Innovations in Geotechnical Engineering: Honoring Jean-Louis Briaud

This paper proposes an empirical relationship for the tip bearing capacity of drilled shafts. The proposed relationship is based on the fracture initiation pressure of the rock mass. A database of 190 drilled shaft and plate load tests in soft rock is compiled. The method of Terzaghi is used to estimate the fracture initiation pressure from the tip stress-displacement relationships. It is shown that the back-calculated fracture initiation pressure is in reasonable agreement with the original and modified Griffith fracture theories. The fracture initiation pressure is then related to the unconfined compressive strength of intact rock, rock mass modulus of deformation, the geological strength index, tip displacement, and drilled shaft tip diameter. The resulting probabilistic empirical relationship is calibrated using the method of maximum likelihood. First-order reliability method is used to calibrate the corresponding resistance factors for use in a load and resistance factor design framework.

In this study, supporting a state highway bridge with auger cast in-place (ACIP) piles in clay soil replacing the drilled shafts that were used in the preliminary design for supporting the bridge was investigated. Hence this study was a multi-phase study where the design capacity of the ACIP pile had to be verified with many other factors that control the rapid construction of the bridge. A full-scale load test was performed to verify the constructability, axial capacity, and skin friction developed in the ACIP pile supported in clay soil was investigated. The design load for the 760 mm (30 in.) pile was 1,150 kN (130 tons) but the test pile was loaded to 4,600 kN (520 tons), four times the design load, and the settlement was 17 mm. In addition to the full-scale load test, four (4) service piles were instrumented and monitored during the initial 600 days in service. The load transfer in the service piles (skin friction and tip resistance) were within the design relationships used in the design and was compared to the load test data. The total load carried by the service piles increased with time and varied from 523 to 754 kN (59–86 tons) and the range was 45–66% of the design load of the ACIP pile. Vipulanandan models such as p-q model, pile model, and three parameter correlation model were used to model the curing, the performance of the test pile, skin resistance, tip resistance, and the time dependent responses of the service piles.

California bearing ratio (CBR) values were estimated from in-situ dynamic cone penetrometer (DCP) tests. A shortened version of the PENCEL pressuremeter, called the modified pressuremeter test (MPPMT) was developed. MPPMT results were compared to DCP based CBR’s. MPPMT data was recorded digitally, using instrumentation and data acquisition. Tests were conducted in base and subgrade soils at three sites in Brevard County, FL. The MPPMT probe is 15 cm (6-in.) long; its diameter is the same as the PENCEL probe, but it is not covered by protective metallic sheathing. It produces a stress-strain response in layers 15 cm (6-in.) or thicker in properly sized holes. MPPMT data were reduced to lift-off pressure, limit pressure, initial elastic modulus, and reload elastic modulus. Statistical correlations were established between these parameters and DCP-CBR values. The results indicated that lift-off pressure and limit pressure both correlated well with CBR. The results also showed a weak correlation between initial elastic moduli and CBR, and a poor correlation between reload elastic moduli and CBR. It was concluded that MPPMT test results are reliable in Central Florida base and subgrade soils.

This paper sets out an approach for utilising the small strain shear modulus of a soil to derive deformation parameters for foundation settlement prediction. This approach is an extension of that described by Mayne and his co-workers, with consideration being given also to the drained behaviour as well as the undrained behaviour of the soils. Both the undrained and drained moduli are related to the small strain shear modulus, with the soil compressibility also being incorporated in the drained case. The deformation parameters derived from this approach have been used to compute the load-settlement relationship for shallow foundations on sand and on clay, and for a single pile in residual soil. In the cases considered, satisfactory agreement is found between measured and calculated load-settlement behavior.

