Conventional Compaction Research Articles

Effect of aggregate gradation on the mechanical strengths and permeability properties of porous concrete

Porous concrete (PC) is a very popular construction material in developed countries and is now finding application in India in parking lots. In this investigation, an effort was made to study the various performances of PC in the laboratory. Different gradations of coarse aggregates namely 4.75–10 mm, 10–12.5 mm, and 12.5–16 mm are considered to characterize PC adopting conventional compaction by tamping rod, additional 5 and 10 compactions by proctor hammer. The effect of varying compaction and the coarse aggregate gradation is studied on axial compressive, flexural tensile, and splitting tensile strengths of PC. In addition, a simple method is proposed to determine the permeability of all PC mixes. The work was extended to know the influence of low-grade fly ash and GGBS as supplementary cementing materials (SCMs) on the strengths and permeability of PC. Though the strength of PC in the presence of SCMs has decreased, the permeability and the estimated porosity of all mixes decreased compared to the 100% cement counterpart. A wide range of PCs were developed to suit several combinations of mechanical strength, density, and permeability depending on the type of application leading to a sustainable solution. The simple test method proposed to determine the permeability of the PC gives satisfactory results.

Asphalt Pavement Compaction and Vehicle Speed Monitoring Using Intelligent Aggregate

The stable skeletal structure formed by the interlocking mechanism of the spatial movement of aggregate particles during compaction is the mechanism by which asphalt pavements are compacted and shaped. A major problem facing conventional compaction monitoring is that lacking the ability to monitor particle movement and a real-time evaluation method for pavement compaction, which can easily lead to problems such as uneven compaction and over-compaction. In addition, vehicle speed is an important parameter for analysing the dynamic response of a pavement. Current vehicle speed monitoring relies on complex field equipment and the collected vehicle speed parameters are difficult to match with other sensors for fusion analysis. In this paper, a method for monitoring the compaction quality of asphalt pavements and a method for collecting vehicle speed is proposed based on intelligent aggregate and aggregates interaction mechanisms. The experimental results show that with the continuous action of the compaction machinery, the compaction state of the asphalt pavement can be reliably captured and monitored by studying the spatio-temporal movement pattern of the intelligent aggregates. Meanwhile, the analysis of the time nodes of intelligent aggregate attitude change under the action of vehicle load allows accurate acquisition of vehicle speed parameters. Therefore, the method proposed in this study can improve the accuracy of asphalt pavement compaction state control as well as the accurate acquisition of vehicle speed. It can provide a reference for the later analysis of the dynamic response of pavement loads and the intelligent compaction of pavements.

A Planar Underactuated Compaction Mechanism with Self-Adaptability for Automated Fiber Placement Heads

Automated fiber placement (AFP) systems accommodate complex-shaped structures by pressing fibers against the non-planar surfaces of mandrels, in which compaction mechanisms are of crucial significance. A conventional compaction mechanism utilizes an independent actuator with compacting rollers to conform surfaces. Compared with these mechanisms, underactuated mechanisms can improve self-adjustability and functionality. This research introduces the concept design and the analysis of a planar underactuated compaction mechanism for automated fiber placement heads. Firstly, the requirements and design premise are determined. Then, a novel planar underactuated compaction mechanism with a bistable structure is constructed based on the metamorphic design theory. Secondly, the analytical models are established to give insight into the motion characteristics of the mechanism. Moreover, the example and simulation results are presented to verify the conceptual design. Furthermore, the standard deviation of the contact force of the planar underactuated compaction mechanism is much lower than that of a conventional compaction mechanism under equal conditions. Finally, the potential application of the underactuated mechanisms is discussed. Thus, this research shows that the designed compaction mechanism increases the adjustability, robustness, and high repeatability in positioning and can be used to simplify the motion planning for AFP systems when producing complex structures.

