Lusu Ni

Development of Pervious Concrete Pile Ground-Improvement Alternative and Behavior under Vertical Loading

Permeable granular columns are used to increase the time rate of consolidation, reduce liquefaction potential, improve bearing capacity, and reduce settlement. However, their behavior depends on the confinement provided by surrounding soil, which limits their use in very soft clays and silts, and organic and peat soils. This research effort aims to develop a new ground-improvement method using pervious concrete piles. Pervious concrete piles provide higher stiffness and strength that are independent of surrounding soil confinement while offering permeability comparable to granular columns. This proposed ground-improvement method can improve the performance of different structures supported on poor soils. To achieve the goal of the research project, four vertical load tests were performed on one granular column and three pervious concrete piles. In this paper, the material properties of pervious concrete, the developed installation method, and the vertical load response of pervious concrete and aggregate piles are presented, and the variation of soil stresses and displacement during pile installation are briefly discussed. The experimental test results show that the ultimate load capacity of the pervious concrete pile was 4.4 times greater than that of an identical granular column. In addition, the ultimate load capacity of a pervious concrete pile installed using the developed technique was 2.6 times greater than a precast pervious concrete pile. The used installation method created nonuniform lateral soil displacement and increased vertical and horizontal soil stresses.

Soil-Pile Interaction for a Small Diameter Pile Embedded in Granular Soil Subjected to Passive Loading

AbstractThe soil-structure interaction of piles used to stabilize failing slopes (i.e., subjected to lateral soil movement known as passive piles) was experimentally investigated using a state-of-the-art soil-structure interaction facility. A 102-mm diameter, 1.58-m-long precast concrete pile was installed in well-graded sand. The pile was instrumented with displacement and tilt gauges at the pile head and strain gauges, a flexible shape acceleration array, and thin tactile pressure sheets along the pile length. Furthermore, the three-dimensional (3D) movements of the soil surface and the top of the pile were monitored using two stereo digital image correlation (DIC) systems. By monitoring the relative movement of the soil surface and pile top, the DIC systems track the progression of the soil-pile interaction that occurs as the lateral displacement of the soil increases. The use of advanced sensors allows simultaneous measurement of the pile lateral movement and the soil-pile interaction pressures along ...

Behavior and Soil–Structure Interaction of Pervious Concrete Ground-Improvement Piles under Lateral Loading

AbstractGranular column ground-improvement methods are widely used to improve bearing capacity and provide a drainage path. However, the behavior of granular columns depends on the confinement provided by the surrounding soil, which limits their use in poor soils. A new ground-improvement method is proposed using pervious concrete piles to provide high permeability while also providing higher stiffness and strength, which are independent of surrounding soil confinement. Building on prior research on the behavior of vertically loaded pervious concrete piles and granular columns, this paper investigates the behavior of laterally-loaded pervious concrete piles and the effects of installation on their response. Two fully-instrumented lateral load tests were conducted on a precast and cast-in-place pile using different installation methods. Advanced sensors measured the soil–structure interaction during installation and under lateral loading. Test results confirmed that laterally-loaded pervious concrete groun...

Installation Effects of Controlled Modulus Column Ground Improvement Piles on Surrounding Soil

AbstractThe installation of foundations and ground improvement systems alters soil stresses affecting their soil-structure interaction and behavior under vertical loading. The installation effects have been investigated for several foundation types, especially for driven piles; however, experimental full-scale investigations of drilled displacement piles are very limited. This paper focuses on investigating the short-term installation effects of controlled modulus columns (CMCs) using an instrumented full-scale field test unit. The soil was instrumented using push-in pressure sensors (PS) and shape acceleration arrays (SAAs) to monitor the evolution of soil horizontal stresses, pore water pressures, and lateral displacements during installation and vertical load test. These sensors were installed at approximately 1D, 2D, 3D, and 4D from the outside surface of the CMC shaft, where D is the diameter of the CMC. The measurements presented in this paper clearly show that the soil experienced an increase of ho...

