extended into three-dimensional stress space. In addition to the isotropic hardening rule, rotational and distortional hardening rules were incorporated into the bounding surface formulation with an associated flow rule. The projection center that is used to map the actual stress point to the imaginary stress point was specified along the K0 line instead of the hydrostatic line or at the origin of the stress space. A simplified form of plastic modulus was used and the proposed model requires a total of 12 material parameters, the same number as that of the single-ellipse time-independent version of the Kaliakin–Dafalias model. The model was validated against the undrained isotropic and anisotropic triaxial test results under compression and extension shearing modes for Kaolin Clay, San Francisco Bay Mud, and Boston Blue Clay. The effects of stress anisotropy and overconsolidation were well captured by the model. The time effect was not included in the formulations presented in this paper.     

Long-Term Trends in Extreme Temperatures in Hong Kong and Southern China

The observed long-term trends in extreme temperatures in Hong Kong were studied based on the meteorological data recorded at the Hong Kong Observatory Headquarters from 1885-2008. Results show that,over the past 124 years, the extreme daily minimum and maximum temperatures, as well as the length of the warm spell in Hong Kong, exhibit statistically significant long-term rising trends, while the length of the cold spell shows a statistically significant decreasing trend. The time-dependent return period analysis also indicated that the return period for daily minimum temperature at 4℃ or lower lengthened considerably from 6 years in 1900 to over 150 years in 2000, while the return periods for daily maximum temperature reaching 35℃ or above shortened drastically from 32 years in 1900 to 4.5 years in 2000. Past trends in extreme temperatures from selected weather stations in southern China from 1951-2004 were also assessed.Over 70% of the stations studied yielded a statistically significant rising trend in extreme daily minimum temperature, while the trend for extreme maximum temperatures was found to vary, with no significant trend established for the majority of stations.     

Development of Residual Forces in Long Driven Piles in Weathered Soils

A large-scale field-monitoring program for studying residual forces in long-driven piles is described. Eleven steel H-piles, 34.2–59.8?m in embedded length, were instrumented with vibrating-wire strain gauges, installed and subjected to static loading tests in a building site in Hong Kong. The residual forces in these piles during and after pile installation were recorded. The development of residual forces as it relates to the pile penetration depth during construction, and in time after the piles were installed, is presented. The measured load transfers in the piles from static loading tests are reported and the effect of the residual forces on the interpretation of load-transfer behavior is studied. The field measurements show that residual forces increase approximately exponentially with penetration depth. The residual forces continue to increase with time after pile driving due to secondary compression of disturbed soils around the pile shaft and other factors. The large residual forces in the long piles significantly affect the interpretation of the pile load distributions. The effect of residual forces on the shaft resistance is significant at shallow depths. Bearing-capacity theory tends to overpredict the true toe resistance of the long piles founded in weathered soils.     

Construction in Hong Kong: Success Factors for ISO9000 Implementation

This paper examines the success factors for the implementation of ISO9000 in the Hong Kong construction industry. The critical factors for construction contractors to successfully implement ISO9000 were identified. An analytic hierarchy process model was then developed to determine the relative importance among those factors. The findings showed that the top management commitment is the most critical factor for the successful ISO9000 implementation, whilst the common goal, teamworking, education and training, and the cultural changes are also the important factors.     

Safety Management in Construction: Best Practices in Hong Kong

Safety issues have gained vital importance throughout the construction industry. Many construction companies around the world are implementing safety, health, and environmental management systems to reduce injuries, eliminate illness, and to provide a safe work environment in their construction sites. This paper describes an exploratory study of site safety management in construction sites’ environments. It explains a successful, modern safety, health and environmental management system for a leading construction company based in Hong Kong. A typical site-specific safety plan was utilized to provide safety guidance throughout the construction project. A safety management survey was conducted to determine the status of safety in the construction sites. All employees of the company and its subcontractors participated in the survey from 20 construction projects. In total, 1,022 valid records were obtained from the construction sites. The analysis provided useful information on eight aspects of construction safety, including safety policy and standards, safety organization, safety training, inspecting hazardous conditions, personal protection program, plant and equipment, safety promotion, and management behavior. The findings of the survey provide practical knowledge to construction project managers and construction safety practitioners in order to make their sites safer. Insights and discussions are given in this paper.     

Construction Mediation Landscape in the Civil Justice System in Hong Kong

Alternative dispute resolution techniques as means to speedily and economically resolve certain types of disputes have been well recognized. In this regard, some jurisdictions have opted to use mandatory adjudication to deal with construction, in particular payment-related disputes. The situation in Hong Kong is a bit different. The Government of the Hong Kong Special Administrative Region aspires to make Hong Kong a hub for arbitration and mediation services for the region. Voluntary mediation has been introduced in the civil procedures rules of the High Court as part of the newly launched Civil Justice Reform. Adverse cost order is used to discourage “refusal to mediate” and “failing to attempt to mediate.” While the new measures that came into effect on April 2, 2009, sound sensible, a better picture on the actual impacts will unfold as more cases reach the Court. Nonetheless, the cost sanction may be able to make the voluntary use of mediation less voluntary.     

