Use of Explosives on The Moon

The utilization of explosives for excavation on the lunar surface is under serious consideration as a part of the design for construction of temporary and permanent bases. An excavation research program has shown that small‐scale explosives blasting in a lunar‐soil simulant will greatly reduce the digging forces required for scoop and dragline excavators. Some crater‐blasting parameters were determined for the lunar soil simulant at one Earth gravity and at 10 Earth gravities using a centrifuge. The size of the craters produced at 10 Earth gs matched those formed at one earth g by scaling according to the weight of the explosive. These data can be applied to explosive‐excavation problems such as habitat construction, burial of nuclear power sources, and the rapid construction of shelters remote from the main base to shield against solar‐flare activity.     

Intelligent Cable Shovel Excavation Modeling and Simulation

Cable shovel excavators are used for primary production of geomaterials in many surface mining operations. A major problem in excavation is the variability of material diggability, resulting in varying mechanical energy input and stress loading of shovel dipper-and-tooth assembly across the working bench. This variability impacts the shovel dipper and tooth assembly in hard formations. In addition, the geometrical constraints within the working environment impose production limitations resulting in low production efficiency and high operating costs. An intelligent shovel excavation (ISE) technology has been proposed as a potential solution to these problems. This paper addresses the requirements of the dynamic models of the cable shovel underlying the ISE technology. The dynamic equations are developed using the Newton–Euler techniques. These models are validated with real-world data and simulated in a virtual prototype environment. The results provide the path trajectories, dynamic velocity and acceleration profiles, and dimensioned parameters for optimum feed force, torques and momentum of shovel boom-dipper assembly for efficient excavation. The optimum digging forces and resistances for the cable shovel excavators are modeled and used to predict optimum excavation performance.     

Creep Modeling in Excavation Analysis of a High Rock Slope

Based on the distinct element method, a numerical procedure is presented for simulation of creep behavior of jointed rock slopes due to excavation unloading. The Kelvin model is used to simulate viscous deformation of joints. A numerical scheme is introduced to create incremental contact forces, which are equivalent to producing creep deformation of a rock-joint system. The corresponding displacement of discrete blocks due to creep deformation of contact joints can be calculated by equilibrium iteration. Comparisons of results between the numerical model and theoretical solutions of a benchmark example show that the presented model has excellent accuracy for analysis of creep deformation of rock-joint structures. As an application of the model, residual deformations of the high rock slopes of the Three Gorges shiplock due to excavation unloading and creep behavior are investigated. By simulating the actual excavation process, the deformation history of a shiplock slope is studied. Good agreement has been achieved between numerical prediction and field measurements. It demonstrates the effectiveness of the presented model in analysis of the creep deformation due to excavation unloading of high rock slopes.     

Experimental Studies on Mechanics of Lunar Excavation

One of the first construction operations for building a stationary habitat on the moon or Mars will be excavation of soil. The reasons for this necessity are manyfold and range from the need to protect inflatable habitats against radiation to creating an underground space for building electrical power plants. Despite the tremendous amount of earth movement that has taken place on this globe, a sound theoretical basis for designing soil‐moving machines does not exist. This paper describes the results of experiments that were developed to evaluate empirically if and how soil could be excavated on the moon. No attempt has bee made to optimize or promote a particular method. The goal of the present study is rather to establish a sound knowledge base to use for the more‐detailed studies needed to design an operational system that will be successful on the moon.     

Theoretical Model of Shield Behavior During Excavation. I: Theory

Closed-type shield tunneling methods were developed together with computer-aided automatic control systems. However, automatic control systems are based on empirical relationships and do not have a precise theoretical background. In this paper, a model of the theoretical dynamic load acting on the shield during excavation is developed, taking into account shield tunnel engineering practices; i.e., the excavated area, the tail clearance, the rotation direction of the cutter face, sliding of the shield, ground loosening at the shield crown, and the dynamic equilibrium condition. To evaluate the validity of the model qualitatively, the simulation of shield behavior and the sensitivity analysis of the model parameters on the shield behavior are carried out in both straight and curve alignments for both sandy and clayey ground. The results for the shield behavior are examined, comparing them with the empirical and the theoretical one, and it is confirmed that the proposed model represents the shield behavior reasonably well.     

