Device for measuring strength and strain softening parameters of saturated clay sample based on full-flow penetration

Abstract

A device for measuring strength and strain softening parameters of a saturated clay sample based on full-flow penetration belongs to the technical field of geotechnical, geological and environmental research. The device mainly comprises two parts: an overlying pressure loading system and a full-flow penetration system. The present invention mainly aims at the problem of incomplete backflow of the soil in the measurement of soil strength and strain softening parameters with a full-flow penetrometer for saturated clay, and applies the working principle of a traditional consolidometer to vertically pressurize a soil sample to ensure the backflow of the soil, thereby improving the applicability of the full-flow penetrometer in the measurement aspect of the soil strength and the strain softening parameters and having important practical value for test research and marine engineering design.

Claims

1. A device for measuring strength and strain softening parameters of a saturated clay sample based on full-flow penetration, wherein the device for measuring strength and strain softening parameters of a saturated clay sample is mainly composed of two parts: an overlying pressure loading system I and a full-flow penetration system II; the overlying pressure loading system I comprises a test workbench, a lever pressure conversion device, a load weight, an annular pressurizing frame, a force transmission shaft, an annular steel ring, a full-flow penetrometer, a cylindrical rigid box, a rigid box base, a rigid box side wall, a rigid box connection flange, a rigid box movable top cover, a top cover positioning rod, a sealable hole, a fixing screw, a drainage valve, geotextile, filter paper and porous stone; the test workbench is placed on flat ground; the load weight and a tail weight are leveled by adjusting the front end of a lever; the lever pressure conversion device is installed on a table surface of the test workbench; and the load weight is connected to the lever pressure conversion device; the cylindrical rigid box is placed on a top surface of the lever pressure conversion device; a cylindrical soil sample is placed inside the cylindrical rigid box; the bottom of the cylindrical rigid box and the rigid box base are connected by the rigid box connecting flange; the rigid box connecting flange is fixed to the rigid box base by the fixing screw on the rigid box connecting flange; the rigid box base is communicated with a drainage channel and is controlled by the drainage valve; the drainage valve is used to control soil drainage conditions in a pressurization process; the top of the cylindrical rigid box is provided with the rigid box movable top cover; the rigid box movable top cover is provided with the sealable hole and the top cover positioning rod for penetrating through the full-flow penetrometer; the positioning rod is used to fix the installation and removal of the annular steel ring and the rigid box movable cover; the sealable hole is used to prevent the soil from being extruded during the penetration and extraction of the full-flow penetrometer; the annular steel ring is fixed to the rigid box movable top cover; the annular pressurizing frame and the annular steel ring are connected by four steel rods; the lever pressure conversion device is connected with the annular pressurizing frame through the force transmission shaft; both ends of the annular pressurizing frame are provided with through holes for the force transmission shaft to pass through, and the middle is provided with through holes corresponding to the sealable hole and the top cover positioning rod of the full-flow penetrometer; the filter paper, the geotextile and the porous stone are respectively laid on the top and the bottom of cylindrical soil sample from inside to outside; the rigid box movable top cover is located on the porous stone on top of the cylindrical soil sample; the full-flow penetrometer and the cylindrical rigid box are assembled; the weight of the load weight is adjusted; and pressure is applied to the soil sample in the rigid box through the annular pressurizing frame; the full-flow penetration system II comprises a full-flow penetrometer, a loading and data collecting system and a full-flow penetrometer bracket; the full-flow penetrometer bracket is placed on the top surface of the test workbench; a shaft of the full-flow penetrometer is connected with a loading motor on the full-flow penetrometer bracket; a load cell is installed on the top end of a probe to measure the size of the penetration resistance of the probe during cyclic penetration and extraction; the loading and data collecting system comprises a loading motor, a load cell, a power supply for power distribution and voltage stabilization, a computer required for data collection, and the like; the motor is used to control the penetration and extraction speed of the full-flow penetrometer to reduce the influence of the penetration speed on the measurement of the soil strength; the signal of the load cell is collected in a test process, and the soil strength is finally estimated by the relationship between the measured pressure signal and the strength.

