CN104155427A - Low back pressure saturation method for loess liquidation experiment - Google Patents
Low back pressure saturation method for loess liquidation experiment Download PDFInfo
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Abstract
The invention discloses a low back pressure saturation method for loess liquidation experiment. The method comprises the following steps: preparing an original or remolded loess test sample; mounting an experiment device; checking the experiment device; preheating the experiment device for more than 20 minutes; mounting the test sample; charging water into a pressure chamber, subsequently adjusting the confining pressure and the back pressure to be zero, zeroing the pore water pressure and the volume change, and finally adjusting the initial shaft pressure to be zero; initializing the confining pressure and the back pressure, and after the confining pressure and the back pressure are stabilized, gradually exerting the confining pressure and the back pressure in sequence step by step. The method adopts the loess test sample which is saturated by using a low back pressure saturation method, the saturability is greater than about 95%, the reproducibility of the experiment is remarkably improved when being compared with that of water head saturation, the analysis on the original loess micro structure before and after the back pressure saturation shows that the horizontal and vertical structure of the test sample is generally complete when the low back pressure saturation method is adopted, the result shows that under the low back pressure condition, the saturability can be improved by using the method, the structure of the test sample is not damaged, and the method has the characteristics of high saturability, relatively high control precision and the like.
Description
Technical field
The invention belongs to soil test research field, relate in particular to a kind of low back-pressure saturation process of loess liquefaction test.
Background technology
Along with the inclination of national development policy, Canal in Loess Area has become the major area of exploitation, and Canal in Loess Area is located in high intensity Zone mostly.Show from investigation and the shop experiment research of ram-jolt example over the ground in the recent period, saturated loess even high-moisture loess also has very high liquefaction potential and fluidised form destruction gesture, other earthquakes than Canal in Loess Area, loess liquefaction disaster has slippage apart from large, and disaster area greatly and have features such as crushing more.The potential reality that saturated loess liquefaction earthquake exists and the situation of rapid economic development have been researched and proposed requirement to earthquake liquefaction disaster and the anti-liquefaction Measures of strengthening loess.
Aspect the research of loess liquefaction test saturation process, obtaining certain achievement at present, these methods are applied in the indoor liquefaction test of loess, but existing loess liquefaction test saturation process still exists certain defect in its application process, mainly there are two shortcomings in existing loess liquefaction test saturation process:
(1) saturation time is long, and sample produces saturated yielding and destroys in the time of long-time immersion;
(2) saturation degree is lower, has residual air when saturated in loess part microporosity, makes saturation of soil sample lower.
These two shortcomings are again conflicting: generally, saturation time is longer, and the saturation degree of soil sample is just higher.Along with further going deep into of loess liquefaction research, how to solve the contradiction between saturation time and saturation degree, find the equilibrium point between the two, make soil sample reach in the short period of time a higher saturation degree, this is by the main direction that is the research of loess liquefaction test saturation process.In addition, in existing loess liquefaction method, most methods is all direct with reference to the saturation process in domestic and international related specifications, and the applicability in loess liquefaction test saturation history does not consider to it.
Summary of the invention
The low back-pressure saturation process that the object of the present invention is to provide a kind of loess liquefaction test, is intended to improve saturation of soil sample and control accuracy.
The present invention is achieved in that a kind of low back-pressure saturation process step of loess liquefaction test is as follows:
Step 1, prepare original state or reinvent loess sample;
Step 2, experimental provision is installed, check test device, to experimental provision preheating more than 20 minutes;
Step 3, installation sample;
Step 4, to after pressure chamber's water-filling, confined pressure and back-pressure are adjusted to zero-bit, pore water pressure and body are become to zero clearing, finally initial axial compression is adjusted to zero-bit;
Step 5, initialization confined pressure and back-pressure apply step by step according to this confined pressure and back-pressure after confined pressure and back-pressure are stable.
Further, the concrete steps of described installation sample are as follows:
The sample stage of experimental provision is transferred to extreme lower position, by latex film with rubber belt lock ring on sample stage, guarantee water-tightly, turn down latex film; On sample stage, place successively permeable stone, filter paper, loess sample is placed on sample stage, on sample, place successively again filter paper and permeable stone, regulate the height of sample stage, make sample just stressed; Dig latex film, it is tightly pricked on axle with bungee.
