It is essential to understand the geotechnical properties of the ground before anything can be built on Earth, the Moon, or elsewhere. The cone penetrometer is a simple but very important instrument that yields quantitative and qualitative information about the geotechnical properties of the material. Quantitative information is the penetration resistance from which density and layering can be inferred, and ground improvement can be evaluated. Qualitative information includes identifying layering and inhomogeneities, as well as the existence of boulders.Cone penetrometers are often proposed for space missions (e.g., Beagle 2, InSight, Philae) and were even used by Apollo astronauts. All cone penetrometers that have been used extra-terrestrially so far have either experienced difficulties with penetration or were designed to penetrate less than 100 mm deep and stop before encountering any meaningful resistance. An optimally developed dynamic cone penetrometer might work better because it requires less reaction force.This research consists of the development of a bespoke dynamic cone penetrometer with variable cone size and hammering energy. Further, this instrument is tested in a large-scale regolith compaction chamber with lunar highlands regolith simulant LHS-1E at a wide range of densities to find the optimal setup where penetration captures enough data by moving slowly but also does not stagnate. Results from dynamic cone penetration tests at many different densities are compared and successfully correlated to cone penetration and nuclear density gauge test results. Calculated coefficients allow for the conversion directly between dynamic and regular cone penetration tests at any density, which shows promise for greater use of dynamic cone penetrometers in lunar applications.

Abstract National Aeronautics and Space Administration (NASA) is preparing to deploy astronauts for detailed exploration of the lunar South Pole, an area primarily composed of lunar highlands regolith. A comprehensive understanding of the composition, properties, and behavior of this surface material is critical to the success of the mission, to advancing the field of lunar exploration research, and future endeavors on the Moon. This study showcases the findings from laboratory tests conducted using a scaled-down model of two types of compaction equipment: a vibrating smooth drum roller (VSDR) and a rolling dynamic compaction (RDC) 4-sided impact roller. The experiments were performed using 1:13 scale models and utilized lunar highland simulant as the test material. Surface settlements, earth pressure cells, and densities were measured to quantify the extent of improvement for these two different compaction techniques. The results indicate that the vibrating smooth drum roller technique outperforms the impact roller in surface settlement, density, earth pressure and acceleration, demonstrating superior performance in compacting lunar highland regolith simulant.

This study, for the first time, explores the possibility of reducing the lime consumption demand for stabilizing a high plasticity clay soil using xanthan gum (XG). A total of 24 different mix-designs, covering three lime-to-soil contents and five XG-to-water concentrations, were tested for standard Proctor compaction and unconfined compressive strength (UCS) to assess the individual and combined stabilization effects of lime and XG over time. The UCS of the compacted soil–XG blends exhibited ‘rise–fall’ responses with increasing XG concentration, peaking at 1.5

This study investigates the stabilization effects of chitosan, guar gum, xanthan gum and sodium alginate (CS, GG, XG and SA, respectively) biopolymers (BPs) on the swelling and consolidation properties of a highly expansive soil. To this end, oedometer swell–consolidation tests (comprising stress-controlled constant-volume swelling, followed by consolidation under incremental loading–unloading) were performed on various BP-stabilized specimens after 1 d and 28 d of curing, and their performance was compared against baseline specimens treated with lime. BP stabilization resulted in notable reductions in the swelling pressure (and its temporal development rate), with extended curing providing additional improvements. While all BPs were effective in mitigating swelling, their long-term efficacy can be ordered as GG ≈ XG > CS ≈ SA. Similarly, all BP-treated specimens exhibited lower compression and swell indices relative to the untreated soil, with CS proving the most effective, followed by GG, XG and SA, which demonstrated similar performance. Moreover, all BPs produced lower consolidation coefficient and hydraulic conductivity values relative to the untreated soil, with further reductions achieved through extended curing. In terms of overall/mean performance, the four BPs exhibited comparable effects on the rate of consolidation and permeability. The BPs, at best, were able to replicate short-term lime treatment results obtained by the pH-deduced lime content demand (3% by mass) of the untreated soil. The study concludes with a comprehensive discussion of the underlying soil–BP interaction mechanisms, i.e. BP-induced clay flocculation and BP gelation-induced reinforcement, elucidating their individual and synergistic effects on the swell–consolidation behavior.

