1 Hammers Impact Force on Pile and Piles Penetration Ji-Cheng Wang Institute of Architectural Engineering, Ningbo University of Technology, Ningbo, Zhejiang, China Jianlin Yu College of Civil Engineering and Architecture, Zhejiang University, Hangzhou, China Ma Shiguo Ningbo Urban Construction Investment Holding Company Limited, Ningbo, Zhejiang, China Xiaonan Gong College of Civil Engineering and Architecture, Zhejiang University, Hangzhou, China Address correspondence to Ji-Cheng Wang, No. 201, Fenghua Road, Jiangbei District, Ningbo, Zhejiang 315211, China. E-mail: wjc1818zju.edu.cn Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/wifa. Abstract Methods of energy and momentum conservation, vibration theories, and model tests are employed to research into impact force of hammer on pile and piles penetration Analytical formula of impact force of hammer on pile is obtained. Comparison of results from the three methods finds that the analytical formula proposed by this paper conforms well to practical situations. Research results Downloaded by Jicheng WANG at 21:22 29 May 2015 M a r i n e G e o r e s o u r c e s Impact force the pile head receives degrades with the increase of hammer weight but increases with the increase of cushion stiffness; Impact time decreases with the increase of cushion stiffness but increases with the increase of hammer weight. Model test shows that, compared with cotton cloth cushion, elastic cushions advantages lie in that relatively small pile head impact force can achieve big pile penetration, and cotton cloth is gradually compacted with the increase of blow counts, hence impact force the pile head receives tends to increase gradually. Keywords INTRODUCTION Hammer piling is simple and economical, and has a great penetrability, hence is widely used. However, hammers impact force on pile is usually very big, thus causing damage to pile head. Besides, hammer weight selection is generally empirical. Hammers impact force on pile is usually calculated through pile driving formula, which are deduced from laws of energy and momentum conservation together with empirical parameters as energy utilization efficiency, coefficient of restitution, etc., such as the widely used Hiley (1925) Formula. Smiths (1960) model used lumped mass as hammer, and used weightless spring as anvil cushion. Helmet and cap cushion were all regarded as part of the pile. Wave equation analysis was used to simulate dynamic response of pile driving (Smith 1960). Rausche, Goble, and Likins (1985) proposed a pile driving dynamic model which was more complex than Smiths (Rausche, Goble, and Likins 1985). Deeks and Randolph (1990, 1991, 1993) built a model comprising piling hammer, anvil cushion, and helmet which was directly attached to pile top and proposed analytical solutions to this model Downloaded by Jicheng WANG at 21:22 29 May 2015 3 considering anvil cushions elasticity and viscoelasticity (Randolph, Banerjee, and Buttefield 1991; Deeks and Randolph 1993, 1995). Koten (1991) researched into a simple hammering model comprising piling hammer and anvil cushion (Koten 1991). Take, Valsangkar, and Randolph (1999) analyzed interaction of piling hammer, anvil cushion, helmet, and cap cushion. The paper used lumped masses for the ram and anvil, a spring for the anvil cushion, and another spring for the cap cushion on the top of a pile. Pile and soil interaction was not considered. Take analyzed blow stress wave on pile top by using mass-spring-dashpot model and numerical computation method (Take, Valsangkar, and Randolph 1999). Runfu and Qing (2000) simplified pile to one dimensional rod and analyzed it by using stress wave solution and proposed a stress solution of pile (Runfu and Qing 2000). Based on one dimensional stress wave theory, Shifang et al. (2003) researched into impact force and penetration by building an interaction model of hammer, pile, and soil and obtained analytical solutions of pile end displacement and velocity (Shifang, Renpeng, and Yunmin 2004). Hehua, Yongjian, and Huaizhong (2004) used different lumped mass for piling hammer and helmet, and parallel spring and dashpot for anvil cushion, and spring for cap cushion, and dashpot for pile, and established an equilibrium equation, and then used the Laplace Transform to deduce analytical solutions of hammering force (Hehua, Yongjian, and Huaizhong 2004; Yongjian et al. 2005). Liyun and Puan (1994) carried out a simulation piling test of small diameter steel pipe pile and concluded that disc spring could improve piling efficiency (Liyun and Puan 1994). Renpeng et al.(2001) monitored pile body stress in piling and obtained relationships among blow count, pile length, and pile bodys maximal stress (Renpeng et al. 2001). Peng-kong and Subrahmanyam (2003) researched into pile driving formula considering pile length factor by using one dimensional wave equation (Peng-kong and Subrah