Insight into Resolving Construction Disputes by Mediation/Adjudication in Hong Kong

Resolving construction disputes using an adversarial approach is considered to be in opposition of the maintenance of a harmonious relationship between two parties. The modern arbitration process may emulate the litigation proceeding leading to delay and cost escalation. During the past decade, the Hong Kong Government has implemented a mediation clause as an alternative mode for settlement of construction disputes. In this paper, the experience and insight into resolving construction disputes by integrating mediation and then arbitration in Hong Kong are highlighted. The state-of-the-art modern mediation process and its philosophical origins are reviewed. The shortcomings of the present system are pinpointed. The success of the adjudication now practiced in the United Kingdom may suggest that there is a place for another process of dispute resolution, which may help improve the situation. The prospect of the proposed mediation/adjudication and then arbitration mechanism is discussed with particular reference to the construction industry in Hong Kong.     

Construction Delays in Hong Kong Civil Engineering Projects

Construction delays are common in civil engineering projects in Hong Kong, inevitably resulting in contractual claims and increased project cost. This study was aimed, first, at gathering the perceptions of civil construction practitioners on how significant are the causes of delay; and, second, investigating whether the suggestions as stated in the report of the Construction Industry Review Committee (the Committee comprises members with good standing and knowledge in the construction and related fields as well as those from other professions who are responsible for examining the current state of the construction industry in terms of its output quantity, the quality of work, its environmental friendliness, site safety, its workforce and the system of supervision) are applicable to and effective at mitigating the corresponding delays with reference to a ranking order established using the mean score method. The extent of the differences in perception among the different respondent groups on these two issues was also examined using the rank agreement factor (RAF), percentage agreement (PA), and percentage disagreement (PD). The differences in the perceptions of the respondents on the significance of delays and the actual causes of delays for the six projects studied were also examined. The results of the study showed that the respondents tended to admit their own faults as shown in the top ten significant causes of delay. A strong consensus was found between the client and consultant groups on the significance of the various causes of delay (PA = 74%) and the effectiveness of mitigation measures (PA = 67%) compared with the other pairs of groups. The consultant and contractor groups held extremely different perceptions regarding the significance of various delay causes (RAF = 4.9 and PD = 32%) and the effectiveness of corresponding mitigation measures (RAF = 6.2 and PD = 47%). It is believed that the findings can provide much more insight for the construction practitioners as well as the researchers and thus help to improve the productivity and overall performance of civil construction projects in Hong Kong.     

Monotonic and Cyclic Behavior of Two Calcareous Soils of Different Origins

The behavior of two calcareous soils—Goodwyn (GW) and Ledge Point (LP)—is studied through a series of monotonic and cyclic triaxial tests. These two soils are selected because they represent two extreme formation conditions in terms of their depositional environments, physical characteristics, and grain strength. The experimental investigation included isotropic compression tests to high stress levels, undrained monotonic shearing tests, and undrained cyclic shearing tests under one-way and two-way loading conditions. Tests were performed on samples with different initial conditions. The experimental results show that, although the overall qualitative stress-strain behavior of both GW and LP soils is similar to that of other silicious soils, significant quantitative differences are observed between the two soils and also between calcareous and silicious soils, especially in terms of volumetric reduction during compression, monotonic and cyclic shear strength, and the strain required to mobilize the strength. This paper explores the mechanical behavior of the two calcareous soils and highlights the similarities and differences between their behavior and also between calcareous and silicious soils.     

Suction-Monitored Direct Shear Testing of Residual Soils from Landslide-Prone Areas

The apparent cohesion due to soil suction plays an important role in maintaining the stability of steep unsaturated soil slopes with deep ground water table. In this paper, a modified direct shear box is used to determine the relationships between the value of this additional cohesion and the associated soil suction. The apparatus incorporates a miniature tensiometer which allows for the simple and direct measurement of suction during shearing. The soil-water characteristic curves and shearing behavior of intact residual soils, being low-to-medium plasticity silts, as well as silty sand, taken from four landslide-prone areas in Thailand, have been investigated. The relatively low air-entry suctions (0–7 kPa) and bimodality of the soil-water characteristic curves gives an indication of the structured pore size distribution of the materials tested. Samples with higher suction tend to display stronger bonding at particle contacts and thus are more brittle. The shear strength is found to increase nonlinearly with suction, though linearization can be reasonably assumed for suction below around 30 kPa. Prediction of shear strength based on soil-water characteristic curves agrees better with ultimate than peak values. A simple equation is proposed for the minimum ultimate strength that can be expected in an unsaturated residual soil with a suction lower than about 30 kPa.