Geosynthetics have been employed as reinforcements to improve pavement behaviours. Previous attempts have been made to compare the performance of geosynthetic-reinforced soils with unreinforced soils through large-scale laboratory tests. However, large-scale testing is considered time-consuming and costly, which reduces the repeatability and reliability of such tests. Therefore, it is crucial to develop a small-scale testing apparatus, which is capable of evaluating the reinforcing effects of geosynthetics in pavements. In this study, a small-scale laboratory testing method was employed to investigate the performance of geocomposites in improving the penetration resistance of the reinforced soil system. Several tests were performed to validate the repeatability of the proposed testing apparatus. The results of this study demonstrate the capability of the developed testing method to produce consistent and repeatable results, which highlights its potential application in measuring the reinforcing effects of geosynthetics in pavements.

NASA is soon to send astronauts to explore the Moon near the lunar South Pole, which is predominantly composed of lunar highlands regolith. Understanding the lunar ground is an essential aspect of this endeavor. This study presents the results of laboratory testing involving a 1:13 scale model of a vibrating drum roller compactor incorporating a lunar highland simulant. Surface settlements, earth pressures, and densities were measured to quantify the extent of improvement. The results demonstrate that the technique is effective in compacting the near-surface regolith simulant. Further studies are required to determine the most effective travel speed and frequency of vibration.

Rolling dynamic compaction (RDC) technology utilises a heavy non-circular module (impact roller) to compact the underlying soil dynamically. The stresses imparted to the soil through this technique and the resulting vibrations, have been the subject of investigation in the field. A finite element (FE) model predicting the settlement and densification of a coarse-grained fill material subject to RDC with a BH-1300 4-sided 8 tonne impact roller has been shown to provide good agreement with that observed in the field. This paper presents estimates using the developed FE model for the peak particle velocity and acceleration, and the maximum stresses applied through each impact upon a coarse-grained soil. Distributions of the results and their empirical formulae are presented herein.

It is generally accepted that, in civil engineering construction projects, the largest element of financial and technical risk generally lies beneath the ground. Indeed, structural foundation failure, construction over-runs and delays can often be attributed to inadequate and/or inappropriate site investigations. Unfortunately, geotechnical engineers have, at their disposal, limited guidance when scoping the extent and nature of site investigations. Often, the scope of geotechnical investigations is not governed by what is needed to characterise appropriately the subsurface conditions but, rather, is driven by budgetary constraints. A pressing need is to arm geotechnical engineers with guidelines that link the scope of a site investigation to ground variability and the probability that the foundation will be under-designed, resulting in some form of failure, or over-designed, resulting in the foundation being larger and more costly than needed. This paper outlines research undertaken to develop such guidance, focusing on the design of pile foundations in variable ground using the probabilistic techniques of random field theory, Monte Carlo simulation and genetic algorithms (GAs). The GA analyses showed that, when the number of boreholes is less than or equal to the number of piles, the boreholes are best located coincident with the piles. A single borehole should be placed at the building's centre-most pile. With two boreholes, they are best located at the sides of the building, and three boreholes should be placed to form an equilateral triangle, as much as possible, while still being near the piles.

A finite element model (FEM) of rolling dynamic compaction (RDC) technology of a BH 1300 4 sided 8 tonne impact roller, developed previously by the authors, has shown to have reasonable agreement with that observed in the field. The use of this FEM is likely to provide high fidelity insights into the capability of the BH 1300 4 sided 8 tonne impact roller, namely in predicting the settlement and densification of an underlying granular material. A parametric study utilising this FEM with respect to initial density and shear strength parameters is undertaken to explore the relationship these properties have to the settlement and densification of a soil subject to RDC with a BH 1300 4 sided 8 tonne impact roller. The empirical relationships constructed within this study are validated against field trials from the literature of the roller improving sandy gravel fill at typical operating speeds of 10 km/h.