Many field studies of integral abutment bridges have focussed on construction and short-term behaviour, while the data on long-term performance are not abundant. In this paper, long-term field monitoring data from an instrumented integral abutment bridge in Fredericton, NB are presented. The primary objective is to add to the limited database of long-term monitoring so that the information might be used to calibrate numerical methods predicting long-term performance over the design life of a bridge. In this paper, data of abutment movements and earth pressures on the abutments over a 9-year monitoring period are presented. Field data indicate that the primary mode of movement for one abutment is translation and a combination of rotation and translation for the other abutment. Data also indicate that the abutments are tilting in opposite directions to one another, resulting in torsion of the bridge superstructure. Finally, of particular interest, is the concern of earth pressure ratcheting. Data do not conclusively show an increase in passive earth pressures behind the abutment over the 9-year monitoring period.

Field testing with ISEEP was conducted at Jennette’s Pier, located in Nags Head, NC. The Pier is subjected to high energy waves on a daily basis, and one of its piles was fitted with a Nortek acoustic beams device that monitors distance from the sensor to the seabed with time. An approach is introduced for assessing the wave-induced bed shear stress and stream power as a function of the wave parameters. The data from ISEEP are used along with the estimated stream power to assess the scour rate at one of the pier’s pile. The computed results are presented for wave heights of 1–5 m and wave periods that ranged from 8 to 17 s. ISEEP data indicted two subsurface sand layers with the lower layer having smaller detachment rate coefficient. This is confirmed by the fact that the lower layer has a coarser grain size distribution with shell fragments. Using an average wave period of 17 s and an average wave height of 3.5 m, results using the ISEEP data with the proposed approach illustrated the possibility of obtaining scour levels similar in magnitude to the monitored data. A direct comparison between measured and computed results with time was however not possible since the time resolution of the collected wave parameters was too coarse, and backfilling of the scour hole with loose sand occurred with time.

Minipile groups have been used to create high load capacity foundations especially where significant space restrictions exist during construction. The interest in such foundations, particularly when the piles are arranged solely around a perimeter, initiated a research project in which geotechnical centrifuge model tests were used to investigate the key geometric parameters affecting the load-settlement behaviour and efficiency of groups of bored, slender, high aspect ratio piles. Circular and square perimeter pile groups were tested along with conventional grid groups. Two modes of failure were observed: either the individual piles pushed into the ground with no obvious settlement of the surrounding soil or as a block with the soil contained within the outer ring of piles settling by the same or similar amount as the piles. The change from block failure to individual pile failure generally occurred at a pile spacing of approximately 2 pile diameters. A complementary numerical modelling study gave insight into the pile-soil interaction and in particular the patterns of displacement as failure changed from individual pile to block mode. Overall, a grid group arrangement was found to be less efficient in terms of load carrying capacity than a perimeter group and the inclusion of a single target pile within a perimeter group could further enhance the group efficiency.

Using the concept of a characteristic load-displacement curve for shallow foundations, a direct design method based on cone penetration testing (CPT) is applied to a database compiled from a total 130 footings on sands. Performance results are based solely on field load test data from large foundations (B >0.5 m) in order to avoid known scaling effects from small model size footings. The footing responses are presented in terms of applied stress (p_F) versus square root of normalized displacements (s/B) so that a single parameter represents the behavior of all size foundations on the particular sand. Furthermore, footing stresses are normalized by the cone tip resistance (q_c) to obtain a unique relationship for shallow foundations on sands. While the method was originally developed from field load tests on square and circular footings, it is now extended to include rectangular foundations via elasticity solutions using a dimensionless length-to-width ratio. Limited data from eight footings on calcareous sands also show compatibility with the derived algorithm.

The load distribution and deflection of offshore piles in Incheon grand bridge are investigated by experimental tests and a lateral load-transfer approach. The emphasis is on an improved wedge failure model developed by considering three-dimensional combination forces and a new hyperbolic p-y criterion. Through comparisons with field case studies, it is found that the method proposed in the present study is more appropriate and realistic for representing the pile-soil interaction for laterally loaded piles in clay than the existing p-y method.

