Shaurav Alam

Evaluation of testing methods for tracking CIPP liners’ life-cycle performance

Abstract Despite the significant investments made in the use of cured-in-place pipe (CIPP) rehabilitation technologies, quality assurance (QA) and quality control (QC) practices can vary widely among municipalities, and CIPP liner evaluations are mostly restricted to periodic CCTV inspections. The information in this paper is derived from a multi-year project funded by the U.S. Environmental Protection Agency (US EPA). The study included a first of its kind retrospective evaluation of retrieved CIPP liners that were in service between 5 and 34 years at 18 different locations. This paper focuses on an assessment of the types of testing that were used during a pilot study to perform the CIPP retrospective evaluation. After performing the suite of tests, both visual inspection and flexural testing were found to be the key QA/QC assessment techniques. However, liners’ specific gravity was also found as a useful QA/QC tool and pursuing several other possibilities for non-destructive or minimally-invasive testing for measuring in situ physical properties of liners appeared feasible.

Soil-binding ability of vegetation roots in enhancing erosion resistance of a shallow slope

Research was undertaken to quantify the root effect of the Johnson grass roots on the resistance increase in resisting surface erosion, in an effort to evaluate soil-binding or anti-erosion ability of the roots. In this study, an innovative means was proposed to evaluate erosion resistance of rooted soils using the traditional slope stability method. The surface erosion was treated as a special slope stability problem on the shallow slip surfaces that are parallel to the slope surface. It was assumed that factors of safety (F.S.) against these shallow slip surfaces are a direct measure of resistance to the surface erosion and the overall slope stability is not our concern. The proposed method to evaluate the surface erosion resistance of rooted soils is simple, straightforward, feasible, and easily implementable. In the research, individual roots in different zones below the slope ground were tested for their tensile strengths, and capabilities to increase shear strength of soil were assessed accordingly. Soil samples with and without roots of the grasses were collected from Ruston, Louisiana. Direct shear tests were conducted to investigate the overall increase in shear strength of the rooted soils. In the slope stability analysis, the anchor reinforcement method (ARM) was developed by considering those individual roots as independent anchor reinforcements. The erosion resistance analyses were performed by utilizing commercial software program Slope/W to evaluate the grass soil-binding capability following the smeared method (SM) and the ARM. Variations in F.S. were investigated for the specific shallow slip surfaces parallel to the slope surface for the plain soil and root-reinforced soil cases.

Experimental Examination of the Mathematical Model for Predicting the Borehole Pressure during Horizontal Directional Drilling

Predicting the borehole pressure during Horizontal Directional Drilling (HDD) is a significant part of HDD. Borehole stability means that pressure on the bore-face must be less than formation fracture pressure and more than the collapse pressure to avoid fluid losses or borehole breakouts. The proposed research is aimed at an analysis comparison between the mud pressure data collected in the real field and the ones the mathematical model predicted. Then the optimal model will be applied to predict the allowable maximum borehole pressure during HDD. Borehole stability during drilling consists of evaluating the drilling fluid weight to maintain the borehole wall integrity. The tensile failure (hydraulic fracturing) and dog-ear shape breakout are two main failure modes around boreholes during HDD. The cavity expansion model was used to calculate maximum and minimum allowable drilling fluid pressure in a bore. Both 2D and 3D finite element (FE) models of maximum borehole pressure were developed by the Drucker-Prager and Mohr-Coulomb theories using ANSYS Parametric Design Language (APDL) to support the customized parametric study. The result showed the maximum mud pressure closely matched the estimation obtained using the Delft equation in this field experiment for shallow layers within clay. The FE modeling procedure used was able to capture the volumetric compressive behavior of the soil around the borehole.