Exploiting different morphologies of non-ferromagnetic interacting precursor’s for preparation of hexaferrite magnets

Sintered cold compacted hexaferrite magnets with appreciable magnetic properties and crystallite alignment were made from non-magnetic precursors without applying an external magnetic field. This work presents a novel approach employing non-ferromagnetic interacting precursors comprising of platelet shaped six-line ferrihydrite and needle shaped goethite nanoparticles. A hydrothermal synthesis route was employed to produce platelet shaped six-line ferrihydrite of ~5 nm thickness. Needle shaped goethite nanoparticles were likewise prepared by hydrothermal synthesis with apparent dimensions of ~10 × 27 × 10 nm 3 extracted from X-ray powder diffraction data. The powder diffraction Rietveld modelling also revealed the presence of an amorphous phase in the six-line ferrihydrite and a SrCO 3 impurity. The presence of needle shaped goethite nanoparticles improves the alignment of magnets, while retaining the coercivity ( H c ), in contrast to hexaferrite magnets prepared from six-line ferrihydrite by spark plasma sintering (SPS). The non-ferromagnetically interacting precursors were directly converted to the SrFe 12 O 19 magnets by pressing them with conventional compaction technique followed by subsequent sintering of the pellets. Decoupling the pressing and sintering step is interesting for industrial production of magnets. The hexaferrite magnets prepared displayed good combination of saturation magnetization M s = 70 Am 2 /kg and coercivity H c = 297 kA/m with some degree of alignment of the crystallites M r / M s = 0.71. This procedure exploits the anisotropic shape of the crystallites and compaction using uniaxial pressure followed by sintering into aligned bulk magnets. Two sets of hexaferrite bulk magnets were prepared by sintering at 900 °C and held for 2 h and 1050 °C with a holding time 0 min. The hexaferrite magnets sintered at 1050 °C were subjected to transmission pole figure analysis. The texture index for each pellet were extracted from the pole figure analysis. Employing needle shaped goethite nanoparticles actually enhanced the alignment of the hexaferrite magnets. The magnet obtained from only six-line ferrihydrite displayed only a slightly improved texture index when compared with mixture of six-line ferrihydrite and goethite nanoparticles. • Two different morphologies comprising platelets and needles were employed in synthesizing SrFe 12 O 19 magnets. • Simple conventional compaction were performed to produce highly aligned SrFe 12 O 19 magnets. • This method requires no magnetic field to align the crystallites along the easy axis. • Magnet with saturation magnetization, M s of 70 Am 2 /kg and coercivity H c of 297 kA/m with 18 kJ/m 3 were produced.

Monitoring Particle Movement under Compaction using SmartRock Sensor: A Case Study of Granular Base Layer Compaction

The quality of base course compaction significantly influences pavement’s overall performance. Compared with conventional compaction methods, the intelligent compaction (IC) uses external accelerometers to track pavement responses during compaction and correlates them with pavement layer characteristics to improve the compaction quality. Very few studies have attempted to present interactions of granular materials from the particle level, i.e., how individual particles are responding under the compactive effort. The recent development of a prototype wireless sensor, SmartRock, made tracking the particle movement at meso-scale possible. Accordingly, this paper has the objective of applying the SmartRock sensors to monitor the motion characteristics (i.e., translation and rotation) of granular particles during the compaction process and evaluate the particle response patterns as insights into understanding the compaction mechanism of the unbound aggregate base layer. The experimental site selected was an airport runway test section, designated as the Smart Runway project located in Hill Air Force Base (AFB) in Layton, Utah, United States. SmartRocks were embedded at the bottom of the granular base layer to collect particle motion data during compaction. Analysis results indicated that particle’s motion behavior was closely related to the compactive effort and material properties. Compaction is a process of gaining interlocking among particles and elasticity in materials, and is achieved through the particle’s three-axial angular position arrangement and vertical translation. The particle movement characteristics observed in the granular base were compared to those in asphalt mixtures, which confirmed the unique responses of bound and unbound pavement layer materials. It is suggested that the characteristics of particle rotation behavior during compaction can potentially be used as a control parameter to monitor compaction conditions.

A Review on Roller Compaction Quality Control and Assurance Methods for Earthwork in Five Application Scenarios