Further, the concrete grammar of step 4 is as follows:
Cover pressure chamber's cover, close pore water pressure valve and opposite pressure valve, survey note body change pen recorder is read to guarantee water-tight, turns down latex film.On sample stage, place successively permeable stone, filter paper, be placed on sample stage cautious loess sample, on sample, place successively again filter paper and permeable stone, regulate the height of sample stage, make sample just stressed; Dig latex film, it is tightly pricked on axle with bungee.
Further, initialization confined pressure and back-pressure described in step 5, making confined pressure initial value is 10kPa, and back-pressure initial value is 0kPa, after stable, applies step by step according to this confined pressure and back-pressure, the large and good loess of cementing properties for dry density, the amplification of every grade of confined pressure and back-pressure is advisable with 30kPa, and pressure reduction is advisable with 20kPa, the saturated later stage because of confined pressure and back-pressure is large and sample immersion after the distortion that causes of local buckling when excessive, can turn in right amount the amplification of confined pressure and back-pressure down, and suitably increase pressure reduction; Less and the poor loess of cementing properties for dry density, when original upload, the amplification of every grade of confined pressure and back-pressure is advisable with 15-20kPa, pressure reduction is advisable with 30kPa, if the later stage exists the excessive situation of distortion while loading, the amplification that reduces confined pressure and back-pressure that can be appropriate and increase pressure reduction.
Further, when test, when pore water pressure value exceedes back-pressure value, or pore water pressure value and body variate are while tending towards stability, should slowly open pore water pressure valve exhaust, after exhaust finishes, close pore water pressure valve and make hole press liter, to can evenly intaking in sample.
Further, in every grade of loading, in the time that confined pressure has loaded, system can initiatively be tested pore pressure parameter B value, after B value tends towards stability, records B value, then carries out back-pressure loading.
Further, the T.T. of saturation testing should be advisable with 60-90 minute, and in test, the time of loadings at different levels is controlled because of the difference of sample, and every grade of load time should be advisable at 10-20 minute.
Further, the opposite pressure loading in test should not be greater than the static strength of saturated loess, and the upper limit standard of opposite pressure is not more than 100kPa.
Further, if while having one of following condition in test, can think that soil sample is saturated, can carry out next step test, otherwise should continue to load, until sample is saturated:
(1) in certain grade of loading, after confined pressure loading finishes, pore pressure parameter B value reaches more than 0.98;
(2) continuous three grades load the B value of surveying when Pore Pressure coefficient B value does not all reach previous stage loading;
(3) while opening pore water pressure valve exhaust, in sample, continue to overflow without bubble, and the volume of discharge water equals the measured water inlet volume of body change measurement mechanism.
Further, it is the triaxial tester with the saturated function of back-pressure that the low back-pressure saturation process of described loess liquefaction test adopts experimental provision, comprise pressure source, Pressure separator, servo-valve, pipeline, confined pressure holding device and valve, back-pressure holding device and valve, pressure test unit and pipeline, body becomes sensor and pipeline, triaxial cell, counter-force pedestal, position adjustable measurement mechanism, exhaust module and valve, pore water pressure sensor, actuator, sample stage etc., when test, on sample stage, also place successively permeable stone, filter paper, sample, wherein sample, filter paper, permeable stone is coated by rubber membrane,
Pressure source is connected with Pressure separator, separation vessel is connected with pressure conversion device by pipeline, pressure conversion device is connected by servo-valve with confined pressure holding device, back-pressure holding device, confined pressure holding device becomes sensor by confined pressure holding device valve and body and is connected, and after body change sensor is connected by pipeline with tensimeter, is connected with triaxial cell; Back-pressure holding device is connected with tensimeter by back-pressure holding device valve, tensimeter becomes after sensor is connected by pipeline and is connected with triaxial cell with body, and triaxial cell is connected with vent port for the exhaust of water-filling (or oil) process triaxial cell.It is upper that sample is placed on pedestal (sample stage), and sample upper and lower surface is equipped with filter paper successively, permeable stone (must boil and can use through boiling water) is connected with pedestal (sample stage), and sample outside is coated with rubber membrane.Back-pressure pressurizer is connected by pipeline with pedestal (sample stage) upper and lower surface, and independent mutually with ambient pressure by the rubber membrane of coated sample.Pore water pressure sensor is connected with pedestal (sample stage) lower surface by the pipeline with valve with degasification module, the exhaust in pore water pressure and the saturation history of measurement sample.