Description

DESCRIPTION OF DRAWINGS

[0013] FIG. 1(a) is a layout diagram of an overlying pressure loading system of the present invention;

[0014] FIG. 1(b) is a module layout diagram of a full-flow penetration system of the present invention;

[0015] FIG. 2 is a layout diagram of a cylindrical rigid box of the present invention;

[0016] FIG. 3(a) is a sectional diagram of a cylindrical rigid box of the present invention;

[0017] FIG. 3(b) is a structural diagram of a shaft of a full-flow penetrometer of the present invention;

[0018] FIG. 3(c) is a top view of a cylindrical rigid box of the present invention;

[0019] FIG. 4 is a detailed diagram of contact between a top cover of a rigid box and an annular pressurizing steel ring in the present invention; and

[0020] FIG. 5 is a top view of an annular pressurizing frame of the present invention.

[0021] In the drawings: 1 test workbench; 2 lever pressure conversion device; 3 load weight; 4 annular pressurizing frame; 5 force transmission shaft; 6 annular steel ring; 7 full-flow penetrometer; 8 cylindrical rigid box; 9 rigid box base; 10 rigid box side wall; 11 rigid box connecting flange; 12 rigid box movable top cover; 13 top cover positioning rod; 14 sealable hole; 15 fixing screw; 16 drainage valve; 17 loading and data collecting system; 18 full-flow penetrometer bracket; 19 geotextile; 20 filter paper; and 21 porous stone.

DETAILED DESCRIPTION

[0022] The specific embodiments of the present invention are described below in detail in combination with the technical solutions and the drawings.

EMBODIMENTS

[0023] Firstly, the test device is assembled. The workbench 1 is placed on flat ground; the overlying pressure loading system is leveled; the porous stone, the geotextile and the filter paper are laid on the bottom of the rigid box in sequence, and an appropriate amount of distilled water is added into the rigid box to ensure that a water surface is higher than the filter paper by a certain height; the drainage valve 16 is turned on; the drainage valve 16 is turned off when the water flows out; the gas below the water surface is drained; a cylindrical soil sample to be tested is cut according to the size of the rigid box and placed in the rigid box 8, and then saturated filter paper with holes of the size like the probe and the geotextile are respectively placed from bottom to top; the shaft of the full-flow penetrometer 7 penetrates through the sealable hole 14 of the top cover and stands on the soil surface; the annular pressurizing frame 4 and the annular steel ring 6 are connected through steel rods and adjusted to 2 cm on the top surface of the rigid box movable top cover 12; and cyclic penetration and extraction tests are prepared.

[0024] Then, vertical pressure is applied to the soil sample. After the device is assembled, under the condition that the vertical pressure is not loaded, by controlling the loading and data collecting system 17, the full-flow penetrometer penetrates into the soil sample surface by a distance of 2 times the diameter of the probe and then stops penetrating. The penetration resistance is collected in the process full-flow penetrometer, which provide the reference to the following cyclic penetration tests. The top cover of the cylindrical rigid box 8 is placed on the soil surface, and the annular steel ring 6 is adjusted to the surface of the rigid box movable top cover 12 to ensure the uniform contact. According to the pre-determined pressure, the weight is applied to the design load.

[0025] Finally, the cyclic penetration and extraction tests are formally conducted by using the full-flow penetrometer. After the overlying pressure reach the design value, the full-flow penetrometer is used to perform the cyclic penetration and extraction tests on the sample soil. The penetration speed is set according to the purpose. Without considering the strain rate, the penetration speed is 0.1 D/s (D is the diameter of the probe). Considering the influence of the strain rate on the soil strength, different penetration rates can be designed according to the test requirements. The full-flow penetrometer continues penetration based on the initial penetration depth, and stops the penetration at a distance of 2 cm from the surface of the soil sample. For the softening characteristics of marine clay, at least 10 cycles of penetration and extraction are performed in the middle of the soil sample. The interval range of penetration and extraction is above 5 cm. After the last cycle is ended, the soil sample is unloaded, the pressurizing frame and the top cover are removed, and a next group of tests are prepared. After the test is completed, the table is cleaned, and data processing is conducted. Analyze the problems and the deficiencies encountered in the test, and prepare the subsequent tests.