Hollow-stem Auger Research Articles

Seismic site characterization baseline data for microzonation and site response analysis of Otuasega Town, Bayelsa State, Niger Delta region of Nigeria

This study presents the findings of a comprehensive geotechnical and seismic site investigation conducted at Otuasega Town located in Bayelsa State within the Niger Delta region of Nigeria. Subsurface exploration involved advancing 10 boreholes to 30 m depth using hollow stem auger drilling. Continuous disturbed and undisturbed soil sampling was performed at 1.5 m intervals for detailed geotechnical testing. Laboratory tests on the recovered soil samples established the index properties, classification, densities and consistency limits of the stratified deposits. The subsurface profile comprised alternating layers of clay, silt and sand typical of deltaic sediments, with the clay fractions exhibiting medium to high plasticity. Shear wave velocity (Vs) profiling using Multichannel Analysis of Surface Waves (WASW) techniques categorised the site predominantly as Site Class C and D based on international standards. The Standard Penetration Test (SPT) N-values ranged from 5 to 10, indicating soft normally consolidated clay conditions typical of the Niger Delta region. Predictive empirical models developed from the field and lab data showed strong correlations for estimating key geotechnical parameters such as SPT blow count, Vs and liquefaction resistance. Ground response analyses using the Vs and SPT data indicated significant site amplification potential, with peak ground accelerations up to 1.5 times the bedrock motion. Liquefaction analysis based on the empirical SPT-based methods revealed a high potential for liquefaction in the sandy layers, especially under strong earthquake shaking. The study characterized the complex sedimentology and provided baseline information for seismic microzonation and site-specific ground response analyses to advance understanding of geohazards in this delta environment.

Influence of rheological properties of concrete foundation on the implementation of continuous flight auger (CFA) piles

During pile-driving operation using a hollow stem auger (CFA-pile), the lowering of the reinforcement cage into the concrete over the last several meters is greatly affected by the rheological properties of the concrete. Concrete is cast without applying vibration requiring a highly fluid consistency. The concrete rest phase inside the boring cavity begins once concreting has been completed; this phase lasts 30 min or longer in some specific cases, extending until the reinforcement cage has been completely lowered, during this time the paste in concrete becomes restructured. No current test or recommendation serves to guarantee an appropriate casting process for successful lowering the reinforcement cage in a pile. A device has been developed to assess the capability of introducing reinforcement cages into plastic concrete. Tests were carried out both in the laboratory and on site. The restructuring of the concrete at rest due to its thixotropy or loss of workability has been evaluated with a rheometer and correlated to the reinforcement embedment capacity. A structural build-up threshold value and a critical static yield stress have been identified. Analysis of the results demonstrated the potential of the research results to improve the concrete mix design criteria for deep foundations produced with the CFA-piles technique.

РЕЗУЛЬТАТЫ ИСПЫТАНИЙ СВАЙ-РИТ ВЕРТИКАЛЬНОЙ СТАТИЧЕСКОЙ НАГРУЗКОЙ В УСЛОВИЯХ СЛАБЫХ ГРУНТОВ ПРИБРЕЖНОЙ ЧАСТИ г. ТУНИСА

The paper is an overview of nationwide testing results demonstrated by pulse-discharge technology piles exposed to the vertical load under conditions of soft soils of Tunis coastal area. Bored cast-in-place piles are constructed through the employment of the pulse-discharge technology (PDT). In the construction norms of France, PDT piles are classified as bored piles, which are cast-in-place using a hollow stem auger; they are reinforced, and their diameter exceeds 25 centimeters. PDT piles are made through the application of high pressure to the surrounding soil in the course of concreting. Photos of testing facilities are provided in the paper. Graphs of cyclic and experimental load testing of piles, complying with the values of design loads for a 10-storey building under construction, are analyzed. The findings obtained by the authors have proven a considerable growth of the PDT pile bearing capacity in comparison with the analytical solutions obtained in accordance with Russian and French construction norms and regulations. It is pointed out that the results of pressuremeter testing can be reasonably used in calculations as stated in the French norms. Negligible pile settlements and the high value of the bearing capacity of piles prove the expediency of employment of this technology in the course of construction of piles in the soft soils of the Tunis shoreline. It is concluded that further elaboration of the PDT pile calculation technique is required.