Successful quality control and quality assurance (QC/QA) of earthwork compaction is critical to the long-term performance of roads, railways, airports, dams, and embankments. The purpose of this paper is to provide insights into the current practice, existing problems, challenges, and future development trends of QC/QA methods from the perspective of bibliometrics and the development stage. A bibliometric analysis is presented. Through quantitative analysis of literature and qualitative analysis of the development stage, insights into the current research practices and future directions of QC/QA methods have been derived from the perspectives of literature, cluster analysis, classification, different types of QC/QA methods, conclusions, and recommendations. It is found that the current QC/QA methods can be roughly divided into conventional compaction, digital rolling compaction, automatic rolling compaction, and intelligent control compaction. Currently, QC/QA methods are mainly confronted with the issues of accurate detection of compaction quality, autonomous optimization and intelligent decision-making of compaction process, multi-machine coordination, QC/QA-related specification formulation, and process standardization. To address these issues, several critical potential research directions are further identified: comprehensive CCI measurement system; simple and realistic mathematical representation of the complex compaction dynamics; parallel computing and distributed management of multi-source heterogeneous data; standardized application workflow and the cost–benefit assessment in the context of the full life cycle; intelligent control theories, methods, and technologies of earthwork compaction based on multidisciplinary integration. The paper enables researchers to obtain a comprehensive understanding of QC/QA methods for earthwork compaction as well as the suggested solutions for future work.

Dry sliding behavior of copper based composite materials prepared using conventional compaction and sintering technique and spark plasma sintering

The study aimed to investigate the dry sliding properties of as received copper based composite materials, with varying silica and copper content, and produced through two different techniques: conventional compaction and sintering and spark plasma sintering (SPS). The SPS process induced pronounced densification and hardness of the materials and a better distribution of constituents when compared to conventionally sintered specimens. The SPS specimens observed the presence of a C layer of varying thickness on their surfaces, transferred from the graphite die used for their production. The thickness and adhesion of the C layer was influenced by the silica content in the specimens. Specimens containing low silica content showed a significant C layer on the pin surface. This C layer was not removed during dry sliding pin on disc testing, thus resulting in very low COF (coefficient of friction) and pin wear. Specimens containing high silica content led to the formation of a sparse C layer on their surfaces due to the low chemical interactions of silica with other atoms or compounds, leading to easy removal during tests and elevated COF magnitude. However, high silica content also led to low adhesion between the friction layer and the worn surfaces, resulting in instability and higher pin wear. The specimens containing moderate silica content were identified as the best composition due to their ability to easily shed the C layer during testing, maintain smooth, compact, and continuous friction layer without any detachment/adherence issues, and demonstrate permissible COF and pin wear in the mild range.

Cost-Effectiveness of Conventional Compaction (CC) and Intelligent Compaction (IC) Methods of Asphalt Pavement Overlay

The use of intelligent compaction (IC) in asphalt overlay includes the use of double-drum IC rollers, a roller measurement system, global position system (GPS) radio/receiver/base station, infrared temperature sensors, and an onboard computer reporting system. GPS based mapping and optional feedback control help to overcome the drawbacks associated with conventional compaction such as identifying soft spots, achieving consistent roller patterns, and monitoring asphalt surface temperature and levels of compaction with adequate quality control or quality assurance (QC/QA). Cost-effectiveness of both compaction types was measured in terms of initial and roadway lifecycle cost based on the cost inputs received from South Korea and other published literatures. Roadway lifecycle cost was reported based on the improvement in in-place density, smoothness, and fatigue life. The results of this study showed that: (1) with IC an approximate 4.1% initial cost reduction can be achieved compared to conventional compaction; (2) QC/QA cost is found to have the most significant effect on the higher initial cost of conventional compaction compared to other associated costs whereas intelligent roller cost is the vital cost category for IC; (3) improvement of in-place air voids and density due to the IC has shown that at 97% field density (or at 3% air void content) the State Highway Agency can save approximately 44% over a 20-year service period; and (4) agency cost is observed to be reduced by approximately 62% with the IC method based on the 25-year analysis period due to the increase in fatigue life.

Hydro-mechanical path dependency of claystone/bentonite mixture samples characterized by different initial dry densities

In the context of the French Cigéo-project, a mixture composed of 70% processed Callovo-Oxfordian claystone spoil and 30% MX80-bentonite could be a potential backfill material, whose installation aims to stabilize the surrounding rock formation and to limit the propagation of the excavation damaged zone. The backfill material must sustain the overburden pressure, despite that it might be exposed to different hydraulic and mechanical paths. The reference concept considers employing conventional compaction techniques, although their employment involves spatial variations in the dry density after compaction. In general, as the initial dry density has a significant impact on the hydro-mechanical behavior of backfill materials, it is of major importance to relate the variations in the initial dry density to differences in the behavior. This experimental laboratory study aimed to analyze how variations in the initial dry density affect the swelling and compression behavior of the claystone/bentonite mixture, in particular in unsaturated state. Further, it evaluated whether those variations affected possible hydro-mechanical path dependences. The experimental program comprised suction-controlled oedometer and constant-volume swelling pressure experiments, in which samples characterized by different initial dry densities were exposed to different hydro-mechanical paths. The analysis of microstructural and water retention characteristics complemented the program. Major results indicated that the magnitude of swelling pressure at a given suction depends considerably on the initial dry density, but it is independent of the imposed hydro-mechanical path. Interestingly, the dependency of the yield behavior on the hydro-mechanical path appears to be more pronounced as the initial dry density increases.

