Characterization, Modeling, and Evaluation of Geotechnical Engineering Systems

An experimental procedure for load monitoring and fracture detection with fiber Bragg grating (FBG) strain sensor arrays on a cylinder with backfilled material is described in this paper. This study was conducted as part of a coal-fire-energy byproduct mitigation technique, where incinerator ash was subjected to enhanced carbonation techniques to craft a material called ash carbon concrete (ACC). ACC is a dual porosity material constituted of variable amounts of incinerator ash, aluminum, carbon dioxide (CO₂), and water for the purpose of encouraging long-term CO₂ mineral sequestration. The simulated carbon-ash retention cylinder (SCARC) was created as a host cell for ACC and FBG monitoring. The optical strain sensors enable the archival of material forming and backfill interaction history. The test results indicate that SCARC can successfully capture the curing expansion and strain development rates of different ACC blends.

The presence of joints complicates the mechanical response of rock. Thus, an understanding of the influence of different mechanical and geometrical properties of joints on rock mechanical behavior is required for the design of rock structures. This paper investigates the mechanical behavior of rock with one nonpersistent joint, and two interconnected nonpersistent joints, for different degrees of persistence of nonpersistent joints, using distinct element model analysis. The results reveal that increasing persistency of nonpersistent joints decreases the strength for both singly and doubly jointed specimens. The strength of singly jointed specimens is greater than that of doubly jointed specimens for any considered persistency and the difference is more pronounced with increasing persistency. The characteristics of the failure of specimens show that failure initiates from discontinuous termini of joint segments and considerable intact material failure occurs for nonpersistent joints with smaller persistency.

A method of determining elastoplastic parameters in laboratory is given in the paper. For marble samples from Fangshan area in Beijing, systematic measurement has been done by tri-axial test, and the whole stress-strain curves can be simplified as a four-linear model corresponding to initial and peak and residual yield surface. Using the isotropic Mohr-Coulomb model, elastoplastic parameters was calculated, such as cohesion strength and friction angle vary with the internal plastic variable. The stress-strain curves of whole process of marble samples can be simplified described by a four-linear model, for there is strong plastic hardening before the peak strength and softening after the peak strength. Using these parameters a slop stability was analyzed by finite element model (FEM) strength reduction method. The results indicated that the degree of plastic deformation will be underestimated if the hardening properties of marble rock not be considered, and the slope safety factor calculated would be greatly increased about 23.6% at the same time. These are useful for engineering design.

Using the 600°C 20MN servo-controlled triaxial rock testing machine of high temperature and high pressure, which is developed independently by China University of Mining and Technology (CUMT) coupled thermo-mechanical deformation and failure experiments under full stress-strain loading at 200°C and 400°C were carried out with Φ200mm × 400mm gas coal specimen from Xinglongzhuang coal mine, Shandong Province. The results indicated that at 200°C, the deformation of the specimens were minor before destruction, only 1.1%, and brittle fracture occurred. Compression-shear failure happened significantly in coal under high stress. And the whole specimen fractured along the shear plane. At 400°C, deformation of specimens were transformed to ductibility, and large deformation occurred in coal before failure, up to 15.1%. The failure mechanism of the specimens was the frame instability that was caused by pore development derived from large numbers of pyrolysis gas discharging. Coal loses carrying capacity with dramatic deformation. The main controlling factors of coal damage is stress at 200°C but temperature at 400°C.

The deformation and fracture of rock mass are processes along with procedural evolution of energy dissipation and energy release. With an aim to explore the principles of evolution process, the loading and unloading tests are carried out of the marble specimens under complex stress path for analysis of evolution principles of axial energy and actual absorbed energy as the strain changes. The present results show (1) under complex stress paths, the axial energy rises nonlinearly as the strain increases; the rate of rise remains low at the initial stage; with the rate growing gradually to critical damage, the rate will turn to an abrupt inflection point and tends to stabiliz;. (2) under complex stress paths, the axial energy, the strain curves and the gross energy all have abrupt inflection points of rate; the point of the axial energy is at the critical damage of corresponding stress-strain curves while the point of the gross energy at the corresponding peak; (3) the change of the confining pressure fails to change the axial energy of the specimen under complex stress paths; however, under different confining pressures, the gross energy-strain curves of the loading axial pressure and unloading confining pressure present differing forms; (4) the rate of the unloading confining pressure does not change the curve form of the axial energy and the gross energy, only to alter the changing rate of the curves under different stages; and (5) under complex stress paths, the increase of the confining stress comes with the increase of the gap between axial energy and gross energy whereas the effect on the unloading rate is just the contrary.

Diaphragm wall panels are constructed in alternating method (or Pilgrim) in Taiwan. Two adjacent primary panels are placed leaving out the secondary panel in between. Following the two primary panels, gaps are closed by the secondary panels. Primary panels have smaller width than secondary panels due to the use of end plates. Nylon sheets are bound along both sides of end plate to make a blocking screen, together with end plates, to prevent the tremie concrete from detouring into the evacuated trench. This paper studies history cases in which just-finished primary panels in very soft and thick clay deposit are tilted away from the adjacent secondary panel under tremie concreting. The force and moment equilibriums of tilting primary panels are analyzed by considering the resistant force from undrained shear strength of soft clay and driving force from the unset concrete in the secondary panel. The factors to cause this incident include panel thickness, panel width, concrete curing time of primary panel, concrete setting rate and concrete placing speed of secondary panel, and the roughness of trench wall. A checklist is established after this investigation to prevent this incident from happening again.