Laboratory Apparatus and Procedures for Preparing Test Specimens of Slurry Mixed Soils

Abstract A laboratory mixing apparatus used to prepare test specimens of columns of soil mixed with slurries consisting of clay, typically bentonite, and granular zero-valent iron (ZVI) is described. The slurries are injected and simultaneously mixed into the soil via a hollow-stem auger to mimic the process that occurs in the field associated with the remediation of source zones contaminated with chlorinated solvents (e.g., carbon tetrachloride and trichloroethylene) using large-diameter (e.g., 2.4 m or 8 ft) hollow-stem augers. The presentation includes descriptions of the testing apparatus and procedures for preparing the test columns, mixing the slurries into the base (host) soil, and determining the resulting vertical distributions in the physical properties (e.g., unit weight, water content, porosity, void ratio, clay content, ZVI content, and degree of saturation) of the post-mixed column specimens. Example results of the vertical distributions in physical properties as well as of treatability studies for base soils that were contaminated with chlorinated solvents are provided to illustrate the use of the laboratory apparatus and testing procedures.

Long‐Term Disturbance of Ground Water Chemistry Following Well Installation

Ground water samples collected from a multilevel sampler shortly after its construction showed significantly higher alkalinity and concentrations of calcium and magnesium than those from nearby wells installed 10 years earlier. The sampler was drilled using a conventional hollow-stem power auger in a sandy, silicate aquifer lying beneath an isthmus between two lakes in northern Wisconsin. Ground water in the study area is of low ionic strength and its chemistry is dominated by silicate mineral weathering. Periodic sampling over two years following installation of the sampler showed that the higher solute concentrations had subsequently decreased. Oxygen isotope signature and other solute species, such as sulfate and chloride, were comparable to those of older wells and did not show any notable trends over time. Independent variation of other chemical species that cannot be derived from aquifer minerals, and the similarly high concentrations in older wells shortly after their installation, suggest that rapid dissolution of fresh mineral surfaces and hyperfine particles generated during drilling has induced the enhanced concentrations. This observation is consistent with the field equivalent of laboratory mineral dissolution experiments that show initially increased dissolution rates that decay over time. Well installations for geochemical sampling in dominantly silicate material may require longer times to reach an equilibrium state than has been previously thought.

Tethered, Down-Hole-Motor Drilling system — A benefit to Mars exploration

Drilling and excavation technology will be fundamental to the exploration of the solar system and the development of scientific outposts. To date, drilling has only been conducted on the moon to the depth of a few meters and on Mars to depths measured in centimeters. But depths on the order of tens to hundreds of meters or even kilometers will be necessary for appropriate chemical and biological sampling or to reach postulated useable volumes of liquid water on Mars. Recent NASA sponsored studies on drilling technology have highlighted the benefits and probable technology path of Tethered, Down-Hole-Motor, Drilling Technology to meet future mission requirements. While demonstrations of some drilling technology has confirmed a basic readiness level for inclusion in mission planning, fundamental rock/bit interaction phenomena and cuttings transport questions could be most directly researched in the context of a deep drilling mission on earth. This paper presents the basic concept of Tethered, Down-Hole-Motor Drilling as it might be developed to work with a broad range of available basic downhole drilling equipment, along with identification of opportunities for technology “leaps”. A recent laboratory demonstration of a similar system (performed by the authors for the Jet Propulsion Laboratory) is described that included a revolutionary new bit system that drilled an 80mm diameter hole in medium strength sandstone to a depth of 2-meters at a total power consumption that is five time less than conventional drilling methods. Comparisons of recorded mass and power consumption for conventional terrestrial drilling methods are made against demonstrated laboratory data and against postulated deep drilling scenarios with Tethered, Down-Hole-Motor, Drilling. Specific experiments are recommended including instrumented testing of bit/rock interaction in various temperature regimes, hollow stem auger performance at depth, and maintaining hole stability in regolithic layers. Experiments are directly linked to their potential benefit in the design and development of new highly efficient, low mass drilling technologies for exploring the solar system.

