Flexural Performance of Drilled Shafts with Minor Flaws in Stiff Clay

Lateral loads are often the primary forces that act on drilled shafts when they support retaining walls, bridge piers, or building foundations. The construction of drilled shafts often inadvertently introduces flaws that are not always detectable with well-performed nondestructive evaluation (NDE) techniques. The effect of such undetectable minor flaws on the lateral-load performance of drilled shafts needs to be assessed and subsequently considered in the design. This paper summarizes a field study that consisted of NDE of six, full-scale drilled shafts with preinstalled voids and lateral-load tests that were performed on the six test shafts. Results from the field study indicated that undetectable (by NDE) void flaws occupying areas of up to 15% of the cross-sectional area of the drilled shaft could reduce free-head shear capacity up to 16%. A subsequent numerical analysis was performed to filter out all variables, other than void flaws, that could affect the lateral-load deformation of drilled shafts. Numerical analysis results validated the field tests measurements. A parametric study of variables affecting the load-deformation behavior of drilled shafts suggests that a reduction in moment capacity of up to 27% is possible with undetected voids present in the shafts that were tested.     

Roughness and Unit Side Resistances of Drilled Shafts Socketed in Clay Shale and Limestone

Rock socketed drilled shafts are being used increasingly to support heavily loaded structures. Rock sockets provide resistance to the load through a combination of side and base resistances. In this study, the effect of drilling tools such as an auger and a core barrel on the unit side resistance was investigated. A total of four field studies were performed on clay shale (compressive strength of 1–2?MPa) and limestone (compressive strength of 10?MPa). Borehole roughnesses produced by the different types of drilling tools in clay shale and limestone were measured using a laser borehole roughness profiler developed in this study to measure roughness to 0.5?mm in the boreholes. Based on the results of this study, it was observed that the drilling tools developed different socket roughnesses, which in turn affected the side resistances of the rock socketed drilled shafts.     

Cutoff Frequencies for Impulse Response Tests of Existing Foundations

The impulse response test is a nondestructive evaluation technique commonly used for quality control of driven concrete piles and drilled shafts where the pile heads are accessible. When evaluating existing foundations, the presence of a pile cap or other structure makes the pile heads inaccessible and introduces uncertainties in the interpretation of impulse response results. A test section was constructed at the National Geotechnical Experimentation Site (NGES) at Northwestern University to examine the applicability of nondestructive testing methods in evaluating deep foundations under inaccessible-head conditions. This paper focuses on the results of impulse response tests conducted atop the three pile caps at the NGES. Based on field experimentation and numerical simulations, a frequency was determined below which the impulse response test could be used for inaccessible-head conditions. This cutoff frequency primarily depends upon the geometry of the pile cap and pile. A case study is presented that describes impulse response tests obtained on a number of drilled shafts both after the shaft was constructed and after grade beams and walls were built. The results of these tests also follow the trends observed in the NGES tests related to cutoff frequency.     

高压旋喷与静压注浆相结合补强加固桩基础

通过某工程实例 ,针对桩基础常见桩身混凝土质量差、承载力不能满足设计要求的问题 ,运用高压旋喷与静压注浆技术解决桩身补强加固的方法 ,达到预期的目的 ,符合使用要求 ,取得较好效果 ,为同类型桩基础处理提供一种可靠的施工方法 .     

Grouting in Difficult Soil and Weather Conditions

Several methods of soil grouting and conventional underpinning are used to stabilize subsoils and repair the foundations of three apartment buildings. Innovative cold weather compaction grouting techniques were used in difficult soil conditions to densify poorly compacted man‐placed fill and soft organic silts beneath building foundations. Penetration grouting using a Portland cement slurry and Pozzolan (flyash) is performed to reduce permeability of the upper subsoils and to fill ineffective and detrimental building perimeter drains. A gravel intrusion jacking method is used to further density upper soils in conjunction with conventional underpinning methods. The project is unique because: (1) Techniques were used that allowed the contractor to drill and densify loose fills and soft natural soils containing cobbles and boulders; (2) the contractor was able to perform grouting and underpinning under extremely adverse weather conditions by using special equipment; and (3) occupants were able to remain in buildings during remedial construction.     