Scaling Laws for Centrifuge Modeling of Capillary Rise in Sandy Soils

The application of geotechnical centrifuge modeling to environmental problems seems promising. In this paper, one aspect of similitude laws concerning the flow of water through soils is investigated. Within the Network of European Centrifuges for Environmental Geotechnic Research, several tests have been carried out to study similitude laws describing the capillary ascension in porous media at different levels of acceleration. The aim of this paper is to present the results obtained at Ruhr-Universit?t Bochum. A fine sand is used in the experiment. For the visualization of capillary height in the soil sample, image processing is used. Different boundary conditions (constant or variable water level) have been investigated and discussed. All these experiments confirm that capillary rise appears scaled by the factor N and time seems to be scaled with N2. Thus, these results support the possibility of extending the use of accelerated small-scale models to the capillary phenomenon in centrifuge and open the way to more complex investigations of flow and pollutant transport in unsaturated soils.     

Geometric Modeling of Inflatable Structures for Lunar Base

A modular inflatable structure consisting of thin, composite membranes is presented for use in a lunar base. Results from a linear elastic analysis of the structure indicate that it is feasible in the lunar environment. Further analysis requires solving nonlinear equations and accurately specifying the geometries of the structural members. A computerized geometric modeling technique, using bicubic Bezier surfaces to generate the geometries of the inflatable structure, was conducted. Simulated results are used to create three‐dimensional wire frames and solid renderings of the individual components of the inflatable structure. The component geometries are connected into modules, which are then assembled based upon the desired architecture of the structure.     

Excavation Game: Computer-Aided-Learning Tool for Teaching Construction Engineering Decision Making

This paper reports on an interactive computer-aided-learning (CAL) tool that was developed for the education of construction engineering students: the excavation game. It builds on the large potential of using CAL in education. CAL tools could offer a better learning environment for students, as they provide an excellent opportunity for applying and testing the management skills learned in classroom, but are difficult to implement in reality. In this research, the CAL tool focuses on improving students’ decision-making skills in the aspects of excavation and related activities. These are excavation equipment, dewatering, and soil-support methods. It also covers mobilization, surveying, safety, overtime shifts, and reporting. Students compete with regard to time, cost, and quality of construction of a given project. The game flow is nonlinear as it depends on students’ decisions. Wrong decisions deviate the construction flow to a path that costs money and time, while reducing quality. This must be corrected costing extra money and time. The game was tested by senior practicing engineering and university professors. Then, it was tested by senior undergraduate construction students. Both groups agreed that the game responds, to a great extent, to the characteristics of effective CAL software, and that the information provided could not be easily assimilated or practiced through the usual tutorial or demonstration educational format. 18% of the professionals and 72% of students indicated the usefulness of the game in applying management and decision-making skills. 60–70% of students believed that it improved their technical skills in dewatering, soil-support, and excavation activities. In addition, 80% of the professionals found the game presenting realistic soil-support and excavation situations, while 72% of students became more appreciative of the interdependencies between activities.     

Geotechnical Physical Modeling for Education: Learning Theory Approach

As physical modeling sees increasing use in geotechnical engineering education, there is a need for a strategic approach for integrating this powerful simulation technique into courses in a way that ensures the greatest benefit for students. For this reason, a learning theory approach, which recognizes the natural learning cycle of students, has been developed. The approach is based on a modified version of the learning theorist David Kolb’s “theory of experiential learning.” The approach emphasizes a variety of learning styles and thus is appealing to a broad range of students. The approach is relatively easy to apply to traditional geotechnical engineering coursework and requires only a modest effort to adopt. It is expected that by using this approach when designing course modules, instructors can increase the likelihood that comprehensive learning will take place. While this paper focuses on physical modeling for geotechnical engineering, the approach presented here has educational applications to an array of other civil engineering topics.     

Dynamic Modeling of Hydraulic Shovel Excavators for Geomaterials

The hydraulic shovel excavator has found significant applications in surface mining, construction, and geotechnical operations due to its flexibility and mobility. The key to high availability and utilization of this shovel is adequate understanding of machine dynamics and machine-formation interactions among other technical, operating, safety, and economic factors. These shovels are capital intensive, complex in design and operation within severely constrained environments. Detailed dynamic modeling and analysis are required to understand their effective utilization for achieving efficient operating performance and economic useful lives. Previous attempts at solving these problems are limited because they do not provide knowledge on the resistive forces and moments for efficient excavation. In this paper, the Newton-Euler techniques are used to develop hydraulic shovel dynamic models with numerical examples. Detailed analysis of the results shows that: (1) the kinematics of the stick-bucket joint (joint 3) is the most critical and effective control of this joint and is important input into efficient excavation design and execution; and (2) the highest resistive moments occur between the duration of 1.5 and 2.0?s after the start of formation excavation and the highest magnitudes are 1,500?Nm (for stick), 900?Nm (for bucket), and 600?Nm (for boom). Based on these results, the path trajectories, dynamic velocity and acceleration profiles, and dimensioned parameters for optimum feed force, torques, and momentum of shovel boom-bucket assembly can be modeled and used for efficient excavation. The optimum digging forces and resistances for the hydraulic shovel excavator can also be modeled and used to predict optimum excavation performance.     