A New Multilevel Ground Water Monitoring System Using Multichannel Tubing

AbstractA new multilevel ground water monitoring system has been developed that uses custom‐extruded flexible 1.6‐inch (4.1 cm) outside‐diameter (O.D.) multichannel HOPE tubing (referred to as Continuous Multichannel Tubing or CMT) to monitor as many as seven discrete zones within a single borehole in either unconsolidated sediments or bedrock. Prior to inserting the tubing in the borehole, ports are created that allow ground water to enter six outer pie‐shaped channels (nominal diameter = 0.5 inch [1.3 cm]) and a central hexagonal center channel (nominal diameter = 0.4 inch [1 cm]) at different depths, facilitating the measurement of depth‐discrete piezometric heads and the collection of depth‐discrete ground water samples. Sand packs and annular seals between the various monitored zones can be installed using conventional tremie methods. Alternatively, bentonite packers and prepacked sand packs have been developed that are attached to the tubing at the ground surface, facilitating precise positioning of annular seals and sand packs. Inflatable rubber packers for permanent or temporary installations in bedrock aquifers are currently undergoing site trials. Hydraulic heads are measured with conventional water‐level meters or electronic pressure transducers to generate vertical profiles of hydraulic head. Ground water samples are collected using peristaltic pumps, small‐diameter bailers, inertial lift pumps, or small‐diameter canister samplers.For monitoring hydrophobic organic compounds, the CMT tubing is susceptible to both positive and negative biases caused by sorption, desorption, and diffusion. These biases can be minimized by: (1) purging the channels prior to sampling, (2) collecting samples from separate 0.25‐inch (0.64 cm) O.D. Teflon sampling tubing inserted to the bottom of each sampling channel, or (3) collecting the samples downhole using sampling devices positioned next to the intake ports. More than 1000 CMT multilevel wells have been installed in North America and Europe to depths up to 260 feet (79 m) below ground surface. These wells have been installed in boreholes created in unconsolidated sediments and bedrock using a wide range of drilling equipment, including sonic, air rotary, diamond‐bit coring, hollow‐stem auger, and direct push. This paper presents a discussion of three field trials of the system, demonstrating its versatility and illustrating the type of depth‐discrete data that can be collected with the system.

Should Grouted Anchors Have Short Tendon Bond Length?

Field measurements associated with the behavior of ten low-pressure grouted anchors installed with a hollow stem auger at the National Geotechnical Experimentation Site at Texas A&M University are presented. The anchors were 0.3 m in diameter and embedded 13.8 m in a stiff to very stiff clay. Six anchors had a tendon bond length of 4.6 m and four had a tendon bond length of 9.2 m. All anchors were load tested to near failure, some were subjected to creep tests, and some to long-term relaxation tests. This study evaluates the load distribution in the soil, grout, and steel tendon; the shear strength of the soil-grout interface compared to engineering soil properties; the relationships between the ultimate load, the creep failure load, the creep threshold load, and the design load; the creep movement rate under load; and the load loss as a function of time. The results show that anchors with shorter tendon bond lengths have higher ultimate capacities and lower creep rates, and transfer the load further away from the supported structure.

Quaternary evolution of ephemeral playa lakes on the Southern High Plains of Texas, USA: cyclic variation in lake level recorded in sediments

Ephemeral playa lakes on the Southern High Plains northeast of Amarillo, Texas, are underlain by more than 10 m of Quaternary lake deposits. Sediments beneath 12 lakes were examined in 76 hollow-stem auger cores and in excavations. Stacked depositional cycles recognized in lake sediments record repeated phases of (1) initial highstand, (2) ephemeral lake, and (3) lake shrinkage and prolonged exposure. Sedimentary and soil structures show that during all phases the lakes were ephemeral, but that the duration and frequency of flooding varied, which caused variation in the relative amounts of accumulation, deflation, and soil formation. The highstand phase is documented by wave-cut benches and lake sediments that extend beyond present lake margins. Mud transported as suspended load was deposited from ponded water. Desiccation resulted in mudcracks and allowed deposition of eolian sand, but exposure episodes were relatively short or infrequent, and vertic soil formation, oxidation of organic material, and deflation of sand were minimal. Decreased frequency and duration of flooding resulting in increased pedogenic modification under conditions similar to those under which modern playa lake sediments accumulate. Eolian silt deposited on dry lake beds and clays deposited in flooded lakes were mixed by vertic soil processes during repeated wetting and drying. Organic material was partly oxidized and partly translocated down roots and cracks, and interbedded upland facies were gleyed. Episodes of lake shrinkage and more frequent exposure are recorded by reddening and formation of calcic horizons within lake muds. Red-brown eolian loam prograded across lake sediments, and calcic soils developed on it. These grassland slope facies record decrease in the size of the playa lakes.