The influence of lateral loads in the offshore environment, such as tides and waves, reduces the stability of the piles under construction and during operation. Scour of the seabed caused by the flow around bridge piers also has a strong influence on the stability and the integrity of offshore structures. In this paper, a comprehensive case study on the offshore bridge piers is highlighted. Special attention was given to the investigation of the collapse of three bridge piers during construction caused by extreme lateral load and seabed scour. To obtain detailed information, an intensive study was carried out to analyze the effect of scour on the stability of battered piles during construction, as well as under in-use conditions. An empirical analysis using HEC-18 (hydraulic engineering circular no. 18, FHWA, 2012) for estimating rock scour was performed along with the results from a multi sonar field test, to accurately estimate the scour depth of the seabed. Through empirical analysis, field test, and numerical analysis, it is shown that the seabed rock scour combined with the relatively short embedded length of piles had critical influence on the stability of these offshore pile foundations.

Geotechnical engineers test and explore less than one millionth of a site’s soil or rock, and based on that information predict how the remaining 999,999 parts will behave under new loads that the project creates. Prediction errors occur from the variability of the site’s soil/rock and the accuracy of the chosen design method. The author presents a design method to quantify the probability of successfully predicting the desired outcome that the owner can understand and choose. Engineers must design to prevent loss of life with very low probabilities of failure, but may minimize financial probability of failure of undesired performance with a higher probability of failure to match the owner’s desires. Following Dr. Briaud’s writing style for technical papers, the engineer can quantify probability of failure accurately without cumbersome calculations.

The drive to reduce dependence on oil has driven the research and use of renewable energy sources available offshore. The tidal current is a promising and consistent source of renewable offshore energy that can be extracted through the use of a tidal current turbine. Since tidal current turbines are currently a young and developing technology with a unique loading mechanism, it is critical to thoroughly understand each component including the foundation to allow for the deployment of a complete system with optimum efficiency and reliability. Suction caissons provide a foundation system for tidal current turbines that provides key advantages during installation and operation while promoting the “green” concept by allowing for removal of the foundation after the end of the design life of the structure. Due to the high cost of testing full-scale suction caissons, physical and or numerical models are typically used to predict the behavior of full-scale foundations under various loading conditions until field observations are available. The response of suction caissons in the multi-pod configuration from three types of modeling (laboratory bench scale, centrifuge scale, and numerical) were analyzed and compared.

Comprehensive geotechnical data have been collected and studied from numerous offshore oil and gas projects developed in the northern region of South China Sea. The basic physical and mechanical properties of the cohesive sediments from the vast shallow water areas in the study region are consistent but very different from that from the deep-water areas. The cohesive soils from the shallow water areas are very low in both plasticity index and clay composition, and more importantly they have a normalized CPT friction ratio significantly lower than the typical value found in other areas while no obvious difference was found in the normalized CPT bearing and pore water pressure properties. A CPT based method which can fully appreciate the CPT friction characterizations was then adopted for the pile driving analysis and provided a satisfactory solution to the abnormal pile behavior often encountered in the study region.

The bump at the end of the bridge has been extensively studied, yet the problem continues to be one of the most chronic issues affecting long term bridge performance. Besides serving as a nuisance to drivers, the bump also amplifies impact loads which can affect deck durability and deterioration at the bridge approach transition; this often leads to repeated maintenance activities throughout the life of the bridge. To alleviate the bump, many transportation agencies have started to use geosynthetic reinforced soil (GRS) both for bridge foundations and approaches. Based on anecdotal experience of driving across these bridge systems, users describe a smooth transition, but the magnitude of differential settlement across the bridge approach transition had not been quantified. This paper describes a pilot study by the Federal Highway Administration to measure the bump at eight bridge sites using inertial pavement profilers and to compare the performance of those bridges supported by GRS to those built with more conventional methods on deep foundations. The results indicate an improvement when using GRS. In addition, the investigation also provides insights on how to use inertial profilers as a transportation performance management tool to monitor bridge approaches.

