Comprehensive Geotechnical Investigations Research Articles

Planning and design of the Gordie Howe International Bridge, North America

The Gordie Howe International Bridge project is providing a new modern border crossing between Windsor, ON, Canada and Detroit, MI, USA. The centrepiece of the project is a 2.5 km long cable-stayed bridge with 853 m main span over the Detroit River and 220 m tall towers on both sides of the river. In addition to the bridge, the project includes ports of entry on both sides of the border and a new freeway interchange with Interstate-75 in Detroit. The project was procured as a public–private partnership that allowed the proponents to propose either a suspension or cable-stayed bridge, with the ultimate selection creating the longest cable-stayed bridge in North America. The paper outlines the need for the new border crossing and results of the environmental assessment process, as well as describing the project evolution from planning through procurement and into detailed design. The scoping of the bridge design parameters is discussed, including: comprehensive geotechnical investigation; load study to develop project-specific live loading; the approach for durability requirements to achieve a service life of 125 years; special considerations for security; wind engineering; and compliance with both Canadian and US design codes. The paper also discusses the approach to achieving an aesthetically pleasing bridge design.

Study on geotechnical engineering investigation method of strong karst deep backfill area in mountain area

Guizhou Province is characterized as mountainous with few flat lands. It also features undulating terrains; widespread karst strata; large karst troughs; karst depressions and falling water caves; and well-developed underground karst caves, karst pipelines, and underground rivers. In such mountainous areas, large-scale construction of karst sites requires large-scale excavation and backfilling. The study site comprises several backfilled layers of 550 m thickness and features complex components and large thickness variations. The influence of the long-term seepage of surface water and groundwater is also apparent. However, the study site also exhibits an uneven settlement of deep backfilled layers and unstable karst foundation. The conventional survey method cannot identify effectively and comprehensively existing problems in engineering geology and hydrogeology according to the problems found in the investigation of large-scale building areas, municipal roads, urban rail transit, and university campuses. Through the combination of building engineering methods, such as new and old topographic and geomorphologic contrast methods, on-site geological surveys, karst hydrogeological surveys, borehole layout principle, drilling method, effective physical exploration test, field in-situ test, and indoor test, the scale and characteristics of karst development in the study site, changes in backfill thickness and material composition, and physical and mechanical properties of rock and soil mass are determined. The results provide comprehensive geotechnical data for the type selection, arrangement, and foundation scheme selection of structures. Through comprehensive analysis and summary, this work establishes a set of comprehensive geotechnical investigation methods for strong backfilled karst areas in mountainous regions. The results are expected to be applicable to other similar sites.

Geotechnical assessment for the ground conditions in Makah Al-Mukarramah city, Saudi Arabia

In the current study, the geotechnical properties of the near-surface geological units are collected, tested, correlated, evaluated, and then mapped. In addition, the groundwater level is estimated through comprehensive geotechnical investigations conducted in and around the entire Holy city of Makkah Al-Mukarramah. Based on the measured standard penetration test (SPT), the soil materials vary from soft to very dense materials where SPT ranges from 4 to >50 and increases with depth. On the other hand, the calculated rock quality designation (RQD), the rock quality spans from very poor to good where RQD changes from 0 to 80%. Accordingly, the ground conditions of Makkah can de differentiated into eight subsoil and rock units with various geotechnical properties. Moreover, it is indicated that the physical and chemical nature of these sub-soil and rock units have a considerable effect on the foundations of the constructions that may be risky in the future. The continuous evaluation of the geotechnical and chemical properties for the future projects on these soils and even rock units is highly recommended. These results will greatly support civil engineers and urban designers in the Makkah Al-Mukarramah municipality.

A case study on utilizing geotextile tubes for tailings dams construction in China

This research presents a successful case, in which geotextile tubes have been used to construct a tailings dam for fine tailings disposal since 2008. Up to the end of 2016, the tailings dam raise has reached 9 m in height. The total height of the dam including the starter dike was 61 m. In order to ensure that the tailings reservoir is safe in its current condition and during future construction, the comprehensive geotechnical investigation and stability analyses of the tailings embankment are conducted in this study. The results show that the application of geotextile tubes in the construction of tailings dam is a good alternative for fine tailings disposal.