Discussion of “Interaction between Laterally Loaded Pile and Surrounding Soil” by Hai Lin, Lusu Ni, Muhannad T. Suleiman, and Anne Raich

First of all, the discussers would like to congratulate the authors for producing a significant amount of good quality data, always useful for checking assumptions and methods. In particular, the use of tactile pressure sheets, despite some shortcomings, opens new possibilities for measurements of stresses in some special conditions and applications. However, a number of points in the paper need further clarification and/or complementation, as stated as follows: 1. Concerning the Broms’s (1964) method in the case of sands, it is said in the paper that it assumes that the pile rotates around its tip and the ultimate soil pressure equals three times the passive pressure. This is not strictly true. In fact, Broms (1964) clearly indicates (Fig. 1) that the center of rotation is not at the toe of the pile. Broms (1964, p. 137) says that “Failure takes place when the pile rotates as a unit around a point located below the ground surface.” Also, “high negative earth pressures develop close to the toe of the laterally loaded pile and it has been assumed for the purpose of analysis that this pressure can be replaced by a concentrated load as shown in Fig. 5(b)” (Fig. 2). In other words, Broms did not assume that the pile rotates around its toe, this was a simplification to derive a simple solution. 2. The authors claimed the measurement of circumferential stresses for the first time. Although their contribution is very significant because they have made a detailed picture of those stresses, reference should have been made to Bierschwale et al. (1981), who measured the stresses around the periphery of a drilled shaft, 915 mm in diameter and 4.6 m in length, embedded into a predominantly clay soil. In addition to installing cells in the vertical direction, three total stress cells were placed in

The Effects of Pile Installation on Vertical and Lateral Response

Pile installation affects the soil-pile interaction and influences the pile behaviors under different loading conditions. Most studies in the literature focus on analytical methods to evaluate the effects of pile installation. Few researches have used experimental approaches to investigate the pile installation effects, especially for piles under lateral load. This research focuses on experimentally investigating the effects of pile installation on the response of pile under vertical and lateral loads. Using the Soil-Structure Interaction (SSI) facility, four laboratory-scale tests have been performed (two vertical load tests and two lateral load tests). The piles were made of pervious concrete with a diameter of 102 mm (4 in). The two piles in vertical load tests have same embedded length of 1,219 mm (48 in) and piles for lateral load test have embedded length of 1,321 mm (52 in). Two installation methods (referred to as precast and installed) were used as part of the experimental program. Precast piles were prefabricated and the soil was placed around them. Installed piles were constructed using a specially designed mandrel system. The load and displacement were measured during the tests. The load-displacement relationships of pervious concrete pile are compared and the effects of the installation method on pile behavior are discussed in this paper.

Pervious Concrete Pile: An Innovation Ground Improvement Alternative

Granular piers are commonly used to improve the mechanical properties and allow for consolidation and drainage of soft clays, silts, and loose sands. The response of granular piers; however, depends on confining stress provided by the surrounding soil, which limits their use in very soft clays, silts, and organic and peat soils. If a material has higher stiffness and strength with properties independent of surrounding soil, and adequate permeability, it will be more suitable to improve sites with poor soil conditions. This research focuses on developing an innovative ground improvement method using pervious concrete piles. A series of laboratory tests were conducted to evaluate the properties of pervious concrete material. Furthermore, large-scale vertical load tests have been conducted to compare the response of a granular pier with a pervious concrete pile and to compare the response of pervious concrete piles installed using two different methods (one with precast pile and the other using a method simulating in-situ or field installation techniques). This paper summarizes the results of the material tests and the preliminary vertical load tests.

Measured Soil-Pile Interaction for Small Diameter Piles Embedded in Granular Soil Subjected to Lateral Soil Movement

This paper presents the experimental data collected in an attempt to directly measure the soil-pile interaction for fully-instrumented passive pile. The fully-instrumented pile was installed in loose well-graded sand and was subjected to lateral soil movement. A precast concrete pile, with a 101.6 mm diameter and 1.581 m long, was reinforced with one No. 4 rebar (diameter = 12.7 mm) located at the center of the pile cross-section. The pile was installed in soil using a stacked soil box configuration. To subject the pile to a lateral soil movement, the top soil box was pushed laterally relative to the bottom soil box. Advanced sensors including tactile pressure sensors wrapped around the pile and a flexible shape acceleration array placed along the length of the pile were used to directly measure the soil-pile interaction pressure and the lateral movement along the length of the pile. Instrumentation also included strain gauges placed on the length of the rebar in the pile, a load cell on the top box, displacement and tilt gauges at the top of the pile. A digital image correlation system was used to monitor the displacement of the soil surface, the soil box and the top of the pile during the test. The paper also describes the details of the test setup and instrumentation, installation procedure, and soil properties. The test results indicate that using the digital image correlation system in combination with other instrumentation, especially the sheet pressure sensors, 135 GeoCongress 2012