The present invention is by the rear soil body saturation degree test of test, adopt low back pressure saturation method to carry out saturated loess sample, its saturation degree is about more than 95%, and the repdocutbility of test increases significantly compared with head is saturated, the intact loess microstructure analysis of the saturated front and back of back-pressure prove to adopt low back pressure saturation method saturated sample level to, vertically intact to structure, verify under low back-pressure condition (back-pressure≤0.1MPa), the method can improve sample saturation degree, and does not destroy the structural of sample simultaneously.The method has the features such as saturation degree is high, control accuracy is more accurate.
Brief description of the drawings
Fig. 1 is the low back-pressure saturation process pedestal connection mode schematic diagram that the embodiment of the present invention provides;
Fig. 2 is the microstructure of the saturated front and back of the back-pressure sample that provides of the embodiment of the present invention;
In figure: microstructure (a) level of saturated front and back sample to before saturated, (b) level to after saturated, (c) vertically to before saturated, (d) vertically to after saturated;
Fig. 3 is saturated front and back sample hole content statistical graphs;
In figure: saturated front and back sample hole content (a) level to, (b) vertically to.
Embodiment
In order to make object of the present invention, technical scheme and advantage clearer, below in conjunction with drawings and Examples, the present invention is further elaborated.Should be appreciated that specific embodiment described herein, only in order to explain the present invention, is not intended to limit the present invention.
In the loess indoor soil mechanical test that the embodiment of the present invention provides, adopt low back-pressure saturation process can obtain having the sample of high saturation and good structural stability.Experimental provision adopts the triaxial tester with the saturated function of back-pressure, as shown above.It comprises pressure source, Pressure separator, servo-valve, pipeline, confined pressure holding device and valve, back-pressure holding device and valve, pressure test unit and pipeline, body change sensor and pipeline, triaxial cell, counter-force pedestal, position adjustable measurement mechanism, exhaust module and valve, pore water pressure sensor, actuator, sample stage etc., when test, on sample stage, also place successively permeable stone, filter paper, sample, wherein sample, filter paper, permeable stone are coated by rubber membrane.
Pressure source is connected with Pressure separator, separation vessel is connected with pressure conversion device by pipeline, pressure conversion device is connected by servo-valve with confined pressure holding device, back-pressure holding device, confined pressure holding device becomes sensor by confined pressure holding device valve and body and is connected, and after body change sensor is connected by pipeline with tensimeter, is connected with triaxial cell; Back-pressure holding device is connected with tensimeter by back-pressure holding device valve, tensimeter becomes after sensor is connected by pipeline and is connected with triaxial cell with body, and triaxial cell is connected with vent port for the exhaust of water-filling (or oil) process triaxial cell.It is upper that sample is placed on pedestal (sample stage), and sample upper and lower surface is equipped with filter paper successively, permeable stone (must boil and can use through boiling water) is connected with pedestal (sample stage), and sample outside is coated with rubber membrane.Back-pressure pressurizer is connected by pipeline with pedestal (sample stage) upper and lower surface, and independent mutually with ambient pressure by the rubber membrane of coated sample.Pore water pressure sensor is connected with pedestal (sample stage) lower surface by the pipeline with valve with degasification module, the exhaust in pore water pressure and the saturation history of measurement sample.
