Yunhan Huang

Installation through fresh cement–clay and uplift after curing require distinct resistance descriptions for premixed helical rigid-core composite piles (PHRCP). We develop a semi-analytical framework combining geometry-strength kernels, identifiable effective parameters, and transparent reference-to-target elimination. Installation and service components are calibrated separately. Model tests included one PHRCP and one ordinary helical pile (HP) at each helix diameter, 66 and 110 mm. PHRCP reduced depth-averaged torque by 34.0% and 32.2% and thrust by 41.7% and 61.8%; measured uplift capacity increased by 136% and 51%. Thrust comparisons are conditional on adopted channel corrections. Coefficients and enlargement δ = 46.6 mm identified at 66 mm were frozen at 110 mm. The transferred diameter was 186.6 mm (−1.4% against the post-test mean); the conditional external-envelope-based capacity estimate was 1896.5 N versus 1792.4 N measured (+5.8%). HP capacity was underestimated by 19.3%, while installation peak agreement did not ensure curve reproduction. Target observations informed model-form selection, so the assessment is a retrospective parameter-transfer check. The formulation makes geometric dependencies and calibration limitations explicit. Single specimens, uncertain strength calibration, post-test geometry, and unverified failure assumptions preclude general predictive or field reliability claims.

Recent studies have demonstrated that installation-induced soil disturbance, advancement ratio, and installation rate can substantially affect the subsequent axial response of helical piles. However, systematic experimental comparisons that simultaneously relate installation torque, axial thrust, and post-installation uplift capacity across multiple geometric and operational variables in clay remain limited. This study investigated the coupled effects of helix pitch, advancement ratio, penetration speed, and shaft style on the installation and uplift behavior of helical anchors in prepared clay. Laboratory model tests were conducted using grouped anchor configurations, and installation torque, installation thrust, and uplift load–depth responses were recorded. An area method was introduced to quantify accumulated installation resistance from torque–depth and thrust–depth curves. Within the tested fixed-advancement-ratio pitch series, the tested pitch–speed combinations produced comparatively moderate variations in installation resistance and uplift capacity when the helix plate diameter was fixed. The installation condition represented by the advancement ratio and corresponding penetration speed influenced penetration–rotation compatibility: lower advancement ratios increased repeated shearing and torque, whereas higher advancement ratios reduced torque but increased thrust. Increasing penetration speed markedly increased accumulated torque but reduced ultimate uplift capacity from 478 N to 315 N. The shaft-style tests showed differences in plugging, suction, and local penetration resistance, with limited variation in helical-anchor uplift capacity. These findings indicate that installation parameters and geometric configuration should be considered together when optimizing helical-anchor installation in clay. The findings provide model-scale references for selecting helical-anchor geometry and installation procedures in prepared kaolin clay under conditions comparable to those tested.

In response to the issue of the size effect of helical anchors in deep-sea areas on their uplift bearing capacity, this study was proposed based on the ratio of the anchor shaft diameter to the anchor helix diameter and the ratio of the pitch to the anchor helix diameter. Eight sets of small-scale anchors were designed for laboratory model tests to study the impact of different anchor shaft diameters to anchor helix diameter ratios and the ratio of the pitch to the anchor helix diameter on uplift bearing capacity. The results indicate that smaller ratios of the anchor shaft diameter to the anchor helix diameter and the pitch to the anchor helix diameter can improve the uplift bearing capacity of helical anchors. In addition, this study found that the uplift bearing capacity of helical anchors decreased with the increase in the ratio of the anchor diameter to the anchor helix diameter and the ratio of the pitch to the anchor helix diameter. Based on this, a prediction equation for the uplift bearing capacity of helical anchors was proposed.

Bilateral helix-stiffened cement mixing piles (BHCMPs) are a new type of robust composite pile. In this paper, the influence of design parameters, such as the diameter of inner helix plates and the number and size of outer mixing helix plates, on the vertical bearing performance of the pile foundation and the behavior of the pile diameter are investigated through laboratory model tests. The results indicate that incorporating a reverse-mixing process in the pile formation of helix-stiffened cement mixing piles can enhance the overall ultimate bearing capacity and strengthen the soil-cement of the piles. In the case of the same double-blade inner drill pipe, for every 22 mm increase in the blades, its ultimate compressive load-bearing capacity was increased by 10% to 25%, and its pullout load-bearing capacity was increased by 15% to 45%. With further increases in the blades, the percentage increase in the compressive and pullout load-bearing capacity was reduced. With an increase in the number of external mixing blades, its compressive load capacity increased in the range of 5% to 20%, and the elevation load capacity increased in the range of 10% to 25%. Increasing the number of reverse-mixing helix plates on the outer casing enhances the soil-cement strength of the pile body by approximately 15–20% for each additional plate. The average strength of the pile-body soil-cement for each additional plate is estimated to be 1 to 1.4 times that of the previous set, indicating that increased mixing iterations can enhance the perimeter soil-cement strength of the pile. The average bond diameter of soil-cement piles with double-blade internal drilling rods could be seen from the diameter of the piles formed, which was 1.02 to 1.21 times the diameter of the blades.

The aim of this paper is to understand the formation mechanism of and establish a predictive model for payment issues faced by contractors in China’s construction industry. Factors critical to such issues were first identified under different categories from literature and verified by a Delphi survey. This paper identified critical factors under three categories, i.e., culture, client’s financial management, and interactions and processes. A focus group was then conducted to understand the roles played by each category of factors. Specifically, the cultural factors explained the origination of payment. By taking an analogy, the current unhealthy culture acted as pathogens of payment issues as a disease in the body of the construction industry; the financial management capability of the client acted as the defense system; and the interactive and process factors played the role as trigger and catalyst. It was followed by a logical deduction assisted by another Delphi survey to understand the associations among the identified factors. The model structure was hence constructed upon the factors and their associations and was then quantified by Bayesian belief network parameter learning with quantitative data collected from a questionnaire survey. As such, the formation mechanism of payment issues was investigated, based on which a Bayesian classifier was established from the perspective of Chinese contractors. The model demonstrated a high accuracy rate of more than 90%. This paper systematically investigated the formation mechanism of payment issues in China’s construction industry and revealed that root causes of payment issues could not be eliminated in a short term. The predictive model endows contractors with advantages in proactively evaluating if they are capable of tackling the risks of potential payment issues without disturbing the current power balance of the industry.