The St. Petersburg subway, one of the deepest running systems in the world, is characterized by complicated engineering geological, geotechnical, and geoenvironmental conditions affecting the serviceability and safety of the tunnels. This paper presents the results of investigations conducted to enhance the long-term stability of St. Petersburg subway tunnels. These investigations were started in 2005 with a field observation. There was indication of deformation and deterioration of the tunnels including cracks, movements of lining elements, structural materials’ disintegration through different types of corrosion, joint deteriorations, and seepage. This prompted a major research effort including analysis of the engineering-geological conditions of the tunnels, analysis of the engineering properties of the surrounding soils, deformation analysis of the tunnels, sampling of the ground water seeping from the tunnels, sampling of the deteriorated materials, and sampling of the salt deposits and microbial products. The relationship between tunnel deformation and engineering geological conditions is discussed.

Post-tensioned foundation slabs is considered as a functional and cost effective solution for playing surfaces on shrink-swell soils such as tennis courts. The post tensioning increases the yield bending moment of the slab and to a lesser extent its stiffness hence, cracking during bending is minimized. Compared with conventional reinforced concrete foundation slabs, cost benefits of the post-tensioned slabs are achieved by reductions in quantities of concrete, steel, and excavation, which in turn reduce labor costs. A tennis court, located in the backyard of Prof. Briaud’s residence in College Station, TX, was founded on a clay formation of high shrink-swell potential. The Briaud’s tennis court (BTC) is a nearly rectangular post-tensioned slab-on-grade with approximate dimensions of 18.3 by 36.6 m and a slab thickness of about 0.1 m. The BTC was constructed in 1990 and has exhibited good foundation slab performance, so far. Subsurface soil conditions at the site were explored, soil index properties were determined and unsaturated soil moisture diffusion and volume change characteristics were assessed. Movements of the post-tensioned court slab were monitored every month for 2 years using 194 surveying points. The period covered was March 2005 to February 2007. The tennis court slab movements are analyzed and discussed in light of subsurface soil moisture diffusion and volume change characteristics. The BTC slab performance showed fluctuations in slab edge movements both heave and drop influenced by seasonal weather variations. Moreover, an adjacent tree significantly affected the BTC slab edge movements’ patterns within its root zone.

This paper presents four applications where the wet mass soil mixing technique was used to solve different geotechnical problems. In the first application, wet soil mixing was used to improve the shear strength of the soil and increase the global stability factor of safety of a gravity retaining wall built near a man-made lake. In the second application, the same technique was used to build a structural support system for large combustion turbines and transfer large loads through soft organic materials to a competent and relatively shallow limestone layer. In the third application, wet soil mixing was used to build a 4.7-m-high gravity retaining wall at a Boeing aircraft hangar. In the fourth and final application, the technique was used to build a water cut-off box to permit the construction of large pile caps below the elevation of the water table.

In this paper, we present experimental and numerical techniques capable of modeling the transient fluid-particle interaction encountered in surface erosion at a particle and pore-scale. The experimental program was carried out utilizing digital particle image velocimetry (DPIV) to measure pore-scale fluid velocity and direct imaging of particles was used to determine particle positions in a particle bed subjected to flow conditions. Direct measurement of the motion of the two phases under conditions of high particle fraction in the particle bed were attained by instantaneous discrimination between the fluid and particle phases, which were refractive-index matched to allow full-field measurements. A two-dimensional transient fully coupled fluid–particle numerical model was utilized to explore the fundamental mechanisms of flood-induced erosion. The fluid was modeled at a pore-scale level using the lattice Boltzmann method (LBM). The particles were modeled using the discrete element method (DEM). Simulations were conducted on beds of different particle diameters and subjected to different fluid velocities to get a better understanding of the dynamics of sheet-flow and bed erosion.

In an effort to determine the residual strength from the laboratory tests, a new type of tests termed “constant-volume triaxial test” was performed on non-saturated specimens of silty sand prepared at varying water contents. The results of the tests disclosed that the water content or saturation ratio is a key parameter governing the residual strength of the non-saturated soil tested in the above manner. Back-analysis was also made to determine the residual strength that might have been mobilized in the landslide triggered at Tsukidate at the time of the May 26, 2003 earthquake. The comparison of these two data showed a reasonable degree of coincidence, indicating that the proposed method of the laboratory triaxial tests would be a promising means for estimating the residual strength of given soils.