A representative sub-surface shear wave velocity model is crucial for seismic hazard studies, as seismic waves are affected by sub-surface characteristics. The offered data in this article were mainly developed based on a quasi-static cone penetration test (q-CPT) collected at the west coast town of Aceh, Indonesia. Microtremor datasets measured at the same locations were employed to extend the depth of the sub-surface models and to validate the models. The in-situ q-CPT data were collected using a locally manufactured Begemann's type cone penetration test apparatus. Twenty seven (27) q-CPT soundings were performed to typical depths of 20 m or measuring cone tip resistances of at least 150 kg/cm2. Several empirical approaches were employed to deduce the sub-surface parameters, including shear wave velocity. To enhance the sub-surface model depth, 23 in-situ microtremor data were recorded using 3 components (3C) of Geobit S100 and RaspberrySHAKE (RS-3D) seismometers at the same locations where the q-CPTs were sounded. At the same time, these microtremor datasets were also utilized to validate the developed sub-surface shear wave velocity models using the forward modeling method. Therefore, all the proposed sub-surface shear wave models presented in this article have been validated. These sub-surface shear wave velocity models can be used for site characterization, i.e., site response analysis, seismic microzonation, or spatial urban planning.

This study investigates the efficacy of sodium alginate (SA), xanthan gum (XG), guar gum (GG) and chitosan (CS) — each applied at five different solid biopolymer-to-water mass ratios (or dosages) and cured for 7 d and 28 d — on the unconfined compressive strength (UCS) performance of a high plasticity clayey soil. Moreover, on identifying the optimum biopolymer-treatment scenarios, their performance was compared against conventional stabilization using hydrated lime. For a given curing time, the UCS for all biopolymers followed a rise–fall trend with increasing biopolymer dosage, peaking at an optimum dosage and then subsequently decreasing, such that all biopolymer-stabilized samples mobilized higher UCS values compared to the unamended soil. The optimum dosage was found to be 1.5% for SA, XG and CS, while a notably lower dosage of 0.5% was deemed optimum for GG. Similarly, for a given biopolymer type and dosage, increasing the curing time from 7 d to 28 d further enhanced the UCS, with the achieved improvements being generally more pronounced for XG- and CS-treated cases. None of the investigated biopolymers was able to produce UCS improvements equivalent to those obtained by the 28-d soil–lime samples; however, the optimum XG, GG and CS dosages, particularly after 28 d of curing, were easily able to replicate 7-d lime stabilization outcomes achieved with as high as twice the soil's lime demand. Finally, the fundamental principles of clay chemistry, in conjunction with the soil mechanics framework, were employed to identify and discuss the clay–biopolymer stabilization mechanisms.

Landing on unprepared lunar surfaces can excavate tons of regolith, send high-velocity lunar regolith particles kilometers from the landing site, and inject particles into lunar orbit. Therefore, lunar launch and landing pads (LLPs) are needed to protect surface and orbital assets from debris damage and to provide solid, impervious surfaces for multiple landings near a permanent lunar facility. LLPs are crucial for spacecraft to be able to land safely and take off from the surface of the Moon. For building an LLP on the lunar surface, bulk regolith manipulation techniques are not well defined for civil engineering and construction processes. Astroport Space Technologies leads an industry and academia research team for advancing the state-of-art with investigations and development of geotechnical engineering and civil engineering processes for bulk regolith manipulation methods, using a "regolith works" toolset for the construction of an LLP. A concept of operations (ConOps) for Astroport's approach to site preparation, excavation, and site leveling for constructing an LLP is described. The ConOps is based uniquely on Astroport's "brickmaking and placement" technology using autonomous robotics for constructing the LLP pavement from molten regolith. The bricklayer technology enables single-step lunar regolith melting, brick forming, and placement without use of grouts or mortar for landing pad creation. The site preparation, excavation, and site leveling processes also produce the feedstock needed for producing bricks and for building the LLP blast protection berms.

