Kyle M. Rollins

Liquefaction Mitigation Using Stone Columns Around Deep Foundations: Full-Scale Test Results

The results presented were developed as part of a larger project analyzing the behavior of full-scale laterally loaded piles in liquefied soil, the first full-scale testing of its kind. Presented here are the results of a series of full-scale tests performed on deep foundations in liquefiable sand, both before and after ground improvement, in which controlled blasting was used to liquefy the soil surrounding the foundations. Data were collected showing the behavior of laterally loaded piles before and after liquefaction. After the installation of stone columns, the tests were repeated. From the results of these tests, it can be concluded that the installation of stone columns can significantly increase the density of the improved ground as indicated by the cone penetration test. Furthermore, it was found that the stone column installation limited the excess pore pressure increase from the controlled blasting and substantially increased the rate of excess pore pressure dissipation. Finally, the stone columns were found to significantly increase the stiffness of the foundation system by more than 2.5 to 3.5 times that in the liquefied soil. This study provides some of the first full-scale quantitative results on the improvement of foundation performance due to stone columns in a liquefiable deposit.

Dynamic Compaction of Collapsible Soils Based on U.S. Case Histories

Dynamic compaction (DC) is an economical approach for mitigating the hazard posed by collapsible soils particularly when they are deeper than 3–4 m. In this paper, case histories are provided for 15 projects at 10 locations in the United States where collapsible soils were treated with DC. For each site the soil properties, compaction procedures, and subsequent improvement are summarized. Although cohesionless and low-plasticity collapsible soils were successfully compacted, clay layers in the profile appeared to absorb energy and severely reduced compaction effectiveness. Correlations are presented for estimating the maximum depth of improvement, the degree of improvement versus depth, the depth of craters, and the level of vibration based on measurements made at the various sites. The compactive energy per volume was typically higher than for noncollapsible soils because collapsible soils are usually loose but relatively stiff. The maximum depth of improvement was similar to that for noncollapsible soils; however, significant scatter was observed about the best-fit line. Improvement was nonuniform with nearly 80% of the total improvement occurring within the top 60% of the improvement zone. The crater depth was related to a number of factors besides the drop energy including the number of drops, drop spacing, and contact pressure. The peak particle velocities were typically lower than those for noncollapsible soils at shorter distances, but the vibrations attenuated more slowly with distance.

Soil–pile separation effect on the performance of a pile group under static and dynamic lateral loads

The effect of soil–pile separation is studied with respect to the performance of a laterally loaded pile group. Full-scale tests, which consist of a combination of a single and a 3 × 5 group pile under static and dynamic lateral loads, present a unique opportunity and allow a rigorous study without arbitrary parameter back-fitting. The coupled soil–pile system is idealized through two-dimensional finite elements with soil models idealized by a hyperbolic-type multiple shear mechanism. Nonlinear spring elements are used to idealize the soil–pile interaction through a hysteretic nonlinear load–displacement relationship. Joint elements with a separation–contact mechanism are used to idealize the separation effect at the soil–pile interface. Ignoring soil–pile separation in static tests overestimates the ultimate lateral load–carrying capacity by 43% for a single pile and 73% for the trailing pile in a closely spaced pile group. Moreover, neglecting soil–pile separation in dynamic tests overestimates the tota...

Vertical loads effect on the lateral pile group resistance in sand

Vertical loads effect on the lateral response of a 3×5 pile group embedded in sand is studied through a two-dimensional finite element analysis. The soil-pile interaction in three-dimensional type is idealized in the two-dimensional analysis using soil-pile interaction springs with a hysteretic nonlinear load displacement relationship. Vertical loads inducing a vertical pile head displacement of 0.1-pile diameter increase the lateral resistance of the single pile at a 60 mm lateral deflection by 8%. Vertical loads inducing the same vertical displacement applied to a pile group spaced at 3.92-pile diameter increase the overall lateral resistance by 9%. The effect on individual piles, however, depends on the pile position. The vertical load decreases the lateral resistance of the leading pile (pile 1) by 10% and increases the lateral resistances of piles 2, 3, 4, and 5 by 9%, 14%, 17%, and 35%, respectively. Vertical loads applied to the pile group increase the confining pressures in the sand deposit confined by the piles but the rate of increase in those outside the group is relatively small, resulting in the difference in a balance of lateral soil pressures acting at the back of and in front of the individual pile.