Design of the load to be placed on footings and piled foundations conventionally includes calculated bearing capacity—a peak, or ultimate, resistance—usually defined as a plastic, or semi-plastic, response to increased load. Such bearing capacity can be found in loading tests on model footings, yet no full-scale tests on footings have show that an ultimate resistance mode has developed unless the load was placed off center—intentionally or not. For pile design, it is recognized that the pile toe is a footing with a long stem and none of the very large number of full-scale tests performed with the pile toe response measured separately from the shaft response, has shown a toe bearing capacity. Instead, the toe responses were similar to those found in tests on full-scale footings, i.e., a gradual, though less than linear, and increase of movement for increasing load. Pile capacity is usually established (interpreted) from the pile-head load-movement of full-scale tests on single piles. However, the design analysis of the response of a pile to load is usually based on modeling a pile as a series of short elements, each with its ultimate resistance, or peak resistance. In most cases, the shaft resistance for each element beyond that peak is either strain-hardening or strain-softening. Therefore, as demonstrated by examples, unless the pile is very short or next to infinitely stiff, the accumulated value of the ultimate shaft resistances of the element is not equal to the pile capacity established from the measured load-movement curve of the pile. Moreover, for pile groups comprising more than about five by five rows of piles, i.e., wide piled foundations, the maximum shaft resistance of the piles in a group is limited to the weight of the soil in-between the piles, and the response of the piles differ between interior and perimeter piles. Design of wide piled foundations and piled rafts must be based on settlement analysis and no contribution from contact stress can be assumed.

A case history is presented where the slopes on a bayou were progressively eroding and failing. An engineered reinforced earth slope was designed and constructed for two separate locations along Buffalo Bayou in Houston, TX, but the implemented slope repairs ultimately failed during or soon after construction. A second reinforced earth slope design was then implemented at one location, but again resulted in slope failure during construction. The authors undertook the project after the second failure. The two prior bank stabilization designs were analyzed to determine the cause(s) of these failures. Aggressive shear strength parameters had been used without consideration of residual shear strength after the initial failures. Additionally, inclinometers indicated that slope failure occurred at elevations below the reinforced section of the slope. The authors considered various options for repairs before a soldier pier cantilever wall system was adopted.

This project dealt with the study of surface erosion of levees, earth dams, and embankments. The objective of the research was to develop tools that would improve the understanding of the process of levee failure due to erosion and reduce the risk of failure. Detailed results of the project have been presented elsewhere. This paper deals with one part of the research, the determination of the amounts, and rates of sediment transport due to the soil erosion. In this research, a large number of physical levee erosion tests were performed at 1-g and at high g’s using a geotechnical centrifuge. Centrifuge tests were performed simulating real (prototype) size levees. The erosion was modeled physically in detail. A Kinect device was used to scan and evaluate the volume of eroded soil and variation of the shape of the channels as a function of time. Three-dimensional images were obtained, and variations of the depth of the eroded channels along their length were plotted. Since some assumptions were made in the process of analyzing the Kinect data, it was necessary to validate the data, and recorded videos taken with a high-speed camera were used to provide images of the soil erosion. These values were compared to the results of the Kinect data. The Kinect results agreed well with the physical models. The Kinect is a low cost sensor, and enabled the measurement of the rate of soil erosion, which if done at all, usually requires expensive equipment. The Kinect device functioned well in the high g environment of the centrifuge experiments. It is believed to be the first use of a Kinect device in a centrifuge.