Nanomechanics Modeling and Simulation of Carbon Nanotubes

Carbon nanotubes (CNTs) have been perceived as having a great potential in nanoelectronic and nanomechanical devices. Recent advances of modeling and simulation at the nanoscale have led to a better understanding of the mechanical behaviors of carbon nanotubes. The modeling efforts incorporate atomic features into the continuum or structural mechanics theories, and the numerical simulations feature quantum mechanical approach and classical molecular dynamics. Multiscale and multiphysics modeling and simulation tools have also been developed to effectively bridge the different lengths and time scales, and to link basic scientific research with engineering application. The general approaches of the theoretical and numerical nanomechanics of CNTs are briefly reviewed. This paper is not intended to be a comprehensive review, but to introduce readers (especially those with traditional civil engineering or engineering mechanics backgrounds) to the new, interdisciplinary, or emerging fields in engineering mechanics, in this case the rapidly growing frontier of nanomechanics through the example of carbon nanotubes.     

Activity Object-Oriented Simulation Strategy for Modeling Construction Operations

The application of an object-oriented (OO) approach including the OO modeling concept and the OO programming mechanisms to develop an activity object-oriented (AOO) simulation strategy for modeling construction operations is introduced. After discussing simulation strategies generally used for construction simulation and analyzing the problems related to the simulation strategies, the AOO simulation strategy that guides modeling or controls simulation experiments for construction simulation is introduced. The AOO simulation strategy considers activities to be objects and is able to overcome some pitfalls that result from other general simulation strategies. In addition, the AOO graphical modeling interface associated with the AOO simulation strategy is described. Finally, comparisons of the graphical model or the simulation results of the AOO simulation system with other simulation tools are illustrated.     

Optimal Design in the Presence of Modeling Uncertainties

The integration of modeling and simulation tools with robust and efficient methods of optimal design offers a rational approach to explore new concepts and designs. However, a widespread adaptation of these tools in the industry design environment will require that they incorporate a systematic analysis of uncertainty in all aspects of the design process. A lack of confidence in designs generated in a simulation-based approach is the result of uncertainties in the predictive capabilities of physics-based models used in the simulations, and poor representation of uncertainties and their propagation in a coupled systems engineering design problem. A data- and knowledge-lean environment, typical of a design process involving novel concepts, further exacerbates the situation; design engineers often make gross assumptions about distributional information of random variables and parameters, thereby adding to the uncertainty associated with the design results. The paper focuses on numerical and analytical tools by which to model uncertainty and risk in a simulation-based design environment, including cases where the uncertainty does not conform to standard probabilistic distributions. A specific focus of the modeling effort is an approach to establish confidence intervals for response predictions available from analytical and numerical models, as well as surrogate approximations used in the design process. Innovative adaptations of formal optimization methods in a nondeterministic design setting are discussed, including design problem formulations that examine the nondeterministic design problem in a multicriteria optimization framework. Simple design problems are used to illustrate the concepts and to underscore the deficiencies in a purely deterministic approach to the design problem.     

Centrifuge Modeling of Earthquake Effects on Buried High-Density Polyethylene (HDPE) Pipelines Crossing Fault Zones

Permanent ground deformation is a severe hazard for continuous buried pipelines. This technical paper presents results from four centrifuge tests designed to investigate the influence of pipe-fault orientation on pipe behavior under earthquake faulting. The experimental setup and procedures are described, and the test results are presented. The test results show that, as expected, pipe axial strain is strongly influenced by the pipe-fault orientation angle, whereas the influence of pipe-fault orientation angle on pipe bending strain is minor. The measured pipe strains were shown to follow the trend predicted by the Kennedy model. Also, through a parametric study using the Kennedy model, the experimental data were extrapolated for cases of pipeline with longer unanchored length. By combing the data from strain gauges and tactile pressure sensors, transverse force–deformation relations or p–y relations for the pipe were determined. The data indicates that the underlying p–y relationship varies along the length of the pipe with a stiffer p–y relationship at points closer to the fault and a softer p–y relationship at points farther away. The stiffer p–y relationship, appropriate for locations moderately close to the fault, was compared with the ASCE Guidelines in 1984 and Turner’s recommendation in 2004 for moist sand. It was found that the force level for the plastic p–y behavior in the centrifuge tests compared favorably with that in the ASCE Guidelines (1984).     