Slope stability assessment is a non-linear engineering problem. The complex relationship between factors that affect slope instability is challenging to investigate theoretically and mathematically. This paper proposes the prediction of slopes safety factor, subjected to circular failure mode using artificial neural network (ANN) and two tree-based models using M5P and random forest (RF) algorithm. A dataset including 46 slope cases was divided into a 70/30 ratio to train and validate the model. The input parameters for slope stability evaluation include slope angle, slope height, cohesion, internal friction angle, unit weight and pore pressure ratio. The corresponding output parameter is a factor of safety (FS). The finest ANN structure was obtained as 6-7-1 using the trial-and-error method. The proposed model chooses elliot as the best activation function at a learning rate and momentum of 0.7 and 0.5 for the accurate estimation of FS. In validation phase of ANN, M5P and RF models, the coefficient of determination (R2) results as 0.94, 0.86 and 0.81, respectively. The result suggests that the developed ANN model provides higher accuracy than tree-based models which can be an effective tool for slope stability assessment. Furthermore, the significance of input variables for FS prediction has been investigated through sensitivity analysis, which identifies the complex relationship between the input and output variables. The accuracy achieved from the prediction model is crucial for preventing the risk of slope failure and increasing the slope safety during preliminary design stage.

This article concludes the discussion on Geotechnical Testing Journal's GTJ-2022-0273, with two objectives: (1) elaborating on the usage of the term "workability" for quantifying soils' consistency property, and (2) evaluating the efficacy of the proposed method and apparatus for soil plasticity determination.

Rolling dynamic compaction (RDC) is a specific type of dynamic compaction, which involves towing a heavy non-circular module at a relatively constant speed. This paper investigates the effects of module mass, operating speed and varying ground conditions on the effectiveness of the 4-sided impact roller using a developed finite element method (FEM)-discrete element method (DEM) model. Numerical results were analysed from four aspects, namely the energy imparted to the ground, soil velocity vectors, module imprint lengths and soil displacements at different depths. It is found that, a heavier module mass induces greater ground improvement in terms of both energy delivered to the soil per impact and the magnitude of soil displacements. The energy imparted to the underlying soil by the module increases with greater operating speed. The rotational dynamics of the module also change with increasing operating speed, whereby the impacts are delivered by the faces of the module at typical operating speeds; however, at faster speeds the impacts are delivered towards the corners of the module and the behaviour is less reproducible. The modelling showed that soil with a higher initial Young’s modulus and a higher internal angle of friction decreases the magnitude of soil displacements, which confirms that the impact roller is less able to significantly improve soils that are stiff or have a high initial shear strength.

This paper presents three aspects of geotechnical engineering research that have been conducted throughout the author's career and concludes with a brief treatment of the use of physical models in teaching. The first research topic deals with quantifying the large-scale spatial variability of the Keswick Clay in Adelaide by means of undrained shear strength data acquired from several private consulting companies and government departments, incorporating a large number of site investigations. The mathematical technique of geostatistics is used, and it is observed that kriging with a spherical model, with a range of influence of 1000 m, a nugget of 1500 kPa(2), and a sill of 2500 kPa(2), is able to generate good estimates of the undrained shear strength of the Keswick Clay that can be used for preliminary design purposes. Secondly, the ground improvement technique of rolling dynamic compaction (RDC) is examined in the field and in the laboratory, and numerically by means of artificial neural networks (ANNs). It is observed that RDC is able to improve the ground to depths in excess of 3 m, and the use of transparent soils in the laboratory provides useful insights regarding the influence of RDC on the subsurface profile. In addition, ANNs facilitate the development of reliable models for the prediction of the level of ground improvement due to RDC. The third and final research topic presented involves ground improvement on the Moon. It is a work-in-progress, and early results are presented in this fascinating and exciting endeavour. The paper concludes with a brief treatment of the use of three different physical models used in teaching. It is observed that incorporating demonstrations involving physical models in teaching is helpful for enhancing student learning and engagement.