The present invention is achieved in that a kind of low back-pressure saturation process step of loess liquefaction test is as follows:
Step 1, prepare original state or reinvent loess sample;
With reference to " Standard for test methods of earthworks " (GBT50123-1999), " earthwork test rule " (SL237-1999), ASTM, Annual Book of ASTM Standards (ASTM D4767-95) and BSI, Shear strength tests (BS1377-8) formulates the saturated accurate standardized method of the low back-pressure of loess;
According to " Standard for test methods of earthworks " (GB/T50123-1999) in relevant regulations prepare original state or reinvent loess sample.
Step 2, experimental provision is installed, check test device, to experimental provision preheating more than 20 minutes;
According to back-pressure saturation device pipeline connection diagram connecting line in BS1377-8 specification; Before each test, should check the connectedness of pipeline.
Before test, should check that latex film has or not damage, in test, permeable stone used should fully saturated (boiling), and in pilot system, all pipelines should be by air emptying.
Open pilot system, preheating more than 20 minutes, ensures the stability of instrument.
Step 3, installation sample;
Step 4, to after pressure chamber's water-filling, confined pressure and back-pressure are adjusted to zero-bit, pore water pressure and body are become to zero clearing, finally initial axial compression is adjusted to zero-bit;
Step 5, initialization confined pressure and back-pressure apply step by step according to this confined pressure and back-pressure after confined pressure and back-pressure are stable.
Further, the concrete steps of described installation sample are as follows:
The sample stage of experimental provision is transferred to extreme lower position, by latex film with rubber belt lock ring on sample stage, guarantee water-tightly, turn down carefully latex film; On sample stage, place according to this permeable stone, filter paper, be placed on sample stage cautious loess sample, on sample, place according to this again filter paper and permeable stone, regulate the height of sample stage, make sample just stressed; Dig carefully latex film, it is tightly pricked on axle with bungee.
Further, the concrete grammar of step 4 is as follows:
Cover pressure chamber's cover, close pore water pressure valve and opposite pressure and keep valve, survey note body change pen recorder is read to guarantee water-tight, turns down carefully latex film.On sample stage, place according to this permeable stone, filter paper, be placed on sample stage cautious Loess Samples, on sample, place according to this again filter paper and permeable stone, regulate the height of sample stage, make sample just stressed; Dig carefully latex film, it is tightly pricked on axle with bungee.
Further, initialization confined pressure and back-pressure described in step 5, making confined pressure initial value is 10kPa, and back-pressure initial value is 0kPa, after stable, applies step by step according to this confined pressure and back-pressure, the large and good loess of cementing properties for dry density, the amplification of every grade of confined pressure and back-pressure is advisable with 30kPa, and pressure reduction is advisable with 20kPa, the saturated later stage because of confined pressure and back-pressure is large and sample immersion after the distortion that causes of local buckling when excessive, can turn in right amount the amplification of confined pressure and back-pressure down, and suitably increase pressure reduction; Less and the poor loess of cementing properties for dry density, when original upload, the amplification of every grade of confined pressure and back-pressure is advisable with 15-20kPa, pressure reduction is advisable with 30kPa, if the later stage exists the excessive situation of distortion while loading, the amplification that reduces confined pressure and back-pressure that can be appropriate and increase pressure reduction.
Further, when test, when pore water pressure value exceedes back-pressure value, or pore water pressure value and body variate are while tending towards stability, should slowly open pore water pressure valve exhaust, after exhaust finishes, close pore water pressure valve and make hole press liter, to can evenly intaking in sample.
Further, in every grade of loading, in the time that confined pressure has loaded, system can initiatively be tested pore pressure parameter B value, after B value tends towards stability, records B value, then carries out back-pressure loading.
Further, the T.T. of saturation testing should be advisable with 60-90 minute, and in test, the time of loadings at different levels is controlled because of the difference of sample, and every grade of load time should be advisable at 10-20 minute.
Further, the opposite pressure loading in test should not be greater than the static strength of saturated loess, and the upper limit standard of opposite pressure is not more than 100kPa.
Further, if while having one of following condition in test, can think that soil sample is saturated, can carry out next step test, otherwise should continue to load, until sample is saturated:
(1) in certain grade of loading, after confined pressure loading finishes, pore pressure parameter B value reaches more than 0.98;
(2) continuous three grades load the B value of surveying when Pore Pressure coefficient B value does not all reach previous stage loading;
(3) while opening pore water pressure valve exhaust, in sample, continue to overflow without bubble, and the volume of discharge water equals the measured water inlet volume of body change measurement mechanism.