Numerical Studies on Bit-Rock Fragmentation Mechanisms

The rock fragmentation process induced by a single button-bit, two neighboring button-bits, and multiple button-bits are numerically studied using the rock and tool interaction code (R-T2D). Through this study, a better understanding of the bit-rock fragmentation mechanisms is gained. It is found that side crack is initiated from the crushed zone or bifurcated from Hertzian crack to propagate approximately parallel to the free rock surface but in a curvilinear path driven by the tensile stress associated with the expansion of the crushed zone during the loading process. In the crushed zone, the mechanism of side crack is mixed tensile and shear failure, but outside the crushed zone, the dominant mechanism of side crack is tensile failure. A semiempirical and semitheoretical relationship among the side crack length, the drilled rock property, and the drilling force is formulated to approximately predict the side crack length. In the simultaneous loading, the interaction and coalescence of side cracks induced by the neighboring button-bits with an optimum line spacing enable formation of largest rock chips, control of the direction of subsurface cracks and a minimum total specific energy consumption. A formula is derived to determine the optimum line spacing on the basis of the drilled rock properties, the diameter and shape of the button-bit, and the drilling conditions. In the rock fragmentation by multiple button-bits, most of the rock between the neighboring button-bits is chipped as a result of the coalescence of side cracks. In the remaining rock, the intensely crushed zones and significant extensional cracks are observed adjacent to the sidewall and the inside of the borehole. Fragment side distribution shows more than 80% of the fragments are fines in the crushed zones as well as the cracked zones, the large fragments be indeed observed, which are the big chips caused by the coalescence of side cracks.     

In Situ Measurement of Nonlinear Shear Modulus of Silty Soil

A new field test method to evaluate in situ nonlinear shear modulus of soils was developed. The method utilizes a drilled shaft as a cylindrical, axisymmetric source for shear loading of soil at depth. The applicability of the test method was studied by conducting small-scale, prototype experiments at a “calibration” field site in Austin, Texas. Numerous conventional in situ and laboratory measurements were performed to characterize the soil at the field site. The “small-scale” nature of the tests involved using a 381?mm (15?in.) diameter, 3.7?m (12?ft) long drilled shaft. Experimental results from this field study provided an opportunity to compare laboratory and field measurements of the G?log?γ and G/Gmax?log?γ curves. This comparison was used to investigate the accuracy of common procedures relating field and laboratory modulus reduction curves. Nonlinear modulus measurements were performed at depths of 1.8?to?2.1?m (6?to?7?ft) in a silt (ML). The field G/Gmax?log?γ curve for this soil at low confining pressures are in general agreement with the laboratory curve from an intact specimen as well as empirical curves.     

Estimating Drilling Parameters for Diamond Bit Drilling Operations Using Artificial Neural Networks

Diamond bit drilling is one of the most widely used and preferable drilling techniques because of its higher rate of penetration and core recovery in the hardest rocks, the ability to drill in any direction with less deviation, and the ability to drill with greater precision in coring and prospecting drilling. Conventional bit analysis techniques include mathematical methods such as specific energy and formation drillability. In this study, artificial neural network (ANN) analysis as opposed to conventional mathematical techniques is used to estimate major drilling parameters for diamond bit drilling, i.e., weight on bit, rotational speed, and bit type. The use of the proposed methodology is demonstrated using an ANN trained with information obtained from 45,000?m of diamond bit drilling operations conducted on several formations and locations in Turkey. The studied formations include shallow carbonates as well as sandstones in the Zonguldak hard coal basin. The neural network results are compared to those obtained from conventional methods such as specific energy analysis. It was observed that the proposed methodology provided satisfactory results both in relatively less documented and drilled formations as well as in well-known formations.     