Rolling dynamic compaction (RDC) utilises a heavy (6 to 12-tonne) non-circular module (impact roller) that pivots about its corners as it is towed, causing the module to fall to the ground and compact the underlying soil dynamically. This paper presents the development of a transient, non-linear finite element (FE) model of the Broons BH-1300 4-sided 8 tonne impact roller, undertaking multiple passes, using LS-DYNA, validated against a field trial and observations presented in the literature for the same coarse-grained material. The results of the numerical analyses demonstrate that the FE model provides reliable predictions of the 4-sided roller as observed in the field. Thus, the use of this FE model may provide high resolution insights into the capability of the impact roller, namely in predicting the settlement and densification of an underlying coarse-grained material. The FE model demonstrates significant soil improvement directly beneath the width of the roller to approximately 1.2 m depth. Residual improvement is shown to extend to approximately 2.5 m depth and 1.25 m laterally.

Rolling dynamic compaction (RDC) is a soil improvement technique, which involves towing heavy (6-15 t), non -circular (3-, 4-, and 5-sided) modules behind a tractor to achieve soil compaction. Both potential and kinetic energies are imparted to the underlying soil as the modules fall and impact the ground. This paper presents a combined, three-dimensional finite element method (FEM)-discrete element method (DEM) model to investigate the behaviour of the 1:13 scale, 3-sided roller. Numerical results are compared against results from a field study using the corresponding full-size, 3-sided roller in two aspects namely, ground settlements and induced peak pressures. It is demonstrated that the numerical results are in very good agreement with the field observations. This paper examines the influence of the twin modules of the 3-sided roller with respect to ground improvement and the results suggest that the soil beneath a single module is improved solely by the module above it. Therefore, the current practice of using the total weight of the 3-sided roller to predict the energy imparted to the ground and the depth of influence should be avoided. The validated numerical model is also used to predict the energy delivered to the soil and the depth of influence of the roller. The energy imparted to the ground is approximately 22.5 +/- 3 kJ per impact with 95% confidence, and the depth of influence is approximately 1.5 m for each of the twin modules of the 13-t, 3-sided roller operating at 11 km/h on granular soils investigated in this study.

Rolling dynamic compaction (RDC) is a ground improvement technique that involves towing a non-circular module forward with a tractor. It is widely used in the construction industry due to its high mobility and relatively small size. However, there remains a paucity of engineering models to predict soil behaviour in different conditions. This paper presents the investigation of sand particle movement during RDC with a three-sided compactor using a 1:10 scale model in the laboratory. Settlements at different depths and cone tip resistance were obtained to determine the increase in soil density, and a high-speed camera was used to capture images so that the displacements of the sand particles could be determined using the particle image velocimetry. The results show limited compaction near the surface where soil is moved laterally due to a combination of bearing failure and the applied frictional stresses, but significant increases in density for initially loose sand to depths of greater than 4 m at full scale. Tests on sand with initial relative density of 0.6 showed only small density increases.

Insufficient or inappropriate soil testing can lead to a range of undesirable consequences, however, there is little research available on-site investigation performance in complex soils. This study investigates site investigation scope in terms of a single borehole and its location relative to the foundation. The results are given in the form of heatmaps showing favourable sampling locations, whereby the optimal location can be found. The method used is statistical in nature, employing Monte Carlo analysis with randomly generated, variable, single layer soils. These soils allow both site investigations and true foundation performance to be conducted, with the resulting statistics analysed. Several site investigation, structural configuration, and soil variability factors are examined, including test type, borehole depth, reduction method, number of piles, building size and investigation performance metric. The results show that investigation quality is maximised by drilling the borehole in proximity to any pile in the foundation, and that failure costs can vary with location by up to 8% of the construction cost.