Numerical simulation of mechanical response of glacial tills under biaxial compression with the DEM

Glacial till deposits in the Greater Toronto Area (GTA) usually comprise fine-grained (clay and silt) and coarse-grained (sand, gravel, cobbles, and boulders) fractions, which are substantially heterogeneous in characteristics. Since coarse-grained fractions are too large to be tested in traditional laboratory equipment, the discrete element method (DEM) is applied in this study to simulate a series of large-scale biaxial tests to study the mechanical characterization of glacial till. This study is based on the results of comprehensive geotechnical investigations for the Eglinton Crosstown Light Rail Transit (LRT) Project in the GTA. The fine-grained till (clayey silt till) examined in this work is collected from the O’Connor Station site. The different proportions, gradations, and sizes of the coarse-grained fractions (gravel) with irregular random shapes and distributions are simulated. The analysis results indicate that the proportion of gravel influences the behavior and mechanical characterization of glacial till. The peak strength and initial modulus of the mixture gradually increase as the volumetric proportion of gravel increases to 30%. Beyond this percentage, the peak strength and initial modulus substantially increase. The failure mode of the sample changes from ductile to brittle with a volumetric proportion of gravel that is greater than 30%. In summary, when the volumetric proportion of gravel is limited to 30%, the gradation and size of the gravel only have a marginal influence on the mechanical characterization of the glacial till. However, a volumetric proportion of the gravel that exceeds 30% has significant impacts on the strength and deformation characteristics of glacial till.

ENGINEERING SITE INVESTIGATION USING 2D ELELCTRICAL RESISTIVITY TOMOGRAPHY AT THE SIKTAN PROPOSED DAM SITE AT ERBIL GOVERNORATE, IRAQI KURDISTAN REGION

2D Electrical Resistivity Tomography (ERT) was carried out at the proposed Siktan Dam site, Erbil Governorate, NE Iraq. The aim of this study is to evaluating the geo-structural setting of the concealed bedrock along the proposed dam axis and the flanks of the proposed dam site. A comprehensive geotechnical investigation consisting of borehole drilling works and electrical resistivity data were carried out to investigate the subsurface formation. Geologically the proposed dam site is located on the Shiranish Formation consisting of dark gray claystone alternating with limestone marlstone and sandstone. Three profiles were taken by Wenner array with 48 electrodes along of each profile which equal 235m, the space between electrodes is 5m. The SYSCAL PRO instrument is used to collect resistivity data and (SYSCAL Switch) were used with 48 electrodes along one line, and which carries out an automatic switching of these electrodes for acquiring profiling data. The data were processed and interpreted by applying 2D inversions TomoLab software. The using of geophysical prospecting in geotechnical investigation is sometimes looked at as a probable rather than certain method when it comes to construct a detailed subsurface layer profiles. The correlation between borehole information and electrical resistivity ranges was done. The combination of geophysical and geotechnical data may greatly improve the quality of buildings construction in civil engineering. From the structural point of view there is no faults have been detected in this location from ERT and boreholes data as well as there is no evidence of the existence of cavities or any other risky resources. The results indicate that the proposed site is suitable for construction of the dam. Boreholes and geotechnical investigations successfully used to verify the results of the resistivity measurements results.

Predicted and measured behaviour of a test embankment on Ballina clay

A test embankment was established on the soft Ballina clay and practising engineers and academics were invited to make predictions of the behaviour of the embankment. Comprehensive geotechnical investigations were performed and the testing data were provided to the predictors. This paper presents Class A and Class C predictions made by the authors for the embankment. In Class A prediction, the soft clay was modelled as a single homogeneous layer. The Class A prediction showed good agreement with measurements for settlement, but not for pore pressure and lateral ground movement. Class C prediction divided the soft clay into two layers based on the information of ground investigation, and achieved better predictions for settlement, pore pressure and lateral movement. Finite element analysis using Plaxis 2D was carried out for the prediction, and Soft Soil Creep model was used for the soft clay. Consolidation parameters were assessed by statistical analysis of the oedometer test data. Sensitivity studies were performed to investigate the influence of parameters on the analysis results. Results of the predictions and sensitivity studies are discussed in the paper.