Centrifuge Modeling of Seismically Induced Uplift for the BART Transbay Tube

The BART Transbay Tube (TBT) is an immersed cut-and-cover subway tunnel that runs from Oakland to San Francisco, California. The loose sand and gravel backfills placed around the tunnel are considered to be liquefiable, and the clays under the backfill are soft in some zones along the alignment. These conditions could potentially result in uplift of the tunnel during strong earthquake shaking. This paper describes centrifuge model tests performed to verify numerical methods used to assess the stability and to evaluate the potential uplift mechanisms of the TBT. The observed mechanisms of uplift were a ratcheting mechanism (sand migrating under the tunnel with each cycle of relative movement), a pore water migration mechanism (water flowing under the tunnel), and a bottom heave mechanism, involving soft soils below the base of the trench. A fourth potential mechanism, viscous flow of liquefied soil, was not observed. The volume of the tunnel relative to the volume of the trench and the densities and permeabilities of the nonhomogeneous backfill were important parameters affecting the uplift of the tunnel. From the experiments reported here and analyses reported by the designers, it was concluded that the magnitude of uplift is limited and, hence, that an expensive ground improvement project to densify the backfill was unwarranted.     

Two-Dimensional Simulation of the Angle of Repose for a Particle System with Electrostatic Charge under Lunar and Earth Gravity

This paper presents a study of the angle of repose of a two-dimensional particle system under the Earth and Moon gravity fields. The particles interact with electrostatic forces in addition to friction. A two-dimensional discrete element method is used in this analysis with two particle shapes, circular and noncircular. The noncircular shape is constructed with overlapping pairs of disks. For the range of parameters studied, the angle of repose shows little sensitivity to gravity. The sensitivity to friction and electrostatic charges can be either significant or negligible, depending on the range of these values. For each contact friction, there is a threshold of electric charge on the particle such that the angle of repose suddenly drops to zero when the charge exceeds this threshold. The existence of this threshold, once validated in three-dimensional systems, may provide an opportunity to measure the electrostatic charges of the lunar dust in situ.     

Discrete Element Modeling of Strength Properties of Johnson Space Center (JSC-1A) Lunar Regolith Simulant

This paper simulates the three-dimensional axisymmetric triaxial compression of JSC-1A lunar regolith simulant under lunar and terrestrial gravity environments under a wide range of confining pressures and relative densities. To accomplish this, the discrete element method (DEM), using Particle Flow Code In Three-Dimensional (PFC3D) software, was employed. The paper focuses on the peak and the critical state (CS) friction angles, which were predicted in the ranges of 35.4°–82.7° and 31.2°–79.8°, respectively, depending on the specimen density and confining pressure. A significant increase in peak and CS friction angles was predicted at near-zero confining pressure. The DEM results validated an empirical model that relates the peak friction angle with the CS friction angle, relative density, and mean effective stress at the CS. Comparison of DEM results with lunar in situ measurements of friction angle, from Apollo missions and other extraterrestrial laboratory experiments under a microgravity environment, shows a favorable agreement.     

Effect of Toe Excavation on a Deep Bedrock Landslide

Observations, data, and analyses that were used to investigate the cause of distress to a single-family residence located adjacent to a major highway cutslope are presented herein. The investigation revealed that the distress in the single-family residence was caused by a deep, large excavation-induced landslide. The excavation, which was made to widen an existing highway, helped trigger the landslide by exposing geologic structures on the cutslope and by unloading the toe of the slope. This case history illustrates some of the ramifications of large highway excavations in natural slopes surrounded by urban areas, e.g., exposing significant geologic features such as shear zones, faults, and folds; the importance of investigating and explaining signs of movement at both the top and toe of a slope; the impact of rainfall on the movement of a large slide mass; and that large slide masses can undergo slow, episodic movement instead of sudden, large movement.     

Construction of Pressurized, Self‐Supporting Membrane Structure on Moon

This paper draws attention to the importance of readiness time (i.e., the time it takes to develop the necessary supporting infrastructure on the Moon for the structure to be ready for use) of a lunar structure. It illustrates a rational process of determining readiness time using for an example the pressurized self‐supporting membrane structure (PSSMS), a concept proposed in 1989. To assess manpower requirement for construction, it is necessary to assess the productivity of a construction crew on the Moon, taking into consideration the hazardous conditions they confront, and the encumbrances due to the use of space suits and other protective systems. These handicaps can be compensated to some extent by making maximum use of mechanical and automatic equipment. The procedure adopted here is to determine the manpower requirement for a similar construction on Earth, then adjust it to the conditions on the Moon. Once the productivity factor relative to Earth is determined, the manpower requirement for lunar construction can be assessed.