In loess indoor soil mechanical test, adopt low back-pressure saturation process can obtain having the sample of high saturation and good structural stability.Experimental provision adopts the triaxial tester with the saturated function of back-pressure.Sample is placed on sample stage, and upper and lower surface is equipped with filter paper, permeable stone (must boil and can use through boiling water) successively, is then connected with counter-force pedestal, and sample outside is coated with rubber membrane.By triaxial cell, sample is applied to ambient pressure (hydraulic pressure, oil pressure or air pressure), back-pressure holding device carries out the saturated of sample, pilot system have pressure keep and control system, maintain with supply saturation history in saturation water.In low back-pressure saturation block, for applying the water pipeline of back-pressure and base connected mode for " upper entering and lower leaving ", utilized head within a short period of time is by the Bas Discharged in sample.In process of the test, when being greater than, pore water pressure value applies buffer brake value, or pore water pressure value and body variate tend towards stability, the crack degasification module that opens, closes exhaust module valve and makes hole press liter after end to be degassed in time, make the inner evenly water inlet of sample, this step can improve saturation efficiency; Apply target back-pressure value simultaneously and be less than soil body static strength, ensured the structural stability of sample.In process of the test, the pore water pressure of sample records (its installation site and back-pressure water side are at homonymy) by the pressure transducer being connected with sample bottom, every grade saturated after can with B value detect judge saturation degree, realized the quantification to saturation degree in saturation history.
Low back-pressure operate in saturation principle:
After triaxial cell's installation is fixing, it is carried out to water filling (or oily, gas), top, pressure chamber vent port unlatching when water filling (or oil) is closed vent port after the surrounding of sample in pressure chamber is full of water (or oil).The required pressure of test instrument is transmitted out by pressure source device and shunt after separation vessel, enter pressure conversion device through pressure control servovalve, enter the confined pressure holding device, the back-pressure holding device that are connected with pressure chamber through servo-valve, realize saturation experiments process to sample ambient pressure apply with back-pressure saturation history in the applying of back-pressure.
Before saturation history starts, first close back-pressure, sample is applied to very little ambient pressure precompressed, then open back-pressure holding device valve, starting to carry out opposite pressure applies, in saturation history, back-pressure head applies from top to bottom, when test, work as pore water pressure value and exceed back-pressure value, or pore water pressure value and body variate are while tending towards stability, should slowly open exhaust module valve, the air in sample is discharged by exhaust module, after exhaust finishes, close exhaust module valve and make hole press liter, to can evenly intaking in sample.In every grade of loading, in the time that confined pressure has loaded, system can initiatively be tested pore pressure parameter B value, after B value tends towards stability, records B value, then carries out the loading of next stage back-pressure.Consider that loess has the metastability of special water sensitivity and saturated loess, the T.T. of saturation testing should be advisable at 60-90 minute, and in test, the time of loadings at different levels is controlled because of the difference of sample, and every grade of load time should be advisable at 10-20 minute.When: 1) in certain grade of loading, after confined pressure loading finishes, pore pressure parameter B value reaches more than 0.98; Or 2) continuous three grades load the B value of surveying when Pore Pressure coefficient B value does not all reach previous stage loading; Or 3) while opening pore water pressure valve exhaust, in sample, continue to overflow without bubble, and the volume of discharge water equals the measured water inlet volume of body change measurement mechanism.Showing that loess sample is saturated completes.In process of the test the stress of sample by body become measurement mechanism, pressure transducer (inside and outside, hole, back-pressure sensor), power sensor records, and realizes data acquisition and storage by data collecting instrument.