Time-varying reliability analysis of Huangtupo Riverside No.2 Landslide in the Three Gorges Reservoir based on water-soil coupling

The filling of the Three Gorges Reservoir in China inevitably deteriorated the slope stability near the reservoir and triggered many landslides, which have become a serious geo-hazard. The fluctuation of the water level and the changes in pore water pressure in the slope lead to stability changes of the reservoir slopes. Taking the Huangtupo Riverside No.2 Landslide (HR2L) as a case study, a comprehensive geotechnical investigation is performed. First, the soil-water characteristics curve (SWCC) and the long-term strength of the slip zone soils and landslide soils are obtained based on the experiments. Second, a numerical simulation is used to obtain the distribution characteristics of the saturation line. Finally, the reliability of the landslide is evaluated. The results show the following: (1) At the same reservoir level, the saturation line will change with different reservoir statuses. (2) When considering the matric suction, the safety factor of the landslide is larger (by 3%) than that without considering this component. (3) As the reservoir water level rises, the safety factor of the slope increases. (4) The slip zone soils of the landslide show significant creep characteristics. Under the effect of creep, the long-term strength decreases gradually. (5) Considering the long-term strength of the slip zone soils, the variation of landslide reliability decreases gradually. The slope stability gradually changes from a less-stable state to a worse state.

Evaluation of Geotechnical Parameters using Geophysical Data

The financial implications and the time required for carrying out a comprehensive geotechnical investigation to characterize a site can discourage prospective private residential building developers, especially where a large area of land is to be investigated for construction purposes. Also, most of the geotechnical test procedures utilized during site investigation only provide information on points tested in the subsurface. This research method suggests an approach of investigating the subsurface condition of a site in order to obtain key subsoil geotechnical properties necessary for foundation design for proposed engineering facilities. Seismic wave velocities generated from near surface refraction were combined with percussion drilling and cone penetration tests to obtain a comprehensive geotechnical investigation. From the results of the seismic refraction method, the bulk density of the soil, Young’s modulus, bulk modulus, shear modulus and allowable bearing capacity of a competent layer that can bear structural load at the particular study site were determined. The most competent layer was found within the depth observed by geotechnical methods. In addition, regression equations were developed in order to directly obtain the bulk density of the soil, Young’s modulus, bulk modulus, shear modulus and allowable bearing capacity from the primary wave velocities.

A case study on a geotechnical investigation of drainage methods for heightening a tailings dam

Safe disposal of contaminated tailings is recognized as the single largest environmental challenge facing the mining industry worldwide. Because suitable land for a new tailings pond is becoming rare and expensive, more and more mine operators tend to heighten the existing tailings dams to improve their storage capacity. However, this could lead to a decrease in the stability of the tailings dams. Based on comprehensive geotechnical investigations of a tailings dam in China, this paper presents a successful case study on heightening an existing tailings dam and extending its operational lifetime using a new drainage technique named the upward bending drain pipes system. The proposed system has 60 upward bending drain pipes arranged in the dam wall. The drain pipes are designed with combinations of slots and holes. With this arrangement, seepage on the hole surfaces changes to seepage on the slot surface, which increases the seepage capability by about 20 times compared with traditional drain systems. Based on a dam stability analysis, it is found that the value of the factor of safety of the dam can be improved around 20 % after slope drainage at an elevation of 2015 m. By using the proposed drainage system, the height of the tailings dam of this mine can be increased from 45 m (elevation 2015 m) up to 60 m (elevation 2030 m), which will increase by 8 million cubic meters the wet tailings storage and will satisfy mine operation for 5 years.

Rock compressibility at the Wairakei–Tauhara geothermal field, New Zealand

Geothermal fluid has been extracted from the Wairakei field in New Zealand since the mid-1950s for electricity generation. This has induced regional subsidence of more than 1 m; in addition, there are a few localised bowls with much greater subsidence. A comprehensive geotechnical investigation with recovery of undisturbed samples from depths of up to 774 m was undertaken with testing of samples from within and outside subsidence bowls to determine material properties, with the aim of improved understanding of subsidence within the Wairakei–Tauhara geothermal system. Results from more than 130 K0 triaxial compression tests on core samples are discussed. Given the volcanic origins of most of the material present, a wide variation in the measured constrained modulus values is not surprising. Scanning electron microscope images reveal differences between the texture of the soft materials and the very stiff materials; these correlate with the constrained modulus values. The applicability of the Terzaghi effective stress equation is considered in relation to the measured property values; the conventional equation remains valid even for the least compressible materials tested.