Numerical Study of an Integral Abutment Bridge Supported on Drilled Shafts

The majority of integral abutment bridges (IABs) in the United States are supported on steel H-piles to provide the flexibility necessary to minimize the attraction of large lateral loads to the foundation and abutment. In Hawaii, steel H-piles have to be imported, corrosion tends to be severe in the middle of the Pacific Ocean, and the low buckling capacity of steel H-piles in scour-susceptible soils has led to a preference for the use of concrete deep foundations. A drilled shaft-supported IAB was instrumented to study its behavior during and after construction over a 45-month period. This same IAB was studied using the finite-element method (FEM) in both two- (2D) and three dimensional (3D). The 3D FEM yields larger overall pile curvature and moments than 2D because in 3D, the high plasticity soil is able to displace in between the drilled shafts thereby “dragging” the shafts to a more highly curved profile while soil flow is restricted by plane strain beam elements in 2D. Measured drilled shaft axial loads were higher than the FEM values mainly due to differences between the assumed and actual axial stiffness and to a lesser extent on concrete creep in the drilled shafts and uneven distribution of loads among drilled shafts. Numerical simulations of thermal and stream loadings were also performed on this IAB.     

Side Resistance In Piles and Drilled Shafts

More than 20 years have passed since a Terzaghi Lecture focused on the topic of deep foundations. However, considerable research has been performed, and experience gained, in this subject area in the intervening period. The objective of this paper is to update the earlier references on deep foundations by summarizing results of important recent research on a few aspects of the topic of side resistance, most notably (1) driven piles in saturated clay, (2) driven piles in siliceous sand loaded in compression and uplift, (3) drilled shafts in clay, and (4) drilled shafts in soft rock. It is concluded that, while simple design relations are available for topic (1), much is still to be learned. Under topic (2), the case is made that loading the pile in compression and uplift produces different values of unit side-shearing resistance. Regarding topics (3) and (4), the effects of details related to construction—such as stress relief, moisture migration from the concrete to the geomaterial, borehole roughness, and borehole smear—are shown to be significant. The final point made is that the design of deep foundations is a complex matter that should be addressed in a design context by engineers who are experienced in the observation of pile behavior, theoretical modeling, and the appropriate use of design methods.     

Process versus Data Oriented Techniques in Pile Construction Productivity Assessment

A large number of problems faces the installation of pile (drilled shaft) foundations: unseen subsurface obstacles, lack of contractor experience, site planning, etc. These problems make it difficult for the estimator to assess the pile construction productivity and cost. Several techniques might be good candidates for this assessment problem. A fundamental question arises: which technique is the most appropriate to solve this assessment problem? This study focuses on answering this fundamental research question. Data were collected through designed questionnaires, site interviews, and telephone calls to experts in different construction companies. Four different techniques were listed as candidates to solve this problem: deterministic, simulation, multiple regression, and artificial neural network (ANN). They were categorized into two groups: process oriented techniques, deterministic and simulation; and data oriented techniques (DOT), regression and ANN. All techniques were used to assess productivity and cost of pile construction. Their results were compared to determine the closest assessment to real world practice. Research results show that the DOT techniques were the most appropriate whereas they had the lowest deviation from real world practice.     

Experimental Investigation and optimization of Process Parameters for Shear Strength of Compound Cast Bimetallic Joints

Joining of A356 alloy and magnesium was carried out by vacuum assisted sand mold compound casting process. Microstructure at the joint interface was studied by using optical microscope, scanning electron microscope, energy dispersive X-ray spectroscopy and X-ray diffractometer. Characterization indicated that a relatively uniform joint interface was obtained. The joint interface was composed of three distinct layers containing Mg₂Al₃ on aluminum side, Mg₁₇Al₁₂?+?δ eutectic structure on magnesium side and Mg₁₇Al₁₂ as middle layer. As a result of interaction between silicon, present in A356 with magnesium, Mg₂Si compound was formed. Push out test was conducted on electronics universal testing machine to measure the shear strength across the joint interface. The important process parameters (grit size of sand paper, insert temperature, pouring temperature and vacuum pressure) were optimized to maximize the shear strength. Optimization was carried out by using response surface methodology, desirability analysis and genetic algorithm (GA) techniques. It was observed that the shear strength increased by 14.21, 8.60 and 4.80% with genetic algorithm, desirability analysis and regression model respectively. GA reported the optimal value of shear strength.     