Table 1 is different specification confined pressure, back-pressure amplification scope table in the back pressure saturation method that provides of the embodiment of the present invention;
Table 2 is different specification pressure differential range tables in the back pressure saturation method that provides of the embodiment of the present invention;
Table 1
Table 2
Code requirement BS 1377-8-1990 pedestal connection mode of the present invention, back-pressure, head apply from top to bottom, confined pressure, back-pressure amplification are 20-30kPa, choosing confined pressure and back-pressure pressure reduction is 15-25kpa, according to the saturated method of back-pressure, with reference to the parameter of recommendation in ASTM D4767-02 and BS1377-8, whole saturation history is controlled at about 60-90 minute, and every grade is detected and judges saturation degree by B value after saturated.The present invention is by the rear soil body saturation degree test of test, adopt low back pressure saturation method to carry out saturated loess sample, its saturation degree is about more than 95%, and the repdocutbility of test increases significantly compared with head is saturated, the intact loess microstructure analysis of the saturated front and back of back-pressure prove to adopt low back pressure saturation method saturated sample level to, vertically substantially intact to structure, verify under low back-pressure condition, the method can improve sample saturation degree, and do not destroy the structural of sample simultaneously, there is the features such as saturation degree is high, control accuracy is more accurate.
The present invention is by the rear soil body saturation degree test of test, adopt low back pressure saturation method to carry out saturated loess sample, its saturation degree is about more than 95%, and the repdocutbility of test increases significantly compared with head is saturated, verified under low back-pressure condition (back-pressure < 0.1MPa), the method has improved sample saturation degree.Adopt the loess saturation degree that low back pressure saturation method obtains to there is the features such as saturation degree is high, control accuracy is more accurate.
By reference to the accompanying drawings the specific embodiment of the present invention is described although above-mentioned; but not limiting the scope of the invention; one of ordinary skill in the art should be understood that; on the basis of technical scheme of the present invention, those skilled in the art do not need to pay various amendments that performing creative labour can make or distortion still within protection scope of the present invention.
Claims (10)
1. a low back-pressure saturation process for loess liquefaction test, is characterized in that, the low back-pressure saturation process step of described loess liquefaction test is as follows:
Step 1, prepare original state or reinvent loess sample;
Step 2, experimental provision is installed, check test device, to experimental provision preheating more than 20 minutes;
Step 3, installation sample;
Step 4, to after pressure chamber's water-filling, confined pressure and back-pressure are adjusted to zero-bit, pore water pressure and body are become to zero clearing, finally initial axial compression is adjusted to zero-bit;
Step 5, initialization confined pressure and back-pressure apply step by step according to this confined pressure and back-pressure after confined pressure and back-pressure are stable.
2. the low back-pressure saturation process of loess liquefaction test as claimed in claim 1, is characterized in that, the concrete steps of described installation sample are as follows:
The sample stage of experimental provision is transferred to extreme lower position, by latex film with rubber belt lock ring on sample stage, guarantee water-tightly, turn down latex film; On sample stage, place according to this permeable stone, filter paper, loess sample is placed on sample stage, on sample, place successively again filter paper and permeable stone, regulate the height of sample stage, make sample just stressed; Dig carefully latex film, it is tightly pricked on axle with bungee.
3. the low back-pressure saturation process of loess liquefaction test as claimed in claim 1, is characterized in that, the concrete grammar of step 4 is as follows:
Cover pressure chamber's cover, close pore water pressure valve and opposite pressure valve, surveying note body change pen recorder reads to guarantee water-tight, turn down latex film, on sample stage, place successively permeable stone, filter paper, loess sample is placed on sample stage, on sample, place successively again filter paper and permeable stone, the height that regulates sample stage, makes sample just stressed; Dig latex film, it is tightly pricked on axle with bungee.
4. the low back-pressure saturation process of loess liquefaction test as claimed in claim 1, it is characterized in that, initialization confined pressure and back-pressure described in step 5, making confined pressure initial value is 10kPa, back-pressure initial value is 0kPa, after stable, apply step by step according to this confined pressure and back-pressure, the large and good loess of cementing properties for dry density, the amplification of every grade of confined pressure and back-pressure is advisable with 30kPa, pressure reduction is advisable with 20kPa, the saturated later stage because of confined pressure and back-pressure are large and sample immersion after the distortion that causes of local buckling when excessive, can turn in right amount the amplification of confined pressure and back-pressure down, and suitably increase pressure reduction, less and the poor loess of cementing properties for dry density, when original upload, the amplification of every grade of confined pressure and back-pressure is advisable with 15-20kPa, pressure reduction is advisable with 30kPa, if the later stage exists the excessive situation of distortion while loading, the amplification that reduces confined pressure and back-pressure that can be appropriate and increase pressure reduction.