The influences of matrix materials on the magnetic and mechanical properties of Fe78Si9B13 soft magnetic composites fabricated by injection molding

Soft magnetic composites are fabricated via metal injection molding (MIM) of amorphous Fe78Si9B13 powder in which three kinds of binders (PA+SA, HDPE+SA, PA+HDPE+SA) are chosen as matrix materials. Because of the interaction between amino in PA and carboxyl in SA, the composite having PA+SA matrix possesses a very good bonding between the matrix and the Fe78Si9B13 particles. Therefore, this sample is pore-free and has the best mechanical and dynamic magnetic properties among the three, having a compressive strength of 52.3 MPa, an effective permeability of 18.3, a coercivity of 34.6 A/m and a total core loss of 1489.3 kW/m3 at the frequency of 100 kHz (50 m T). However, when the PA is replaced by HDPE in the matrix, the bonding between the matrix and the metal particles become weaker, leading to decreased magnetic and mechanical properties. Compared to the composites fabricated by conventional compaction method reported in other researches, the soft magnetic composites fabricated by injection molding exhibit much improved DC-bias property, with the incremental permeability measured at a frequency of 100 kHz decreasing only by 18 % at a bias magnetic field of 100 Oe.

Application of data-intelligence algorithms for modeling the compaction performance of new pharmaceutical excipients

BackgroundPharmaceutical excipient development is an extensive process requiring a series of pre-formulation studies to evaluate their performance. The present study compares the conventional compaction and compression pre-formulation studies with artificial intelligence (AI) modeling to predict the performances of thermally and chemically modified starches obtained from Livingstone potato.ResultsThe native starch was modified by three methods, and we obtained the following starches; pregelatinized starch (PS), ethanol dehydrated pregelatinized starch (ES), and acid hydrolyzed starch (AS). Microcrystalline cellulose (Avicel® PH101) was employed as a reference since its use in tablet direct compression has been established. The role of compaction pressure on the degree of volume reduction of the tablets was studied using Kawakita and Heckel models which highlighted that when the starch is modified by pregelatinization followed by ethanol dehydration, and/and or acid hydrolysis modification, a directly compressible starch can be obtained that can plastically deform. The data-intelligence results indicated the reliability of the AI-based models over the linear models. Hence, the comparative results demonstrated that the Adaptive neuro-fuzzy inference system (ANFIS) outperformed the other two models in modeling the performance of all of the four excipients with considerable performance accuracy.ConclusionThe compressibility indices have shown matching characteristics of AS and ES to Avicel® PH101 in terms of direct compressibility potential than PS. Moreover, the data intelligence modeling demonstrates the reliability and satisfactory of ANFIS as a hybrid model over the other two models with increased performance skills in modeling the compaction properties of these novel pharmaceutical excipients.

Research on Intelligent Compaction Technology of Subgrade Based on Regression Analysis

A remote monitoring system with the intelligent compaction index CMV as the core is designed and developed to address the shortcomings of traditional subgrade compaction quality evaluation methods. Based on the actual project, the correlation between the CMV and conventional compaction indexes of compaction degree K and dynamic resilient modulus E is investigated by applying the one‐dimensional linear regression equation for three types of subgrade fillers, clayey gravel, pulverized gravel, and soil‐rock mixed fill, and the scheme of fitting CMV to the mean value of conventional indexes is adopted, which is compared with the scheme of fitting CMV to the single point of conventional indexes in the existing specification. The test results show that the correlation between the CMV and conventional indexes of clayey gravel and pulverized gravel is much stronger than that of soil‐rock mixed subgrades, and the correlation coefficient can be significantly improved by fitting CMV to the mean of conventional indexes compared with single‐point fitting, which can be considered as a new method for intelligent rolling correlation verification.