Influence of Borehole Stabilization Techniques on Standard Penetration Test Results

Abstract The standard penetration test (SPT) is an extensively used and generally accepted field test for determining engineering characteristics of soils. However, there are many variables inherent in the performance of the test. The influence of some of the major variables on SPT results are examined under methods of borehole stabilization (drilling fluid, hollow stem augers, and driven casing); methods of raising and lowering the drive weight (cathead and rope and a mechanically released free-fall hammer); and nine different soil sites. Soil profiles at these locations were reasonably uniform with depth, and included sands, silts, and clays. Borehole depths ranged from 16 to 30 m, with ground-water levels varying from near surface to very deep. Standard penetration tests were performed by experienced drilling crews, using standard procedures as outlined in ASTM Method for Penetration Test and Split-Barrel Sampling of Soils (D 1586), at intervals of 1.5 m. Results were analyzed using standard statistical procedures and presented in both graphical and tabular summaries. Results indicate that use of casing gives SPT values different (higher above the ground-water level, lower below) than those obtained using drilling fluid or hollow stem augers in sands; whereas no significant difference was observed among the three methods in fine-grained soils. SPT values obtained using a mechanically released free-fall hammer were comparable to values obtained with the cathead and rope method using a level of care no higher than that routinely exercised in the field.

Exploration for Ground-Water Contamination

To discover if ground water beneath a site is contaminated, the usual request for proposal specifies constructing monitoring wells and performing chemical tests to determine the presence of possible contaminants. In many cases, the indiscriminate construction of wells as a first step may be misleading, or worse, may present a liability. Frequently, insufficient information is available for determining how deep the wells should be, where they should be perforated, or what materials should be used for well construction. This paper suggests the use of hollow-stem auger borings as an alternative to monitoring wells for initial site exploration. Ground-water sampling data and near-surface data such as water level information are obtained with the borings and facilitate the proper siting, design, and construction of monitoring wells if they are determined to be necessary. The auger holes are immediately sealed after sampling to minimize cross-contamination. The results of an initial hollow-stem auger discovery program can be used in developing criteria for well design. Some myths regarding drilling materials and well construction materials are examined.

Migration of contaminants in groundwater at a landfill: A case study: 2. Groundwater monitoring devices

Six types of devices for groundwater monitoring were used on an experimental basis in the investigation of the plume of contamination in the unconfined sandy aquifer at the Borden landfill. These include: standpipe piezometers, water-table standpipes, an auger-head sampler, suction-type and positive-displacement-type multilevel point-samplers, and bundle-piezometers. With the exception of the first two, each of these devices provides a means of obtaining vertical sample profiles of groundwater from a single borehole. The auger-head sampler, which is a device that is attached to the cutting head of conventional continuous-flight hollow-stem augers, yields samples from relatively undisturbed aquifer zones as the augers are advanced downward in the borehole from one depth of sampling to another. This method is a rapid means of aquiring water-quality profiles for mapping the distribution of a contaminant plume. The other three profiling devices can be used to establish permanent networks for groundwater-quality monitoring. A suction-type multilevel sampler consists of twenty or more narrow polyethylene or polypropylene tubes contained in a PVC casing that is capped at the bottom. Each tube extends to a different depth and is attached to a small screened sampling point that extends through the casing to draw water from the aquifer when suction is applied. A positive-displacement multilevel sampler is similar except that each sampling point is connected to a positive-displacement pumping device located inside the PVC casing adjacent to the screen. Use of the suction-type multilevel sampler is limited to zones where the water table is less than the suction-lift depth of 8 or 9 m. The positive-displacement sampler can be used even if the water table is at a much greater depth. A bundle-piezometer consists of 1.2-cm O.D. flexible polyethylene tubes, each with a short screened section at the bottom, fastened as a bundle around a semi-rigid center-piezometer constructed of thick-walled 2-cm O.D. PVC pipe. In shallow water-table areas water is withdrawn from each of the tubes and from the PVC piezometer by suction. In areas with a deep water table, samples are obtained by bailing with a narrow tube with a check valve on the bottom or by displacement using a double- or triple-tube gas-drive sampler. The positive-displacement multilevel sampler or use of the gas-drive samplers in the bundle-piezometers provide the best opportunities for collecting samples that can be filtered and have preservatives added without the water being influenced excessively by degassing or by oxygen invasion. Networks of these three types of devices for multilevel groundwater monitoring were installed in the Borden aquifer by means of hollow-stem augers. The devices are particularly well suited for use in aquifers composed of cohesionless sand or gravel that have little or no clay and groundwater flow that is primarily horizontal. When 8-cm diameter hollow-stem augers are used, as many as eight polyethylene tubes are included conveniently in each bundle-piezometer. If augers with a larger hollow-stem are used, more tubes can be assembled in each bundle.