Rheology of pyrite slurry and its dispersant for the biooxidation process

Rheology of slurry significantly influenced the grindability, fine grinding performance and energy consumption of industrial minerals in wet grinding. The solid concentration, particle size, temperature and the dispersant, which affected the rheological characteristics of pyrite slurry and the biooxidation process were investigated in this study. This research aimed at the wet grinding process improved by the control of slurry rheology and getting a biocompatible dispersant.The results revealed that the viscosity increased with the solid concentration, which was in agreement with the Chong model. There was a critical concentration (40 wt.%) that led to the flow behavior of slurry transformed from Newtonian fluids to shear-thinning non-Newtonian fluids which fitted to the Casson model. It was also found that the apparent viscosity of slurry increased with the decrease of the particle size and the temperature at high solid concentration.Sodium Hexametaphosphate (SH) was selected experimentally as an effective dispersant for the mineral slurry. The appropriate concentration of SH was also determined at the range from 0.005 wt.% to 0.05 wt.%. The addition of dispersants could reduce the viscosity and yield stress, increase the zeta potential (ζ) of suspension pronouncedly. No negative effects on the growth rate of microorganisms and the pyrite biooxidation were observed. Therefore, dispersant separation and recovery process could be avoided.     

Survey of Residential Foundation Design Practice on Expansive Soils in the San Francisco Bay Area

The San Francisco Bay Area, California has experienced significant population growth over the last 60 years. The design practices for residential foundations have evolved substantially over this period, as a result of improved geologic characterizations, better engineering understandings of foundation performance, building code changes, and project litigation. The majority of residential foundations are constructed on expansive soils and bedrock, with the primary movement as a result of swell due to wetting of materials in an arid environment. A survey of design practice of practicing geotechnical engineers in the bay area was conducted using a written questionnaire and telephone interviews to compile data regarding the most commonly used design procedures, design details, drainage recommendations, and construction monitoring practices. The results of this survey are compiled and presented in this paper. Three primary foundation systems were identified in the survey as being commonly used in the bay area—rigid footing grids, drilled piers, and mats/slabs. To illustrate problems that have occurred with each of these foundation systems, case histories are presented for recent bay area expansive soil projects for each of these three foundation types.     

Analytical Method for Load-Transfer Characteristics of Rock-Socketed Drilled Shafts

The load-settlement behavior of rock-socketed drilled shafts under axial loading is investigated by a load-transfer approach. Special attention is given to the shear load-transfer function and an analytical method for estimating load-transfer characteristics of rock-socketed drilled shafts. A nonlinear triple curve is employed to determine the shear load-transfer function of rock-socketed drilled shafts based on the constant normal stiffness direct shear tests and the Hoek-Brown failure criterion. An analytical method that takes into account the soil coupling effect was developed using a modified Mindlin’s point load solution. Through comparisons with field case studies, it is found that the proposed methodology in the present study is in good agreement with the general trend observed by in situ measurements and, thus, represents a significant improvement in the prediction of drilled shaft shear behavior.     

Drilled Shaft Defects: Detection, and Effects on Capacity in Varved Clay

This paper presents the results of nondestructive integrity tests (NDTs) and axial static load tests on drilled shafts constructed in varved clay at the National Geotechnical Experimentation Site in Amherst, Mass. The shafts were constructed with built-in defects to study: (1) the effectiveness of conventional NDT methods in detecting construction defects and (2) the effect of defects on the capacity of drilled shafts. Defects included voids and soil inclusions occupying 5–45% of the cross section as well as a soft bottom. Nine organizations participated in a blind defect prediction symposium, using a variety of NDT techniques. Most participants located defects that were larger than 10% of the cross sectional area. However, false positives and inability to locate smaller defects and multiple defects in the same shaft were encountered. Static load tests indicated that (1) minor defects had little or no effect on skin friction; (2) a soft bottom resulted in a 33% reduction in end bearing relative to a sound bottom; and (3) reloading resulted in a 20–30% reduction in the geotechnical capacity.     