In modern foundation engineering, emphasis is given to settlement, rather than to bearing capacity, Décourt (1999) and Fellenius (1999). In Brazil, as in many other countries, the standard penetration test, SPT is, by far, the most used in situ test. The efficiency of the Brazilian SPT is about 72% and its penetration resistance is designated, as N₇₂. A very important improvement of this test was introduced by Décourt and Quaresma Filho (1991, 1994), the SPT-T. After the sampler penetration into the ground, the torque required to overcome the friction between the sampler and the soil, T, is measured and the concept of equivalent N (N_eq) is introduced, where N_eq = T(kgf.m/1.2 or N.m/12), Décourt (1991). This test provides two quite different and very useful measurements at the same point. The settlement of footings is computed as proposed by Décourt (1994b, 1999), the input data being given by routine penetration tests, SPT, SPT-T, and CPT. The main objective of any good foundation design is to provide equal settlements for all footings. The program ZDSM (zero differential settlement method) computes, for a stipulated settlement value, the stresses, and the dimensions of all footings (assumed square). Saprolitic soils can be very easily and precisely analyzed via the SPT-T instead of the SPT, using N_eq instead of the N_SPT, as the latter is not reliable for such soils, Décourt and Niyama (1994). However, for lateritic soils (LS), up to now, there is no straightforward test that can be used. The use of the shear modulus for low strains, G₀, also as an index test, like it is now being proposed, seems to be very promising. For shallow foundations on rock, it is important to identify its material weaknesses, weathering and fracturing, and to improve its mass properties, by reinforcing it. The main goal is to turn the natural rock into a material, at least as stiff as the high resistance reinforced concrete that might be used for the structure (f_ck≈50MPa). A new method for designing safe, fast, and economical foundations on rocks is now being proposed.

This article provides a review of particle transport in porous media in geotechnical engineering with the focus on particle mobilization and identifies three current challenges and cross-disciplinary applications in this broad subject. The subject of particle transport consists of three phases: mobilization, transport, and potential deposition in porous media. This review shows that particle transport in porous media continues to be an evolving subject. Three aspects that are still not understood in particle mobilization are identified and explained, they are (1) relationship between soil erosion behavior and soil index properties, (2) effect of physicochemical characteristics of the permeating fluid on particle mobilization, and (3) statistical nature of the quantifiers (such as critical velocity) of particle mobilization and the associated complications in identifying the particle mobilization quantifiers. This review cites the rich and cross-disciplinary literature in particle transport in porous media. It also shows that, as new engineering applications emerge, particle transport in porous media continues to evolve and new tools become available to advance the knowledge of this multidisciplinary subject.

Since offshore platforms are designed by component, it is of interest to understand how the performance of the overall system is related to the performance of the components in the jackets and the foundations. The objective of this study is to evaluate the reliability of components and systems for case study platforms using the updated understanding of hurricane hazards and platform performance obtained from recent hurricanes. The major conclusion is that the probability of failures for the overall platform systems decreases with an increase in the number of legs, primarily due to an increase in redundancy in pile foundation systems as the number of piles increases. These results highlight the importance of checking the capacities of the jacket and foundation systems in addition to checking components in design.

Anti-ram perimeter barriers have been used as perimeter protection of facilities such as power plants, airports, and embassies against unrestricted vehicle access. One of the perimeter protection systems is soil-embedded piles installed as either single piles or an in-line group of piles. There exists a critical need to develop reliable design guidelines for a robust and cost-effective piles resisting vehicle impacts. This paper reviews a comprehensive study performed to investigate the effectiveness of piles to successfully stop approaching vehicles. For design of impact-resistant piles, a number of factors including soil strength and stiffness, pile strength and stiffness, mass of vehicle, and approach velocity needs to be considered. In this study, the performance of single piles and groups of in-line piles was evaluated through dynamic component testing, full-scale crash testing, engineering analysis, and numerical simulations. Two full-scale crash tests were conducted according to ASTM F2656 on single piles. In the first test, a 0.35-m diameter steel tube embedded 2 m in stiff clay successfully stopped a 2,300-kg pickup truck traveling at a speed of 97.2 km/h. In the second test, a 6,808-kg medium-duty truck with a velocity of 82.9 km/h impacted a W14x109 steel pile embedded 3 m in dense crushed limestone. Another two full-scale crash tests were performed on group of inline piles. The first one was a test on a group of four piles designed to arrest a 2,300-kg pickup truck with a velocity of 100 km/h. The second one was a test on a group of eight in-line piles designed to arrest a 6,800-kg truck with an approaching velocity of 80 km/h. Tests results were then used to calibrate the numerical simulations. Using the numerical simulation results and the experimental data, a simple yet effective model TAMU-POST was developed to determine the performance of piles under impact to ensure the integrity of anti-ram perimeter barriers installed around the civil infrastructures. The predictions by TAMU-POST resulted in estimates comparable to those obtained from the full-scale crash tests and numerical simulations.