Boosting Compaction in B-Tree Based Key-Value Store by Exploiting Parallel Reads in Flash SSDs

Append-only B-tree based key-value stores provide superior search and update performance based on their structural characteristics; however, they periodically require the compaction task that incurs significant I/O overhead. In this paper, we present that the compaction’s degraded read performance deteriorates the overall performance in ForestDB, a representative append-only B-tree engine. We demonstrate that despite the exceptional performance of the SSD, the cause of the slow read performance is the underutilization of the SSD’s internal parallelism due to the read operations using synchronous I/O. Furthermore, this paper proposes a novel compaction method that improves the compaction’s read performance by exploiting SSD’s internal parallelism by requesting multiple read operations in a batch using the asynchronous I/O technique. We implemented our proposed methods on ForestDB using two Linux asynchronous I/O interfaces, AIO and io_uring. The evaluation results confirm that our method drastically improves the compaction’s read performance up to ten times compared to the conventional compaction method. In particular, we confirmed that the proposed method using io_uring, the latest asynchronous I/O interface, is effective regardless of the file I/O mode and outperforms the others in all cases.

Evaluation of polyurethane dense graded concrete prepared using the vacuum assisted resin transfer molding technology

In recent years, the polyurethane (PU) was widely investigated and applied in pavement engineering as a sustainable binder to develop pavment materials with superior mechanical and functional properties. However, the two-component PU binders exhibit rapid curing and thus it is difficult to control the material workability through paving and compaction. Hence, the precast mehtod concept has been proposed to obtain good workability as well as the optimal engineering performances of the polyurethane mixtures (PUMs) used in pavement. In the current study, a method based on the vacuum assisted resin transfer molding (VARTM) technology was developed for the precast PUMs. The results showed that the optimal VARTM-based preparation method is to perfusion the normally compacted specimens with 2 ~ 4 wt% PU content to obtain the optimal compaction uniformity and mechanical properties. Based on the developed methods, the water and freeze-thaw sensitivity of the VARTM-formed PUM samples were evaluated by performing laboratory tests. According to the immersion Marshall stability and freeze-thaw splitting tests, the VARTM-formed PUM samples showed improved Marshall and water stability comparing the performance of samples developed using a conventional compaction method. Given the above excellent performances, the VARTM-formed PUMs were validated to serve as the rapid repair pavement materials or pavement materials with high waterproof performance requirements, for example, the bridge deck paving materials. This research has made a breakthrough in the construction technology of PUMs to a large extent. It has made significant contributions to the further application and promotion of PU binder in transportation infrastructures.

Roller compaction of rock-fill with automatic frequency control

A new intelligent compaction method for vibratory soil compaction rollers that automatically and continuously adjusts the vibration frequency to obtain resonance in the coupled roller–soil system was evaluated in full-scale field tests on a 1 m high rock-fill embankment. This method has been called automatic frequency control (AFC). Compacting at the resonant frequency results in maximised deformations in the soil by optimising the dynamic behaviour of the system and improving the interaction between the drum and the soil. The embankment was also compacted conventionally at a fixed standard frequency in order to quantify the difference between the two methods. Applying AFC resulted in a higher degree of compaction of the embankment layer. The effect was most significant at the top of the embankment, where considerable compression was obtained – in contrast to the very loose material resulting from conventional compaction – thus eliminating the need for subsequent static passes. Spot tests showed a considerably stiffer embankment surface after a high number of passes using AFC. Other observed benefits of AFC include a more homogeneously compacted embankment, which benefits long-term behaviour, up to 15% reduced fuel consumption, reduced environmental impact and less machine wear.

RETRO: Reintroducing Tests for Improved Reverse Order Fault Simulation

Reverse order fault simulation and its variations provide a test compaction option with a low computational effort that is applicable even when test constraints or complex fault models preclude the application of other conventional test compaction procedures. This is the scenario considered in this brief. Reverse order fault simulation procedures remove unnecessary tests from a test set without otherwise modifying it. Reverse order fault simulation is typically applied once after the complete test set has been generated. This brief observes that when other test compaction procedures are not applied, forward-looking reverse order fault simulation sometimes yields a smaller test set if it is applied more often during the test generation process. However, applying it more often also increases the computational effort. This brief explains this phenomenon and describes a procedure that uses the new insights to improve the ability of forward-looking reverse order fault simulation to achieve test compaction at a reduced computational effort. The experimental results for benchmark circuits are presented to support the discussion.