新型纳米水泥护壁堵漏材料在刚果(金)钻探中的应用

刚果(金)钻探项目位于加丹加铜钴矿带上,该带地质构造强烈,岩石风化和破碎程度普遍较高,不利于钻孔的施工.某钻孔在施工时遇到破碎段,需要进行水泥封固,采用常规水泥工艺封固失败,本次采用了新的纳米水泥护壁堵漏材料进行护壁堵漏后取得了成功;与常规水泥封孔相比,其候凝时间由之前的7天缩短至36小时,大大提高了工程进度,降低了勘...     

Field Behavior of an Integral Abutment Bridge Supported on Drilled Shafts

The abutments of integral bridges are traditionally supported on a single row of steel-H-piles that are flexible and that are able to accommodate lateral deflections well. In Hawaii, steel-H-piles have to be imported, corrosion tends to be severe in the middle of the Pacific Ocean, and the low buckling capacity of steel-H-piles in scour-susceptible soils has led to a preference for the use of drilled shaft foundations. A drilled shaft-supported integral abutment bridge was monitored from foundation installation to in-service behavior. Strain gauge data indicate that drilled shaft foundations worked well for this integral bridge. After 45 months, the drilled shafts appear to remain uncracked. However, inclinometer readings provide a conflicting viewpoint. Full passive earth pressures never developed behind the abutments as a result of temperature loading because thermal movements were small and the long term movements were dominated by concrete creep and shrinkage of the superstructure that pulled the abutments towards the stream. In the stream, hydrodynamic loading during the wet season had a greater effect on the abutment movements than seasonal temperature cycling. After becoming integral, the upright members of the longitudinal bridge frame were not vertical because the excavation and backfilling process caused deep seated movements of the underlying clay resulting in the drilled shafts bellying out towards the stream. This indicates the importance and need for staged construction analysis in design of integral bridges in highly plastic clays. Also, the drilled shaft axial loads from strain gauges are larger than expected.     

三山岛北部海域金矿海上钻探施工关键技术

海上钻探施工离不开钻探平台的支撑。三山岛北部海域金矿钻探施工采用山东省第三地质矿产勘查院自主研发的海上钻探平台,目前已完成钻探工作量达12万米,最大钻孔深度达1 973.46 m,在海域岩金勘查领域具有重要意义。结合海上钻探工程实施情况,介绍了钻探平台的安装和拆卸作业,并重点对钻孔结构、钻进方法、金刚石钻进参数及冲洗液等工艺技术进行了系统研究,提出确保钻探工程顺利实施的若干质量保证措施,形成了一套完整的适用于浅海海域固体矿产勘查钻探工程的技术方案,为类似浅海钻探项目提供一定的技术参考。     

Drillability Studies of E-Glass: Polyurethane Foam: Vinyl Ester Sandwich Composites

The present work is concerned with the effect of drilling parameters such as cutting force, torque, speed, feed rate on the quality of drilled holes of polyurethane foam-E-glass-vinyl ester sandwich composite structure. The quality of the drilled hole is critical to the life of the fasteners in sandwich structures. The sandwich structures are subjected to drilling, using HSS drill bits with different diameters of 3, 4, 5 and 8 mm at various cutting speeds of 550, 920, 1470 and 2300 rpm and the feed rates of 0.011, 0.022, 0.032 and 0.045 mm/rev using pillar sensitive drilling machine with the aid of drill tool dynamometer. The experiment revealed that the thrust force is influenced by the diameter and the torque by the feed rate. Four different grades of sandwich composites were selected for study and it is observed that at constant speed, the quality of the drilled hole increases with the increase in speed and tends to be poor as the diameter of the hole increases.