Full-scale axial uplift tests were performed on single-helix helical anchor groups in stiff and soft clay to evaluate any beneficial group effects for uplift behavior. Groups of four helical anchors in a 2 × 2 square arrangement with relative center-to-center anchor spacing of 1.5, 2, 3, and 4 times the anchor plate diameter were tested. The results of the load tests indicated that the behavior of anchor groups was different in stiff clay and in soft clay. In the stiff clay, group efficiencies (capacity of group compared to sum of capacities of individual) were less than 100% for all relative anchor spacings but efficiency increased with relative spacing. By contrast, in the soft clay, group efficiencies were all greater than 100% for all relative anchor spacings but the efficiency appears to be independent of relative spacing. The results are presented and compared with tests on a single-helix anchor of the same diameter to evaluate group efficiency and with a single-helix anchor of the same equivalent area as the four individual anchors in the group. When the behavior of the groups is compared to a single anchor of equivalent area, the group efficiency was on average approximately 200% and in some cases as much as 300%.

Municipal waste is another non-textbook material, generally highly fibrous, heterogeneous, erratic, highly compressible, and displaying significant long-term settlement caused by plastic creep and decomposition. On the basis of the review of a number of case records, neither undisturbed sampling nor field testing is practical. On the other hand, since displacement is often the critical issue and since displacements are measurable in situ, it would seem that the use of a remote sensing system of direct measurements should be adopted where such displacements are critical. Sampling of strongly decomposed waste may be problematic because of caving problems. Conventional laboratory testing methods cannot generally be used, because the structure of the waste in the field is really indeterminate, and cannot therefore be reliably duplicated in the laboratory. Also, the pronounced fibrosity of the samples renders conventional testing of dubious value, generally yielding misleading results. Another important consideration is the fact that waste is subject to decomposition and that the stipulation of constant strength parameters like cohesion and friction is therefore not valid. This consideration appears to be largely disregarded by the profession.

Mechanically stabilized earth (MSE) is one of the major geotechnical engineering innovations of the late 20th century. Invented in 1957 and first reported in 1963 by French engineer-architect Henri Vidal, after pondering the mechanics of sand and pine needles, his reinforced earth product revolutionized civil engineering and the construction of earth retention and support structures worldwide, offering dramatic structural, and economic advantages compared to previous design approaches. Now generically known as mechanically stabilized earth (MSE), a creative application of the technology is for back-to-back walls, hundreds of which are in service for roadway and pedestrian ramps, railway systems, and other applications. MSE walls, especially in a back-to-back configuration, are a significant innovation in geotechnical engineering and construction. This paper brings together elements of MSE theory and practice to provide a comprehensive understanding, enabling practitioners to best use this innovative technology.

This paper presents a discussion of geotechnical design considerations when utilizing the post grouting construction technique. Post grouting of drilled shaft tips using pressure grouting techniques can significantly increase the ultimate capacity of the shafts. The paper also describes two case histories. The first case history is a project where exceptionally high end bearing capacities were developed. On one shaft, an ultimate end bearing capacity of over 925 kg was developed on a 1.2 m diameter shaft founded in a sand stratum. The second case history is a project consisting of multiple post-grouted shafts installed on a bridge overpass project where the density of the bearing sand stratum varied across the site. The project specified load test showed lower than expected achievable end bearing capacities, and therefore a revised design was developed to extend the depths of shafts to develop additional skin friction capacity. However, an alternate post grouted shaft design was proposed and approved. The alternate design included post grouting all the production shafts, and thus allowed the successful completion of the project without the need to increase the planned shaft depths.