Resistivity Survey of the Subsurface Conditions in the Estuary of the Rio de la Plata

An electrical resistivity survey was performed at the estuary of the Rio de la Plata, as part of more comprehensive geotechnical investigations of the subsurface conditions. The studies were required for the emplacement of a 3.5-m-diameter conduit proposed for the discharge of the treated wastewater of the city of Buenos Aires. The soil profile at the site consists mainly of clays and silts underlain by a layer of dense sand. The dense sand layer is a confined aquifer, and the project required that the depth to the sand layer be perfectly determined. Previous geophysical surveys at the site and the general geotechnical conditions showed the inadequacy of seismic methods, which are usually adopted in similar environments. The resistivity method was determined to be a reliable alternative, even though there has been little experience in surveying shallow depth water for geotechnical investigations. The four-electrode Schlumberger electrode array was adopted for the resistivity survey. Some of the test devices were developed especially for the purpose of this project. Calibration of the method was achieved with data obtained from boreholes. The results show that the resistivity technique performed satisfactorily to the 40m depth required in this project. As a result of the survey, the next geotechnical investigation was focused on a more reduced area and the required number of boreholes was reduced substantially.

Swimming Pools Supported by Dissimilar Bearing Strata

Investigation of damaged swimming pools in Southern California reveals that severe damage often occurs when the earth materials or bearing support is provided by material having different engineering properties. This often occurs in hillside area where steep slopes and alluvial filled canyons are found. Consolidation of man-made earth fill, colluvium, and alluvium is generally much greater than the parent bedrock found on many residential lots. Consolidation and creep can occur over a period of time due to changes in moisture content as fill and other earth materials become saturated. It is important that a comprehensive geotechnical investigation be carried out, even for this simplest of engineered structures. Damage to swimming pools can be mitigated by supporting the base of the pool entirely on bedrock, using deep foundations such as piers or piles.

Mining subsidence in Lethbridge, Alberta

Coal mining in Lethbridge began in 1872 and continued until 1965. Workings were by underground room and pillar techniques on a single near-horizontal seam. Parts of the city, and particularly the recently developed or soon to be developed areas, to the north and west of the city, are underlain by mine workings. This has necessitated comprehensive geotechnical investigations to evaluate potential subsidence hazards and to enable guidelines for construction precautions to be developed. Because of the relatively uniform conditions throughout the area, the borehole data accumulated during these investigations illustrate well some aspects of the process of mining subsidence above abandoned workings. Another interesting aspect of the Lethbridge case history is the phenomenon of soil cracking that occurs around the edge of worked seams. Even though calculated potential tensile strains are small, it appears that they can be concentrated to form thin cracks in the very stiff, unsaturated overburden soils. These cracks can subsequently be exploited by surface erosion processes and result in voids or soft zones, which are a potential hazard to construction. Key words: mining subsidence, void migration, soil cracking, development guidelines.

Structural settlements at a major power plant : Konstantinidis, B; Van Reissen, G; Schneider, J P In: Settlement of Shallow Foundations on Cohesionless Soils: Design and Performance (papers to the ASCE Convention, Seattle, 10 April 1986)P54–73. Publ New York: ASCE, 1986 (Geotechnical Special Publication No 5)

The foundation design for the Intermountain Generating Station was based on comprehensive geotechnical investigations that included cone penetrometer tests, borings, pressuremeter tests, seismic velocity surveys, as well as conventional and special laboratory tests. Settlement predictions made based on the results of these investigations were compared to actual settlement monitoring data obtained during construction. The paper presents a summary of geotechnical data pertinent to settlement predictions and monitoring as well as a detailed discussion of the advantages and shortcomings of the various field and laboratory techniques used to evaluate soil compressibility.