EXPERIMENTAL EXAMINATION OF SELECTED LIMIT STATES OF STRUCTURAL LINERS AT LOCATIONS OF RING FRACTURE

While designing rehabilitation solution for deteriorated pressurized potable water mains, presence discontinuities in the pipe’s walls must be considered. This experimental work involves investigation of three limit states e.g. flexure, shear and axial that could cause liner instability as a result of internal water pressure and uneven ground movement at a broken location e.g. ring fracture - frequently found in small diameter cast iron pipes suffering from loss of beam support. It is reasonable to assume that natural settlement of the bedding materials has long been completed for pipes that have been buried for many years. Therefore, the differential ground movements induced by frost, moisture changes in ‘reactive’ clays or a nearby excavation causes a transverse fracture on the brittle cast iron pipes. The liner product needs to be able to accommodate such movements, which tend to take the form of flexure, shear or axial displacement. Six testing specimens were prepared (each comprised of two 4 ft long sections of a 70-year old 6 in. ID cast iron pipe) by forming a simulated transverse ring break at their lengthwise middle point and then lining them with a fiber reinforced CIPP liner. For pressurized condition test, three specimens were capped and subjected to three-point flexural, pull, and shear loading using custom-built testing apparatus. In the non-pressurized condition similar steps were followed except the caps were hollow. The behavior of the pipe and the liner was monitored with increased deflection, and geometrical changes in the liners were noted. Strain and stress measurements in the axial and hoop directions within the liner structure at the location of the ring failure were also monitored. Conclusions were made regarding governing failure mechanisms for fiber-reinforced CIPP liners subjected to angular and axial displacement.

ESTIMATING RESIDUAL STRENGTH OF DETERIORATED 96" INTERCEPTOR AND STRENGTH ENHANCEMENT PROVIDED BY LINING METHODS USING COMPUTER MODELING AND FORENSIC INVESTIGATION TOOLS

In 1985¸ the Trinity River Authority of Texas (TRA) completed the construction of Elm Fork Relief Interceptor Segment 1-Aconsisting of 17,200 linear ft of a 96-in. diameter reinforced concrete pipe. A 1999 investigation revealed significant wall losses triggering the installation of a parallel 104-in. pipeline of similar capacity in 2007. In 2008 Espey Consultants were retained by TRA to evaluate different avenues for restoring the structural integrity and functionality of the original pipeline. Their investigation revealed that up to 30% of the wall thickness had been lost to corrosion for the majority of the length of the pipeline, and in some limited sections even greater wall loss, mainly in the crown region. The severe degree of corrosion demonstrated partially deteriorated and limited fully deteriorated pipe condition; however, completely neglecting the contribution of the host pipe resulted in a wall thickness that was likely to compromise the required hydraulic capacity. In an attempt to estimate the remaining structural capacity of the pipe, an extensive forensic engineering investigation was undertaken consisting of mechanical and chemical testing of physical cores taken from the pipe in 1999. Information from laboratory testsalong with information from a laser profiler study of the pipes inner geometrygeotechnical information, ground and surface water loads, and data regarding original design parameters were used to construct a detailed 3-D finite element (FE) model of the in-situ pipe. Structural enhancement provided by two common rehabilitation methods, CIPP and GIPP, was superimposed on the FE model. An extensive parametric study was undertaken to gain insight as to possible contribution of the host pipe in resisting the various external loads and the anticipated structural capacity of the rehabilitated structure.

Experimental Investigation of Pipe Soil Friction Coefficients for Direct Buried PVC Pipes

Soil friction is an important design factor for restrained buried pipes with internal pressure. Utilizing the bedding soil for thrust restraint eliminates the need for thrust blocks and makes pipe installation simpler. A full scale experimental investigation of soil-pipe friction coefficients was performed for an innovative, direct buried, restrained, PVC pipe under controlled laboratory conditions. The experimental work covered a wide range of soil types, over burden pressures and moisture contents. Measurements included force needed to overcome friction between pipe and its surrounding bedding, total pipe movement along its longitudinal axis, rigid body movement, and elongation of pipe under applied axial force. Based on the experimental data, three approaches are proposed for calculating the friction force of a buried restrained PVC pipe installed using the cut-and-cover method. The values reported in this paper are considered conservative and higher friction coefficient values can be anticipated over time due to consolidation and aging of the bedding soil around the pipe.