Measured Pile Setup During Load Testing and Production Piling: I-15 Corridor Reconstruction Project in Salt Lake City, Utah

As part of the I-15 Corridor Reconstruction Project through downtown Salt Lake City, nine sets of full-scale load tests were performed at locations selected as representative of the subsurface conditions along the corridor alignment. Static compression, uplift, and lateral load tests were conducted at each test site location. The test program included dynamic monitoring of pile installation and restrike events using high-strain testing and analysis methods. Dynamic test results from restrike events on companion piles compared well with the measured static axial compression load test capacities. Subsurface conditions along the alignment range from deep clays to dense alluvial sands above the groundwater table. The piles derive their support from shaft friction or a combination of shaft friction and endbearing, depending on the strata present. The test and subsequent production piles are consistently indicating large capacity gains with time (setup), regardless of the subsurface conditions. The setup in the soft to stiff lakebed clays is attributed to remolding of the clays during pile driving and subsequent reconsolidation. The setup in the dense sands is comparable with setup described by others in dense marine sands. Relationships were developed to predict long-term pile capacity based on dynamic test results from the end of installation and on data from the beginning of restrike. These relationships are being used during production pile installation and restrike events as an integral part of pile evaluation, troubleshooting, and quality control/quality assurance acceptance procedures.

Passive Force-Deflection Curves for Skewed Abutments

The passive force-deflection relationship for abutment walls is important for bridges subjected to thermal expansion and seismic forces, but no test results have been available for skewed abutments. To determine the influence of skew angle on the development of passive force, laboratory tests were performed on a wall with skew angles of 0, 15, 30, and 45°. The wall was 1.26 m wide and 0.61 m high, and the backfill consisted of dense compacted sand. As the skew angle increased, the passive force decreased substantially, with a reduction of 50% at a skew of 30°. An adjustment factor was developed to account for the reduced capacity as a function of skew angle. The shape of the passive force-deflection curve leading to the peak force transitioned from a hyperbolic shape to a more bilinear shape as the skew angle increased. However, the horizontal displacement necessary to develop the peak passive force was still between 2 and 4% of the wall height. In all cases, the passive force decreased after the peak value, which would be expected for dense sand; however, at higher skew angles, the drop in resistance was more abrupt. The residual passive force was typically 40% lower than the peak force. For nearly all skew angles, the transverse shear resistance exceeded the applied shear force on the wall so that transverse movement was minimal. Computer models using the plane strain friction angle were able to match the measured force for the no skew case as well as for skewed cases when the proposed adjustment factor was used.

Effects of Ground Failure on Buildings, Ports, and Industrial Facilities

Soil liquefaction occurred at many sites during the 2010 Maule, Chile, earthquake, often leading to ground failure and lateral spreading. Of particular interest are the effects of liquefaction on built infrastructure. Several buildings were damaged significantly due to foundation movements resulting from liquefaction. Liquefaction-induced ground failure also displaced and distorted waterfront structures, which adversely impacted the operation of some of Chiles key port facilities. Important case histories that document the effects of ground failure on buildings, ports, and industrial facilities are presented in this paper.

Effects of Ground Failure on Bridges, Roads, and Railroads

The long duration and strong velocity content of the motions produced by the 27 February 2010 Maule earthquake resulted in widespread liquefaction and lateral spreading in several urban and other regions of Chile. In particular, critical lifeline structures such as bridges, roadway embankments, and railroads were damaged by ground shaking and ground failure. This paper describes the effects that ground failure had on a number of bridges, roadway embankments, and railroads during this major earthquake.

Simplified Hybrid p-y Spring Model for Liquefied Soils

AbstractThe beam-on-Winkler foundation (BWF) method is a popular analysis approach for computing the lateral pile response resulting from both inertial and kinematic loading. However, there is significant uncertainty regarding how to properly represent the load-resistance (i.e., p-y) behavior of liquefied soils. This confusion stems from the significant variability observed with the phenomenon and the large number of p-y spring models for liquefied soils that have attempted to account for that variability. In an attempt to develop a practical but broadly applicable approach, a simplified hybrid p-y spring model is presented. This hybrid model incorporates aspects of existing p-y spring models for liquefied soil and is applicable to a wide range of soil types, relative densities, pile/shaft diameters, and loading conditions. Comparisons with a variety of published case histories involving single piles indicate that the hybrid p-y spring model provides reasonable estimates of response for both kinematic and...

Comparison of Deep Foundation Performance in Improved and Non-Improved Ground Using Blast-Induced Liquefaction

The results presented in this paper were developed as part of a larger project analyzing the behavior of full-scale laterally loaded piles in liquefied soil, the first full-scale testing of its kind. This paper presents the results of a series of full-scale tests performed on deep foundations in liquefiable sand, both before and after ground improvement, where controlled blasting was used to liquefy the soil surrounding the foundations. Data were collected showing the behavior of laterally loaded piles before and after liquefaction. After the installation of stone columns, the tests were repeated. Based on the results of these tests, it can be concluded that the installation of stone columns can significantly increase the density of the improved ground as indicated by the cone penetration test. The stone columns were found to significantly increase the stiffness of the foundation system, by more than 2.5 to 3.5 times that in the liquefied soil. However, in non-liquefied ground, the improvement from stone columns could be more than compensated for by increasing the piles. In liquefied soil, however, more than doubling the number of piles or increasing shafts diameters by 50 percent did not nearly match the improved performance of the treated ground. This study provides some of the first full-scale quantitative results on the improvement of foundation performance due to stone columns in a liquefiable deposit.