Swelling behavior of unsaturated claystone/ bentonite mixtures

This laboratory experimental program investigated the impact of variations in the expansive mineral content, the grain size distribution of employed bentonite, the initial dry density and the selected hydration path on the water retention characteristics and swelling properties of processed Callovo-Oxfordian claystone and its mixtures with MX80 bentonite. The French reference concept for the disposal of nuclear waste in deep sedimentary rock formations envisages the reemployment of excavated material as backfill material, which is installed in situ by means of conventional compaction techniques. The investigations were of special interest as the major issues involving in situ compacted backfill materials were portrayed. Experiments showed that the impact of variations in the dry density on the water retention characteristics of all materials vanished as suctions exceeded 100 MPa. The negligible impact of variations in the initial dry density on the collapse behavior of claystone/ bentonite mixtures remained questionable.

Combined impact of selected material properties and environmental conditions on the swelling pressure of compacted claystone/bentonite mixtures

Mixtures composed of 70% crushed Callovo-Oxfordian claystone and 30% MX80-bentonite are considered as materials, that could be used for backfilling a future radioactive waste repository in deep sedimentary rock formations. Their characterization is of interest, as the replacement of fractions of crushed claystone by bentonite enhances the chemo-hydro-mechanical performance of backfill. The materials are envisaged to be installed directly in the drifts and shafts by means of conventional compaction techniques. The hydro-mechanical behavior of materials containing expansive mineral phases, and especially their swelling behavior, is known to be significantly affected by the initial material properties and environmental and stress conditions. The present study aimed to assess the combined impact of variations in the material properties and environmental conditions, particularly the grain size distribution, dry density and saturating solution chemistry, on the swelling pressure of the mixtures, by conducting a comprehensive laboratory experimental program. The results revealed that the adjustment of the grain size distribution of employed bentonite enhanced the compaction behavior and, in turn, the swelling behavior of the mixtures. Generally, swelling pressures of mixtures were less affected by the employed saline and alkaline solutions than those of crushed claystone. The measured swelling pressures were exponentially related to the initial dry density of the expansive mineral phase, regardless of the grain size distribution. Based upon the finding that the expansive mineral phase being present in crushed claystone contributed to measured swelling pressures, a new approach was introduced to calculate the dry density of the expansive mineral phase in bentonites and their mixtures with non-expansive or less-expansive materials.

Strong correlation between the laboratory dynamic CBR and the compaction characteristics of sandy soil

Construction of earth structures involves the use of compacted soils. In roads construction quality controls like the bearing capacity of the subgrade, base and subbase layers, CBR values and compaction characteristics are primarily important. In Sweden, it has become interesting to correlate new testing parameters collected by simple tests to the conventional compaction parameters collected from modified Proctor tests. This action will help in assessing the bearing capacity of the selected material simply and quickly using the recent developed techniques instead of the conventional techniques which have been considered as time consuming methods. The aim of this study is to demonstrate that the laboratory dynamic California bearing ratio (CBRLD) test can be used as a method of compaction assessment of selected subgrade soil. Moreover, it has been demonstrated in this study that the CBRLD can strongly be correlated to the compaction densities and molding water contents using polynomial correlation and a best-fit multiple regression model for a wide range of molding water contents. In addition, the repeatability of the dynamic laboratory CBR test was examined as discussed in the current article.

A new uniaxial compression tester: development and application

Powder flow characterization with some of the conventional shear testers can be costly, time consuming and requires a trained operator, therefore the application of a cheaper, simpler, and sometimes faster uniaxial compaction tester (UCT) have often been suggested as an alternative. However, it has been known for many years that the results derived from the two methods are not necessarily the same, due to the lower state of compaction attained in the traditional design of UCT. Additionally, the traditional design of UCT tends to give a wide scatter in the results. To overcome these limitations of the UCT, this work developed an easy-to-use uniaxial tester in order to reduce the difference between flow properties reported by the two techniques. In this regard, flow functions of four powders in the cohesive and very cohesive range were measured with shear testers, conventional uniaxial compaction tester (UCT) and the new uniaxial tester at the University of Greenwich (“Greenwich Uniaxial Tester” or GUT). A method in the style of Janssen approach for correcting wall friction effect on the compaction stress of UCT was applied. Results showed the unconfined yield strength attained from GUT is in line with the results obtained from shear testers while the results from UCT are well below the shear tester results suggesting the advantage of the new GUT.