A tilted eight-story reinforced concrete building with one-story basement on a thick soft clay deposit is leveled with a special two-stage grouting program. The first grouting stage conducted by injecting mild setting grout through sleeved pipe is used to stabilize soft soil zone in depth. As soon as the foundation soil is hard enough to act as a reaction block, the second stage of grouting is conducted in which quick setting grout is injected right under mat foundation to jack and level the building. The grouting duration at each grouting tube and grouting order of each cycle monitored by a central processing computer is scheduled each day based on the elevation surveying results. The elevated volume of mat foundation due to grouting and resettled volume from excessive pore water pressure dissipations are estimated from the elevation surveying results. This can be used to evaluate the grouting efficiency and verify the building being successfully and permanently leveled.

Approach slabs are used in bridges to reduce the differential settlement between the bridge abutment and the approaching road pavement. In ideal conditions the approach slab is simply supported at the abutment and cast on a uniform, well-compacted surface. In reality compaction specifications under an approach slab are not fully achieved due to the difficulty of compacting in a restricted area. A very conservative method of designing an approach slab would be to assume that the fill underneath provides no elastic support to the approach slab, and to design the slab as simply supported over the entire length. Most codes and design guides take into account that the fill underneath the slab provides a varying degree of support to the approach slab and require the designer to use an effective span factor. South African (TMH7 and SANRAL) design codes and guidelines give very general design criteria for the design of an approach slab with no consideration for site-specific conditions. SANRAL recommends an effective span factor of 0.67 in the "code of procedure for the planning and design of highways and road structures in South Africa." This paper considers the influence of varying elastic support conditions on the effective span of an approach slab. Different support conditions are investigated, varying from well-compacted to poorly compacted and the recommended "rule of thumb" given in the SANRAL design guide is assessed.

Cast-in-place concrete tubular piles have been recently introduced into road construction to serve as ground-improving columns that sustain a considerable portion of the embankment load. With respect of the characteristics of such piles in geometry and stiffness, traditional settlement-predicting approaches for composite ground may be no longer suitable. This study discusses the load-carrying behavior of composite ground with particular focus on the variation in the load share of piles. Based on the Mindlin's and the Boussinesq's solutions, a new model is developed to calculate the additional stresses generated respectively by the resistances of pile base, pile shaft and soil plug, as well as the surcharge directly acted on the ground. A case history is presented to demonstrate how the model works and also to examine the consistency between the measurements and predictions.

The foundations placed on near ground surfaces exert maximum contact pressures within the immediate vicinity of the soil-foundation contact line. The subsurface soil at this level and down to half the width of the foundation or beyond is considered within the strain influence zone responsible for most of the settlement of foundations. Stabilization using cement and lime is thought as a measure to improve the bearing capacity of Al-Qatif expansive soil in Saudi Arabia. The geotechnical engineers frequently recommend foundations to exert downward loads greater than the swelling pressure. This requires the supporting ground not to fail under bearing pressures and excessive settlement. Untreated Al Qatif soils were tested for unconfined compressive strength. Their respective bearing values were estimated using the Terzaghi approach and the Hoek-Brown failure criteria. Different dosages of lime and cement were added at different moisture conditions and curing periods. Improvement as calculated using Terzaghi and Hoek-Brown criterion were demonstrated for different types of treatment. This approach can be utilized to adopt higher bearing capacity values often needed in typical expansive soils.

Red clay is a common roadbed filler, some of which has only weak expansibility and is easy to shrink and crack when dehydrated. Based on Dongxin freeway construction projects in Hunan province and referring to the existing research results, we have analyzed the characteristics of red clay subgrade settlement deformation and determined the several kinds of common curve fitting models by analyzing the site measured settlement data of multiple sets of cross section of the red clay subgrade in Dongxin freeway. We then could analyze the correlation between the measured settlement curves and the settlement prediction model. The results show that the power function curve best reflects the change rules of the red clay subgrade settlement and deformation.

The aim of this paper is to describe the evaluation method used for qualification of the site under study. The site is located in Abu Sid Block 14 at Khartoum State. In situ and laboratory testing were carried out to make the data available for the evaluation. Based on geotechnical investigation, the top clay soil is potentially expansive, and problems are expected to occur due to the soil heave associated with increase in its moisture content, if certain measures are not taken during construction stage. Such measures and precautions have to be considered to avoid excessive movements especially under lightly loaded buildings, floors, and underground structures. Many recommendations were derived to make optimum use of the site as a residential area.

The present work is an attempt to better understand the flexural behavior of an instrumented reinforced concrete beam with the cyclic four-point load test. Here, an analytic model that computes the load-moment and load-deformation relationships by taking into account the nonlinearity of section caused by stiffness reduction due to tensile cracking and the validity of moment of inertia is developed. Validity of this model is verified by the excellent agreement between the analytic modeling results and the theoretical solution. The experimental results are compared with the modeling result for assessing applicability of the optic fiber sensor in the beam specimen. After that, a curved beam member representing a smart tunnel lining segment (STLS) is loaded using the same manner. The comparison on flexural behavior shows that the proposed analytic model can provide the best prediction.