5. the low back-pressure saturation process of loess liquefaction test as claimed in claim 1, it is characterized in that, when test, when pore water pressure value exceedes back-pressure value, or pore water pressure value and body variate are while tending towards stability, should slowly open pore water pressure valve exhaust, after exhaust finishes, close pore water pressure valve and make hole press liter, to can evenly intaking in sample.
6. the low back-pressure saturation process of loess liquefaction test as claimed in claim 1, is characterized in that, in every grade of loading, in the time that confined pressure has loaded, system can initiatively be tested pore pressure parameter B value, after B value tends towards stability, records B value, then carries out back-pressure loading.
7. the low back-pressure saturation process of loess liquefaction test as claimed in claim 1, it is characterized in that, the T.T. of saturation testing should be advisable with 60-90 minute, and in test, the time of loadings at different levels is controlled because of the difference of sample, and every grade of load time should be advisable at 10-20 minute.
8. the low back-pressure saturation process of loess liquefaction test as claimed in claim 1, is characterized in that, the opposite pressure loading in test should not be greater than the static strength of saturated loess, and the upper limit standard of opposite pressure is not more than 100kPa.
9. the low back-pressure saturation process of loess liquefaction test as claimed in claim 1, is characterized in that, if while having one of following condition in test, can think that soil sample is saturated, can carry out next step test, otherwise should continue to load, until sample is saturated:
(1) in certain grade of loading, after confined pressure loading finishes, pore pressure parameter B value reaches more than 0.98;
(2) continuous three grades load the B value of surveying when Pore Pressure coefficient B value does not all reach previous stage loading;
(3) while opening pore water pressure valve exhaust, in sample, continue to overflow without bubble, and the volume of discharge water equals the measured water inlet volume of body change measurement mechanism.
10. the low back-pressure saturation process of loess liquefaction test as claimed in claim 1, it is characterized in that, it is the triaxial tester with the saturated function of back-pressure that the low back-pressure saturation process of described loess liquefaction test adopts experimental provision, comprise pressure source, Pressure separator, servo-valve, pipeline, confined pressure holding device and valve, back-pressure holding device and valve, pressure test unit and pipeline, body becomes sensor and pipeline, triaxial cell, counter-force pedestal, position adjustable measurement mechanism, exhaust module and valve, pore water pressure sensor, actuator, sample stage etc., when test, on sample stage, also place successively permeable stone, filter paper, sample, wherein sample, filter paper, permeable stone is coated by rubber membrane,
Pressure source is connected with Pressure separator, separation vessel is connected with pressure conversion device by pipeline, pressure conversion device is connected by servo-valve with confined pressure holding device, back-pressure holding device, confined pressure holding device becomes sensor by confined pressure holding device valve and body and is connected, and after body change sensor is connected by pipeline with tensimeter, is connected with triaxial cell; Back-pressure holding device is connected with tensimeter by back-pressure holding device valve, and tensimeter becomes after sensor is connected by pipeline and is connected with triaxial cell with body, and triaxial cell is connected with vent port for the exhaust of water-filling or oily process triaxial cell; Sample is placed on pedestal, and sample upper and lower surface is equipped with filter paper successively, permeable stone is connected with pedestal, and sample outside is coated with rubber membrane; Back-pressure pressurizer is connected by pipeline with pedestal upper and lower surface, and independent mutually with ambient pressure by the rubber membrane of coated sample; Pore water pressure sensor is connected with pedestal lower surface by the pipeline with valve with degasification module, the exhaust in pore water pressure and the saturation history of measurement sample.
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| CN111595689A (en) * | 2020-06-22 | 2020-08-28 | 昆明理工大学 | Dynamic triaxial experimental instrument for carbon dioxide saturation and water head back pressure saturation |
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