关于土工试验规范的思考——以三轴CD和高压固结试验为例
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摘要
工程勘察建设中采用土工试验规范指导岩土体测试,但有些试验方案的设计考虑得并不全面,一些处于特殊状态下的土体,需对其测试数据进一步分析,从而获得合适的参数。通过试验研究、数据分析,发现三轴固结排水试验(CD)采用质量差计算排水量大于固结阶段理论排水量,将导致破坏时的最大主应力偏大。随着围压的增加,最大主应力误差增大,建议CD试验固结排水量等于土体质量损失计算出的排水量减去剪切排水量;高压固结试验可获得土体的先期固结压力,对于深层土,需要更大压力下的数据提供曲线的直线部分,数据量的多少也会影响e-lgp曲线的拟合形态。通过层层嵌套式拟合土体稳定变形量随固结压力变化趋势,预测大于3 200 kPa压力段土体的稳定变形量,再结合卡萨格兰德法,为传统试验室配备高压固结仪确定深部土体先期固结压力提供了新的方法。
Laboratory test standards are widely using the geotechnical investigation for various engineering projects. However, some of the standard procedures need to be modified for soils under special conditions so that the tested parameters are reasonable. As examples, it is observed that, in the drained and consolidated triaxial(CD) test, the quantity of drainage from the different water weight is greater than the theoretical drainage quantity, this will result in the increase the testing error since a larger actual major effective stress at failure. It is suggested that, in the CD test, the consolidated drainage be calculated as the loss of soil mass subtracts the drainage during the shearing. The pre-consolidation pressure of cohesive soils can be obtained from the one-dimensional consolidation test to the enough high consolidation pressure. To obtain an accurate pre-consolidation pressure of soil samples, higher consolidation pressure is required for stiff soil or soil sample from a great depth. Before applying the Casagrande method, the soil deformation at pre-consolidation pressures greater than 3200 kPa can be estimated from the previous testing pressures. These modifications provide efficient ways of test soil properties.
Laboratory test standards are widely using the geotechnical investigation for various engineering projects. However, some of the standard procedures need to be modified for soils under special conditions so that the tested parameters are reasonable. As examples, it is observed that, in the drained and consolidated triaxial(CD) test, the quantity of drainage from the different water weight is greater than the theoretical drainage quantity, this will result in the increase the testing error since a larger actual major effective stress at failure. It is suggested that, in the CD test, the consolidated drainage be calculated as the loss of soil mass subtracts the drainage during the shearing. The pre-consolidation pressure of cohesive soils can be obtained from the one-dimensional consolidation test to the enough high consolidation pressure. To obtain an accurate pre-consolidation pressure of soil samples, higher consolidation pressure is required for stiff soil or soil sample from a great depth. Before applying the Casagrande method, the soil deformation at pre-consolidation pressures greater than 3200 kPa can be estimated from the previous testing pressures. These modifications provide efficient ways of test soil properties.
引文
[1] 公路土工试验规程( JTG E40-2007)[S].
[2] 北京地区建筑地基基础勘察设计规范(DBJ 11-501-2016)[S].
[3] 土工试验规程(SL237-1999)[S].
[4] 铁路工程土工试验规程(TB10102-2010)[S].
[5] 常士骠,张苏民.工程地质手册(第四版)[M].北京:中国建筑工业出版社,2007.
[6] 魏道垛,胡中雄.上海浅层地基土的前期固结压力及有关压缩性参数的试验研究[J].岩土工程学报,1980,2(4):13-22.
[7] 张淑焕.确定先期固结压力的新方法[J].港口工程,1988(6):44-49.
[8] 土工试验方法标准(GB/T 50123-1999)[S].
[2] 北京地区建筑地基基础勘察设计规范(DBJ 11-501-2016)[S].
[3] 土工试验规程(SL237-1999)[S].
[4] 铁路工程土工试验规程(TB10102-2010)[S].
[5] 常士骠,张苏民.工程地质手册(第四版)[M].北京:中国建筑工业出版社,2007.
[6] 魏道垛,胡中雄.上海浅层地基土的前期固结压力及有关压缩性参数的试验研究[J].岩土工程学报,1980,2(4):13-22.
[7] 张淑焕.确定先期固结压力的新方法[J].港口工程,1988(6):44-49.
[8] 土工试验方法标准(GB/T 50123-1999)[S].